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  • Electron microscopy  (561)
  • Calcium
  • Fluoride
  • Springer  (868)
  • MDPI Publishing
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  • 1
    Digitale Medien
    Digitale Medien
    Leucaena hedgerow intercropping and cattle manure application in the Ethiopian highlands III. Nutrient balances (1999)
    Springer
    Biology and fertility of soils 28 (1999), S. 204-211 
    Details
    ISSN: 1432-0789
    Schlagwort(e): Key words Alley cropping ; Calcium ; Magnesium ; Nitrogen ; Phosphorus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract  Balances between nutrients applied or mineralized and nutrients removed in maize grain and stover were calculated in a hedgerow intercropping experiment in which Leucaena leucocephala and L. pallida prunings and cattle manure were applied. Hedgerow intercropping (also called alley cropping) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. In control treatments, nutrient depletion per season was in the order of 7–19 kg N ha–1, 4–12 kg P ha–1, 10–26 kg K ha–1, 0–2 kg Ca ha–1 and 3–6 kg Mg ha–1. N fertilizer reversed the depletion of N, but it accelerated the depletion of the other nutrients. Manure and at least two applications of leucaena prunings resulted in net positive balances of N, K, and Ca between amounts applied or mineralized and amounts removed by maize. The amounts of P and Mg applied with, or mineralized from, prunings or manure were insufficient to offset the negative balances of these nutrients.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003740050484
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  • 2
    Digitale Medien
    Digitale Medien
    Leucaena hedgerow intercropping and cattle manure application in the Ethiopian highlands I. Decomposition and nutrient release (1999)
    Springer
    Biology and fertility of soils 28 (1999), S. 182-195 
    Details
    ISSN: 1432-0789
    Schlagwort(e): Key words Alley cropping ; Calcium ; Magnesium ; Nitrogen ; Phosphorus ; Intercropping
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract  A litter bag technique was used to study the decomposition and release of N, P, K, Ca, and Mg from Leucaena leucocephala and L. pallida prunings and cattle manure in a hedgerow intercropping trial conducted in the Ethiopian highlands. Hedgerow intercropping (also called alley cropping or alley farming) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. Manure was the most resistant to decomposition, losing only 15% of its dry matter (DM) in 15 weeks, compared to 41–57% lost by leucaena prunings. Large quantities of K (up to 104 kg ha–1) were mineralized from prunings and manure, but Ca and Mg were mostly immobilized. More N and P were released from prunings than from manure, which resulted in net immobilization of these nutrients in the initial stages of decomposition and net mineralization in later stages. Between the leucaenas more N was mineralized and less Ca and Mg were immobilized when L. leucocephala prunings were applied than when L. pallida prunings were applied. Fertilizer N increased DM decomposition and N mineralization. Mineralization of the nutrients was constrained by lignin and polyphenol contents. It is concluded that leucaena mulch and cattle manure may be significant sources of N and K for crop growth, but external sources of P, Ca and Mg may be required, particularly in acid soils which have low contents of these nutrients. However, this fertility effect has to be evaluated against the competition effect of trees to predict crop response.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003740050482
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  • 3
    Digitale Medien
    Digitale Medien
    Leucaena hedgerow intercropping and cattle manure application in the Ethiopian highlands II. Maize yields and nutrient uptake (1999)
    Springer
    Biology and fertility of soils 28 (1999), S. 196-203 
    Details
    ISSN: 1432-0789
    Schlagwort(e): Key words Alley cropping ; Calcium ; Magnesium ; Nitrogen ; Phosphorus ; Leaf pruning
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract  The effects of Leucaena leucocephala and L. pallida prunings and cattle manure on maize nutrient uptake and yield were investigated in a hedgerow intercropping trial in the Ethiopian highlands. Hedgerow intercropping (also called alley cropping) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. For each leucaena species, the experiment had 16 treatments resulting from a factorial combination of four levels of leucaena leaf prunings (no prunings applied; first prunings applied; first and second prunings applied; first, second and third prunings applied), two levels of air-dried cattle manure (0 and 3 t dry matter ha–1) and two levels of N fertilizer (0 and 40 kg N ha–1 as urea). Uptake of N, P and K increased significantly with application of the three nutrient sources, but uptake of Ca and Mg either did not respond or decreased with application of prunings and manure. All the three factors increased maize grain and stover yields significantly, usually with no significant interactions between the factors. At least two applications of prunings were required to significantly increase nutrient uptake and maize yield. Maize in the row closest to the hedge did not respond to these nutrient inputs. It is concluded that hedgerow intercropping, with or without manure application, can increase crop yields moderately (to 2–3 t ha–1 maize grain yields) in the highlands, but P, Ca and Mg may have to be supplied from external sources if they are deficient in the soil. Additional N is still required for higher yields (〉4 t ha–1 maize grain yields). However, quantification of the competition effects of the trees is also required to confirm these results.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003740050483
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  • 4
    Digitale Medien
    Digitale Medien
    On the mechanism of cesium-induced voltage and current tails in single ventricular myocytes (1999)
    Springer
    Journal of biomedical science 6 (1999), S. 161-175 
    Details
    ISSN: 1423-0127
    Schlagwort(e): Myocytes single ; Cesium ; Voltage and current tails ; Na-Ca exchange ; Calcium ; Cadmium ; Nickel
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The mechanisms by which different concentrations of cesium modify membrane potentials and currents were investigated in guinea pig single ventricular myocytes. In a dose-dependent manner, cesium reversibly decreases the resting potential and action potential amplitude and duration, and induces a diastolic decaying voltage tail (Vex), which increases at more negative and reverses at less negative potentials. In voltage-clamped myocytes, Cs+ increases the holding current, increases the outward current at plateau levels while decreasing it at potentials closer to resting potential, induces an inward tail current (Iex) on return to resting potential and causes a negative shift of the threshold for the inward current. During depolarizing ramps, Cs+ decreases the outward current negative to inward rectification range, whereas it increases the current past that range. During repolarizing ramps, Cs+ shifts the threshold for removal of inward rectification negative slope to less negative values. Cs+-induced voltage and current tails are increased by repetitive activity, caffeine (5 mM) and high [Ca2+]o (8.1 mM), and are reduced by low Ca2+ (0.45 mM), Cd2+ (0.2 mM) and Ni2+ (2 mM). Ni2+ also abolishes the tail current that follows steps more positive than ECa. We conclude that Cs+ (1) decreases the resting potential by decreasing the outward current at more negative potentials, (2) shortens the action potential by increasing the outward current at potentials positive to the negative slope of inward rectification, and (3) induces diastolic tails through a Ca2+-dependent mechanism, which apparently is an enhanced electrogenic Na-Ca exchange.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02255900
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  • 5
    Digitale Medien
    Digitale Medien
    A biogeochemical study of the Podili and Tirupati area of Andhra Pradesh, India (1999)
    Springer
    Environmental geology 37 (1999), S. 313-316 
    Details
    ISSN: 1432-0495
    Schlagwort(e): Key words Biogeochemical study ; Dung ; Urine ; Milk ; Fluoride ; Grazing animals ; Podili ; Tirupati
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract  The fluoride content of dung, urine and milk of grazing animals, for example cow, she-buffalo, doe and ewe, was studied in the Podili area, India, (endemic fluorosis) and also in Tirupati (non-fluorosis) for the purpose of comparison. The data reveal that the fluoride content of the urine of animals is suitable for the preparation of biogeochemical atlases studying the environmental effect in relation to health.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002540050389
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  • 6
    Digitale Medien
    Digitale Medien
    Auxin augments conductance of K+ inward rectifier in maize coleoptile protoplasts (1999)
    Springer
    Planta 208 (1999), S. 38-45 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Key words: Auxin ; Calcium ; Coleoptile growth ; K+-inward rectifier (channel) ; pH ; Zea (coleoptile protoplasts)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. Potassium is taken up by maize (Zea mays L.) coleoptile cells via a typical plant inward rectifier (K ir ). Sufficient conductance of this channel is essential in order to maintain auxin-stimulated cell elongation. It was therefore investigated whether the activity of this channel is subject to direct or indirect control by this growth hormone. Patch-clamp measurements of whole coleoptile protoplasts revealed no appreciable effect of externally applied 10 μM or 100 μM α-naphthaleneacetic acid (NAA) on the activity of K ir over test periods of ≥ 18 or ≥ 8 min, respectively. When, however, K ir was recorded in the cell-attached configiuration and 10 μM NAA administered to the bath medium, the conductance of K ir increased significantly in 13 out of 18 protoplasts over the control. This rise occurred at a fixed protoplast voltage after a lag period of less than 10 min and exhibited no voltage dependency. The absence of response to NAA of protoplasts in the whole-cell configuration indicates that auxin perception and channel control is linked via a soluble cytoplasmic factor and that this mediator is washed out or modified upon perfusion of the cytoplasm with pipette solution. To search for this expected diffusible factor the K ir current was recorded before and after elevation of Ca2+ and H+ in the cytoplasm. In the whole-cell configuration the increase in Ca2+ from a nanomolar value to 〉1 μM by means of Ca2+-release from the caged precursor Na2-DM-nitrophen left K ir unaffected. The whole-cell K ir conductance was also not affected upon addition of 10 mM Na+-acetate to the bath medium, an operation used to lower the cytoplasmic pH. This excludes a primary role for the known auxin-evoked rise in cytoplasmic Ca2+ and H+ in K ir activity. We postulate that another, as yet unknown, mechanism mediates the auxin-evoked stimulation of the number of active K ir channels in the plasma membrane.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004250050532
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  • 7
    Digitale Medien
    Digitale Medien
    Relocalization of the calcium gradient and a dihydropyridine receptor is involved in upward bending by bulging of Chara protonemata, but not in downward bending by bowing of Chara rhizoids (1999)
    Springer
    Planta 209 (1999), S. 414-423 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Key words:Chara (rhizoid ; protonema) ; Calcium ; Calcium channel ; Fluorescent-dihydropyridine ; Gravitropic tip growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. The localization of cytoplasmic free calcium and a dihydropyridine (DHP) receptor, a putative calcium channel, was recorded during the opposite graviresponses of tip-growing Chara rhizoids and Chara protonemata by using the calcium indicator Calcium Crimson and a fluorescently labeled dihydropyridine (FL-DHP). In upward (negatively gravitropically) growing protonemata and downward (positively gravitropically) growing rhizoids, a steep Ca2+ gradient and DHP receptors were found to be symmetrically localized in the tip. However, the localization of the Ca2+ gradient and DHP receptors differed considerably during the gravitropic responses upon horizontal positioning of the two cell types. During the graviresponse of rhizoids, a continuous bowing downward by differential flank growth, the Ca2+ gradient and DHP receptors remained symmetrically localized in the tip at the centre of growth. However, after tilting protonemata into a horizontal position, there was a drastic displacement of the Ca2+ gradient and FL-DHP to the upper flank of the apical dome. This displacement occurred after the apical intrusion and sedimentation of the statoliths but clearly before the change in the growth direction became evident. In protonemata, the reorientation of the growth direction started with the appearence of a bulge on that site of the upper flank which was predicted by the asymmetrically displaced Ca2+ gradient. With the upward shift of the cell tip, which is suggested to result from a statolith-induced displacement of the growth centre, the Ca2+ gradient and DHP receptors became symmetrically relocalized in the apical dome. No major asymmetrical rearrangement was observed during the following phase of gravitropic curvature which is characterized by slower rates of bending. Labeling with FL-DHP was completely inhibited by a non-fluorescently labeled dihydropyridine. From these results it is suggested that FL-DHP labels calcium channels in rhizoids and protonemata. In rhizoids, positive gravitropic curvature is caused by differential growth limited to the opposite subapical flanks of the apical dome, a process which does not involve displacement of the growth centre, the calcium gradient or calcium channels. In protonemata, however, it is proposed that a statolith-induced asymmetrical relocalization of calcium channels and the Ca2+ gradient precedes, and might mediate, the rearrangement of the centre of growth, most likely by the displacement of the Spitzenkörper, to the upper flank, which results in the negative gravitropic reorientation of the growth direction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004250050744
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  • 8
    Digitale Medien
    Digitale Medien
    Commonalities between pollen/stigma and host/pathogen interactions: calcium accumulation during stigmatic penetration by Brassica oleracea pollen tubes (1999)
    Springer
    Sexual plant reproduction 12 (1999), S. 194-202 
    Details
    ISSN: 1432-2145
    Schlagwort(e): Key words.Brassica ; Calcium ; Epidermis ; Host/Pathogen ; Pollen/stigma
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. Parallels have been explored between the early stages of stigmatic penetration by pollen tubes and the infection of epidermal cells by fungal pathogens. In a striking resemblence to events following the infection of Hordeum sp. by Erysiphe graminis, X-ray microanalysis has revealed the accumulation of calcium at the stigmatic surface following pollinations in Brassica oleracea. X-ray mapping strongly indicates the calcium to be localised at the points at which either the pollen grain or its tube makes contact with the surface of the stigmatic papilla. No definitive measures were made of the concentration of calcium at these sites, but controls indicated the levels to be well in excess of those found in the cytosol. X-ray microanalysis at the pollen/stigma interface failed to detect the presence of silicon, an element frequently accumulated by epidermal cells in response to pathogenic challenge. The phenylpropanoid biosynthesis pathway is activated by many plant hosts following infection by fungal pathogens, and the accumulation of autofluorescent material in the stigma 24 h after contact with self pollen strongly indicates this pathway also to be activated after pollination. The timing of this response, however, suggests that phenolic products are unlikely to be involved in the rejection of self pollen. These data are discussed in the perspective of current views of defence systems present in angiosperm epidermal cells, and why these mechanisms fail to identify and reject incompatible pollen tubes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004970050192
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  • 9
    Digitale Medien
    Digitale Medien
    Magnetic properties of human liver and brain ferritin (1999)
    Springer
    European biophysics journal 28 (1999), S. 263-267 
    Details
    ISSN: 1432-1017
    Schlagwort(e): Key words Human liver ; Human brain ; Ferritin ; Electron microscopy ; Mössbauer spectroscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: Abstract Human brain (globus pallidus) and liver tissues were investigated by means of electron microscopy (EM), Mössbauer spectroscopy (MS) and SQUID magnetometry techniques. Based on MS measurements, the iron present was identified to be in the ferritin-like form (61–88%) and in the form of a low-spin iron species (the balance). Its overall concentration was estimated as 1.5(3) mg in the brain and 2.4(5) mg in the liver, per gram of lyophilized tissue. The average core diameter was determined by EM measurements to be equal to 7.5(1.3) nm for the liver and 3.3(5) nm for the brain. Magnetization measurements carried out between 5 and 300 K yielded an estimation of an average blocking temperature, KT BL, as equal to 6.7 K and 8.5 K for the liver and the brain, respectively. From the dependence of KT BL on the external magnetic field it was concluded that the ferritin-like cores in the studied samples can be regarded as non-interacting particles. Finally, the uniaxial magnetic anisotropy constant was determined to be 6×103 J/m3 for the liver and 4×104 J/m3 for the brain.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002490050208
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  • 10
    Digitale Medien
    Digitale Medien
    Types, numbers and distribution of synapses on the dendritic tree of an identified visual interneuron in the brain of the locust (1999)
    Springer
    Cell & tissue research 296 (1999), S. 645-665 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Descending contralateral movement detector (DCMD) ; Identified neuron ; Vesicles ; Electron microscopy ; 3-D reconstruction ; Locust ; Schistocercagregaria (Insecta)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  The descending contralateral movement detector (DCMD), an identified descending interneuron in the brain of the locust Schistocerca gregaria has been investigated by using light and electron microscopy. We describe the fine structure, distribution and numbers of synapes that it receives from another identified brain neuron, the lobular giant movement detector (LGMD), and from unidentified neurons. The DCMD dendrites emerging from the integrative segment vary in form and number between individuals and sexes but always form a flattened dendritic domain. The arborizations and the integrative segment appear to be exclusively postsynaptic. Two types of synaptic contacts (Type 1 and 2) onto the DCMD can be discerned as having either round (Type 1) or pleiomorphic synaptic vesicles (Type 2) and by large (Type 1) or small (Type 2) subsynaptic appositions. Contact zones of Type 1 synapses are smaller than those of Type 2. LGMD-synapses are of Type 1 and occur intermingled with presynaptic sites of unidentified units. Some branches of the DCMD receiving input from unidentified units are devoid of contacting LGMD processes. Synapses of both types are randomly distributed over the DCMD integrative segment and at fibres with similar sizes.Type 1 synapses are much more frequent than Type 2 synapses and their number is negatively correlated with fibre diameter. For a whole DCMD dendritic arborization, a total of 8500 active zones of chemical synapses has been calculated, including a mininum of 2250 LGMD-synapses and about 1000 Type 2 synapses. The DCMD may thus receive a considerable amount of input from as yet unidentified neurons.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051325
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  • 11
    Digitale Medien
    Digitale Medien
    Metaphase-specific cell death in meiotic spermatocytes in mice (1999)
    Springer
    Cell & tissue research 296 (1999), S. 359-369 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Apoptosis ; Electron microscopy ; Meiosis ; Spermatocytes ; Spermatogenesis ; Testis ; TUNEL ; Mouse (10 strains)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  Apoptosis of male germ cells is a widespread but little-understood phenomenon in many animal species. The elucidation of its mechanisms could be useful in the understanding of male infertility. We have examined the distribution of dying cells with the terminal transferase-mediated nick-end labeling (TUNEL) method and by an electron-microscopic procedure in the testes of 10 mouse strains, viz., C57BL/10 (B10), SL/NiA (SL), C57BL/6 (B6), C3H/He (C3H), BALB/c (BALB), DBA2 (DBA), CBA/J (CBA), MRL/MpJ-+/+ (M+), MRL/MpJ-lpr/lpr (lpr), and wild-type NJL mice (Mus musculus musculus). In the testes of the B10, NJL, SL, B6, C3H, BALB, DBA, and CBA mice, very few TUNEL-positive cells are distributed in the seminiferous tubules, whereas in the testes of the M+ and lpr mice, many TUNEL-positive cells, which are restricted to stage XII seminiferous tubules, have been identified. The most important finding is that many metaphases of meiotic spermatocytes show a marked TUNEL-positive reaction. Some metaphases show apoptotic morphology electron-microscopically. These results suggest that the testes of MRL strains will provide a useful model for the study of the mechanism of metaphase-specific apoptosis in meiotic spermatocytes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051296
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  • 12
    Digitale Medien
    Digitale Medien
    Effect of high-level oxygen exposure on the peroxidase activity and the neuromelanin-like pigment content of the nerve net in the earthworm, Lumbricus terrestris (1999)
    Springer
    Cell & tissue research 295 (1999), S. 349-354 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Neuromelanin ; Neuron ; Peroxidase ; Oxygen metabolism ; High-definition light microscopy ; Electron microscopy ; Ultrastructure ; Cytochemistry ; Substantia nigra ; Lumbricusterrestris (Annelida)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Histochemical examination of 1-μm tissue sections from the dorsal nerve plexus of the earthworm, Lumbricus terrestris, reveals multiple brown intraneuronal granules. These granules contain material morphologically and histochemically consistent with neuromelanin. When viewed with transmission electron microscopy, these were seen as single membrane-enclosed biphasic granules with diameters of 370–730 nm. Exposure of L. terrestris to high-level environmental oxygen resulted in an increase in the number of neuromelanin-like pigment granules within the neurons of the circular muscle layer. As measured by ortho-phenylenediamine hydrochloride, the endogenous peroxidase activity of extracts from worms incubated in high-level environmental oxygen was 51% more than controls. The endogenous peroxidase activity was localized in situ with 3,3-diaminobenzidine (DAB) and was found to increase in and around the neuromelanin-like pigment-containing neurons within the circular muscle layer. These studies suggest that the nerve net of L. terrestris may serve as a model to study the role of neuromelanin production in oxidative stress and its relationship to endogenous peroxidases.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051241
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  • 13
    Digitale Medien
    Digitale Medien
    Op/op mice defective in production of functional colony-stimulating factor-1 lack macrophages in muscularis externa of the small intestine (1999)
    Springer
    Cell & tissue research 295 (1999), S. 485-493 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Immunohistochemistry ; Electron microscopy ; Interstitial cells of Cajal ; F4/80 ; CSF-1 ; Kit-receptor ; Mouse (op/op)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The osteopetrotic (op/op) mutant mouse possesses an inactivating mutation in the colony-stimulating factor-1 (CSF-1) gene, which results in the absence of certain macrophages and in osteopetrosis, following a lack of osteoclasts. Studies of the op/op mouse indicate that CSF-1-dependent tissue macrophages may belong to a trophic and/or scavenger subpopulation, which through their effect on other cell types can significantly affect tissue functions, and that cells which are CSF-1 independent have antigen presentation and immunological functions.We have previously identified a cell system of regularly distributed macrophages in the muscularis externa of the small intestine and wanted to extend these studies to the op/op mouse.The present investigations with light- and electron-microscopic methods using fluorescent dextran, methylene blue and immunohistochemistry (F4/80, anti-kit receptor, anti-CD3, anti-CD45R/B220) show that macrophages are absent from the muscle layers, with only an occasional macrophage present in the subserosa. In the lamina propria and submucosa, macrophage numbers are reduced. In all other respects the muscularis externa appears normal, including normal organization and number of interstitial cells of Cajal. Control and op/op mice both lack cells expressing CD3 (T lymphocytes), CD45R/B220 (B lymphocytes) and mast cells in the muscularis externa. This leaves the muscularis externa macrophages as the most likely source of local cytokine production under such conditions as postoperative ileus and intussusception in infants, where the muscularis externa appears to be one target of cytokines. We conclude that the lack of macrophages, combined with the preservation of otherwise normal structure, will make the op/op mouse a valuable model by which to assess the functions and relative importance of the muscularis externa macrophages in relation to intestinal motility under normal and pathological conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051254
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  • 14
    Digitale Medien
    Digitale Medien
    Caveolin and its cellular and subcellular immunolocalisation in lung alveolar epithelium: implications for alveolar epithelial type I cell function (1999)
    Springer
    Cell & tissue research 295 (1999), S. 111-120 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Caveolin ; Caveolae ; Lung ; Alveolar epithelial type I cell ; Immunocytochemistry ; Electron microscopy ; Confocal laser scanning microscopy ; Rat (CD)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Caveolae are flask-shaped invaginations of the plasmalemma which pinch off to form discrete vesicles within the cell cytoplasm. Biochemically, caveolae may be distinguished by the presence of a protein, caveolin, that is the principal component of filaments constituting their striated cytoplasmic coat. Squamous alveolar epithelial type I (ATI) cells, comprising approximately 95% of the surface area of lung alveolar epithelium, possess numerous plasmalemmal invaginations and cytoplasmic vesicles ultrastructurally indicative of caveolae. However, an ultrastructural appearance does not universally imply the biochemical presence of caveolin. This immunocytochemical study has utilised a novel application of confocal laser scanning and electron microscopy unequivocally to localise caveolin-1 to ATI cells. Further, cytoplasmic vesicles and flask-shaped membrane invaginations in the ATI cell were morphologically identified whose membranes were decorated with anti-caveolin-1 immunogold label. Coexistent with this, however, in both ATI and capillary endothelial cells could be seen membrane invaginations morphologically characteristic of caveolae, but which lacked associated caveolin immunogold label. This could reflect a true biochemical heterogeneity in populations of morphologically similar plasmalemmal invaginations or an antigen threshold requirement for labelling. The cuboidal alveolar epithelial type II cell (ATII) also displayed specific label for caveolin-1 but with no ultrastructural evidence for the formation of caveolae. The biochemical association of caveolin with ATI cell vesicles has broad implications for the assignment and further study of ATI cell function.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051217
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  • 15
    Digitale Medien
    Digitale Medien
    Changes of calcium distribution in ovules ofTorenia fournieri during pollination and fertilization (1999)
    Springer
    Protoplasma 208 (1999), S. 149-155 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Calcium ; Electron energy loss spectroscopy ; Embryo sac ; Torenia fournieri ; Fertilization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Calcium distribution in ovules ofTorenia fournieri was studied by electron energy loss spectroscopy and transmission electron microscopic visualization of calcium antimonate precipitates. High calcium levels were found in the ovules ofT. fournieri. Calcium is situated mainly in extracellular regions before fertilization, including the surface of embryo sac, in the mucilage, and among the cells of the egg apparatus. Intracellular calcium was found only in the nucellar cells around the embryo sac and in the epidermis of the central axis and funiculus. After pollination, a labyrinthine structure (coralloid-like cell wall formation) develops on the micropylar surfaces of the egg apparatus that contain high levels of calcium. Calcium levels increase in the degenerating synergid after the penetration of the pollen tube. Calcium-antimonate precipitates are abundant in vacuoles of the disrupted synergid and pollen tube cytoplasm.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01279085
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  • 16
    Digitale Medien
    Digitale Medien
    Cellulose and calcium lower the incidence of chemically-induced colon tumors in rats (1999)
    Springer
    Plant foods for human nutrition 54 (1999), S. 295-303 
    Details
    ISSN: 1573-9104
    Schlagwort(e): Calcium ; Cellulose ; Colon tumors ; Folic acid
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract In a 30-week preliminary study and a follow-up 22-week study (2 × 2 factorial), dimethylhydrazine (DMH)injections effectively induced colon tumors in Fischer-344rats. How this incidence of colon tumors might be affected by cellulose (preliminary study) or by calcium and folic acid (follow-up study) was examined. Cellulose in the dietappeared to provide some protection against DMH-induced colon tumors, but the protective effect of calcium was moreevident; normal levels of calcium (500 mg per 100 g diet), but not of folic acid (0.1 mg per 100 g diet), provided protection against colon tumors. The effect due to calciumwas observed whether viewed in terms of total number of tumors (p lt 0.01) or number of tumors per tumor-bearing rat(p 〈 0.01).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008149107282
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  • 17
    Digitale Medien
    Digitale Medien
    Calcium and the regulation of mammalian ciliary beating (1999)
    Springer
    Protoplasma 206 (1999), S. 234-240 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Cilia ; Calcium ; Acetylcholine ; Trachea ; Epithelium ; Video microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary This report summarizes our recent work on the role of intracellular Ca2+ ([Ca2+]i) in regulating mammalian ciliary beat frequency (CBF). CBF from a single ovine cilium and [Ca2+]i from the same cell were measured by digital video phase contrast microscopy and fura-2 ratiometric imaging video microscopy, respectively. Cells were stimulated with two exposures to 10 μM acetylcholine (ACh). CBF was recorded during the first and [Ca2+]i during the second stimulation. ACh increased [Ca2+]i and CBF transiently with indistinguishable kinetics and, early in culture, even induced [Ca2+]i oscillations and ciliary frequency modulations with the same peak-to-peak time interval. Cells treated with 1 μM thapsigargin, an inhibitor of the endoplasmic-reticulum Ca2+-ATPase, showed transient [Ca2+]i and CBF increases, again with similar kinetics, which often remained at an elevated plateau. Application of ACh to cells pretreated with thapsigargin produced decreases in both [Ca2+]i and CBF. Finally, changing extracellular Ca2+-concentrations induced corresponding changes in [Ca2+]i that were associated with kinetically similar CBF changes. These data strongly suggested that [Ca2+]i is a critical signal to regulate CBF in mammalian tracheal epithelial cells. In an initial effort to provide constraints on the number and type of reactions that link changes in [Ca2+]i to changes in CBF, simultaneous recordings of both signals from a single cell were analyzed. Such recordings provided higher resolution of the kinetic responses of CBF and [Ca2+]i to ACh as well as they allowed direct assessment of the coupling between [Ca2+]i and CBF. Simultaneous measurements revealed that [Ca2+]i and CBF were perfectly correlated within the CBF measurement time resolution, except for the period of the fastest changes in both signals during the initial ACh exposure. There, changes in CBF lagged the changes in [Ca2+]i by 1–3 ciliary beat cycles (ca. 150–450 ms).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01288210
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  • 18
    Digitale Medien
    Digitale Medien
    The intracellular events triggered by the self-incompatibility response inPapaver rhoeas (1999)
    Springer
    Protoplasma 208 (1999), S. 99-106 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Papaver rhoeas ; Self-incompatibility ; Calcium ; Signal transduction ; Cell-cell recognition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary In recent years self-incompatibility (SI) has come to be recognised as an important model system for studying cell-cell interactions and signalling in flowering plants. In this article we discuss the intracellular events associated with the SI response in the field poppy,Papaver rhoeas. The SI response inP. rhoeas is known to involve a Ca2+-based signalling pathway, activated following molecular interactions on the surface of incompatible pollen tubes. Evidence demonstrates that, following a transient increase in the concentration of cytosolic free Ca2+ ([Ca2+];) initiated by the SI response, phosphorylation of certain cytosolic proteins occurs, followed by activation of pollen gene expression. The magnitude of this transient Ca2+ wave and the localisation of cytosolic [Ca2+]i following the SI response are discussed. We also describe the character of the proteins specifically phosphorylated in the SI response and the nature of the protein kinases involved in their phosphorylation. Finally, we consider the possibility that the end result of the SI response inP. rhoeas may be analogous to programmed-cell-death mechanisms such as those seen in developmental processes and defence responses in various plant cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01279079
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  • 19
    Digitale Medien
    Digitale Medien
    Phase and aggregation behaviour of double-chain cationic surfactants from the class of N-alkyl-N-alkyl′-N, N-dimethylammonium bromide surfactants (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 856-867 
    Details
    ISSN: 1435-1536
    Schlagwort(e): Key words Double chain surfactants ; Aggregates ; Phase diagrams ; Lamellar phases ; Electron microscopy ; SANS
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract We present the phase diagrams and the properties of newly synthesised double-chain cationic N-alkyl-N-alkyl′-N,N-dimethylammonium bromide surfactants [C x C y DMABr (x = 12, 14 and 16; y = 10, 11, 12, 14 and 16)]. All the systems studied form liquid-crystalline lamellar phases but with different morphologies: unilamellar vesicles at low surfactant concentrations, multilamellar vesicles and tubular aggregates for surfactant concentrations between 2 and 10 wt% and at even higher concentrations planar bilayers of surfactant molecules in the classical Lα phase. The phase diagrams were determined with macroscopic and microscopic methods (polarisation microscopy, freeze-fracture transmission electron microscopy, scanning electron microscopy and differential interference contrast microscopy). The properties of the surfactant solutions were determined with differential scanning calorimetry measurements for Krafft point determination and small-angle neutron scattering measurements for interlamellar spacing and bilayer thickness. Finally, conductivity and viscosity measurements for phase characterisation were carried out.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003960050462
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  • 20
    Digitale Medien
    Digitale Medien
    Synthesis of colloids and films of Pr, Er and Yb with nonaqueous solvents (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 164-173 
    Details
    ISSN: 1435-1536
    Schlagwort(e): Keywords Nanostructures ; Thin films ; Vapor deposition ; Electron microscopy ; Optical properties
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract Colloidal dispersions of Yb, Er and Pr have been prepared by chemical liquid deposition. The metals were cocondensed at 77 K with 2-methoxyethanol and ethanol to produce solvated metal atoms. The particle size of the dispersions was determined by transmission electron microscopy to range from 52 to 1080 Å; the particles had spherical shapes. After solvent evaporation under vacuum, active solids and amorphous powder were deposited over Cu and Al metal. Dispersion stability, particle size, UV/Vis absorption and zeta potential were studied. The solids prepared by solvent evaporation were characterized by Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The films prepared on Al were studied by scanning electron microscopy. The most stable colloid was obtained using 2-methoxyethanol: several concentrations were stable for several months and the zeta potential indicated that this colloid stability is mainly due to solvation effects. FTIR spectroscopy of the solids indicated solvent incorporation in the film. This observation was corroborated by thermal analysis. Information on the thermal stability of the films was obtained by TGA. The UV/Vis absorption spectrum was measured at several concentrations under different conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003960050381
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  • 21
    Digitale Medien
    Digitale Medien
    Calcium, polarity and osmoregulation in Fucus embryos: one messenger, multiple messages (1998)
    Springer
    Experimental biology online 3 (1998), S. 1-14 
    Details
    ISSN: 1430-3418
    Schlagwort(e): Calcium ; Polarity ; Growth ; Signalling ; Cell volume control ; Fucus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract This review addresses the role of cytosolic Ca2+in the regulation of embryonic polarity, polarised growth and osmotic control of cell volume with particular emphasis on the marine alga Fucus. Evidence is presented that the control of cell elongation in plants and algae requires the co-ordinate control of cell turgor and vesicle exocytosis, all of which are regulated by cytosolic Ca2+. In the Fucus embryo, polarised growth of the rhizoid cell requires sustained elevation of Ca2+ at the rhizoid apex whereas osmotic cell volume control is effected by transient elevations of cytosolic Ca2+. The mechanisms by which these signals are generated and their different downstream responses are discussed. Answers to questions of how specificity of signalling can be achieved by signal-response pathways which share common components will require more detailed knowledge of the interactions between different components and the spatial and temporal patterns of their activation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s00898-998-0011-5
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  • 22
    Digitale Medien
    Digitale Medien
    Aluminum and calcium distribution patterns in aluminum-intoxicated roots of Allium cepa do not support the calcium-displacement hypothesis and indicate signal-mediated inhibition of root growth (1998)
    Springer
    Planta 205 (1998), S. 175-180 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Key words:Allium ; Aluminum ; Calcium ; Root ; Rhizotoxicity ; Toxicity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. The aluminum and calcium distributions in the root tips of aluminum-intoxicated onions, Allium cepa L., were mapped using PIXE (particle-induced X-ray emission) microanalysis. Not enough aluminum was present to have replaced, atom-for-atom, more than a minor fraction of the calcium. Furthermore, no inverse relationship between variations in aluminum and calcium concentrations was observed for pairs of adjacent 30-μm-diameter regions. Our observations, therefore, do not support the hypothesis that aluminum substantially reduces the quantity of bound calcium by competing with calcium for binding sites. Instead we suggest that reductions in calcium content are a non-local and indirect consequence of aluminum-intoxication. We found that aluminum accumulates almost exclusively in a surface layer. Observations of wounded roots indicated that exposed internal tissue binds aluminum avidly, so we contend that the surface accumulation pattern indicates that little aluminum penetrates into the interior of the root. We argue that aluminum does not directly inhibit growth in the interior of the apical root meristem because root growth rate was unaffected by root cap removal which should greatly increase the aluminum concentration in the exposed interior region. We hypothesize that growth inhibition in the interior of the meristem is mediated by a signal initiated or disrupted by excess aluminum in the periphery of the meristem.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004250050309
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  • 23
    Digitale Medien
    Digitale Medien
    Association of nickel versus transport of cadmium and calcium in tonoplast vesicles of oat roots (1998)
    Springer
    Planta 204 (1998), S. 390-396 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Key words:Avena (root ; tonoplast) ; Calcium ; Cadmi‐um ; Nickel ; Tonoplast ; Transport (ion)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. The plant vacuole has long been suspected of being a site for accumulation of Ni in plant roots, but testing this hypothesis directly by vacuole isolation is technically difficult and has not been reported. Here, we have attempted to determine if Ni can be transported into isolated oat (Avena sativa L.) root tonoplast vesicles as an alternative approach toward understanding the importance of the vacuole in Ni accumulation in roots. We found that, in contrast to Ca and Cd, Ni did not affect the proton gradient of vesicles (MgATP energized or artificially created), and further, that Cd/H antiport activity was not affected by the presence of Ni. Nickel was associated with vesicles, but relative rates of accumulation/association of metals with vesicles were Ca 〉 Cd  Ni. Protonophores and the potential Ni ligands citrate and histidine, and nucleoside triphosphates or PPi did not stimulate Ni association with vesicles. Comparison of Ni versus Ca and Cd associated with vesicles using various membrane perturbants indicated that while Ca and Cd are rapidly and principally antiported to the vesicle sap, Ni is only slowly associated with the membrane in a not-easily dissociated condition. Our results indicate the absence of an Ni/H antiport or Ni-nucleotide-dependent pump in oat root tonoplasts, and support the contention that the vacuole is not a major compartment for Ni accumulation in oat roots.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004250050271
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  • 24
    Digitale Medien
    Digitale Medien
    Blue light but not red light induces a calcium transient in the moss Physcomitrella patens (Hedw.) B., S. & G. (1998)
    Springer
    Planta 206 (1998), S. 278-283 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Key words: Aequorin ; Blue light ; Calcium ; Moss ; Photomorphogenesis ; Physcomitrella
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. In caulonemal filaments of the moss, Physcomitrella patens, which had been incubated in darkness, 3 s irradiation with blue light (λmax 450 nm) at fluence rates of 100 μmol m−2 s−1 and above caused a transient␣increase in cytosolic calcium ion concentration, [Ca2+]cyt, which was both intensity- and time-dependent. Measurements of [Ca2+]cyt were made using moss transformed with the cDNA for apoaequorin and reconstituting the Ca2+-dependent photoprotein aequorin in the cytosol by incubation in coelenterazine.␣In response to blue light at fluence rates of 100–1000 μmol photons m−2 s−1, [Ca2+]cyt increased transiently from a basal level of approximately 50 nM to between 200 and 700 nM. Irradiation with red light did not evoke any measurable change in [Ca2+]cyt. The presence of calcium in the incubating medium was not required for the increase in [Ca2+]cyt to occur. A mutant strain, gad-139, was identified which required an irradiance of only 1 s to evoke a response. The kinetics showed a delay of approximately 6 s from the beginning of illumination before the beginning of the increase in [Ca2+]cyt. The data suggest that the activation of a photoreceptor rather than the direct opening of calcium channels is involved in this blue-light response.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004250050401
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  • 25
    Digitale Medien
    Digitale Medien
    Distribution of calmodulin protein and mRNA in growing pollen tubes (1998)
    Springer
    Sexual plant reproduction 11 (1998), S. 131-139 
    Details
    ISSN: 1432-2145
    Schlagwort(e): Key words Calmodulin ; mRNA ; Calcium ; Pollen tube ; Agapanthus umbellatus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  Pollen tube growth is a vital process for angiosperm fertilisation and is dependent on the presence of a tip-focused gradient of cytosolic free calcium ([Ca2+]c). In order to clarify some of the target molecules which convey the Ca2+ signal information, we investigated calmodulin distribution during tube growth. Fluorescently labelled calmodulin was pressure microinjected into pollen tubes and its distribution monitored by confocal microscopy. Calmodulin distributes evenly throughout the cell, but some of its binding sites form a V-shaped collar behind the apical region. This specific association dissipates upon growth arrest, and suggests an interaction of calmodulin with cytoskeletal-bound target proteins. The distribution of calmodulin mRNA was also analysed by microinjection of fluorescently labelled mRNA. No specific pattern was observed, with an even localisation in the body of tube and a lower concentration in the cell apex. Studies with localised application of inhibitors/activators indicate that calmodulin plays a crucial role in tip elongation but does not direct tube orientation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004970050130
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  • 26
    Digitale Medien
    Digitale Medien
    A calcium-dependent ergosterol mutant of Saccharomyces cerevisiae (1998)
    Springer
    Current genetics 34 (1998), S. 93-99 
    Details
    ISSN: 1432-0983
    Schlagwort(e): Key words Ergosterol ; Antifungal ; Calcium ; Fenpropimorph ; Azole ; ERG24 gene
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract ERG24 is the structural gene for the C14-sterol reductase in yeast. A lack of activity in that enzyme, mediated either by the morpholine fungicides or the insertional inactivation of ERG24, causes the accumulation of the aberrant sterol ignosterol. Cells producing this sterol are unable to grow aerobically in the routine laboratory medium, YPD. However, growth does occur on a synthetic defined medium. A novel calcium-dependent phenotype associated with alterations in the ergosterol biosynthetic pathway in yeast is described. In addition, reduction of yeast growth with an azole inhibitor of the C-14 sterol de-methylase was also modulated by an excess of calcium ions in the culture medium. These results define a new effect of ergosterol deficiency and provide important practical implications for utilizing morpholine and azole sterol biosynthetic-inhibiting fungicides.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002940050371
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  • 27
    Digitale Medien
    Digitale Medien
    Morphological and physical characterization of the capsular layer of Vibrio cholerae O139 (1998)
    Springer
    Archives of microbiology 170 (1998), S. 339-344 
    Details
    ISSN: 1432-072X
    Schlagwort(e): Key wordsV. cholerae O139 ; Lipopolysaccharide ; Electron microscopy ; Freeze-substitution technique ; Capsule
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The morphological and physical characteristics of the capsule of Vibrio cholerae O139 were examined. An electron microscopic study using the freeze-substitution technique showed that all of the V. cholerae strains of the O139 serogroup examined have a very thin fibrous layer on the outside of the outer membrane. In contrast, the mutants of strain O139, strain MO10T4 (which lacks capsule synthesis), and strain Bengal-2R1 (which fails to synthesize both the capsule and the O-antigen of lipopolysaccharide) were all found to have lost the surface layer. In addition, the capsule layer could also not be observed on the surface of V. cholerae strain O1. To determine the biological characteristics of the capsule of strains of the O139 serogroup, we investigated the serum killing activity and bacterial phagocytosis by polymorphonuclear leukocytes. The O139 strains were more resistant to the serum killing activity than were the V. cholerae O1 strain and the O139 mutant strains, thus suggesting that the existence of the capsule gave a serum-resistant character to the O139 strains. The surface character of the O139 strains had the same hydrophobic character as did that of the O139 mutant strains and the O1 strain. In addition, all the V. cholerae O1 and O139 strains examined, including the mutant strains, were effectively ingested by the human polymorphonuclear leukocytes. The number of ingested bacteria was not significantly different among the strains, and the ingestion of the acapsular O139 mutants thus showed that the capsule does not play an antiphagocytic role. These data suggest that the capsule of V. cholerae O139 has a physiological function different from that of the ordinal hydrophilic capsule that is found in invasive bacteria such as Klebsiella pneumoniae.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002030050651
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  • 28
    Digitale Medien
    Digitale Medien
    Phylogenetic affiliation and ultrastructure of uncultured magnetic bacteria with unusually large magnetosomes (1998)
    Springer
    Archives of microbiology 169 (1998), S. 136-147 
    Details
    ISSN: 1432-072X
    Schlagwort(e): Key words Magnetic bacteria ; Biomineralization ; Magnetite ; 16S rRNA ; In situ hybridization ; Ultrastructure ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Natural enrichments of magnetic bacteria from the Itaipu lagoon near Rio de Janeiro were dominated by coccoid-to-ovoid morphotypes that produced unusually large magnetosomes. To determine the phylogenetic position of these unusual microorganisms, 16S rRNA genes were retrieved from bacteria magnetically separated from sediment of the Itaipu lagoon by in vitro amplification and cloning of PCR products into a plasmid vector. Partial sequencing of the obtained clones revealed two clusters of closely related sequences affiliated to a distinct lineage consisting exclusively of magnetic bacteria within the α-subclass of Proteobacteria. For a detailed phylogenetic analysis, several almost complete sequences of the 16S rRNA genes were determined. One representative clone of each cluster provided a PCR template for the in vitro transcription of group-specific polynucleotide probes complementary to a variable region of the 16S rRNA molecule. At least three different morphotypes of magnetic bacteria were reliably identified by post-embedding hybridization of ultra-thin sections. Electron microscopic analyses of hybridized cells enabled for the first time a detailed description of the morphological variety and ultrastructure of phylogenetically identified, uncultured magnetic bacteria. Two distinct coccoid bacteria were identified by the transcript probe complementary to the 16S rRNA sequence mabrj12, whereas the probe complementary to the sequence mabrj58 allowed the identification of an ovoid morphotype that displayed magnetosomes with the largest volumes observed to date.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002030050553
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  • 29
    Digitale Medien
    Digitale Medien
    Heat shock effects on second messenger systems of Neurospora crassa (1998)
    Springer
    Archives of microbiology 170 (1998), S. 191-200 
    Details
    ISSN: 1432-072X
    Schlagwort(e): Key words Heat shock ; Ethanol ; cAMP ; Protein ; kinase A ; cGMP ; Inositol phosphates ; Calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Exposure of growing hyphae of Neurospora crassa to heat shock (44 °C) or ethanol (2.6 M) for 1 h induced a significant increase in the cAMP level, which reached a maximum approximately 2 min after the beginning of treatment and then decreased to control values despite continued heat or ethanol exposure. A 10-s heat shock or a 5-s ethanol shock also resulted in a transient cAMP increase 2 min after the pulse. Heat shock or ethanol treatment led to an increase in the amount of catalytic subunits of the cAMP-dependent protein kinase A in the nucleus almost synchronously with the increase of cAMP in the cytoplasm. The concentration of cGMP decreased a few seconds after the beginning of heat shock (44 °C) or ethanol treatment (2.6 M) to approximately 50% of the control level. Exposure to heat shock (44 °C, 1 h) led to an increase in the amount of inositol phosphates 0.5–2 min after the onset of heat shock. Thereafter, inositol phosphate levels dropped to control values despite continued heat exposure. Incubation of growing hyphae with cAMP or 8-Br-cAMP led to a two- to threefold increase of inositol phosphates 10–300 s after the beginning of incubation. Heat treatment furthermore caused a rapid release of calcium from vacuoles as determined by Fura-2 measurement of the calcium content released from isolated vacuoles. These heat-shock-dependent second messenger changes may play a role in the heat-shock-induced phase shifts of the circadian clock and heat-shock-induced conidiation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002030050633
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  • 30
    Digitale Medien
    Digitale Medien
    X-ray diffractometry and electron microscopy of DNA from Bacillus subtilis bound on clay minerals (1998)
    Springer
    Sciences of soils 3 (1998), S. 1-10 
    Details
    ISSN: 1432-9492
    Schlagwort(e): Transformation ; Clay-DNA complexes ; Nucleases ; X-ray diffraction ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract DNA bound on clay minerals, sand, and humic acids has been shown, both in vitro and in situ, to be capable of transforming bacteria and to resist degradation by nucleases, which could result in the crypticity of genes in soil and other natural habitats. To determine where DNA is bound on clay minerals, which may help to explain how bound DNA becomes resistant to degradation by nucleases but retains the ability to transform competent cells, chromosomal DNA from Bacillus subtilis bound on montmorillonite (M) and kaolinite (K) was examined by X-ray diffractometry and transmission and scanning electron microscopy. X-ray diffraction analysis showed that the basal spacings of M and K were not altered, indicating that this DNA did not significantly intercalate the clays. Scanning and transmission electron microscopy showed that the binding of this DNA was primarily on the edges of M and K, although some binding was also apparent on the planar surfaces. Based on the results of these studies, it is postulated that: 1.extension from the edges of the clays enables the unbound end of DNA to interact with receptor sites on competent cells and result in their transformation; and 2.binding on clays alters the electron distribution and/or conformation of DNA, which reduces its hydrolysis by nucleases.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s10112-998-0001-3
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  • 31
    Digitale Medien
    Digitale Medien
    Calcium distribution in fertile and sterile anthers of a photoperiod-sensitive genic male-sterile rice (1998)
    Springer
    Planta 204 (1998), S. 183-192 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Key words: Anther ; Calcium ; Male sterility ; Oryza (fertility) ; Pollen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. Potassium antimonate was used to locate Ca2+ in fertile and sterile anthers of a photoperiod-sensitive genic male-sterile rice (Oryza sativa L. japonica). During the development of fertile anthers, abundant calcium precipitates accumulated in the anther walls and on the surface of pollen grains and Ubish bodies at the late developmental stage of the microspore, but not in the cytoplasm of pollen grains. Following the accumulation of starch grains in pollen, calcium precipitates on pollen walls diminished and increased in parenchymatous cells of the connective tissue. In sterile anthers, calcium precipitates were abundant in the middle layer and endothecium, but not in the tapetum, as was found in fertile anthers. A special cell wall was observed between the tapetum and middle layer of sterile anthers that appeared to relate to distinctive calcium accumulation patterns and poor pollen wall formation in the loculi. The formation of different patterns of antimonate-induced calcium precipitates in the anthers of photoperiod-sensitive genic male-sterile rice indicates that anomalies in the distribution of calcium accumulation correlate with the failure of pollen development and pollen abortion.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004250050245
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  • 32
    Digitale Medien
    Digitale Medien
    Sutural mineralization of rat calvaria characterized by atomic-force microscopy and transmission electron microscopy (1998)
    Springer
    Cell & tissue research 294 (1998), S. 93-97 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Calvaria ; Mineralization ; Calcium ; Phosphorus ; Apatite ; Atomic-force microscopy ; Transmission electron microscopy ; Rat (Sprague Dawley)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  The application of transmission electron microscopy (TEM) and atomic-force microscopy (AFM) aid the acquisition of detailed structural information on the process of hard tissue formation. The sutural mineralization of rat calvaria is taken as a model for a collagen-related mineralization system. After cryofixation or chemical fixation an anhydrous tissue preparation technique with no staining procedures is used. The atomic-force microscope and the transmission electron microscope are used for structural analysis of the mineralizing region of the sutural tissue. With the application of AFM the collagen macroperiod is shown to be well represented in the unmineralized sutural tissue. At the mineralization front the collagen fibrils are found to be thickened and to change to a characteristic stacked platelet structure. Using TEM the macroperiod is faintly visible before mineral crystallites have formed and is more prominent after the apatite crystallization has started in the fibrils. In this step a needle-like structure of the newly formed apatitic crystals is visible.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051159
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  • 33
    Digitale Medien
    Digitale Medien
    Distribution and submicroscopic immunogold localization of cellular prion protein (PrPc) in extracerebral tissues (1998)
    Springer
    Cell & tissue research 292 (1998), S. 77-84 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Prion protein (PrPc) ; Electron microscopy ; Secretory granules ; Membrane ; Extracerebral tissues ; Hamster ; Human
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  In transmissible spongiform encephalopathies (TSE), such as scrapie in animals and Creutzfeldt-Jakob disease in humans, the central event is the conversion of a host-encoded amyloidogenic protein (PrPc) into an abnormal isoform (PrPsc) that accumulates as amyloid in TSE brain. PrPc is a membrane sialoglycoprotein synthesized in the central nervous system and elsewhere. We have examined the ultrastructural localization of PrPc in numerous hamster and some human extracerebral tissues, by means of a post-embedding electron-microscopic method combined with immunogold labeling. In stomach, intestine, lung, and kidney from hamsters, and in stomach, kidney, and spleen from humans, immunogold labeling specific for PrPc is observed on various cellular substructures related to secretory pathways: Golgi apparatus, secretory globules, and plasma membrane. In mucous epithelial cells of stomach and intestine, PrPc appears to be concentrated in secretory globules, suggesting a role for PrPc in the secretory function of the digestive tract. The secretory aspect of PrPc may be a key to understanding the physiopathological mechanisms underlying TSE.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051036
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  • 34
    Digitale Medien
    Digitale Medien
    A role for vesicles in human basophil secretion (1998)
    Springer
    Cell & tissue research 293 (1998), S. 1-22 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Piecemeal degranulation ; Histamine ; Charcot-Leyden crystal protein ; Anaphylactic degranulation ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  The evidence for vesicular transport as a mechanism for secretion by human basophils is reviewed. Initially, direct electron-microscopic inspection of experimentally produced and sequentially biopsied contact allergy skin lesions revealed a unique form of secretion termed piecemeal degranulation, characterized by the slow emptying of secretory granule contents (with retention of empty containers) in the absence of extrusion of entire granules. Budding of small vesicles to/from secretory granules was observed, and cytoplasmic vesicles were abundant. A generalized degranulation model was proposed to unify classical regulated secretion and this new form of secretion. Investigation of the mechanism(s) of secretion from human basophils required the development of numerous tools and resources. Chief among these were: (a) isolation and purification of circulating basophils; (b) identification of specific growth factors to increase the supply of this rare granulocyte; (c) understanding of secretogogue mechanisms and reliable analyses of secreted basophil products; and (d) development of ultrastructural preparations allowing imaging of small vesicles and quantifiable small electron-dense tags for granule materials in small vesicles. Applications of these tools to well-defined models of basophil secretion have established a role for vesicles as a mechanism for effecting secretion of histamine and the Charcot-Leyden crystal protein from activated human basophils.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051093
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  • 35
    Digitale Medien
    Digitale Medien
    Maturation of rat dendritic cells during intrahepatic translocation evaluated using monoclonal antibodies and electron microscopy (1998)
    Springer
    Cell & tissue research 294 (1998), S. 503-514 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words Dendritic cells ; Maturation ; Intrahepatic translocation ; Immunohistochemistry ; Electron microscopy ; Rat (Wistar)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Specific populations of hepatic sinusoidal cells were stained with monoclonal antibodies that recognize monocytes/macrophages (ED1), tissue macrophages (Kupffer cells) (ED2), MHC class II (Ia) antigen (MRC OX6), and dendritic cells/γ,δ T-cells (MRC OX62) and analyzed by light and electron microscopy. The majority of ED1+ and/or ED2+ cells were localized to the hepatic parenchyma, whereas OX6+ and/or OX62+ cells were more densely distributed within Glisson’s sheath than in the hepatic parenchyma. Double-immunoperoxidase staining of normal liver for ED1, ED2, and OX6 identified dendritic cells (DC) of two different phenotypes, ED1+ED2–OX6+ and ED1–ED2–OX6+. DC can be classified into three different types based on ultrastructural characteristics. The first type (type I) is characterized by one or more long cytoplasmic processes and a well-developed lysosomal system. The second type (type II) has an inconspicuous lysosomal system, abundant hyaloplasm, and characteristic short cytoplasmic processes. The third type (type I–II) has cytologic features intermediate between those of type I and type II DC. At the electron-microscopic level, these three cell types are found in the sinusoidal lumen, whereas the majority of type II DC are located in the space of Disse and Glisson’s sheath. Furthermore, some OX6-labeled elongated DC appeared to traverse the lumen of sinusoids through endothelial pores to enter the space of Disse. One hour after intravenous injection of latex particles (0.81 μm in diameter), numerous latex-laden dendritic cells (ED1+OX6+, type I and type I–II) were detected in the lumen of hepatic sinusoids, but not in the space of Disse or Glisson’s sheath. These findings suggest that normal rat liver contains resident dendritic cells which downregulate phagocytic activity and mature into potent accessory cells during migration from the portal vein toward the central vein. These DC then traverse the sinusoidal lumen to the hepatic lymph system via the space of Disse.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410051201
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  • 36
    Digitale Medien
    Digitale Medien
    Interaction of the Escherichia coli DnaA protein with bacteriophage k DNA (1998)
    Springer
    Molecular genetics and genomics 259 (1998), S. 679-688 
    Details
    ISSN: 1617-4623
    Schlagwort(e): Key words Bacteriophage λ ; DnaA-DNA interactions ; Electron microscopy ; DNA-protein complexes ; Escherichia coli
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Interaction of the Escherichia coli DnaA (replication initiator) protein with restriction fragments of phage λ DNA demonstrated differential binding of DnaA along the whole λ DNA. Interaction of DnaA with the λ replication region (from the promoter p R to the origin of replication, oriλ) demonstrated a strong binding of DnaA to the region around the p o promoter where synthesis of a short antisense oop RNA is initiated. The four sequences protected by DnaA (two 9mers and two 5mers) are not related even to a relaxed DnaA box. The pattern of protection of these four sequences and the location of three DNase I hypersensitive sites in the λ DNA r strand, together with results of mobility shift assays and electron microscopy studies, may indicate an interaction involving DnaA monomers bound to different DNA positions on one side of the helix and the formation of higher-order nucleoprotein structures. Therefore, it is tempting to suggest that DnaA, in addition to its activity in regulation of replication and transcription, could be considered as a factor which structures certain chromosomal regions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004380050863
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  • 37
    Digitale Medien
    Digitale Medien
    Apoptosis and redox homostasis: On a possible mechanism of action of Bcl-2 (1998)
    Springer
    Protoplasma 205 (1998), S. 10-20 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Proto-oncogene product Bcl-2 ; Calcium ; Mitochondria ; Plasma membrane NADH oxidoreductase ; Transcription factor NF-κB
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary We discuss the involvement of several mammalian redox systems in the regulation of apoptosis. We focus especially on the role that mitochondria and the still ill-characterized plasma membrane NADH-oxidoreductase system play in apoptosis. The latter system was shown to respond to downregulation of mitochondrial function; inhibition of either system induces apoptosis. Apoptosis induced by inhibitors of the oxidase involves both Bcl-2 and calcineurin, two proteins recently shown to be capable of forming a tight complex. We suggest that Bcl-2 acts as an antioxidant, but in an electron sense rather than in an oxygen sense.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01279288
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  • 38
    Digitale Medien
    Digitale Medien
    Cytosolic Ca2+ and H+ buffers in green algae: A reply (1998)
    Springer
    Protoplasma 203 (1998), S. 210-213 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Allosteric interaction ; Calcium ; Cytosolic buffer capacity ; Exchange buffer ; Eremosphaera viridis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The explanation of the coupling between butyrateinduced changes in cytosolic pH and pCa by means of a H+/Ca2+ exchange buffer as proposed by Plieth et al. [Protoplasma (1997) 198: 107–124; 199: 223] was questioned by Schönknecht and Bethmann [Protoplasma (1998) 203: 206–209]. They suggested an allosteric control of binding similar to the Hill equation. Fitting the measured pH-pCa coupling shows that a distinction between the models requires data which would be outside the experimentally accessible range. Plausibility considerations provide a support for the exchange buffer. The Hill equation is just a phenomenological approach which does not account for the diversity of allosteric mechanisms. The benefits of the exchanger model are firstly its mechanistic simplicity and secondly its flexibility as the same set of equations can also be used for an allosteric interaction between H+- and Ca2+-binding sites. The model can easily be extended to include future more detailed data. Finally, the cytosolic buffer capacities for H+ and Ca2+ are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01279478
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  • 39
    Digitale Medien
    Digitale Medien
    Electron and X-ray microscopic analyses of reaggregated materials obtained after fractionation of dissolved sporopollenin (1998)
    Springer
    Protoplasma 204 (1998), S. 13-21 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Sporopollenin ; Solubilisation ; 2-Aminoethanol ; Reaggregation ; Electron microscopy ; X-ray microscopy ; Thypha angustifolia L
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Exines fromTypha angustifolia L. pollen were dissolved in hot 2-aminoethanol. The solubilisate was successively fractionated and reaggregated via a dialysis cascade with dialysis tubings of different exclusion volumina. Four fractions of reaggregated material with different molecular mass were obtained. Fraction 1 with a molecular mass above 25,000 Da, fraction 2 with a molecular mass between 10,000–25,000 Da, fraction 3 with a molecular mass between 5,000–10,000 Da, and fraction 4 of a molecular mass lower than 5,000 Da. The fractions were comparatively analysed by scanning and transmission electron microscopy and X-ray microscopy. The material of the fractions with a molecular mass above 10,000 Da exhibit high congruence to the initial material. Analysis of the reaggregated material with the lowest molecular mass revealed special distinct substructures which in form and size showed high similarities to substructures of exines described in literature. In detail, spherical substructures consisting of an electron-dense core surrounded by an electron-transparent corona and in addition elongated substructures with a distinctive surface sculpture were detected.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01282289
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  • 40
    Digitale Medien
    Digitale Medien
    Callose deposition and breakdown, followed by phytomelan synthesis in the seed coat ofGasteria verrucosa (Mill.) H. Duval (1998)
    Springer
    Protoplasma 201 (1998), S. 221-230 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Callose ; Electron microscopy ; Gasteria verrucosa ; Phenolics ; Phytomelan ; Seed coat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary In the seed coat ofGasteria verrucosa the deposition of phytomelan takes place during seed development in three stages. Phytomelan is a black cell wall material which is chemically very inert. First the radial walls and part of the transverse cell wall of the outer epidermis of the outer integument become thickened by exocytosis of dictyosome vesicles. Callose is deposited at the tangential plasma membrane against those walls. After the callose deposition about two thirds of the original cell volume is filled with callose. During the second stage the callose is broken down, probably into glucose monomers or small polymers. At the same time cellulose is deposited at the outer tangential plasma membrane, forming a wall between the dissolving callose and the plasma membrane. In the third phase small granules appear in the solution of dissolved callose. which grow out and finally fuse to form a block of phytomelan, consisting of spherical 15-nm units. Remarkable is the function of the callose: it determines the size of the phytomelan block, and it probably functions as carbohydrate source for the phytomelan synthesis and/or for the cellulose inner layer. In this study transmission electron microscopy and cryo scanning electron microscopy are used to study the three developmental stages of the formation of the phytomelan layer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01287418
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  • 41
    Digitale Medien
    Digitale Medien
    Prevention and Treatment of Postmenopausal Osteoporosis (1998)
    Springer
    Pharmacy world & science 20 (1998), S. 198-205 
    Details
    ISSN: 1573-739X
    Schlagwort(e): Bisphosphonates ; Calcium ; Hormone Replacement Therapy ; Menopause ; Osteoporosis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The purpose of the review is to outline the interventions, both pharmacological and non‐pharmacological, available to prevent postmenopausal osteoporosis (PMO) and treat the established disease. Current suggested guidelines for the most cost‐effective treatment and prophylactic strategies are included following a consideration of the available options. As life expectancy has increased so has the incidence of PMO which has major quality of life implications for the sufferers and economic implications for the authorities responsible for their treatment. PMO represents a significant public health problem and although more effective treatments are becoming available prevention of the disease by taking account of existing risk factors is preferable. Indeed, a population approach to prevention may be more cost effective than screening for the disease. Attention to dietary calcium intake and exercise regimes have been shown to be effective prophylactic measures premenopausally, while the treatment of choice is hormone replacement therapy (HRT). HRT treats other postmenopausal symptoms in addition to PMO and is available in many presentations, containing different hormones, at different doses intended for different routes of administration. The optimum treatment duration is controversial and may contribute to some of the risks associated with HRT such as endometrial and breast carcinoma and venous thromboembolism (VTE). Newer effective treatments include the bisphosphonates and novel formulations of calcitonin, but older approaches such as vitamin D, anabolic steroids and fluoride are still utilised in some circumstances. However, most promise has been shown by synthetic hormonal modulators currently being trialled.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008682921480
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  • 42
    Digitale Medien
    Digitale Medien
    Virus assembly inHincksia hincksiae (Ectocarpales, Phaeophyceae) An electron and fluorescence microscopic study (1998)
    Springer
    Protoplasma 203 (1998), S. 153-167 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Algae ; Virus assembly ; DAPI staining ; Electron microscopy ; Hincksia hincksiae ; Immunofluorescence ; Marine double-stranded DNA virus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The filamentous brown algaHincksia hincksiae can be infected by a large icosahedral double-stranded DNA virus (HincV-1). The virus shows extended latency and is replicated only in cells homologous to sporangia. Virus formation was studied by transmission electron microscopy, DAPI staining, and β-tubulin immunofluorescence. Inhibition of cytokineses results in multinucleate cells, which are the first indication of virus replication in productive cells; the microtubular cytoskeleton does not seem to be affected by the virus. Replication of viral DNA begins in the nuclei, which increase in size and eventually disintegrate. Virus assembly takes place in a mixed nucleo-/cytoplasm. Capsids bud from cisternae, which are interpreted as modified endoplasmic reticulum aggregated to virus assembly centres. The internal membranous component of the virus is thus derived from the endoplasmic reticulum. The particles are empty (electron translucent) when assembled, and the nucleoprotein core seems to be packaged subsequently through an opening in the capsid. A number of fine structural features not previously reported from brown algae and related to virus formation are described. Our results on Hincksia hincksiae virus are compared with observations made on various other icosahedral DNA viruses infecting eukaryotic algae and animals.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01279472
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  • 43
    Digitale Medien
    Digitale Medien
    Mitochondrial Ca2+ Transients in Cardiac Myocytes During the Excitation–Contraction Cycle: Effects of Pacing and Hormonal Stimulation (1998)
    Springer
    Journal of bioenergetics and biomembranes 30 (1998), S. 207-222 
    Details
    ISSN: 1573-6881
    Schlagwort(e): Calcium ; cardiac myocytes ; confocal microscopy ; Fluo 3 ; Indo 1 ; isoproterenol ; mitochondria
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Physik
    Notizen: Abstract Using laser scanning confocal microscopy, our objective was to measure mitochondrial, nuclear, and cytosolic free ionized Ca2+ in adult rabbit cardiac myocytes loaded with Ca2+-indicating fluorophores. When myocytes were loaded with Fluo 3 at 37°C, the fluorophore was loaded extensively into the cytosol and nucleus, but poorly into mitochondria, and Fluo 3 fluorescence transients after field stimulation were confined to the cytosol and nucleus. In contrast, after loading at 4°C, Fluo 3 also entered mitochondria, and large transients of mitochondrial Fluo 3 fluorescence then occurred after stimulation. Isoproterenol (1 μM) increased the magnitude of Ca2+ transients and their subsequent rate of decay, an effect more marked in the cytosol and nucleus than in mitochondria. As pacing frequency was increased from 0.5 to 2 Hz, diastolic mitochondrial Ca2+ rose markedly in the absence but not in the presence of isoproterenol. Resting Ca2+ estimated by Indo 1 ratio imaging using UV/visible laser scanning confocal microscopy was about 200 nM in all compartments. During field stimulation, Ca2+ transiently increased to 671, 522, and 487 nM in cytosol, interfibrillar mitochondria, and perinuclear mitochondria, respectively. Isoproterenol increased these respective peak values to 1280, 750, and 573 nM. These results were consistent with those obtained in Fluo 3 experiments. We conclude that rapid mitochondrial Ca2+ transients occur during excitation–contraction coupling in adult rabbit cardiac myocytes, which may be important in matching mitochondrial metabolism to myocardial ATP demand during changes in cardiac output.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1020588618496
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  • 44
    Digitale Medien
    Digitale Medien
    Pancreatic islets cultured on extracellular matrix: An excellent preparation for microfluorometry (1998)
    Springer
    Methods in cell science 19 (1998), S. 255-268 
    Details
    ISSN: 1573-0603
    Schlagwort(e): Calcium ; In vitro ; Insulin secretion ; Islets of Langerhans ; Metabolism
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We have examined the use of extracellular matrix (ECM) as a substratum for mouse pancreatic islet cultures with special reference to microfluorometry work. We find the techniques for obtaining and maintaining ECM-producing cell cultures and coating of glass straightforward. The islets attached readily to ECM-coated glass and with time spread out. Cultures were probed for glucose responses after one day, one week and two weeks. Upon stimulation with 10 mM glucose, the well-established initial changes in [Ca2+]i, (monitored with Fura-2), as well as oscillations upon prolonged exposure, were observed. At 20 mM glucose only an elevated level without oscillations was seen. Similar responses were observed during the two weeks in culture. After one week in culture or more, single cell measurements of qualitative changes in [Ca2+]i and cell membranepotential (monitored with the dye bis-(1,3-dibutyl-barbituric acid) trimethine oxonol (DiBAC4(3)) could be performed concurrently on single cells at the islet periphery with ordinary fluorescence microscopy equipment. Simultaneous measurements of NAD(P)H and flavine adenine dinucleotide (FAD) fluorescence as well as measurements of rhodamine 123 fluorescence for mitochondrial membrane potential showed stable metabolic responses to glucose over the entire culture period. The islets had clearly elevated insulin secretion at 10 and 20 mM glucose compared to the secretion at 3 mM. In conclusion, mouse pancreatic islets cultured for up to two weeks on ECM-coated glass coverslips provide a functionally well- preserved and reproducible preparation for microfluorometry. The largest benefit of the method is that whole islet responses as well as single cell responses at the islet periphery can be monitored, using the same preparation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009712630494
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  • 45
    Digitale Medien
    Digitale Medien
    Genetic variability and diversity for protein and calcium contents in finger millet (Eleusine coracana (L.) Gaertn) in relation to grain color (1998)
    Springer
    Plant foods for human nutrition 52 (1998), S. 353-364 
    Details
    ISSN: 1573-9104
    Schlagwort(e): Calcium ; Finger millet ; Genetic diversity ; Genetic variability ; Grain quality ; Protein
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Analysis of 36 genotypes of finger millet ( Eleusine coracana (L.) Gaertn) with varying seed colors revealed a wide range of protein and calcium contents. White seeded genotypes had higher protein contents, while brown seeded types had a wide range of values. The brown seeded genotype GE 2500 had the highest protein content. Although protein content had significant negative association with calcium content, white seeded types had moderate levels of calcium. The genotypic coefficients of variability were moderate and high for protein and calcium, respectively. High heritability coupled with high genetic advance indicated their governance by additive gene action. A negative significant correlation was observed between protein content and grain yield. Mahalanobis D 2 analysis grouped the 36 genotypes into eight clusters. Clustering pattern failed to indicate any relationship between genetic diversity and geographic diversity. Based on genetic diversity and performance, the genotypes MS 1168, MS 174 and CO 13 were found to be suitable for use as parents in a hybridization program for improving yield; the genotypes MS 1168, MS 174 and MS 2869 for protein and Malawi 1915 and CO 11 for calcium. Protein and calcium contents contributed less to genetic divergence.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008074002390
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  • 46
    Digitale Medien
    Digitale Medien
    Renewing olfactory receptor neurons in goldfish do not require contact with the olfactory bulb to develop normal chemical responsiveness (1997)
    Springer
    Journal of comparative physiology 181 (1997), S. 425-437 
    Details
    ISSN: 1432-1351
    Schlagwort(e): Key words Olfactory receptor cells ; Olfactory bulbectomy ; Olfactory axotomy ; Electrophysiology ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract This study investigated whether contact with the olfactory bulb was necessary for developing and renewing olfactory receptor neurons (ORNs) to attain normal odorant responsiveness, and whether the anatomical and functional recoveries of the olfactory epithelium were similar in both bulbectomized (BE) and bilaterally axotomized (AX) preparations. In vivo electrophysiological recordings were obtained in response to amino acids, a bile acid [taurolithocholic acid sulfate(TLCS)] and a pheromonal odorant [17α, 20β,-dihydroxy-4-pregnen-3-one (17,20P)] from sexually immature goldfish. Both transmission and scanning electron microscopy indicated that the olfactory epithelium degenerated in BE and AX goldfish. Within 1–2 weeks subsequent to the respective surgeries, responses to high concentrations (〉0.1 mmol · l−1) of the more stimulatory amino acids remained, whereas responses were no longer obtainable to TLCS and 17,20P. At 4 weeks, responses to amino acid stimuli recovered to control levels, while responses to TLCS and 17,20P were minimal. By 7 weeks post bilateral axotomy, the olfactory epithelium recovered to a condition similar to control sensory epithelium; however, the rate of degeneration and proliferation of receptor neurons in BE preparations appeared to remain in balance, thus blocking further recovery of the olfactory epithelium. At 7 weeks post surgery, odorant responses of AX and BE goldfish to TLCS and 17,20P were still recovering.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003590050126
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  • 47
    Digitale Medien
    Digitale Medien
    Scots pine needle injuries at subarctic industrial sites (1997)
    Springer
    Trees 11 (1997), S. 378-387 
    Details
    ISSN: 0931-1890
    Schlagwort(e): Key words Pinus sylvestris (L.) ; Electron microscopy ; Heavy metals ; Multi-stress-symptoms ; SO2
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract  Injuries to needles of Scots pines (Pinus sylvestris L.) growing in nutrient-poor soils on the Kola Peninsula collected in April 1991 were studied on a gradient of increasing distances (10 – 115 km) from the Monchegorsk nickel smelter, Russia, which emits SO2, Ni and Cu. The condition of the mesophyll cells was quantified from needles of the two latest age classes using a light and an electron microscope. The damage to the ultrastructure consisted of multistress symptoms caused by excess sulphur, heavy metals, frost, acidic precipitation and ozone. Injuries were most commonly manifested in the form of dark, irregularly shaped chloroplasts with protrusions and light thylakoids and plastoglobuli. These symptoms gradually disappeared with increasing distance and decreasing deposition rate. Concentrations of sulphur, copper and nickel decreased towards more distant sites where normal levels of the latter two elements were reached. Sulphur concentrations remained above background throughout the distance gradient. In the closest plots to the smelter area, cell collapse under the stomata and epidermis related to acute SO2 and heavy metal effects was found, whereas further away symptoms were more diverse, pointing towards the effects of ozone, acidic deposition and thereby decreased frost tolerance. The additive multistress symptoms were clearly seen in the area up to 40 km from the smelter where needle Cu concentration was above 110 ppm, Ni concentration above 39 ppm and S concentration above 1343 ppm.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004680050099
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  • 48
    Digitale Medien
    Digitale Medien
    Overdrive excitation in the guinea pig sinoatrial node superfused in high [K+]o (1997)
    Springer
    Journal of biomedical science 4 (1997), S. 179-191 
    Details
    ISSN: 1423-0127
    Schlagwort(e): Sinoatrial node ; High potassium ; Overdrive excitation ; Oscillatory afterpotential and prepotential ; Calcium ; Tetrodotoxin ; Sodium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The aim of the present experiments was to study the characteristics and mechanisms of the rhythm induced by overdrive (‘overdrive excitation’, ODE) in the sinoatrial node (SAN) superfused in high [K+]o (8–14 mM). It was found that: (1) overdrive may induce excitation in quiescent SAN and during a slow drive; (2) in spontaneously active SAN, overdrive may accelerate the spontaneous discharge; (3) immediately after the end of overdrive, a pause generally precedes the onset of the induced rhythm; (4) during the pause, an oscillatory potential (Vos) may be superimposed on the early diastolic depolarization (DD); (5) during the subsequent late DD, a different kind of oscillatory potential appears near the threshold for the upstroke (ThVos) which is responsible for the initiation of spontaneous activity; (6) once started, the induced rhythm is fastest soon after overdrive; (7) faster drives induce longer and faster spontaneous rhythms; (8) the induced action potentials are slow responses followed by DD with a superimposed Vos, but ThVos is responsible for ODE; (9) the induced rhythm subsides when ThVos miss the threshold and gradually decay; (10) low [Ca2+]o abolishes ODE; (11) in quiescent SAN, high [Ca2+]o induces spontaneous discharge through ThVos and increases its rate by enhancing Vos and shifting the threshold to more negative values, and (12) tetrodotoxin abolishes ODE as well as the spontaneous discharge induced by high [Ca2+]o. In conclusion, in K+-depolarized SAN, ODE may be present in the apparent absence of calcium overload, is Ca2+- and Na+-dependent and is mediated by ThVos and not by Vos.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02255647
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  • 49
    Digitale Medien
    Digitale Medien
    Effects of calcium and magnesium on strontium distribution coefficients (1997)
    Springer
    Environmental geology 32 (1997), S. 219-229 
    Details
    ISSN: 1432-0495
    Schlagwort(e): Key words Strontium ; Calcium ; Magnesium ; Distribution ; Distribution coefficient ; Kd ; Competing cations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract  The effects of calcium and magnesium on the distribution of strontium between a surficial sediment and simulated wastewater solutions were measured as part of an investigation to determine strontium transport properties of surficial sediment at the Idaho National Engineering Laboratory (INEL), Idaho. The investigation was conducted by the U.S. Geological Survey and Idaho State University, in cooperation with the U.S. Department of Energy. Batch experimental techniques were used to determine strontium linear sorption isotherms and distribution coefficients (K d's) using simulated wastewater solutions prepared at pH 8.0±0.1 with variable concentrations of calcium and magnesium. Strontium linear sorption isotherm K d's ranged from 12±1 to 85±3 ml/g, increasing as the concentration of calcium and magnesium decreased. The concentration of sorbed strontium and the percentage of strontium retained by the sediment were correlated to aqueous concentrations of strontium, calcium, and magnesium. The effect of these cation concentrations on strontium sorption was quantified using multivariate least-squares regression techniques. Analysis of data from these experiments indicates that increased concentrations of calcium and magnesium in wastewater discharged to waste disposal ponds at the INEL increases the availability of strontium for transport beneath the ponds by decreasing strontium sorption to the surficial sediment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002540050210
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  • 50
    Digitale Medien
    Digitale Medien
    Effects of xenon on intracellular Ca2% release in human endothelial cells (1997)
    Springer
    Experimental biology online 2 (1997), S. 1-17 
    Details
    ISSN: 1430-3418
    Schlagwort(e): Calcium ; Endothelium ; Xenon ; Anesthesia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Using human endothelial cells loaded with the Ca2% indicator Fura2 the effects of xenon on changes in intracellular Ca2% were studied. The basal level of intracellular Ca2% is not affected upon incubation of the cells in buffer saturated either with 100% xenon or with 70% xenon/30% air, a concentration which corresponds in humans to the minimum alveolar concentration necessary to induce anesthesia in 50% of patients. A defined cellular response such as the Ca2% change induced by application of adenosine triphosphate (ATP) makes it possible to study the signalling chain between the stimulus and the various forms of Ca2% response. ATP induces a typical Ca2% fingerprint composed of an internal Ca2% release consisting of several oscillations plus an additional Ca2%-induced Ca2% influx from the outside. The latter is absent in Ca2%-free medium. When cells are incubated with xenon, only the first part of the ATP-induced Ca2% response is found corresponding to the internal release of Ca2%; the subsequent Ca2%-induced Ca2% influx does not take place. If xenon is removed, a fast recovery is observed and the cells again show both parts of the Ca2+ response. Such selective inhibition of Ca2+-induced Ca2+ influx is not obtained when xenon is replaced by N2; the ATP response of the cell remains the same as that of untreated cells. Similar effects of xenon treatment can also be observed when the cells are treated with thapsigargin, a specific inhibitor of the SERCA systems. The Ca2+-induced Ca2+ release is almost completely suppressed in the presence of xenon. We conclude that xenon may act on the cellular level on defined sites of the mechanisms regulating the Ca2+-release-activated Ca2+ channels of the plasma membrane and that this property may be related to its anesthetic effect.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s00898-997-0003-x
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  • 51
    Digitale Medien
    Digitale Medien
    Effects of brefeldin-A and monensin on organelle distribution and morphology in the preimplantation mouse embryo (1997)
    Springer
    Development genes and evolution 206 (1997), S. 503-514 
    Details
    ISSN: 1432-041X
    Schlagwort(e): Key words Preimplantation mouse embryo ; Brefeldin-A ; Monensin ; Golgi ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  The intracellular trafficking of integral membrane and secreted proteins is likely to be a key element involved in the morphogenesis and differentiation of the early mammalian embryo. In this study, we used transmission electron microscopy (TEM) to analyse the effects of brefeldin-A (BFA) and monensin, well known inhibitors of vesicular protein trafficking in somatic cells, on the structure of preimplantation mouse embryos. Both BFA and monensin distinctively altered the morphology of Golgi compartments in the blastomeres of treated morulae. BFA-treated morulae lacked recognizable Golgi complexes but possessed heterogeneous organelle clusters consisting of an abundance of smooth tubular and vesicular membrane compartments in addition to mitochondria, endosomes and lysosomes. Treatment of morulae with monensin was associated with swelling of Golgi compartments in addition to altering the morphology of mitochondria, lysosomes and the plasma membrane. BFA, and to a lesser extent monensin, inhibited cytokinesis as evidenced by the detection of binucleate blastomeres. In addition, BFA induced morulae to decompact. These latter effects have not been reported previously for these agents in mammalian somatic cell lines or other vertebrate or invertebrate embryos. These results provide the first demonstration of the structural effects of BFA and monensin on cells of the early mammalian embryo, some of which are consistent with the known actions of these agents on components of the vesicular protein trafficking system in mammalian somatic cells. This information serves as a foundation for the further use of these agents in studies of vesicular protein trafficking as an agent of preimplantation morphogenesis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004270050081
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  • 52
    Digitale Medien
    Digitale Medien
    Hydrogen fluoride effects on plasma membrane composition and ATPase activity in needles of white pine (Pinus strobus) seedlings pretreated with 12 h photoperiod (1997)
    Springer
    Trees 11 (1997), S. 248-253 
    Details
    ISSN: 0931-1890
    Schlagwort(e): Key words ATPase ; Fluoride ; Lipids ; Pine ; Plasma membrane
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract  Eastern white pine (Pinus strobus L.) seedlings were pretreated with 12 h photoperiod to induce dormancy. Dormant plants were fumigated with 0.5 ppb (0.4 μg m–3) or 2.0 ppb (1.6 μg m–3) hydrogen fluoride (HF) for 2 – 28 days. Plasma membranes were isolated from needles of treated and control seedlings to determine their chemical composition and ATPase activity. For all analyses, only those plants which did not show needle necrosis were selected. The amount of plasma membrane phospholipid expressed on a plasma membrane protein basis was higher after 2 days in the 0.5 ppb HF treatment as compared to controls. After 2 days of 2.0 ppb HF treatment as well as after 8 and 28 days of both HF treatments phospholipid to protein ratios in fluoride treated seedlings were lower as compared to control levels. A decrease in sterol levels could be observed after 2 days in both HF treatments. A large increase in the ratio of sterols to proteins was observed in plasma membranes of eastern white pine seedlings treated with 0.5 ppb HF for 28 days. Increased sterol to phospholipid ratios were observed after 8 and 28 days in 0.5 ppb and after 2 and 8 days of 2.0 ppb HF treatment. A decrease in ATPase activity was observed after 8 days with both fluoride treatments. Drastic increase of ATPase activity was observed after 28 days of HF treated plants. Observed changes of sterol and phospholipid levels after only 2 days of fumigation suggest early fluoride effects on plasma membrane composition during plant dormancy.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00009671
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  • 53
    Digitale Medien
    Digitale Medien
    Calcium distribution in fertilized and unfertilized ovules and embryo sacs of Nicotiana tabacum L. (1997)
    Springer
    Planta 202 (1997), S. 93-105 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Key words: Antimonate precipitation ; Calcium ; Embryo sac ; Fertilization ; Nicotiana (fertilization) ; Synergid
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. Potassium antimonate was used to localize Ca2+ in tobacco ovules from 0 to 7 d after anthesis in pollinated and emasculated flowers. Antimonate binds “loosely bound” Ca2+ into calcium antimonate; less-soluble forms are unavailable and free calcium usually escapes. Ovules are immature at anthesis. Abundant calcium precipitates in nucellar cells surrounding the micropylar canal. A difference between calcium in the two synergids emerges at 1 d, which is enhanced in pollinated flowers. The future receptive synergid accumulates more precipitates in the nucleus, cytoplasm and cell walls. After fertilization, micropyle precipitates diminish, and the ovule is unreceptive to further tube entry. In emasculated flowers 6 d after anthesis, ovular precipitates essentially disappear; however, flowers pollinated at 4–5 d and collected 2 d later largely restore their prior concentration of precipitates. Ovular precipitates occur initially in the nucellus, then the embryo sac, and finally the synergid and micropylar filiform apparatus. Possibility, calcium is released from the embryo sac, although no structural evidence of exudate formation was observed. Calcium precipitates in the ovule correlate with the ability of the ovule to be fertilized, suggesting that successful pollen tube entry and later development may require calcium of the class precipitated by antimonate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004250050107
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  • 54
    Digitale Medien
    Digitale Medien
    Calcium-induced sperm fusion in Zea mays L. (1997)
    Springer
    Sexual plant reproduction 10 (1997), S. 74-82 
    Details
    ISSN: 1432-2145
    Schlagwort(e): Key words Zea mays ; Calcium ; Sperm fusion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  In this study, we examined morphological changes of isolated maize (Zea mays L.) sperm cells in the presence of Brewbaker and Kwack salts (BKS) or the individual components of BKS using light, transmission electron and scanning electron microscopy. Freshly isolated sperms are 7.5 μm in diameter. Treatment with BKS for 5 h resulted in large cells with a diameter up to 41 μm. Staining of sperm nuclei with 4′, 6-diamidino-2-phenylindole (DAPI) revealed two or more nuclei in a single cell, suggesting that BKS induces cell fusion. Treatment with each BKS component showed that cell fusion occurs only in the presence of calcium nitrate. Use of several calcium salts showed the same results, suggesting that the calcium ion, alone, is responsible for the observed cell fusion. Further studies were conducted to examine the relationship between calcium distribution and sperm location in pollen tubes using chlorotetracycline and DAPI. Growing maize pollen tubes exhibited a high membrane calcium region within 20–50 μm from the tip. The Sperms are found no closer than 90 μm to the tip of the tube, suggesting that sperms are located in a low calcium region prior to being released to the degenerating synergid.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004970050070
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  • 55
    Digitale Medien
    Digitale Medien
    The Role of Reactive Oxygen Species in Mitochondrial Permeability Transition (1997)
    Springer
    Bioscience reports 17 (1997), S. 43-52 
    Details
    ISSN: 1573-4935
    Schlagwort(e): Calcium ; cyclosporin A ; lipid peroxidation ; mitochondria ; mitochondrial membrane permeability transition ; protein oxidation ; reactive oxygen species
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract We have provided evidence that mitochondrial membrane permeability transition induced by inorganic phosphate, uncouplers or prooxidants such as t-butyl hydroperoxide and diamide is caused by a Ca2+-stimulated production of reactive oxygen species (ROS) by the respiratory chain, at the level of the coenzyme Q. The ROS attack to membrane protein thiols produces cross-linkage reactions, that may open membrane pores upon Ca2+ binding. Studies with submitochondrial particles have demonstrated that the binding of Ca2+ to these particles (possibly to cardiolipin) induces lipid lateral phase separation detected by electron paramagnetic resonance experiments exploying stearic acids spin labels. This condition leads to a disorganization of respiratory chain components, favoring ROS production and consequent protein and lipid oxidation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1027335217774
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  • 56
    Digitale Medien
    Digitale Medien
    Cellular specificity of the gravitropic motor response in roots (1997)
    Springer
    Planta 203 (1997), S. S115 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Key words:Arabidopsis ; Auxin ; Calcium ; Distal elongation zone ; Gravitropism (root) ; Zea
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. A number of features of the gravitropic response of roots are not readily accounted for by the classical Cholodny-Went theory. These include the observations that (i) in the later stages of the response the growth gradient is reversed with no evident reversal of the auxin gradient; (ii) a major component of the acceleration of growth along the upper side occurs in the distal elongation zone (DEZ), a group of cells located between the meristem and the main elongation, not within the central elongation zone; and (iii) the initiation of differential growth in the DEZ appears to be independent of the establishment of auxin asymmetry. Alternative candidates for mediation of differential growth in the DEZ include calcium ions and protons. Gravi-induced curvature is accompanied by polar movement of calcium toward the lower side of the maize root tip and the DEZ is shown to be particularly sensitive to growth inhibition by calcium. Also, gravistimulation of maize roots causes enhanced acid efflux from the upper side of the DEZ. Evidence for gravi-induced modification of ion movements in the root tip includes changes in intracellular potentials and current flow. It is clear that there is more than one motor region in the root with regard to gravitropic responses and there is evidence that the DEZ itself consists of more than one class of responding cells. In order to gain a more complete understanding of the mechanism of gravitropic curvature, the physiological properties of the sub-zones of the root apex need to be thoroughly characterized with regard to their sensitivity to hormones, calcium, acid pH and electrical perturbations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00008099
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  • 57
    Digitale Medien
    Digitale Medien
    Plant responses to environmental stress: regulation and functions of the ArabidopsisTCH genes (1997)
    Springer
    Planta 203 (1997), S. S35 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Key words:Arabidopsis ; Calcium ; Calmodulin ; Cell wall ; Gene regulation (TCH genes) ; Xyloglucan endotransglycosylase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. Expression of the ArabidopsisTCH genes is markedly upregulated in response to a variety of environmental stimuli including the seemingly innocuous stimulus of touch. Understanding the mechanism(s) and factors that control TCH gene regulation will shed light on the signaling pathways that enable plants to respond to environmental conditions. The TCH proteins include calmodulin, calmodulin-related proteins and a xyloglucan endotransglycosylase. Expression analyses and localization of protein accumulation indicates that the potential sites of TCH protein function include expanding cells and tissues under mechanical strain. We hypothesize that at least a subset of the TCH proteins may collaborate in cell wall biogenesis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00008113
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  • 58
    Digitale Medien
    Digitale Medien
    Neuropeptide Y-immunoreactive intracardiac neurones, granule-containing cells and nerves associated with ganglia and blood vessels in rat and guinea-pig heart (1997)
    Springer
    Cell & tissue research 289 (1997), S. 445-454 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Intracardiac neurones ; Innervation ; Heart ; Neuropeptide Y ; Immunocytochemistry ; Electron microscopy ; Rat (Sprague Dawley) ; Guinea-pig (Dunkin Hartley)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract. Intrinsic neuropeptide Y-containing neurones in rat and guinea-pig hearts were studied at the ultrastructural level by the pre-embedding peroxidase-antiperoxidase immunocytochemical technique. Intracardiac neuronal cell bodies were often weakly or moderately immunostained, and the labelling was usually pronounced in the Golgi complex, multivesicular bodies, some cisterns of granular endoplasmic reticulum and large granular vesicles. Neuropeptide Y-immunoreactive nerve fibres were also observed in association with intracardiac neurones. A subpopulation of neuropeptide Y-immunoreactive granule-containing cells in the rat heart are described for the first time and were very heavily labelled; other granule-containing cells were non-immunoreactive, but were contacted by neuropeptide Y-containing nerves. Preterminal regions of nerve fibres that were located in nerve bundles were only weakly neuropeptide Y-immunoreactive, in contrast to the heavy labelling observed in varicosities that contained many synaptic vesicles. Many neuropeptide Y-immunoreactive nerve fibres were associated with the coronary vasculature and were particularly prominent in the walls of small arteries and arterioles where labelled nerve varicosities were present close to the smooth muscle cells. Immunoreactive nerves were also seen in the myocardium, usually near to capillaries. In axonal varicosities, the central core of large granular vesicles was immunolabelled, and electron-dense immunoreactive material outlined the membranes of small and large clear vesicles. The significance of neuropeptide Y-immunoreactive intracardiac neurones and granule-containing cells and the origin of associated labelled nerve fibres in the heart are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050890
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  • 59
    Digitale Medien
    Digitale Medien
    Immuno-electron microscopy reveals that the excitotoxin quinolinate is associated with the plasma membrane in human peripheral blood monocytes/macrophages (1997)
    Springer
    Cell & tissue research 290 (1997), S. 633-639 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Quinolinic acid ; Interferon-γ ; Kynurenine ; Electron microscopy ; Immunocytochemistry ; Excitotoxicity ; Human
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract.  Quinolinate (QUIN), a tryptophan-derived excitotoxin, was localized ultrastructurally in human peripheral blood monocytes/macrophages (MØ) by immuno-electron microscopy. A combined carbodiimide/glutaraldehyde/paraformaldehyde-based fixation procedure was developed for optimal retention of QUIN in the cell as well as minimal loss of ultrastructure; a silver-enhanced colloidal gold detection system was used for electron-microscopic analysis. Gold particles representing QUIN immunoreactivity were associated with the inner side of the plasma membrane in normal MØ. The number of gold particles increased significantly when QUIN levels were elevated by treatment with its precursor kynurenine, but location of the gold particles remained essentially the same under this condition. Treatment with interferon-γ increased the number of Golgi bodies, vacuoles and pseudopodia, reflecting the activated state of the cell. Significantly increased numbers of gold particles representing QUIN were detectable in approximately the same location as in the case of kynurenine treatment. Combined treatment with kynurenine and interferon-γ maximally increased the number of gold particles at the periphery of the cell. The pseudopodia were intensely stained with gold particles, while they were not detectable in the inner part of the cytoplasm or in any other organelle even under this activated condition. The significance of the specific location of QUIN revealed in the present study and its relation to the release and subsequent actions of QUIN are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050969
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  • 60
    Digitale Medien
    Digitale Medien
    Synaptic exocytosis of dense-core vesicles in blue crab (Callinectes sapidus) stomach muscles (1997)
    Springer
    Cell & tissue research 289 (1997), S. 517-526 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Neuromuscular junction ; Synaptic vesicles ; Vesicle fusion ; Electron microscopy ; Callinectes sapidus (Crustacea)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract. Neuromuscular terminals of a single motoneuron to four muscles (CPV7a, GM5a, CV2, and CV3) in the stomach of the blue crab Callinectes sapidus showed structural evidence for the exocytotic release of dense-core vesicles exclusively at synapses. The primary evidence was the appearance of dense cores in the synaptic cleft, accompanied by indentations of the presynaptic or postsynaptic membrane. In their simplest form, these consisted of an omega-shaped figure of the presynaptic membrane enclosing one dense core, denoting release of a single dense-core vesicle. A larger indentation of the presynaptic membrane enclosing several dense cores denoted multiple release. A more complex form of multiple release was where the presynaptic membrane was normal, but the postsynaptic membrane elaborated into a sac projecting into the granular sarcoplasm and filled with dense cores. The postsynaptic sac in some instances was compressed into a thin, fingerlike extension, which lacked dense cores and, at its distal end, separated into small cisternae, suggesting a mechanism for membrane recycling. Profiles depicting single and multiple releases of dense-core vesicles were found more frequently at neuromuscular terminals that release relatively large amounts of transmitter with a single stimulus, such as CV2 and CV3, compared to those releasing smaller amounts, such as CPV7a and GM5a. The disparity in release sites among the four muscles of this single motor unit and the fact that many of the multiple-release figures were closely adjacent to the active zones for transmitter release suggest a possible modulatory role for dense-core vesicles in synaptic transmission. Such modulation may be long lasting, as implied by the postsynaptic sacs, which may permit prolonged release of the contents of their dense cores into the synaptic cleft. This is in keeping with the functional role of these stomach muscles, which is to be continuously active for long periods of time.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050897
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  • 61
    Digitale Medien
    Digitale Medien
    Immunoreactive excitatory amino acids in the parietal eye of lizards, a comparison with the pineal organ and retina (1997)
    Springer
    Cell & tissue research 287 (1997), S. 275-283 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Parietal eye ; Pineal organ ; Retina ; Glutamate ; Aspartate ; Immunocytochemistry ; Electron microscopy ; Lacerta muralis ; Lacerta agilis ; Lacerta viridis (Lacertilia)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract. The fine structure of the organ and the localization of the excitatory amino acids glutamate and aspartate were studied in the parietal eye of lizards by postembedding immunoelectron microscopy. The parietal eye contains cone photoreceptor cells, secondary neurons, and ependymal and lens cells. The photoreceptors form long inner and outer segments, some of them being paired as ”twin-photoreceptors” by zonulae adherentes. Perikarya of neurons bear sensory cilia (containing 9×2+0 pairs of tubules) extending into the intercellular space. No neurohormonal terminals are present in the parietal eye. A higher immunoreactivity to glutamate than to aspartate is found in the photoreceptors and in the secondary neurons of the parietal eye. Glutamate immunogold labeling is more intense in the axonal processes of photoreceptors and neurons and in most of the nerve fibers of the parietal nerve running to the brain stem. Weak aspartate and glutamate immunoreactivity can be detected in the ependymal and lens cells. A similar distribution of immunoreactive amino acids is found in the photoreceptors, secondary neurons, and ependymal glial elements of the pineal organ, and retina of the lateral eye of the same animals. Immunoreactive glutamate accumulates in the axons of photoreceptors and secondary neurons of the parietal eye suggesting that this excitatory amino acid acts as a synaptic mediator in the neural efferentation of the organ. Thus, the efferent light-conducting pathway of the parietal organ is similar to that of the pineal organ and lateral eye retina. As the Mullerian cells of the retina, the ependymal and lens cells of the parietal eye and the ependymal-glial cells of the pineal organ may play a role in the metabolism and/or elimination of excitatory amino acids released by photoreceptors.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050752
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  • 62
    Digitale Medien
    Digitale Medien
    Expression of basic fibroblast growth factor-like immunoreactivity in the nuclei of regenerating hepatocytes (1997)
    Springer
    Cell & tissue research 288 (1997), S. 517-527 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Liver ; Subcellular fractions ; Immunohistochemistry ; Electron microscopy ; Rat (Wistar)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract. This study, utilizing rats subjected to two-thirds partial hepatectomy or sham operation, was designed (1) to investigate the content of basic fibroblast growth factor (bFGF) in the subcellular fractions of regenerating and sham-operated rat livers by immunoblot experiments and enzyme-linked immunosorbent assay (ELISA), (2) to show that bFGF immunoreactivity and proliferating cell nuclear antigen (PCNA) immunoreactivity are markers for hepatocellular mitosis before and after partial hepatectomy, and (3) to observe the location and fine structure of the bFGF immunoreaction within the regenerating liver with special attention to bFGF immunoreactivity in the nuclei of regenerating hepatocytes. Immunoblot experiments and ELISA showed a transient increase in high-molecular-weight forms of bFGF in the nuclear subcellular fraction of regenerating liver 48 h after partial hepatectomy. By light microscopy, bFGF and PCNA immunoreactivities were detected in the nuclei of regenerating hepatocytes. Electron microscopy demonstrated bFGF-like immunoreactivity mainly in the nuclear euchromatin and rarely in the heterochromatin or nucleoli of regenerating hepatocytes. The transient increase in high-molecular-weight forms of bFGF in the nuclear euchromatin of regenerating hepatocytes, together with the concomitant expression of PCNA in the regenerating liver, suggests an important role of the high-molecular-weight forms of bFGF in hepatocyte proliferation and/or mitosis, although authentic bFGF with a molecular form of 18 kDa is not considered to be involved in hepatic regeneration.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050837
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  • 63
    Digitale Medien
    Digitale Medien
    Micro-heterogeneity of pectins and calcium distribution in the epidermal and cortical parenchyma cell walls of flax hypocotyl (1997)
    Springer
    Protoplasma 198 (1997), S. 9-19 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Calcium ; Demethylation ; Epidermal wall ; Polygalacturonate ; Polygalacturonic acid-Ca2+ conformation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Pectic polysaccharides are major components of the plant cell wall matrix and are known to perform many important functions for the plant. In the course of our studies on the putative role of pectic polysaccharides in the control of cell elongation, we have examined the distribution of polygalacturonans in the epidermal and cortical parenchyma cell walls of flax seedling hypocotyls. Pectic components have been detected with (1) the nickel (Ni2+) staining method to visualize polygalacturonates, (2) monoclonal antibodies specific to low (JIM5) and highly methylesterified (JIM7) pectins and (3) a combination of subtractive treatment and PATAg (periodic acid-thiocarbohydrazide-silver proteinate) staining. In parallel, calcium (Ca2+) distribution has been imaged using SIMS microscopy (secondary ion mass spectrometry) on cryo-prepared samples and TEM (transmission electron microscopy) after precipitation of calcium with potassium pyroantimonate. Our results show that, at the tissular level, polygalacturonans are mainly located in the epidermal cell walls, as revealed by the Ni2+ staining and immunofluorescence microscopy with JIM5 and JIM7 antibodies. In parallel, Ca2+ distribution points to a higher content of this cation in the epidermal walls compared to cortical parenchyma walls. At the ultrastructural level, immunogold labeling with JIM5 and JIM7 antibodies shows a differential distribution of pectic polysaccharides within cell walls of both tissues. The acidic polygalacturonans (recognized by JIM5) held through calcium bridges are mainly found in the outer part of the external wall of epidermal cells. In contrast, the labeling of methylesterified pectins with JIM7 is slightly higher in the inner part than in the outer part of the wall. In the cortical parenchyma cells, acidic pectins are restricted to the cell junctions and the wall areas in contact with the air-spaces, whereas methylesterified pectins are evenly distributed all over the wall. In addition, the pyroantimonate precipitation method reveals a clear difference in the Ca2+ distribution in the epidermal wall, suggesting that this cation is more tightly bound to acidic pectins in the outer part than in the inner part of that wall. Our findings show that the distribution of pectic polysaccharides and the nature of their linkages differ not only between tissues, but also within a single wall of a given cell in flax hypocotyls. The differential distribution of pectins and Ca2+ in the external epidermal wall suggests a specific control of the demethylation of pectins and a central role for Ca2+ in this regulation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01282126
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  • 64
    Digitale Medien
    Digitale Medien
    Osmoregulatory mutants that affect the function of the contractile vacuole inChlamydomonas reinhardtii (1997)
    Springer
    Protoplasma 200 (1997), S. 99-111 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Chlamydomonas reinhardtii ; Contractile vacuole ; Electron microscopy ; Videomicroscopy ; Osmoregulation ; Osmoregulatory mutants
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Four independent osmoregulatory mutants,osml, osm3,osm4, and osm7, were isolated on the basis of their requirement for growth medium of high osmotic strength. In normal low-osmoticstrength medium, in contrast to wild-type cells, the mutants grow poorly or not at all; in distilled water mutant cells are immobilized and eventually swell and burst. The mutants were examined by ordinary brightfield and phase-contrast microscopy, videomicroscopy, and electron microscopy. The four mutants showed different defects in the contractile vacuole (CV) cycle. Timing of various stages of the CV cycle showed thatosm1 was affected primarily in the early stage of the cycle when the CV begins to grow,osm3 primarily in midcycle when vacuoles fuse to form the CV proper,osm7 at a late stage of the cycle at docking and fusion of the CV with the plasma membrane, andosm4 during contraction of the CV. At the electron microscopic level, in dilute medium, mutant cells by comparison with wild-type cells had large autophagosomes, swollen mitochondria, and dilated ER cisternae. Although electron microscopy showed general abnormalities of the contractile vacuoles consistent with the videomicroscopic observations of living cells, no obvious vacuole membrane abnormalities were seen which would explain the mutational defects. The mutations help define the separate processes that contribute to the coordinated CV cycle inChlamydomonas, and open the way to eventual isolation of some of the genes responsible for CV function.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01280738
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  • 65
    Digitale Medien
    Digitale Medien
    Structure and behavior of contractile vacuoles inChlamydomonas reinhardtii (1997)
    Springer
    Protoplasma 198 (1997), S. 73-84 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Chlamydomonas reinhardtii ; Contractile vacuole ; Osmoregulation ; Videomicroscopy ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The contractile vacuole (CV) cycle ofChlamydomonas reinhardtii has been investigated by videomicroscopy and electron microscopy. Correlation of the two kinds of observation indicates that the total cycle (15 s under the hypo-osmotic conditions used for videomicroscopy) can be divided into early, middle, and late stages. In the early stage (early diastole, about 3 s long) numerous small vesicles about 70–120 nm in diameter are present. In the middle stage (mid-diastole, about 6 s long), the vesicles appear to fuse with one another to form the contractile vacuole proper. In the late stage (late diastole, also about 6 s long), the CV increases in diameter by the continued fusion of small vesicles with the vacuole, and makes contact with the plasma membrane. The CV then rapidly decreases in size (systole, about 0.2 s). In isosmotic media, CVs do not appear to be functioning; under these conditions, the CV regions contain numerous small vesicles typical of the earliest stage of diastole. Fine structure observations have provided no evidence for a two-component CV system such as has been observed in some other cell types. Electron microscopy of cryofixed and freeze-substituted cells suggests that the irregularity of the profiles of larger vesicles and vacuoles and some other morphological details seen in conventionally fixed cells may be shrinkage artefacts. This study thus defines some of the membrane events in the normal contractile vacuole cycle ofChlamydomonas, and provides a morphological and temporal basis for the study of membrane fusion and fluid transport across membranes in a cell favorable for genetic analysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01282133
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  • 66
    Digitale Medien
    Digitale Medien
    Pectin immunolocalization and calcium visualization in differentiating derivatives from poplar cambium (1997)
    Springer
    Protoplasma 199 (1997), S. 151-160 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Calcium ; Cambium ; Ionic microscopy ; Immunolocalization ; Pectins ; Populus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Calcium distribution and pectin esterification patterns in the cambial zone of poplar branches were studied with ionic microscopy and immunological tools respectively. Dynamic changes correlating with cell growth and cell differentiation were observed both on the xylem and on the phloem sides. In expanding cell walls of xylem derivatives, unesterified pectins were restricted to cell junctions and middle lamellae, occasionally accompanied by calcium ions. In contrast, in differentiating and mature phloem cells, acidic pectins and Ca2+ were present all over the walls leading to early stiffening of the polysaccharide network. Significant labelling was detected with JIM5 antibodies in some dictyosomes suggesting exocytosis of low methylated polymers towards the cell walls. At cell junctions, unesterified pectins might originate from the activity of pectinmethylesterases localized in these areas. Thus un- and deesterified pectins might be located in different cell wall domains whose distribution, varying with cell type, will confer specific extensibility to the wall matrix.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01294503
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  • 67
    Digitale Medien
    Digitale Medien
    Selective UV-induced damage to short-wavelength receptor cells in the butterflyPapilio xuthus (1997)
    Springer
    Protoplasma 200 (1997), S. 112-115 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Electron microscopy ; UV-induced cell damage ; Photoreceptor ; Eye ; Lepidoptera
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary A technique that allows the specific inactivation of short-wavelength-sensitive photoreceptive cells has been needed for a long time. Such a technique could be useful in studies on the role(s) of UV-receptors in circadian rhythmicity, recognition of floral patterns, homing behaviour, and mate selection in arthropods. We provide ultrastructural evidence that short-wavelength receptor cells can be selectively damaged without affecting other spectral-cell types. Since the method does not require the killing of the experimental animal, the latter can be used in behavioural or other follow-up tests.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01280739
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  • 68
    Digitale Medien
    Digitale Medien
    Photoreceptor Guanylate Cyclases: A Review (1997)
    Springer
    Bioscience reports 17 (1997), S. 429-473 
    Details
    ISSN: 1573-4935
    Schlagwort(e): Calcium ; guanylate cyclase ; photoreceptor
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract Almost three decades of research in the field of photoreceptor guanylate cyclases are discussed in this review. Primarily, it focuses on the members of membrane-bound guanylate cyclases found in the outer segments of vertebrate rods. These cyclases represent a new guanylate cyclase subfamily, termed ROS-GC, which distinguishes itself from the peptide receptor guanylate cyclase family that it is not extracellularly regulated. It is regulated, instead, by the intracellularly-generated Ca2+ signals. A remarkable feature of this regulation is that ROS-GC is a transduction switch for both the low and high Ca2+ signals. The low Ca2+ signal transduction pathway is linked to phototransduction, but the physiological relevance of the high Ca2+ signal transduction pathway is not yet clear; it may be linked to neuronal synaptic activity. The review is divided into eight sections. In Section I, the field of guanylate cyclase is introduced and the scope of the review is briefly explained; Section II covers a brief history of the investigations and ideas surrounding the discovery of rod guanylate cyclase. The first five subsections of Section III review the experimental efforts to quantify the guanylate cyclase activity of rods, including in vitro and in situ biochemistry, and also the work done since 1988 in which guanylate cyclase activity has been determined. In the remaining three subsections an analytical evaluation of the Ca2+ modulation of the rod guanylate cyclase activity related to phototransduction is presented. Section IV deals with the issues of a biochemical nature: isolation and purification, subcellular localization and functional properties of rod guanylate cyclase. Section V summarizes work on the cloning of the guanylate cyclases, analysis of their primary structures, and determination of their location with in situ hybridization. Section VI summarizes studies on the regulation of guanylate cyclases, with a focus on guanylate cyclases activating proteins. In Section VII, the evidence about the localization and functional role of guanylate cyclases in other retinal cells, especially in “on-bipolar” cells, in which guanylate cyclase most likely plays a critical role in electrical signaling, is discussed. The review concludes with Section VIII, with remarks about the future directions of research on retinal guanylate cyclases.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1027365520442
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  • 69
    Digitale Medien
    Digitale Medien
    SUR1 (CSG1 / BCL21), a gene necessary for growth of Saccharomyces cerevisiae in the presence of high Ca2+ concentrations at 37° C, is required for mannosylation of inositolphosphorylceramide (1997)
    Springer
    Molecular genetics and genomics 255 (1997), S. 570-579 
    Details
    ISSN: 1617-4623
    Schlagwort(e): Key words Saccharomyces cerevisiae ; Calcium ; Copper ; Sphingolipid ; CSG1
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Saccharomyces cerevisiae cells require two genes, CSG1/SUR1 and CSG2, for growth in 50 mM Ca2+, but not 50 mM Sr2+. CSG2 was previously shown to be required for the mannosylation of inositol-phosphorylceramide (IPC) to form mannosylinositolphosphorylceramide (MIPC). Here we demonstrate that SUR1/CSG1 is both genetically and biochemically related to CSG2. Like CSG2, SUR1/CSG1 is required for IPC mannosylation. A 93–amino acid stretch of Csg1p shows 29% identity with the α-1, 6-mannosyltransferase encoded by OCH1. The SUR1/CSG1 gene is a dose-dependent suppressor of the Ca2+-sensitive phenotype of the csg2 mutant, but overexpression of CSG2 does not suppress the Ca2+ sensitivity of the csg1 mutant. The csg1 and csg2 mutants display normal growth in YPD, indicating that mannosylation of sphingolipids is not essential. Increased osmolarity of the growth medium increases the Ca2+ tolerance of csg1 and csg2 mutant cells, suggesting that altered cell wall synthesis causes Ca2+-induced death. Hydroxylation of IPC-C to form IPC-D requires CCC2, a gene encoding an intracellular Cu2+ transporter. Increased expression of CCC2 or increased Cu2+ concentration in the growth medium enhances the Ca2+ tolerance of csg1 mutants, suggesting that accumulation of IPC-C renders csg1 cells Ca2+ sensitive.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004380050530
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  • 70
    Digitale Medien
    Digitale Medien
    Milk composition and lactational output in the greater spear-nosed bat, Phyllostomus hastatus (1997)
    Springer
    Journal of comparative physiology 167 (1997), S. 389-398 
    Details
    ISSN: 1432-136X
    Schlagwort(e): Key words Milk composition ; Lactation ; Calcium ; Bats ; Phyllostomatidae
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Growth rates of mammalian young are closely linked to the ability of the mother to provide nutrients; thus, milk composition and yield provide a direct measure of maternal investment during lactation in many mammals. We studied changes in milk composition and output throughout lactation in a free-ranging population of the omnivorous bat, Phyllostomus hastatus. Fat and dry matter of milk increased from 9 to 21% and from 21 to 35% of wet mass, respectively, throughout lactation. Energy increased from 6 to 9 kJ · g−1 wet mass, primarily due to the increase in fat concentration. Total sugar levels decreased slightly but non-significantly. Mean sugar level was 4.0% of wet mass. Protein concentration increased from 6 to 11% of wet mass at peak lactation and then decreased as pups approached weaning age. Total milk energy output until pups began to forage was 3609 kJ. Milk levels of Mg, Fe, Ca, K, and Na averaged 0.55 ± 0.26, 0.23 ± 0.2, 8.75 ± 4.17, 5.42 ± 2.11, and 9.87 ± 4.3 mg · g−1 dry matter, respectively. Of the minerals studied, calcium appears to be most limiting in this species. The high degree of variability in foraging time, milk composition and milk yield between individuals at the same stage of lactation could potentially yield high variance in reproductive success among females of this polygynous species.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003600050088
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  • 71
    Digitale Medien
    Digitale Medien
    The plasma membrane calcium pump: Recent developments and future perspectives (1996)
    Springer
    Cellular and molecular life sciences 52 (1996), S. 1091-1100 
    Details
    ISSN: 1420-9071
    Schlagwort(e): Calcium ; ATPase ; calmodulin ; ion pumps
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The Ca2+ pump of the plasma membrane (PMCA) is regulated by a number of agents. The most important is calmodulin (CaM), which binds to a domain located in the C-terminal portion of the pump, removing it from an autoinhibitory site next to the active site. The CaM-binding domain is preceded by an acidic sequence which contains a hidden signal for endoplasmic reticulum (ER) retention. Chimeras of the PMCA and endoplasmic reticulum (SERCA) pumps have revealed the presence of a strong signal for ER retention in the first 45 residues of the SERCA pump. Four gene products of the PMCA pump are known: two of them (1 and 4) are ubiquitously expressed, two (2 and 3) are specific for nerve cells and may be induced by their activation. Mutagenesis work has identified four residues in three of the transmembrane domains of the pump which may be components of the trans-protein Ca2+ path. The mutation of two of these residues alters the membrane targeting of the pump.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01952107
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  • 72
    Digitale Medien
    Digitale Medien
    Effects of long-term open-air exposure to fluoride, nitrogen compounds and SO2 on visible symptoms, pollutant accumulation and ultrastructure of Scots pine and Norway spruce seedlings (1996)
    Springer
    Trees 10 (1996), S. 157-171 
    Details
    ISSN: 1432-2285
    Schlagwort(e): Conifer ; Fluoride ; Nitrogen ; Sulphur dioxide ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Effects of SO2, aqueous fluoride (NaF) and a solution of nitrogen compounds (NH4NO3) on the visible symptoms, pollutant accumulation and ultrastructure of Scots pine (Pinus sylvestris L.) and Norway spruce [Picea abies (L.) Karst.] seedlings were studied in an open-air experiment lasting for 3 consecutive years. Visible injury symptoms were most pronounced in combination exposures and whenever F was applied. Visible symptoms correlated well with needle pollutant concentrations. Exposure to NaF increased needle F contents particularly when F was applied with SO2 or NH4NO3. This suggests that a reduction in N or SO2 emissions, in F polluted areas, could improve the condition of conifers via decreased accumulation of phytotoxic F in the needles. Norway spruce needles accumulated 2–10 times as much S and F as those of Scots pine. Microscopic observations showed various changes in the needle mesophyll cell ultrastructure. In both species, exposure to SO2 increased significantly the amount of cytoplasmic vacuoles, suggesting detoxification of excess sulphate or low pH. F treatments resulted in a significant enlargement of plastoglobuli in Scots pine and a darkening of plastoglobuli in Norway spruce. All exposures enhanced the accumulation of lipid bodies. An increased portion of translucent plastoglobuli was most pronounced in N treatments. Many of the ultrastructural changes and visible symptoms appeared only as number of years exposed increased, indicating that long-term experiments are needed. Both visible symptoms and ultrastructural changes pointed to the more pronounced sensitivity of Norway spruce compared to Scots pine. Ultrastructural results mostly supported earlier qualitative observations of F, N and SO2 effects on needle mesophyll cell ultrastructure. However, no reduction of thylakoids in SO2 containing exposure or curling of thylakoids in F exposure could be detected in the present study.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02340767
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  • 73
    Digitale Medien
    Digitale Medien
    Effects of long-term open-air exposure to fluoride, nitrogen compounds and SO2 on visible symptoms, pollutant accumulation and ultrastructure of Scots pine and Norway spruce seedlings (1996)
    Springer
    Trees 10 (1996), S. 157-171 
    Details
    ISSN: 0931-1890
    Schlagwort(e): Key words Conifer ; Fluoride ; Nitrogen ; Sulphur dioxide ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract  Effects of SO2, aqueous fluoride (NaF) and a solution of nitrogen compounds (NH4NO3) on the visible symptoms, pollutant accumulation and ultrastructure of Scots pine (Pinus sylvestris L.) and Norway spruce [Picea abies (L.) Karst.] seedlings were studied in an open-air experiment lasting for 3 consecutive years. Visible injury symptoms were most pronounced in combination exposures and whenever F was applied. Visible symptoms correlated well with needle pollutant concentrations. Exposure to NaF increased needle F contents particularly when F was applied with SO2 or NH4NO3. This suggests that a reduction in N or SO2 emissions, in F polluted areas, could improve the condition of conifers via decreased accumulation of phytotoxic F in the needles. Norway spruce needles accumulated 2 – 10 times as much S and F as those of Scots pine. Microscopic observations showed various changes in the needle mesophyll cell ultrastructure. In both species, exposure to SO2 increased significantly the amount of cytoplasmic vacuoles, suggesting detoxification of excess sulphate or low pH. F treatments resulted in a significant enlargement of plastoglobuli in Scots pine and a darkening of plastoglobuli in Norway spruce. All exposures enhanced the accumulation of lipid bodies. An increased portion of translucent plastoglobuli was most pronounced in N treatments. Many of the ultrastructural changes and visible symptoms appeared only as number of years exposed increased, indicating that long-term experiments are needed. Both visible symptoms and ultrastructural changes pointed to the more pronounced sensitivity of Norway spruce compared to Scots pine. Ultrastructural results mostly supported earlier qualitative observations of F, N and SO2 effects on needle mesophyll cell ultrastructure. However, no reduction of thylakoids in SO2 containing exposure or curling of thylakoids in F exposure could be detected in the present study.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00009644
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  • 74
    Digitale Medien
    Digitale Medien
    Cell signaling and heat shock protein expression (1996)
    Springer
    Journal of biomedical science 3 (1996), S. 379-388 
    Details
    ISSN: 1423-0127
    Schlagwort(e): Heat shock ; Calcium ; Sodium ; Inositol 1,4,5-trisphosphate ; Heat shock protein 70 kd ; Intracellular pH ; Protection
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Exposure of cells and organs to heat shock is associated with numerous changes in various cellular metabolic parameters and overexpression of proteins collectively known as heat shock proteins (HSP). In this communication we review the cell-signaling events that are altered in response to heat shock as they relate to the subsequent induction of HSP 70 kd (HSP-70) expression. We also review the mechanisms by which HSP-70 is involved in conferring cytoprotective effects. The possibility of altering HSP expression through manipulations of the cell-signal process has clinical importance.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02258043
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  • 75
    Digitale Medien
    Digitale Medien
    Decline in snail abundance due to soil acidification causes eggshell defects in forest passerines (1996)
    Springer
    Oecologia 105 (1996), S. 351-360 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Snails ; Calcium ; Eggshell ; Avian reproduction ; Acidification
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract On poor soils in the Netherlands an increasing number of great tits, Parus major, and of other forest passerines produce eggs with defective shells and have low reproductive success as a result of calcium deficiency. A similar increase in eggshell defects has been observed in Germany and Sweden. Snail shells are the main calcium source for tits in forests where defective eggshells do not occur, but are very little taken in forests where tits often have eggshell defects. We investigated whether a decrease in snail abundance on poor soils could be responsible for the decline in eggshell quality, and if so, what caused this decrease. Snail density in forests where tits have eggshell defects was much lower than in forests where tits do not have such defects. Snail density correlated with the calcium content and to a lesser extent with pH of the litter layer. Liming of a calciumpoor forest soil with few snails resulted in snail densities comparable to those on calcium-rich soils after 4 years. Snail density has declined on calcium-poor soils over the last two decades, but not on calcium-rich soils. Acid deposition has caused a decline of soil calcium on poor soils. We conclude, therefore, that anthropogenic acidification has caused a decline in snail populations, resulting in an increase in eggshell defects in birds in forests on poor soils.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00328738
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  • 76
    Digitale Medien
    Digitale Medien
    Bimodal solubilization of phospholipid-cholesterol vesicles in 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) solutions. Formation of filamentous and helical microstructures depends on negatively charged lipids (1996)
    Springer
    European biophysics journal 25 (1996), S. 67-73 
    Details
    ISSN: 1432-1017
    Schlagwort(e): Key words Gallstone ; Cholesterol monohydrate crystals ; Phase separation ; Light scattering ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: Abstract Phospholipid/cholesterol vesicles were solu-bilized by 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS). Above 30 mol% cholesterol (Ch) in the lipid vesicles several remarkable changes of the solubilization process were observed. (i) Two modes of solubilization: The effective detergent to lipid ratio Rc(M) for the formation of mixed micelles decreased from Rc(M) = 43 ± 3 at low lipid concentrations, [L]≤ 0.15 mm, to Rc(M) = 2.4 ± 0.3 above [L] = 0.5 mm (40 mol% Ch, T = 20 °C). (ii) At subsolubilizing CHAPS concentrations, filamentous and helical microstructures were formed, similar to those which were observed in native and model bile. (iii) The number of observed fibers was about two orders of magnitude higher in the presence of the negatively charged lipids phosphatidylglycerol (PG) and phosphatidic acid (PA) compared to the zwitterionic phosphatidylcholine (PC). Fiber formation began after 16–18 h using PG and PA compared to 3–4 days in the presence of PC. Screening of the charged lipids by NaCl effectively reduced the formation of fibers. Assuming binding of Na+ to the charged lipid aggregates, an intrinsic binding constant Kint = 0.6 M–1 was determined by applying the Gouy-Chapman theory. After the addition of CHAPS to PG/Ch vesicles, a fast initial solubilization of the vesicles (〈1 min) to mixed micelles (rh = 2.3 ± 0.2 nm) and small vesicles (rh = 23 ± 1 nm) was observed, followed by an intermediate period of 2 h, after which the formation of fibers occurred (〉15 h). The microstructures are visualized by darkfield and electron microscopy. The method of vesicle solubilization is compared to the dilution of concentrated micellar solutions, which is usually applied to model bile systems.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002490050019
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  • 77
    Digitale Medien
    Digitale Medien
    Endophytic establishment of Azorhizobium caulinodans through auxin-induced root tumors of rice (Oryza sativa L.) (1996)
    Springer
    Biology and fertility of soils 21 (1996), S. 293-302 
    Details
    ISSN: 1432-0789
    Schlagwort(e): Key words Ammonium excretion ; Azorhizobium caulinodans ; Auxine ; 2 ; 4-Dichlor-phenoxy-acetic acid ; Nitrogen fixation ; Paranodulation ; Rice ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Rice seedlings developed nodule-like tumors (para-nodules) along primary and secondary roots when treated with the auxin 2,4-dichlor-phenoxy-acetic acid (2,4-D). Histologically, these tumors appeared as cancerous out-grown lateral-root primordes and were thus comparable with stem nodules of the legume Sesbania rostrata. Azorhizobium caulinodans (a diazotroph known as a specific endophyte of Sesbania rostrata) was introduced and became established inside rice para-nodules and in root tissues around tumor bases. The infection with A. caulinodans followed a typical “crack-entry” invasion at places where para-nodule tumors had emerged through the root cortex and epidermis. The bacteria settled with high cell densities in intercellular spaces of the induced tumors and betwen root cortical cells. Infection of plant cells took place both in the epidermis and in cortical tissue. Intracellularly established A. caulinodans was found inside the cytoplasm, surrounded by membrane-like structures. N2 fixation by tumor-inhabiting Azorhizobium sp. was increased at low O2 tensions (1.5–3 kPa) compared with an untreated control. Only a little activity remained at O2 tensions of 5 kPa and above. The present results confirm that root-tumor induction offers a suitable method of establishing diazotrophs endophytically in the roots of gramineous crops.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00334906
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  • 78
    Digitale Medien
    Digitale Medien
    Endophytic establishment of Azorhizobium caulinodans through auxin-induced root tumors of rice (Oryza sativa L.) (1996)
    Springer
    Biology and fertility of soils 21 (1996), S. 293-302 
    Details
    ISSN: 1432-0789
    Schlagwort(e): Ammonium excretion ; Azorhizobium caulinodans ; Auxine 2.4-Dichlor-phenoxy-acetic acid ; Nitrogen fixation ; Paranodulation ; Rice ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Rice seedlings developed nodule-like tumors (para-nodules) along primary and secondary roots when treated with the auxin 2,4-dichlor-phenoxy-acetic acid (2,4-D). Histologically, these tumors appeared as cancerous out-grown lateral-root primordes and were thus comparable with stem nodules of the legume Sesbania rostrata. Azorhizobium caulinodans (a diazotroph known as a specific endophyte of Sesbania rostrata) was introduced and became established inside rice para-nodules and in root tissues around tumor bases. The infection with A. caulinodans followed a typical “crack-entry” invasion at places where paranodule tumors had emerged through the root cortex and epidermis. The bacteria settled with high cell densities in intercellular spaces of the induced tumors and between root cortical cells. Infection of plant cells took place both in the epidermis and in cortical tissue. Intracellularly established A. caulinodans was found inside the cytoplasm, surrounded by membrane-like structures. N2 fixation by tumor-inhabiting Azorhizobium sp. was increased at low O2 tensions (1.5–3 kPa) compared with an untreated control. Only a little activity remained at O2 tensions of 5 kPa and above. The present results confirm that root-tumor induction offers a suitable method of establishing diazotrophs endophytically in the roots of gramineous crops.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00334906
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  • 79
    Digitale Medien
    Digitale Medien
    Fine surface structure of enterotoxemic Escherichia coli O139:K12 strains associated with swine edema disease (1996)
    Springer
    Archives of microbiology 166 (1996), S. 357-360 
    Details
    ISSN: 1432-072X
    Schlagwort(e): Key wordsEscherichia coli ; Capsule ; Serotype ; Edema disease ; Electron microscopy ; Cell adhesion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The fine structure of the cell surface of seven enterotoxemic Escherichia coli (ETEEC) O139:K12 strains isolated from piglets with edema disease were examined electron microscopically using both the negative-staining method and the freeze-substitution fixation method. Densely packed, fine fibers were observed; they consisted of a capsule layer approximately 25 nm thick around the cell surfaces of strains 107/86, IW-2, ED-3, ED-43, and ED-61, all of which have a capacity to adhere strongly to HEp-2 cells. In contrast, no such structure was observed on the surface of strains RK-O139 or ED-1, both of which adhere only weakly to HEp-2 cells. These results suggest that the capsule structure might be associated with the ability to adhere to HEp-2 cells and, as a result, also potentially play some role in ETEEC infection.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002030050395
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  • 80
    Digitale Medien
    Digitale Medien
    A current assessment of photosystem II structure (1996)
    Springer
    Bioscience reports 16 (1996), S. 159-187 
    Details
    ISSN: 1573-4935
    Schlagwort(e): Electron microscopy ; photosystem II ; thylakoid membrane
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract This review covers the recent progress in the elucidation of the structure of photosystem II (PSII). Because much of the structural information for this membrane protein complex has been revealed by electron microscopy (EM), the review will also consider the specific technical and interpretation problems that arise with EM where they are of particular relevance to the structural data. Most recent reviews of photosystem II structure have concentrated on molecular studies of the PSII genes and on the likely roles of the subunits that they encode or they were mainly concerned with the biophysical data and fast absorption spectroscopy largely relating to electron transfer in various purified PSII preparations. In this review, we will focus on the approaches to the three-dimensional architecture of the complex and the lipid bilayer in which it is located (the thylakoid membrane) with special emphasis placed upon electron microscopical studies of PSII-containing thylakoid membranes. There are a few reports of 3D crystals of PSII and of associated X-ray diffraction measurements and although little structural information has so far been obtained from such studies (because of the lack of 3D crystals of sufficient quality), the prospects for such studies are also assessed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01206204
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  • 81
    Digitale Medien
    Digitale Medien
    Calcium pools, calcium entry, and cell growth (1996)
    Springer
    Bioscience reports 16 (1996), S. 139-157 
    Details
    ISSN: 1573-4935
    Schlagwort(e): Calcium ; serca pump ; endoplasmic reticulum ; cell growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract The Ca2+ pump and Ca2+ release functions of intracellular Ca2+ pools have been well characterized. However, the nature and identity of Ca2+ pools as well as the physiological implications of Ca2+levels within them, have remained elusive. Ca2+ pools appear to be contained within the endoplasmic reticulum (ER); however, ER is a heterogeneous and widely distributed organelle, with numerous other functions than Ca2+ regulation. Studies described here center on trying to determine more about subcellular distribution of Ca2+ pools, the levels of Ca2+ within Ca2+ pools, and how these intraluminal Ca2+ levels may be physiologically related to ER function. Experiments utilizingin situ high resolution subcellular morphological analysis of ER loaded with ratiometric fluroescent Ca2+ dyes, indicate a wide distribution of inositol 1,4,5-trisphosphate (InsP3)-sensitive Ca2+ pools within cells, and large changes in the levels of Ca2+ within pools following InsP3-mediated Ca2+ release. Such changes in Ca2+ may be of great significance to the translation, translocation, and folding of proteins in ER, in particular with respect to the function of the now numerously described luminal Ca2+-sensitive chaperonin proteins. Studies have also focussed on the physiological role of pool Ca2+ changes with respect to cell growth. Emptying of pools using Ca2+ pump blockers can result in cells entering a stable quiescent G0-like growth state. After treatment with the irreversible pump blocker, thapsigargin, cells remain in this state until they are stimulated with essential fatty acids whereupon new pump protein is synthesized, functional Ca2+ pools return, and cells reenter the cell cycle. During the Ca2+ pool-depleted growth-arrested state, cells express a Ca2+ influx channel that is distinct from the store-operated Ca2+ influx channels activated after short-term depletion of Ca2+ pools. Overall, these studies indicate that significant changes in intraluminal ER Ca2+ do occur and that such changes appear linked to alteration of essential ER functions as well as to the cell cycle-state and the growth of cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01206203
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  • 82
    Digitale Medien
    Digitale Medien
    Regulation of melatonin production and intracellular calcium concentrations in the trout pineal organ (1996)
    Springer
    Cell & tissue research 286 (1996), S. 315-323 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Pineal organ ; Melatonin ; Norepinephrine ; Calcium ; Fura-2 ; Photoreceptor ; Rainbow trout ; Oncorhynchus mykiss (Teleostei)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract. The present in vitro study correlates measurements of the melatonin production from trout pineal organs with those of the intracellular calcium concentration in pinealocytes. Melatonin production increases with decreasing irradiance and shows maximal values in darkness. Some pinealocytes exhibit spontaneous calcium oscillations, although most of them have a stable basal calcium concentration. Diminishing extracellular calcium and enhancing magnesium reduces melatonin release in the light-and dark-adapted state. The application of Co2+ decreases melatonin secretion in the mesopic and scotopic range, reversibly blocks spontaneous calcium oscillations, reduces the basal intracellular calcium concentration in non-oscillating pinealocytes, and inhibits the KCl-induced rise in intracellular calcium. Application of glutamate, norepinephrine, isoproterenol, or dopamine has no significant effect on melatonin secretion. Norepinephrine does not influence the calcium concentration in any of the trout pinealocytes. Treatment with the GABAA-receptor agonist muscimol causes a slight reduction of melatonin release in the mesopic and scotopic range of illumination, without affecting intracellular calcium concentrations. Thus, Co2+ and low calcium/high magnesium buffer reduce melatonin release through an action on the calcium concentration in trout pinealocytes and not through a blockade of synaptic transmission. All the data show that the trout pineal organ synthesizes and releases melatonin in relation to the irradiance of the incident light and that neuronal inputs have a minor, if any, influence on melatonin synthesis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050701
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  • 83
    Digitale Medien
    Digitale Medien
    Desmin filaments in the electrocytes of the electric organ of the electric eel Electrophorus electricus (1996)
    Springer
    Cell & tissue research 285 (1996), S. 387-393 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Electrocyte ; Intermediate filaments ; Desmin ; Cytoskeleton ; Electron microscopy ; Electrophorus electricus (Teleostei)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract. Desmin protein is an abundant constituent of the intermediate filaments in the electrocytes of the electric organ of the electric eel Electrophorus electricus. Polyclonal antibodies were raised against purified desmin from the electric organ and used for immunolabeling of the protein in reconstituted filaments. In thick sections of the main electric organ that has been stained with fluorescein-labeled desmin-specific antibodies, light microscope revealed a diffuse meshwork of desmin filaments dispersed in the cytoplasm of electrocytes. In the region under the membrane, the immunostaining was slightly more intense than elsewhere. The meshwork of intermediate filaments composed of desmin was examined by electron microscopy of the main electric organ. Immuno-gold labeling demonstrated a widespread meshwork of desmin filaments in the cytoplasm and in close association with the plasma membrane. These observations suggest that intermediate filaments play a role in the maintenance of the morphology of electrocytes and, as an intracellular meshwork spanning the width of the cell, they may contribute to the organization of the intracellular compartments.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050654
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  • 84
    Digitale Medien
    Digitale Medien
    Nitric oxide synthase-containing neurones and nerve fibres within cardiac ganglia of rat and guinea-pig: an electron-microscopic immunocytochemical study (1996)
    Springer
    Cell & tissue research 284 (1996), S. 19-28 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Innervation ; Heart ; Intracardiac neurone ; Nitric oxide ; Immunocytochemistry ; Electron microscopy ; Rat (Sprague Dawley) ; Guinea-pig (Dunkin Hartley)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract. The nitric oxide synthase-immunoreactivity and NADPH-diaphorase activity of intracardiac neurones in the rat and guinea-pig was studied at the ultrastructural level. While some nitric oxide synthase-containing intracardiac neurones were very heavily labelled, with electron-dense immunoprecipitate distributed throughout the neuronal cell bodies and their processes, most of the labelled neurones exhibited a lighter and more patchy distribution of nitric oxide synthase-immunoreactive material. Synapses made by nitric oxide synthase-negative nerve fibres with labelled intracardiac neurones were seen. Conversely, many nitric oxide synthase-containing nerve fibres that made synaptic contacts with unlabelled intracardiac neurones were also observed. Some small granule-containing cells were nitric oxide synthase-immunoreactive and were associated with unlabelled nerve terminals, while non-immunoreactive small granule-containing cells that were innervated by nitric oxide synthase-immunoreactive nerves were also seen. Small patches of osmiophilic electron-dense material were observed in the cytoplasm of NADPH-diaphorase-positive intracardiac neurones. This is the first description of the ultrastructural distribution of nitric oxide synthase-immunoreactivity and NADPH-diaphorase activity in a subpopulation of intracardiac neurones of rat and guinea-pig heart and provides further evidence in support of a role for nitric oxide in the local control of the heart by intrinsic neurones.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050563
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  • 85
    Digitale Medien
    Digitale Medien
    Studies on the structure of ocellar photoreceptor cells of Drosophila melanogaster with special reference to subrhabdomeric cisternae (1996)
    Springer
    Cell & tissue research 284 (1996), S. 77-85 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Ocellus ; Photoreceptor cells ; Retinal degeneration ; Subrhabdomeric cisternae ; Electron microscopy ; Immuno-electron microscopy ; Phosphatidylinositol transfer protein ; Drosophila melanogaster (Insecta)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract. We studied the structure of ocellar photoreceptor cells of Drosophila melanogaster, particularly the subrhabdomeric cisternae which our previous studies have shown to be essential structures for turnover of photoreceptive membranes in compound eyes. Each ocellus contained elongated photoreceptor cells with rhabdomeres positioned distally. In the subrhabdomeric regions, endocytotic invaginations were frequently observed, suggesting active turnover of photoreceptive membranes. In the vicinity of the photoreceptive microvilli, membranous structures similar to the subrhabdomeric cisternae in compound eyes were observed. These membranous structures were immunopositive for the rdgB protein, a phosphatidylinositol transfer protein that is localized to the subrhabdomeric cisternae in compound eyes. The ocellar photoreceptor cells of the retinal degeneration mutants (rdgA,B) were also studied. In these mutants, retinal degeneration has been reported to start, in compound eyes, with the disappearance of the subrhabdomeric cisternae. We found that the ocellar subrhabdomeric cisternae also disappear during the initial stage of retinal degeneration. From these observations, we conclude that the mechanism of photoreceptive membrane turnover in ocellar photoreceptor cells involves the rdgB and probably the rdgA proteins which are associated with subrhabdomeric cisternae, as is the case for photoreceptive membrane turnover in compound eyes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050568
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  • 86
    Digitale Medien
    Digitale Medien
    Chordotonal sensilla embedded in the epidermis of the soft integument of the cricket, Teleogryllus commodus (1996)
    Springer
    Cell & tissue research 284 (1996), S. 125-142 
    Details
    ISSN: 1432-0878
    Schlagwort(e): Key words: Chordotonal organ ; Scolopidium ; Mechanoreceptor ; Sensilla ; Electron microscopy ; Phylogenesis ; Teleogryllus commodus (Insecta)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract. More than 50 chordotonal sensilla, or scolopidia, embedded entirely in the integument were found in each side of the genital chamber wall in the female cricket, Teleogryllus commodus. Their cell bodies lie among the epidermal cells, and the tips of their dendrites terminate in the cuticle. About half of them contain two sensory cells (two-cell scolopidium), the others only one (one-cell scolopidium). The sensory cell in the one-cell scolopidium is the type-1 cell. In the two-cell scolopidium one is type-1 and the other type-2. Regardless of the number of sensory cells, they are all amphinematic. In the two-cell scolopidium only the type-2 dendrite, rich in microtubules, penetrates into the cuticle, bifurcates and terminates in the tube enclosed by an attachment cell; the type-1 never extends into the cuticle. On the other hand, the type-1 cell in the one-cell scolopidium projects its apex into the cuticle. The unique topography and structure of these scolopidia lead to the following hypothesis about the phylogenetic relationship between the scolopidia and other kinds of sensilla: the type-1 scolopidial sensory cell buried in the integument may be the original model, which through the loss of the long regular axoneme has given rise to type-2 cells. Modification of the apical region, the tubular body or ramification, may have lead to the cuticular sensilla corresponding to the development of the cuticular apparatus, and the scolopidia may have been withdrawn into the body cavity to form ordinary chordotonal organs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004410050573
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  • 87
    Digitale Medien
    Digitale Medien
    Effect of caffeine on cytosolic Ca2+ level and cytoplasmic streaming inNitella axilliformis (1996)
    Springer
    Protoplasma 190 (1996), S. 164-171 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Caffeine ; Cytoplasmic streaming ; Calcium ; Nitella
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The effect of caffeine on cytosolic Ca2+ level and rate of cytoplasmic streaming was studied inNitella. External application of caffeine induced both a transient rise in cytosolic Ca2+ level and a decline in the rate of cytoplasmic streaming ofNitella. When EGTA-injected cells were bathed in EGTA-containing medium, external application of caffeine inhibited cytoplasmic streaming but induced no transient rise in cytosolic Ca2+ level. These results suggest that the inhibitory effect of caffeine on cytoplasmic streaming is independent of cytosolic Ca2+ level.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01281315
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  • 88
    Digitale Medien
    Digitale Medien
    Lysosomotropic agents activate the capacity for calcium dependent pinocytosis in starvedAmoeba proteus: evidence for a mechanism involving phospholipase A2 (1996)
    Springer
    Protoplasma 192 (1996), S. 20-27 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Amino acid ester ; Calcium ; Dantrolene ; Endocytosis ; Lysosome ; Phospholipase A2
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Pinocytosis induced by Na+ was assayed by phase contrast microscopy in 8–12 days starvedAmoeba proteus. These cultures were inactive with respect to calcium-dependent Na+-induced pinocytosis, but treatment with amino acid methyl and ethyl esters increased their capacity for pinocytosis. Besides promoting pinocytosis these compounds also stimulated calcium-sensitive secretion of lysosomal enzymes from normal, 2–3 days starved, cells. Only uncharged 1-forms of the amino acid esters were effective. Also other lysosomotropic compounds including monodansylcadaverine, glycine-phenylalanine-2-naphthylamide, NH4Cl, and the ionophores monensin and A23187 activated starved cells. The effect of these agents (except A23187) was inhibited by the drug dantrolene suggesting that activation is a consequence of release of Ca2+ from intracellular stores. Several of the lysosomotropic agents also lost their activating effect in the presence of phospholipase A2 (PLA2) inhibitors. To investigate whether or not PLA2 activity in the cell culture could imitate the effect of the lysosomotropic agents, we incubated starved cells with snake venom PLA2s. These enzymes caused rapid, dantrolene-sensitive activation of the cells. Measurement of endogenous PLA2in “normal” cells revealed significant cellular activity but no significant secretion of the enzyme into the culture medium was observed. Together the studies with enzyme inhibitors and dantrolene suggest that the process by which lysosomotropic agents affect pinocytosis involves activation of PLA2 and release of Ca2+ from intracellular stores.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01273241
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  • 89
    Digitale Medien
    Digitale Medien
    Structural basis for the red light induced repolarization of tip growth in caulonema cells ofCeratodon purpureus (1996)
    Springer
    Protoplasma 192 (1996), S. 189-198 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Calcium ; Microfilaments ; Microtubules ; Moss protonema ; Phototropism ; Phytochrome
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Two dynamic changes are associated with the phytochrome-regulated phototropic response in tip cells of the mossCeratodon purpureus: a tip-located gradient shift of chlortetracy-cline (CTC)-stained calcium and a structural reorganization of apical microfilaments (MFs). We examined the interdependence of these processes. Cells were treated with the antimicrotubule drug oryzalin, the antimicrofilament drug cytochalasin-D, and the calcium channel blocker nifedipine. respectively. The effects on phototropic growth, on the structural alignment of the cytoskeleton (microtubules, MTs; microfilaments) and on the distribution of CTC-stained calcium were studied under each of these conditions. In gravitropically growing tip cells the apical MFs form a cortical collar-like structure, consisting of actin bundles with a parallel axial alignment. These MFs point towards the presumptive growing point, a weakly stained region in the tip of the cell from which bundles are absent. MTs are present in the cortex and in the endoplasm of the tip, predominantly oriented longitudinally. The MTs converge within the central apex. The cells show a steep tip-to-base CTC-calcium gradient with its highest signal in the central apex. Destruction of MTs by 1 μM oryzalin induces several translocational effects: (i) the growing zone and phototropic outgrowth shift from the apex to subapical parts of the cell; (ii) the structural integrity of the apical MFs and the tip-to-base alignment of the CTC-calcium gradient are disturbed; and (iii) the red light induced gradient shift and the reorientation of MFs proceed in an expanded area spanning from the tip to subapical parts of the cell. Cytochalasin-D (10 μg/ml) destroys the MFs. Under these conditions tip growth stops and the phototropic outgrowth is suppressed. The apical MT-structure and the CTC-calcium gradient are not influenced by the agent. Unilateral red light still induces the light-directed translocation of the gradient. Tip cells “memorize” a unilateral irradiation applied during growth inhibition with cytochalasin-D. After recovery in darkness the cells start to grow in the former light direction. The restoration of the MFs precedes the outgrowth. The structural alignment of the rebuilt actin bundles indicates the future growth direction. The calcium channel blocker nifedipine (10 βM) also inhibits tip growth and concurrently phototropic outgrowth. Nifedipine destroys the CTC-calcium gradient and apical MFs; MTs are not influenced by the channel blocker.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01273891
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  • 90
    Digitale Medien
    Digitale Medien
    In situ immunocytochemical evidence that a homolog of protein translation elongation factor EF-1α is associated with microtubules in carrot cells (1996)
    Springer
    Protoplasma 190 (1996), S. 141-150 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Calcium ; Calmodulin ; Carrot cells ; Elongation factor-1-alpha ; Immunofluorescence microscopy ; Microtubule-associated protein
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Evidence indicates that elongation factor-1α (EF-1α), a ubiquitous and abundant protein factor involved in the first step of peptide elongation, is also associated with the cytoskeleton in a variety of organisms. Although the effects of these associations on EF-1α's translational function have not been examined, the associations do appear to result in non-passive effects on the cytoskeleton. A carrot homolog of EF-1α, pp 50, has been reported to interact with microtubules in vitro, inducing the formation of microtubule bundles that can be dissociated by Ca2+/calmodulin. The characterization of anti-pp 50 antibodies is reported here. Immunocytochemistry, using anti-pp 50 and anti-tubulin antibodies, was used to investigate the co-localization of pp 50 and microtubules in situ. In carrot protoplasts fixed after detergent lysis, at least a fraction of pp 50 appears to be associated with microtubules. Treatment of such protoplasts with amiprophos-methyl (APM) reduced both the presence of microtubules and the co-localizing pp 50-associated fluorescence. In taxol-treated protoplasts, increases in both microtubules and the colocalizing pp 50-associated fluorescence were observed. When carrot protoplasts were fixed prior to detergent extraction, confocal laser scanning microscopy likewise revealed co-localization. Furthermore, what is likely to be a fluorescence resonance energy transfer (FRET) between fluorochromes associated with anti-pp 50 and anti-tubulin reporters was observed, indicating that some pp 50 is intimately associated with microtubules. The in situ cytoarchitectural evidence is consistent with a function previously proposed for pp 50 based on in vitro experiments — that pp 50 is a plant microtubuleassociated protein (MAP) whose function can be modulated by a Ca2+/calmodulin signal transduction mechanism in plant cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01281313
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  • 91
    Digitale Medien
    Digitale Medien
    Polyanion-mediated mineralization — a kinetic analysis of the calcium-carrier hypothesis in the phytoflagellatePleurochrysis carterae (1996)
    Springer
    Protoplasma 190 (1996), S. 181-188 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Calcium ; Coccolithofore ; Mineralization ; Polyanion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Polyanions are postulated intermediates in biomineralization because they sequester large numbers of calcium ions and occur in high concentrations at mineralizing foci in distantly related organisms. In this study mineral ion and polyanion metabolism was examined inPleurochrysis carterae to determine whether polyanions function as intermediate calcium-carriers during coccolith (mineralized scale) formation. In this organism mineralization occurs intracellularly in coccolith-forming saccules, and mature coccoliths are extruded through the plasma membrane into the coccosphere. The polyanions (acidic polysaccharides known as PS-1 and PS-2) are synthesized in medial Golgi cisternae and transported to the coccolith-forming saccule prior to the onset of mineral deposition; they also cover the mineral surface of mature coccoliths. Pulse-chase experiments with45Ca2+ and14CO3 − show the calcium uptake into the coccolith-forming saccule is much slower than carbonate uptake. The extended intracellular half-life of calcium ions destined for the coccosphere suggests that calcium is initially sequestered in more distal Golgi elements (perhaps in association with the polyanions) and enters the coccolith-forming saccule only after passage through the endomembrane system. This is consistent with previous cytochemical studies showing that the polyanions are complexed with calcium prior to mineral deposition. It has been suggested that polyanions may be degraded at the mineralization front in order to free calcium ions for precipitation with available carbonate or phosphate ions. However, this study demonstrates that the polyanions are not degraded; essentially all PS-1 and PS-2 are eventually secreted with the mineral phase into the coccosphere. The kinetics of mineral ion and polyanion secretion are consistent with a polyanion-mediated calcium transport; however, the manner in which calcium might be sequestered by and freed from the polyanions is still obscure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01281317
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  • 92
    Digitale Medien
    Digitale Medien
    Caffeine inhibits cell plate formation by disrupting membrane reorganization just after the vesicle fusion step (1996)
    Springer
    Protoplasma 195 (1996), S. 144-155 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Cytokinesis ; Tobacco ; Caffeine ; Callose ; Calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary We have re-examined the effects of caffeine on cell plate formation in synchronized tobacco BY-2 cells by means of cryofixation, immunocytochemistry, and calcium staining techniques. Because cryofixation preserves structural intermediates of cell plates that are not seen in chemically fixed cells, this methodology has enabled us to define not only when caffeine acts but also which assembly steps are inhibited. Caffeine acts at an early stage of cytokinesis, just after the Golgi-derived vesicles have arrived at the cell equator and begun to fuse with each other via thin (20 nm) membrane tubules. This initial round of fusions produces a delicate membrane network which in control cells is rapidly converted in a more substantial tubulo-vesicular network covered by a thick, fuzzy coat on its cytoplasmic surface. Caffeine disrupts the conversion of the fragile, thin, fusion tube-generated membrane network into the more stable tubulo-vesicular network, the assembly of its fuzzy coat, and the budding of clathrin-coated vesicles from its surface. Normally, the tubulo-vesicular network also provides the structural framework for calcium-dependent callose synthases that deposit a callose layer over the lumenal surface of the cell plate membranes. In the presence of caffeine, no stabilizing callose layer is formed, and the thin tubule membrane network fragments into vesicles of variable sizes. Cell plates in caffeine-treated cells stained with chlortetracycline, a fluorescent stain of membrane-associated calcium, also display a significant reduction in fluorescence at the cell plate, suggesting a major decrease in cell plate membrane-associated calcium. However, this latter finding needs to be confirmed by more sophisticated calcium measuring techniques. Current theories of the mechanism of action of caffeine, including its ability to disrupt local calcium gradients, are discussed within the new ultrastructural context that this study provides. Our findings, finally, suggest a new method for isolating just fused but not further matured cell plate forming vesicles for biochemical studies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01279193
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  • 93
    Digitale Medien
    Digitale Medien
    Localized membrane-wall adhesions inPelvetia zygotes (1996)
    Springer
    Protoplasma 190 (1996), S. 39-52 
    Details
    ISSN: 1615-6102
    Schlagwort(e): F-actin ; Plasma membrane ; Cell wall ; Calcium ; Hydrogen ; Peptide RGD ; Tip growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Membrane-wall adhesions in zygotes of the brown algaPelvetia were visualized following plasmolysis. Strands of cytoplasm remained firmly attached to the cell wall at discrete adhesion sites during plasmolysis. Adhesion sites were uniformly distributed in ungerminated zygotes, but were concentrated in the apical 5 μm of the elongating rhizoid in germinated zygotes. Few adhesions were detected along the flanks of the rhizoid or in the thallus region of germinated zygotes. The structure, physiology and function of apical adhesions in the rhizoid were characterized. F-actin was found at adhesion sites in plasmolyzed zygotes labeled with rhodamine phalloidin, and disruption of cortical F-actin reduced the number of adhesions. Manipulation of cytosolic H+ and Ca2+ activities also disrupted adhesions. On the extracellular surface, the number of adhesions was reduced by inhibition of cellulose synthesis, protease cleavage of wall proteins, and changes in extracellular H+ and Ca2+ activities. Chronic treatment with the synthetic peptide RGDS, which prevents cell adhesion in fibroblasts, also reduced adhesion number. The number of adhesions per cell did not correlate with growth rate, but was inversely correlated with the ability to establish new rhizoid growth sites. The results indicate that membrane wall adhesions containing F-actin on the cytoplasmic face are localized in the growing rhizoid apex. The adhesions may be structurally related to focal adhesions in animal cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01281193
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  • 94
    Digitale Medien
    Digitale Medien
    Localization of calcium during somatic embryogenesis of carrot (Daucus carota L.) (1996)
    Springer
    Protoplasma 190 (1996), S. 107-118 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Calcium ; Confocal scanning laser microscopy ; Daucus carota ; Embryogenesis ; Fluo-3 dye ; Proton microprobe
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The distribution of free cytosolic Ca2+ was studied during somatic embryogenesis of carrot using confocal scanning laser microscopy with fluo-3 as a fluorescent Ca2+ indicator. Chlorotetracycline fluorescence, antimonate precipitation and proton induced X-ray emission analysis were used as additional methods to confirm the results obtained with fluo-3. The process of embryogenesis was found to coincide with a rise in the level of free cytosolic Ca2+. The level of Ca2+ was low in proembryogenic masses and relatively high in later stages of embryogenesis. The highest signal was found in the protoderm of embryos from the late globular to the torpedo-shaped stage. A gradient in fluorescence intensity was often observed along the longitudinal axis of the embryos. The most conspicuous intracellular signal was found in the nucleus. Other organelles did not take up the dye and were always without fluorescence. The changes in [Ca2+]c are discussed in relation to physiological processes which are known to be important during somatic embryogenesis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01281199
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  • 95
    Digitale Medien
    Digitale Medien
    Mineral content modifications during ripening of asparagus (Asparagus officinalis, L.) (1996)
    Springer
    Plant foods for human nutrition 49 (1996), S. 13-26 
    Details
    ISSN: 1573-9104
    Schlagwort(e): Asparagus ; Ripening ; Minerals ; Calcium ; Magnesium ; Sodium ; Potassium and phosphorus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The essential elements: calcium (Ca), magnesium (Mg), sodium (Na) potassium (K) and phosphorus (P) were analyzed in fresh asparagus to determine the effect of the ripening of the asparagus on the mineral content. Asparagus samples were classified in two groups by diameter (〈11 mm and 〉14 mm). Asparagus from a sample group with the same diameter were divided into two portions (apical and basal) according to distance from the tip. The concentrations of calcium, magnesium and phosphorus increased with the ripening process of the asparagus while the content of sodium decreased when the white asparagus turned into a green ripening state. No significant differences were established for potassium. The green ripening state was the group with the greater concentration of calcium, magnesium and phosphorus. Statistically significant differences (p〈0.001) were observed between portions of asparagus (tip and rest of stem) in the contents of the five mineral elements analyzed. The levels of mineral elements investigated increased notably in the tip of the asparagus with the exception of sodium and potassium of which the levels in the apical portion decreased or hardly modified. The variance analyses determined statistically significant differences (p〈0.001) in the concentration of magnesium, sodium and phosphorus between asparagus diameters (〈11 and 〉14 mm) and no significant differences (p〉0.05) were found for calcium and potassium. The mean element levels were (mg/kg dry weight): Ca=3240±1186; Mg=1818±490; Na=368±86; K=37297±4167 and P=6809±2491.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01092518
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  • 96
    Digitale Medien
    Digitale Medien
    Characterization of the calmodulin gene family in wheat: structure, chromosomal location, and evolutionary aspects (1996)
    Springer
    Molecular genetics and genomics 252 (1996), S. 684-694 
    Details
    ISSN: 1617-4623
    Schlagwort(e): Key words Aneuploid ; Calcium ; Root ; Triticum ; Wild wheat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  Calmodulin is a ubiquitous transducer of calcium signals in eukaryotes. In diploid plant species, several isoforms of calmodulin have been described. Here, we report on the isolation and characterization of calmodulin cDNAs corresponding to 10 genes from hexaploid (bread) wheat (Triticum aestivum). These genes encode three distinct calmodulin isoforms; one isoform is novel in that it lacks a conserved calcium binding site. Based on their nucleotide sequences, the 10 cDNAs were classified into four subfamilies. Using subfamily-specific DNA probes, calmodulin genes were identified and the chromosomal location of each subfamily was determined by Southern analysis of selected aneuploid lines. The data suggest that hexaploid wheat possesses at least 13 calmodulin-related genes. Subfamilies 1 and 2 were both localized to the short arms of homoeologous-group 3 chromosomes; subfamily 2 is located on all three homoeologous short arms (3AS, 3BS and 3DS), whereas subfamily 1 is located only on 3AS and 3BS but not on 3DS. Further analysis revealed that Aegilops tauschii, the presumed diploid donor of the D-genome of hexaploid wheat, lacks a subfamily-1 calmodulin gene homologue, whereas diploid species related to the progenitors of the A and B genomes do contain such genes. Subfamily 3 was localized to the short arm of homoeologous chromosomes 2A, 2B and 2D, and subfamily 4 was mapped to the proximal regions of 4AS, 4BL and 4DL. These findings suggest that the calmodulin genes within each subfamily in hexaploid wheat represent homoeoallelic loci. Furthermore, they also suggest that calmodulin genes diversified into subfamilies before speciation of Triticum and Aegilops diploid species.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02173974
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  • 97
    Digitale Medien
    Digitale Medien
    Characterization of the calmodulin gene family in wheat: structure, chromosomal location, and evolutionary aspects (1996)
    Springer
    Molecular genetics and genomics 252 (1996), S. 684-694 
    Details
    ISSN: 1617-4623
    Schlagwort(e): Aneuploid ; Calcium ; Root ; Triticum ; Wild wheat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Calmodulin is a ubiquitous transducer of calcium signals in eukaryotes. In diploid plant species, several isoforms of calmodulin have been described. Here, we report on the isolation and characterization of calmodulin cDNAs corresponding to 10 genes from hexaploid (bread) wheat (Triticum aestivum). These genes encode three distinct calmodulin isoforms; one isoform is novel in that it lacks a conserved calcium binding site. Based on their nucleotide sequences, the 10 cDNAs were classified into four subfamilies. Using subfamily-specific DNA probes, calmodulin genes were identified and the chromosomal location of each subfamily was determined by Southern analysis of selected aneuploid lines. The data suggest that hexaploid wheat possesses at least 13 calmodulin-related genes. Subfamilies 1 and 2 were both localized to the short arms of homoeologous-group 3 chromosomes; subfamily 2 is located on all three homoeologous short arms (3AS, 3BS and 3DS), whereas subfamily 1 is located only on 3AS and 3BS but not on 3DS. Further analysis revealed thatAegilops tauschii, the presumed diploid donor of the D-genome of hexaploid wheat, lacks a subfamily-1 calmodulin gene homologue, whereas diploid species related to the progenitors of the A and B genomes do contain such genes. Subfamily 3 was localized to the short arm of homoeologous chromosomes 2A, 2B and 2D, and subfamily 4 was mapped to the proximal regions of 4AS, 4BL and 4DL. These findings suggest that the calmodulin genes within each subfamily in hexaploid wheat represent homoeoallelic loci. Furthermore, they also suggest that calmodulin genes diversified into subfamilies before speciation ofTriticum andAegilops diploid species.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02173974
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  • 98
    Digitale Medien
    Digitale Medien
    The irreversibility of inner mitochondrial membrane permeabilization by Ca2+ plus prooxidants is determined by the extent of membrane protein thiol cross-linking (1996)
    Springer
    Journal of bioenergetics and biomembranes 28 (1996), S. 523-529 
    Details
    ISSN: 1573-6881
    Schlagwort(e): Calcium ; cyclosporin A ; mitochondria ; mitochondrial permeability transition pore ; protein oxidation ; reactive oxygen species
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Physik
    Notizen: Abstract We have previously shown that mitochondrial membrane potential (δψ) drop promoted by prooxidants and Ca2+ can be reversed but not sustained by ethylene glycol-bis(β-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA) unless dithiothreitol (DTT), a disulfide reductant, is also added [Valle, V. G. R., Fagian, M. M., Parentoni, L. S., Meinicke, A. R., and Vercesi, A. E. (1993).Arch. Biochem. Biophys. 307, 1–7]. In this study we show that catalase or ADP are also able to potentiate this EGTA effect. When EGTA is added long after (12 min) the completion of swelling or δψ elimination, no membrane resealing occurs unless the EGTA addition was preceded by the inclusion of DTT, ADP, or catalase soon after δψ was collapsed. Total δψ recovery by EGTA is obtained only in the presence of ADP. The sensitivity of the ADP effect to carboxyatractyloside strongly supports the involvement of the ADP/ATP carrier in this mechanism. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of solubilized membrane proteins shows that protein aggregation due to thiol cross-linkage formed during δψ drop continues even after δψ is already eliminated. Titration with 5,5′-dithio-bis(2-nitrobenzoic acid) supports the data indicating that the formation of protein aggregates is paralleled by a decrease in the content of membrane protein thiols. Since the presence of ADP and EGTA prevents the progress of protein aggregation, we conclude that this process is responsible for both increased permeability to larger molecules and the irreversibility of δΩ drop. The protective effect of catalase suggests that the continuous production of protein thiol cross-linking is mediated by mitochondrial generated reactive oxygen species.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02110442
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  • 99
    Digitale Medien
    Digitale Medien
    Transmission electron microscopy procedure for endothelial cell cultures with angiogenesis (1996)
    Springer
    Methods in cell science 18 (1996), S. 15-18 
    Details
    ISSN: 1573-0603
    Schlagwort(e): Angiogenesis ; Endothelial cells ; Angiogenesis analysis ; Electron microscopy ; Cell culture
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Determination of the structural characteristics of angiogenesis requires a procedure protective of the forming vascular fibers and the endothelial cell monolayer exhibiting cord formation. This report describes in situ fixation of angiogenic cultures in 96-well plates and the subsequent double embedding processing for electron microscopy. Cross sections of the monolayer are obtained without damage of the incipient capillaries.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00123518
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  • 100
    Digitale Medien
    Digitale Medien
    Changes in sodium, calcium and magnesium ion concentrations in sturgeon (Huso huso) urine and in kidney morphology (1996)
    Springer
    Journal of comparative physiology 165 (1996), S. 527-533 
    Details
    ISSN: 1432-136X
    Schlagwort(e): Sturgeon ; Kidney ; Urine ; Magnesium ; Calcium ; Huso huso
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract During adaptation to brackish water the young great sturgeon Huso huso is able to regulate its serum osmolarity and ion concentrations. After transfer from fresh water to brackish water the ion concentrations in the urine increase and the urine becomes isoosmotic to the blood serum after 24h. The Na+ and K+ concentrations in the urine increase during the first 12 h by 4.4 and 7.7 times, respectively, later decreasing again. The Mg2+ and Ca2+ concentrations in the urine increase by 3.4 and 14 times during the first 72h in brackish water and remain high thereafter. These results suggest that the kidneys play an important part in the regulation of serum osmolarity and in the removal of Ca2+; however, in contrast to teleosts, Mg2+ must be removed extrarenally. During adaptation to a hyperosmotic medium the diameters of the Malpighian bodies, the glomeruli and the diameter of the tubules initially all decrease, but the distal tubules become morphologically differentiated into two regions and the diameter of the distal section later increases again. It is suggested that this is the site of Ca2+ secretion into the urine.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00387513
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