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  • Ultrastructure  (1,098)
  • calcium  (441)
  • Springer  (1,539)
  • 2000-2004  (43)
  • 1990-1994  (323)
  • 1985-1989  (337)
  • 1980-1984  (407)
  • 1975-1979  (429)
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  • 1
    Electronic Resource
    Electronic Resource
    A microcalorimetric study of the association of hexacyanoferrate(II) ions with calcium and magnesium ions in aqueous solution (1981)
    Springer
    Journal of solution chemistry 10 (1981), S. 411-418 
    Details
    ISSN: 1572-8927
    Keywords: Flow microcalorimetry ; enthalpy ; ion association ; ferrocyanide ; calcium ; magnesium ; aqueous solution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Using flow microcalorimetry, the ion association reaction M2+(aq)+Fe(CN) 6 4− (aq)=MFe(CN) 6 2− (aq) (M=Ca, Mg) has been studied at 25°C over the ionic strength range 0.02 to 0.08 mol-dm−3. Analyses of the data to obtain ΔHo, the enthalpy change at infinite dilution, are described. The value obtained for ΔHo is sensitive to the kind of functions used to correct for non-ideal behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00658009
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of the calmodulin inhibitor R24571 (calmidazolium) on rat embryos cultured in vitro (1984)
    Springer
    Cellular and molecular life sciences 40 (1984), S. 992-994 
    Details
    ISSN: 1420-9071
    Keywords: Morphogenesis ; mammalian embryo ; calcium ; calmodulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The possible effects of inhibition of the calcium-binding protein, calmodulin, on mammalian morphogenesis have been investigated by culturing rat embryos in vitro from 9 1/2 to 11 1/2 days of development in the presence of R24571 (calmidazolium), a specific inhibitor of calmoldulin. Embryos cultured in 10−2 mM R24571 for 48 h show inhibited development and exhibit a range of morphogenetic abnormalities including assymetry and neural tube defects. Embryos exposed to R24571 for the first 24 h of a 48 h culture are more severely affected than embryos exposed to R24571 for the last 24 h.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01946475
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  • 3
    Electronic Resource
    Electronic Resource
    Dystrophin and the integrity of the sarcolemma in Duchenne muscular dystrophy (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 175-177 
    Details
    ISSN: 1420-9071
    Keywords: Dystrophin ; calcium ; skeletal muscle ; muscular dystrophy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary It is suggested that in Duchenne muscular dystrophy the absence of dystrophin, which is probably a cytoskeletal protein underlying the sarcolemma, causes changes in stretch-activated cation channels rather than direct mechanical tearing of the surface membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01954866
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  • 4
    Electronic Resource
    Electronic Resource
    Cerebrovascular autoregulation is resistant to calcium channel blockade with nimodipine (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 305-306 
    Details
    ISSN: 1420-9071
    Keywords: Baboon ; 133xenon ; cerebral blood flow ; cerebrovascular resistance ; autoregulation ; nimodipine ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In normal baboons cerebrovascular resistance changed along with blood pressure to maintain blood flow constant. This ‘autoregulation’ was not significantly altered in animals treated with a dose of the calcium channel blocker nimodipine causing selective cerebral vasodilation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01951818
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  • 5
    Electronic Resource
    Electronic Resource
    Morphological evidence for calcium storage in the chromatoid body of rat spermatids (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 377-378 
    Details
    ISSN: 1420-9071
    Keywords: Chromatoid body ; spermatids ; calcium ; microtubules ; morphology ; pyroantimonate ; rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Morphological evidence for probable Ca2+ storage in the vesicular elements of the rat spermatid chromatoid body is documented using the K-pyroantimonate method, combined with EDTA chelation. Some vesicles are related to the microtubules associated with the chromatoid body. A possible involvement of Ca2+ in the intracellular movement and/or structural integrity of the chromatoid body is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01957484
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  • 6
    Electronic Resource
    Electronic Resource
    Arachidonic acid mobilization in platelets: The possible role of protein kinase C and G-proteins (1988)
    Springer
    Cellular and molecular life sciences 44 (1988), S. 101-104 
    Details
    ISSN: 1420-9071
    Keywords: Platelets ; calcium ; phospholipase A2 ; G-proteins ; arachidonic acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary A major route for the release of arachidonic acid from platelet phospholipids appears to be catalyzed by a phospholipase A2 that can be stimulated by a rise of cytosolic Ca2+. This paper discusses certain other mechanisms for regulation of this process. Release of arachidonic acid by calcium ionophores is potentiated by pretreatment with stimulators of protein kinase C; e.g. diglyceride, phorbol esters and the terpene diester mezerein. This effect appears to be coincident with phosphorylation of a certain group of proteins (not 47 KDa protein), and is sensitive to depletion of ATP, activation of Ca2+ dependent phosphatase, and the kinase C inhibitor H-7, but is unaffected by Na+/H+ exchange inhibitors. Recent results in other cell types strongly indicate that phospholipase A2 is also directly under control of certain GTP-binding proteins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952189
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of acid precipitation on reproduction in birds (1990)
    Springer
    Cellular and molecular life sciences 46 (1990), S. 962-970 
    Details
    ISSN: 1420-9071
    Keywords: Acid deposition ; reproduction ; birds ; insects ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Acidification in aquatic habitats reduces the reproductive success of both piscivorous and non piscivorous birds, mainly by reducing the food supply. Piscivorous birds find some compensation in an increased transparency of the water, non piscivorous birds in less competition for invertebrate prey by fish. Acidification in forests often has large impacts on insect populations but how this affects forest birds is unknown. Some woodpeckers and nuthatches temporarily benefit from an increase in standing dead timber. In advanced stages of forest dieback the breeding density of forest birds is very much reduced, but species of open woodland increase. Calcium deficiency reduces the reproductive output of some passerine species, but the extent of this phenomenon is unknown. Increased exposure to toxic metals has reduced the reproductive success of some lake dwelling species. It is difficult to assess the effect of acid precipitation on birds since acidification affects ecosystems in many ways, the evidence is largely correlative and reliable estimates of the population size are often lacking. Future studies should concentrate on carefully selected indicator species suitable for detailed data collection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01939390
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  • 8
    Electronic Resource
    Electronic Resource
    Difference of the inhibitory action of verapamil on the positive inotropic effect of Ca2+ between spontaneously hypertensive and normotensive rat myocardium (1984)
    Springer
    Cellular and molecular life sciences 40 (1984), S. 1392-1393 
    Details
    ISSN: 1420-9071
    Keywords: Rat myocardium ; myocardium, rat ; hypertensive rats ; spontaneously ; atrium ; papillary muscle ; verapamil ; inotropic effect ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Verapamil, a calcium entry blocker, had a greater inhibitory effect on the positive inotropic effect of excess Ca2+ in SHR than in NWR, suggesting that the cardiac responsiveness to verapamil was enhanced in SHR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01951906
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  • 9
    Electronic Resource
    Electronic Resource
    Increase in cellular cyclic GMP level by potassium stimulation and its relation to ciliary orientation inParamecium (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 62-64 
    Details
    ISSN: 1420-9071
    Keywords: Cyclic GMP ; calcium ; Paramecium ; triton-extracted model ; ciliary reversal ; excitable membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Physiological roles of cyclic GMP in the control of ciliary movement inParamecium caudatum were investigated. We found that 1) an increase in cellular cyclic GMP level was observed in association with recovery from the ciliary reversal produced by K stimulation, and 2) the presence of cyclic GMP inhibited the Ca-induced ciliary reversal in triton-extracted models. These results suggest that cyclic GMP plays a key role in the control of the Ca-mediated ciliary reversal mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01975897
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  • 10
    Electronic Resource
    Electronic Resource
    Calcitonin-like peptide in the shrimpPalaemon serratus (Crustacea, Decapoda) during the intermolt cycle (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 419-420 
    Details
    ISSN: 1420-9071
    Keywords: Crustacean ; calcitonin ; radioimmunoassay ; calcium ; molt
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary A molecule immunologically related to salmon calcitonin has been detected in the hemolymph of the shrimpPalaemon serratus. Its concentration varies inversely with the calcium level during the molt cycle; a maximum (14 ng/ml) is found in the post-molt stage and a minimum (0.5 ng/ml) during the premolt stage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02118638
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  • 11
    Electronic Resource
    Electronic Resource
    Ionic currents in morphogenesis (1988)
    Springer
    Cellular and molecular life sciences 44 (1988), S. 657-666 
    Details
    ISSN: 1420-9071
    Keywords: Ionic currents ; vibrating probe ; membrane potential ; fucoid egg polarization ; animal-vegetal polarity ; polarization ; voltage gradients ; calcium ; vesicle secretion ; Achlya ; oocytes ; insect follicle ; insect ovariole ; polarized transport ; egg activation ; mouse blastomere ; epithelial morphogenesis ; limb bud
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Morphogenetic fields must be generated by mechanisms based on known physical forces which include gravitational forces, mechanical forces, electrical forces, or some combination of these. While it is unrealistic to expect a single force, such as a voltage gradient, to be the sole cause of a morphogenetic event, spatial and temporal information about the electrical fields and ion concentration gradients in and around a cell or embryo undergoing morphogenesis can take us one step further toward understanding the entire morphogenetic mechanism. This is especially true because one of the handful of identified morphogens is Ca2+, an ion that will not only generate a current as it moves, but which is known to directly influence the plasma membrane's permeability to other ions, leading to other transcellular currents. It would be expected that movements of this morphogen across the plasma membrane might generate ionic currents and gradients of both electrical potential and intracellular concentration. Such ionic currents have been found to be integral components of the morphogenetic mechanism in some cases and only secondary components in other cases. My goal in this review is to discuss examples of both of these levels of involvement that have resulted from investigations conducted during the past several years, and to point to areas that are ripe for future investigation. This will include the history and theory of ionic current measurements, and a discussion of examples in both plant and animal systems in which ionic currents and intracellular concentration gradients are integral components of morphogenesis as well as cases in which they play only a secondary role. By far the strongest cases for a direct role of ionic currents in morphogenesis is the polarizing fucoid egg where the current is carried in part by Ca2+ and generates an intracellular concentration gradient of this ion that orients the outgrowth, and the insect follicle in which an intracellular voltage gradient is responsible for the polarized transport from nurse cell to oocyte. However, in most of the systems studied, the experiments to determine if the observed ionic currents are directly involved in the morphogenetic mechanism are yet to be done. Our experience with the fucoid egg and the fungal hypha ofAchlya suggest that it is the change in the intracellular ion concentration resulting from the ionic current that is critical for morphogenesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01941026
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  • 12
    Electronic Resource
    Electronic Resource
    Novel oscillations in cell suspensions ofDictyostelium discoideum (1990)
    Springer
    Cellular and molecular life sciences 46 (1990), S. 1063-1065 
    Details
    ISSN: 1420-9071
    Keywords: Dictyostelium ; cell communication ; biological rhythms ; oscillations ; cAMP ; folate ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary With a light-scattering technique, two novel rhythms were discovered in cell suspensions ofDictyostelium discoideum. One is a damped oscillation with a period of 2 to 2.5 min (at 23°C) induced by folate in EDTA-dissociated undifferentiated cells. The other is a sinusoidal oscillation with a period of about 12 min occasionally observed with late differentiated cells. Obviously, the repertoire of rhythms of this simple eukaryotic organism is larger than previously assumed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01940674
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  • 13
    Electronic Resource
    Electronic Resource
    Biochemical events associated with rapid cellular damage during the oxygen-and calcium-paradoxes of the mammalian heart (1990)
    Springer
    Cellular and molecular life sciences 46 (1990), S. 41-48 
    Details
    ISSN: 1420-9071
    Keywords: Cardiac muscle ; cell damage ; calcium ; calcium-paradox ; oxygen-paradox ; oxygen radicals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The O2− and Ca2+-paradoxes have a number of features in common and it is suggested that release of cytosolic proteins in both paradoxes is initiated by the activation of a sarcolemma NAD(P)H dehydrogenase which can generate a transmembrane flow of H+ and e− and also oxygen radicals or recox cycling which damage ion channels and membrane proteins (phase I). Entry of Ca2+ through the damaged ion channels then exacerbates the damage by further activating this system, either directly or indirectly, and the redox cycling and/or oxygen radicals cause further damage to integral and cytoskeletal proteins of the sarcolemma resulting in microdamage to the integrity of the membrane (phase II) and the consequent release or exocytosis of cytoplasmic proteins and, under specialised condition, the blebbing of the sarcolemma. The system may be primed either by removal of extracellular Ca2+ or by raising [Ca2+]i by a variety of measures, these two actions being synergistic. The system is initially activated in the Ca2+-paradox by the membrane perturbation associated with removal of extracellular Ca2+; prolonged anoxia in the metabolically active cardiac muscle causes a depletion of the ATP supply, particularly in the absence of glucose, and hence a rise in [Ca2+]i in phase I of the oxygen paradox with the consequent activation of the NAD(P)H oxidase at the sarcolemma. Oxygen radicals are probably generated in both paradoxes and may have a partial role in the genesis of damage, but are not essential in the Ca2+-paradox which continues under anoxia. Massive entry of Ca2+ also activates an intracellularly localised dehydrogenase (probably at the SR) which produces myofilament damage by redox cycling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01955410
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  • 14
    Electronic Resource
    Electronic Resource
    The role of intracellular messengers in adrenocorticotropin secretion in vitro (1990)
    Springer
    Cellular and molecular life sciences 46 (1990), S. 26-40 
    Details
    ISSN: 1420-9071
    Keywords: Opiomelanocortin ; cyclic adenosine 3′,5′-monophosphate (cAMP) ; calcium ; phosphatidylinositol (PI) ; glucocorticoids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Adrenocorticotropin (ACTH), an opiomelanocortin peptide, is secreted from anterior pituitary corticotrophs upon stimulation with corticotropin-releasing hormone (CRH), arginine vasopressin (AVP) and several other neuropeptides. CRH, the most potent secretagogue of ACTH, stimulates ACTH secretion and biosynthesis by increasing the production of cyclic adenosine 3′,5′-monophosphate (cAMP) within corticotrophs. AVP, which is a weak secretagogue of ACTH but strongly potentiates CRH-stimulated ACTH secretion, operates through the phosphatidylinositol (PI) transduction pathway. Both CRH and AVP increase cytosolic free [Ca2+] within normal corticotrophs indicating a role for Ca2+ in ACTH secretion. Glucocorticoids inhibit ACTH synthesis by suppressing transcription of the proopiomelanocortin (POMC) gene and attenuate ACTH release by decreasing cAMP accumulation stimulated by CRH. This review focuses on the roles of these intracellular messengers in ACTH secretion from normal anterior pituitary cells in vitro, and discusses the possible interactions between the cAMP, calcium and PI transduction pathways. Future areas of research are suggested such as identification of protein substrates of cAMP-dependent and Ca2+-dependent kinases within normal corticotrophs and evaluation of their role in ACTH biosynthesis and secretion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01955409
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  • 15
    Electronic Resource
    Electronic Resource
    Aluminium in repair membranes and Al, Ca and Pi in the haemolymph of Al-injected shell-repairing snails (Helix pomatia L.) (1991)
    Springer
    Cellular and molecular life sciences 47 (1991), S. 224-226 
    Details
    ISSN: 1420-9071
    Keywords: aluminium ; snail ; shell-repair ; calcium ; phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In AlCl3-injected shell-repairing snails,Helix pomatia L., the Al-associated decrease of the weights of the shell-repair membranes was unrelated to the Al-concentration in the membranes. In the haemolymph the concentration of Al was related to the dose of injected Al, while the concentration of Ca was increased by the highest Al-dose only. No phosphate was detected in either controls or Al-injected snails. It is concluded that Al inhibits the growth of the CaCO3-crystals by mechanisms other than incorporation in, or adsorption to, the crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01958141
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  • 16
    Electronic Resource
    Electronic Resource
    Oviposition behaviour of Dacus tryoni: The effects of some sugars and salts (1985)
    Springer
    Entomologia experimentalis et applicata 39 (1985), S. 61-71 
    Details
    ISSN: 1570-7458
    Keywords: Dacus tryoni ; Tephritidae ; Diptera ; fruit flies ; oviposition ; egg laying ; behaviour ; taste receptors ; chemoreceptors ; stimulant ; deterrent ; fructose ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Résumé Des mouches fruitières gravides du Queensland (Dacus tryoni), confinées au laboratoire dans des chambres d'oviposition sont stimulées par la présence de β-D(-)fructose, à pondre significativement plus d'oeufs dans un substrat gélosé. Ce composé est un véritable stimulant d'oviposition, accroissant le nombre d'oeufs déposés par mouche, plutôt que simplement localisant l'oviposition dans les substrats le contenant. Le fructose est effectif seulement lorsqu'il est accessible aux récepteurs gustatifs tarsaux et labelliaux et, apparement, agit en stimulant de plus fréquentes insertions de l'ovipositeur dans le substrat; le contact du fructose avec uniquement l'ovipositeur inséré, n'accroît pas l'oviposition. Le seuil de concentration pour obtenir une stimulation par le fructose est de 4 mM; la résponse maximale se produit à 50 mM et au delà, auxquelles concentrations l'oviposition est augmentée d'un facteur 6 par rapport au témoin, qu'il y ait ou non possibilité de choix de substrat. Le sucrose (testé à 100 et 1 000 mM) et le D-glucose (testé à 100 et 500 mM) ne stimulent pas l'oviposition chez D. tryoni. Le fructose favorise fortement l'oviposition grâce aux trous existants dans une surface impénétrable, et dans les conditions naturelles, D. tryoni l'utilise probablement comme un marqueur pour localiser les ruptures dans la peau des fruits, où l'insertion est plus facile. La présence de chlorure de calcium molaire dans la gélose fructose inhibe fortement l'oviposition, même lorsqu'il est inaccessible aux récepteurs gustatifs tarsaux et labelliaux. Le chlorure de sodium molaire n'est pas inhibiteur. Les ions calciums déploient apparemment leur effet inhibiteur par l'intermédiaire de récepteurs gustatifs localisés sur l'ovipositeur.
    Notes: Abstract Gravid Queensland fruit flies (Dacus tryoni) are stimulated by the presence of β-D(-) fructose to lay significantly more eggs in an agar substrate. Fructose is only effective when accessible to the tarsal and/or labellar gustatory sensilla; it greatly increases oviposition through holes in an impenetrable membrane. Threshold for the fructose effect is 4 mM, maximal response being at 50 mM and above. Sucrose and glucose are not oviposition stimulants for D. tryoni. In the field situation D. tryoni probably uses fructose as a marker to locate breaks in the skin of ripe fruit, where insertion of the ovipositor is easier. The flies are deterred from ovipositing in fructose agar by the presence of molar calcium chloride, even when this is inaccessible to the tarsal and labellar gustatory sensilla. Molar sodium chloride is not inhibitory. Calcium ions apparently exert their inhibitory effect via gustatory sensilla located on the ovipositor.
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    URL: http://dx.doi.org/10.1007/BF00338525
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  • 17
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    Biology and ultrastructure of the mycophagus, soil testate amoeba, Phryganella acropodia (Rhizopoda, Protozoa) (1990)
    Springer
    Biology and fertility of soils 9 (1990), S. 101-109 
    Details
    ISSN: 1432-0789
    Keywords: Phryganella acropodia ; Testate amoeba ; Growth rate ; Rhizopoda ; Feeding ; Fungal species ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Clones of Phryganella acropodia were cultivated under different trophic conditions with bacteria as the food source. The doubling time was estimated to be 3 days. The edibility of four species of fungi, Aspergillus niger, Cunninghamella echinulata, Penicillium echinulatum and Stilbella bulbicola, was tested, but only Penicillium enchinulatum and Stilbella bulbicola were eaten and digested by the amoeba. An ultrastructure examination showed that there are two contractile vacuoles, many dictyosomes, a single nucleus with several nucleoli, and peroxisomes. The pseudopodia are filiform when attached to the substrate but change to lobose when the animal is floating. A thin organic membrane covers the aperture of resting forms.
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    URL: http://dx.doi.org/10.1007/BF00335791
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  • 18
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    Ultrastructure of differentiating preameloblasts from tooth germs of the permanent dentition ofMacaca mulatta andMacaca arctoides (1981)
    Springer
    Calcified tissue international 33 (1981), S. 603-618 
    Details
    ISSN: 1432-0827
    Keywords: Preameloblasts ; Tooth germs ; Monkey ; Enamel ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Cytodifferentiation of inner enamel epithelium and the adjacent connective tissue from the tip of the cervical loop to the initiation of enamel elaboration in twoMacaca species was examined. Ten- to twelve-month-old specimens were fixed by perfusion and the permanent tooth buds were prepared for transmission electron microscopy. At the cervical loop proper, inner enamel epithelium cells have lobed nuclei, a paucity of cytoplasm, and wide extracellular spaces; the basal lamina facing the dental papilla is straight. With increasing distance from the tip of the cervical loop, the following changes occur gradually: (a) preameloblasts elongate from 15 to 45 µm, and their organelles, particularly mitochondria and profiles of rough endoplasmic reticulum, become more numerous; (b) extracellular spaces decrease between preameloblasts starting at the basal (infranuclear) end; (c) the basement membrane becomes convoluted and associated with aperiodic fibers; (d) preodontoblast projections penetrate the aperiodic fibers; (e) collagen fibers subjacent to the basement membrane increase in density, with particularly thick fibers paralleling the aperiodic fibers. These modifications occur within three-fourths of the distance from the tip of the cervical loop to the mineralization front. The condensation of preodontoblasts is followed immediately by predentin synthesis. Concomitantly, the basement membrane breaks down and the aperiodic fibers are engulfed by preameloblasts. Preameloblast projections penetrate junctional predentin, contact mineralized dentin, and enamel synthesis ensues. At this stage the ameloblast is 45 µm long, the nucleus is central or basal, the Golgi apparatus has migrated apically, but the Tomes' process has not yet formed. The results indicate that odontogenesis inMacaca monkeys more closely resembles human odontogenesis than does that in the murine rodents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02409498
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  • 19
    Electronic Resource
    Electronic Resource
    Coquille de l'oeuf de caille: Étude ultrastructurale et cristallographique (1978)
    Springer
    Calcified tissue international 25 (1978), S. 145-159 
    Details
    ISSN: 1432-0827
    Keywords: Bird egg shell ; Ultrastructure ; Calcification ; Electron diffraction ; Microanalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The egg-shell of Japanese quail was studied by several techniques. Semithin sections (1μm thick) of non-decalcified shell were observed by normal and polarized light microscopy. Thin sections of non-decalcified shell, examined by transmission electron microscopy, permitted us to observe the forms and dimensions of crystals of calcite within different layers of the shell: mammilary layer, layer of cones, palissade layer and surface crystal layer. There appears to be two distinct zones in the layer of cones as well as in the superficial crystal layer. Electron microdiffraction revealed the orientation of calcite crystals in the columns. Some crystal defects (twins?) were described and the possibility of their artefactual formation during ultramicrotomy is discussed. Localization of Ca, Mg, P and S were made by X-ray microanalysis of semithin sections. This technique shows that shell membranes, and chiefly the true cuticle, are also mineralized but, in these layers, minerals are not crystallized. Otherwise the distribution of Mg is not uniform throughout the shell thickness; it is less concentrated in the external zone of the layer of cones. These results together with observation of developing shells by scanning electron microscopy allowed us to propose a scheme for shell organization of the quail egg. This organization was related with decalcification which occurs during hatching.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02010763
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  • 20
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    Ultrastructural and microanalytical aspects of developing osteodentin in rat incisors (1977)
    Springer
    Calcified tissue international 24 (1977), S. 215-222 
    Details
    ISSN: 1432-0827
    Keywords: Mineralization ; Osteodentin ; Intracellular ; Ultrastructure ; Microanalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Newly formed osteodentin obtained from the anterior extremities of fetal or young rat incisors was observed by means of electron microscopy and electron probe X-ray microanalysis. Cells related to osteodentin formation frequently showed membrane bound intracellular bodies containing varying amounts of fine, needle-shaped crystals, which were identified as apatite. The intracellular clusters of apatite crystals were extruded from the cells through membrane fusion or cellular degeneration. These extracellular clusters seemed to be gradually incorporated into the mineralizing collagenous matrix, which developed around them. Frequent occurrence of dense, dotshaped or filamentous profiles suggested that the dense bodies seen in the perinuclear regions or in the Golgi area were the sites of crystal formation. Energy dispersive X-ray point analysis showed that the intracellular or extracellular apatite clusters contained sulfur in a concentration higher than was present in the mineralizing collagenous matrix. Furthermore, wave dispersive X-ray line analysis showed that the concentration of sulfur was higher in the osteodentin matrix than in the dentin matrix. The sulfur detected is presumed to be contained in acid mucopolysaccharides, which were distributed more heavily in the osteodentin matrix than in the dentin matrix. On the basis of these data, it was concluded that the unique chemical and structural characteristics of the osteodentin result primarily from the incorporation of apatite clusters of intracellular origin and associated acid mucopolysaccharides.
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    URL: http://dx.doi.org/10.1007/BF02223319
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    Studies on the biology of fish bone. III. Ultrastructure of osteogenesis and resorption in osteocytic (cellular) and anosteocytic (acellular) bones (1979)
    Springer
    Calcified tissue international 28 (1979), S. 43-56 
    Details
    ISSN: 1432-0827
    Keywords: Bone resorption ; Osteogenesis ; Fish bone ; Osteocytes ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The comparative ultrastructure of fish bone osteogenesis and resorption induced by scale removal was described in the osteocytic (cellular-boned)Carassius auratus and the anosteocytic (acellular-boned)Tilapia macrocephala. Osteocytes, present in osteocytic bone, were lacking in anosteocytic bone. In osteocytic bone the osteoblast secreted a collagenous preosseous matrix in which it became enmeshed and then was termed a preosteocyte. When the preosseous matrix mineralized, the preosteocyte was termed an osteocyte and was completely surrounded by bone. In anosteocytic bone the osteoblasts receded from the mineralizing front and never became trapped as osteocytes. During resorption, types A and B resorptive cells, present in both bone types, invaded the matrix and demineralized the osseous zone. These cells were characterized by large amounts of granular endoplasmic reticulum and intracellular inclusions containing crystal-like material. Although functionally similar to mammalian osteoclasts, these cells lacked a characteristic ruffled border and were not multinucleated. The osteocytes of cellular bone did not appear to be involved during demineralization.
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    URL: http://dx.doi.org/10.1007/BF02441217
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    In vitro formation of mineralized nodules by periodontal ligament cells from the rat (1992)
    Springer
    Calcified tissue international 50 (1992), S. 459-467 
    Details
    ISSN: 1432-0827
    Keywords: Periodontal ligament fibroblast ; Mineralized nodule ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The purposes of this study were to determine whether periodontal ligament (PDL) cells are capable of producing mineralized nodules in vitro and to analyze ultrastructural features of the nodules. Rat PDL cells were obtained from coagulum in the socket at 2 days after tooth extraction and cultured at confluence in standard medium containing Dulbecco's Modified Eagle's Medium supplemented with 10% FBS and antibiotics. To test mineralized nodule formation, cells were further cultured for an additional 3 weeks in the standard medium containing (1) ascorbic acid (50 μg/ml) and sodium β-glycerophosphate (10 mM), (2) ascorbic acid, sodium β-glycerophosphate, and dexamethasone (5 μM), or (3) ascorbic acid alone. Cells were then fixed in 2.5% glutaraldehyde, postfixed in 1% OsO4, and prepared for light and electron microscopy. Threedimensional nodules containing mineralized matrices were formed only when the cells were cultured in the presence of ascorbic acid and dexamethasone. They were composed of multilayered fibroblasts (up to 13 layers), and highly organized collagen fibrils with 64 nm cross-banding patterns between the cell layers. The fibroblasts in the nodules exhibited an elongated shape with a high degree of cytoplasmic polarity throughout the nodule, and have the morphological features of PDL fibroblasts as seen in vivo. Mineral deposition with needle-like crystals was initiated on collagen fibrils located in intercellular spaces of the upper cell layers and became increasingly heavier towards the bottom half of the nodules. X-ray microanalysis and electron diffraction analysis confirmed that mineral deposition contained calcium and phosphate in the form of immature hydroxyapatite. These nodules contained neither osteoblasts nor osteocytes, and have their own morphological organization and characteristics which differ from those formed by bone cells in culture. Therefore, these data suggest that PDL cells are capable of forming mineralized tissue in vitro with the morphological characteristics different from bone mineralized nodules.
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    URL: http://dx.doi.org/10.1007/BF00296778
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    Heterogeneity of calcium compartmentation: Electron probe analysis of renal tubules (1986)
    Springer
    The journal of membrane biology 94 (1986), S. 191-196 
    Details
    ISSN: 1432-1424
    Keywords: calcium ; kidney proximal tubule ; electron probe ; X-ray microanalysis ; mitochondria ; cytoplasmic calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The objective of this study has been to determine the intracellular localization of calcium in cryofixed, cryosectioned suspensions of kidney proximal tubules using quantitative electron probe X-ray microanalysis. Two populations of cells have been identified: 1) „Viable” cells, representing the majority of cells probed, are defined by their relatively normal K/Na concentration ratio of ∼4∶1. Their measured Ca content is 4.1±1.4 (sem) mmol/kg dry wt in the cytoplasm and 3.1 ± 1.1 mmol/kg dry wt in the mitochondria, or an average cell calcium content of ∼3.8 mmol/kg dry wt. 2) “Nonviable” cells, defined by the presence of dense inclusions in their mitochondria and a K/Na concentration ratio of ∼1. The Ca content is 15±2 mmol/kg dry wt in the cytoplasm and 685±139 mmol/kg dry wt in the mitochondria of such cells. Assuming 25 to 30% of the cell volume is mitochondrial, the overall calcium content of such nonviable cells is ∼ 210 mmol/kg dry wt. The presence of these inclusions in 4 to 5% of the cells would account for the average total Ca content measured in perchloric acid extracts of isolated proximal tubule suspensions (≈ 18 nmol/mg protein or 12.6 mmol/kg dry wt). Whole kidney tissues display a large variability in toal Ca content (4.5 to 18 nmol/mg protein, or 3.4 to 13.5 mmol/kg dry wt), which could be accounted for by inclusion in 0 to 4% of the cells. The electron probe X-ray microanalysis (EPXMA) data conclusively demonstrate that thein situ mitochondrial Ca content of viable cells from the kidney, proximal tubule is low and support the idea that mitochondrial Ca may regulate dehydrogenase activity but probably does not normally control cytosolic free Ca.
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    URL: http://dx.doi.org/10.1007/BF01871198
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    Calcium-induced fusion of didodecylphosphate vesicles: The lamellar to hexagonal II (HII) phase transition (1987)
    Springer
    The journal of membrane biology 95 (1987), S. 255-263 
    Details
    ISSN: 1432-1424
    Keywords: didodecylphosphate ; calcium ; membrane fusion ; lamellar phase ; hexagonal phase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Electron microscopic techniques have been employed to investigate the ability of didodecylphosphate vesicles (diameter approx. 900 Å) to fuse in the presence of Ca2+. As revealed by negative staining, Ca2+ induces extensive fusion and large vesicles with diameters up to 7000 Å are formed. In a processsecondary to fusion, the fused vesicles display a tendency to flatten and are subsequently transformed into extended tubular structures. Freeze-fracture electron microscopy, in conjunction with31P NMR and selected area electron diffraction measurements indicate that the tubes are packed in a hexagonal (HII) array and that the amphiphiles are converted from the lamellar to the hexagonal HII phase. The relationship between membrane fusion and the lamellar-to-hexagonal phase transition is discussed in terms of formation and abundance of transiently stable inverted micellar intermediates at contact regions between two interacting membranes. A model for the conversion of the (vesicular) lamellar into the (tubular) hexagonal HII phase is presented, taking into account the molecular shape of the amphiphile. The relevance of using simple synthetic amphiphiles as models for phospholipid bilayers and complex biomembrane behavior is briefly discussed.
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    URL: http://dx.doi.org/10.1007/BF01869487
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    Ultrastructural evidence of GABA-ergic inhibition and glutamatergic excitation in the pacemaker nucleus of the gymnotiform electric fish, Hypopomus (1994)
    Springer
    Journal of comparative physiology 174 (1994), S. 267-280 
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    ISSN: 1432-1351
    Keywords: Electric fish ; Pacemaker ; GABA ; Glutamate ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The medullary pacemaker nucleus of Hypopomus triggers each electric organ discharge (EOD) by a single command pulse. It consists of electrotonically coupled ‘pacemaker’ cells, which generate the rhythm, and ‘relay’ cells, which follow the pacemaker cells and excite the spinal motoneurons of the electric organ. The pacemaker cells receive two inputs from the complex of the diencephalic prepacemaker nucleus (PPn), a GABA-ergic inhibition and a glutamatergic excitation. Relay cells, on the other hand, receive two glutamatergic inputs, one from a subnucleus of the PPn, the PPn-C, and a second from the sublemniscal prepacemaker nucleus (SPPn). We have labelled afferents to the pacemaker nucleus by injecting HRP to specific sites of the prepacemaker complex. By using immunogold-labelled antibodies and en-grid staining techniques, we demonstrated GABA and glutamate immunoreactivity in labelled synaptic profiles of ultra-thin sections of the pacemaker nucleus. The two types of synapses were interspersed on the surfaces of pacemaker cells, with GABA-immunoreactive synapses apparently representing the GABA-mediated input of the ‘PPn-I’, an inhibitory subdivision of the PPn, and glutamate-immunoreactive synapses representing the input of the ‘PPn-G’, an excitatory subdivision of the PPn. Only glutamate-immunoreactive synapses were found on relay cells.
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    URL: http://dx.doi.org/10.1007/BF00240210
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    The need for speed. II. Myelin in calanoid copepods (2000)
    Springer
    Journal of comparative physiology 186 (2000), S. 347-357 
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    ISSN: 1432-1351
    Keywords: Key words Crustacean ; Sensorimotor ; Ultrastructure ; Multilamellar sheath ; Myelinated axons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Speed of nerve impulse conduction is greatly increased by myelin, a multi-layered membranous sheath surrounding axons. Myelinated axons are ubiquitous among the vertebrates, but relatively rare among invertebrates. Electron microscopy of calanoid copepods using rapid cryofixation techniques revealed the widespread presence of myelinated axons. Myelin sheaths of up to 60 layers were found around both sensory and motor axons of the first antenna and interneurons of the ventral nerve cord. Except at nodes, individual lamellae appeared to be continuous and circular, without seams, as opposed to the spiral structure of vertebrate and annelid myelin. The highly organized myelin was characterized by the complete exclusion of cytoplasm from the intracellular spaces of the cell generating it. In regions of compaction, extracytoplasmic space was also eliminated. Focal or fenestration nodes, rather than circumferential ones, were locally common. Myelin lamellae terminated in stepwise fashion at these nodes, appearing to fuse with the axolemma or adjacent myelin lamellae. As with vertebrate myelin, copepod sheaths are designed to minimize both resistive and capacitive current flow through the internodal membrane, greatly speeding nerve impulse conduction. Copepod myelin differs from that of any other group described, while sharing features of every group.
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    URL: http://dx.doi.org/10.1007/s003590050435
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    Calcium transport affinity, ion competition and cholera toxin effects on cytosolic Ca concentration (1987)
    Springer
    The journal of membrane biology 96 (1987), S. 243-249 
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    ISSN: 1432-1424
    Keywords: cholera toxin ; ionophore ; calcium ; brush-border membrane vesicles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The physiological relevance of an apparent ionophore activity of cholera toxin towards Ca2+ has been examined in several different systems designed to measure affinity, specificity, rates of ion transfer, and effects on intracellular ion concentrations. Half-maximal transfer rates across porcine jejunal brush-border vesicles were obtained at a concentration of 0.20 μM Ca2+. When examined in the presence of competing ions the transfer process was blocked by very low concentrations of La3+ or Cd2+. Sr2+, Ba2+ and Mg2+ were relatively inefficient competitors for Ca2+ transport mediated by cholera toxin. The relative affinities observed would be compatible with a selectivity for Ca2+ transfer at physiological ion concentrations, as well as an inhibition of this ionophore activity by recognized antagonists of cholera toxin such as lanthanum ions. Entry rates of Ca2+ into brush-border vesicles exposed to cholera toxin were large enough to accelerate the collapse of a Ca2+ gradient generated by endogenous Ca, Mg-ATPase activity. The treatment of isolated jejunal enterocytes with cholera toxin caused a significant elevation in cytosolic Ca2+ concentrations as measured by Quin-2 fluorescence. This effect was specifically prevented by prior exposure of the cholera toxin to excess ganglioside GM1. We conclude that cholera toxin has many of the properties required for promoting transmembranes Ca2+ movement in membrane vesicles and appears to be an effective Ca2+ ionophore in isolated mammalian cells.
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    URL: http://dx.doi.org/10.1007/BF01869306
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    Ultrastructure of cells in the cambial region during winter hardening and spring dehardening in Salix dasyclados Wim. grown at two nutrient levels (1987)
    Springer
    Trees 1 (1987), S. 151-163 
    Details
    ISSN: 1432-2285
    Keywords: Cambial activity ; Frost hardiness ; Phenology ; Salix ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The ultrastructure of cells in the cambial region of Salix dasyclados Wim. (clone 78056) was studied during the development of winter hardiness and the onset of cambial activity in spring. Plants were grown at relative growth rates (RG) of 8% and 12% respectively, resulting in different nitrogen content in the stems. Frost hardiness of the plants was estimated by standardized freezing tests. Plants with a higher nitrogen status ceased growth later and started re-growth earlier in spring than plants with lower nitrogen content. Differences in ability to withstand low temperatures during autumn and spring were found between plants grown in the two nutrient treatments. During the development of frost hardiness in the autumn, the number of meristematic cells in the cambial region decreased. The cessation of meristematic activity was accompanied by cell wall thickening and ultrastructural changes in the cells. Frost hardiness increased from the ability to survive -6° C in October to survival of -80° C at the beginning of December. From November to February the cambial region comprised a layer of 2–3 thick-walled cells with conspicuous ultrastructural features. Starch accumulated in plastids in September, decreased during November to March and then increased again in accordance with changes of frost hardiness. Onset of cambial activity began between the end of March and the beginning of April, as shown by increased vacuolization of meristematic cells and mitotic activity. By April, the starch content had increased and lipolysis was observed. Frost hardiness had decreased, and plants with low and high nitrogen content were able to survive -15° C and -10° C, respectively. After budburst, all axillary shoot parts were damaged at temperatures below-3° C.
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    URL: http://dx.doi.org/10.1007/BF00193558
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    Fluorimetric determination of calcium by ion-pair extraction with cryptand 2.2.1 and eosin (1990)
    Springer
    Microchimica acta 102 (1990), S. 259-269 
    Details
    ISSN: 1436-5073
    Keywords: calcium ; cryptand 2.2.1 ; fluorimetric determination ; ion-pair extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A fluorimetric study on the extraction of calcium into 1,2-dichloroethane as an ion-pair, formed between the cryptand 2.2.1-calcium complex and the eosinate anion, is described. Optimum conditions for extraction are established and a new fluorimetric determination of ultratraces of calcium is proposed. A linear working range from 1.5 ng ml−1 (detection limit) to 100 ng ml−1 of calcium and a relative standard deviation of ± 2.9% at the 70 ng ml−1 level are obtained. The equilibrium constants involved in the extraction process have been calculated and refined by the Letagrop-DISTR program. The proposed method has been tested for the direct determination of calcium in sugars.
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    URL: http://dx.doi.org/10.1007/BF01244767
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    Arsenazo, 2-(4-arsonophenyl(azo-7-(4-antipyril)azo-1,8-dihydroxy-3,6-naphtalene disulphonic acid as reagent for calcium ions. New parameters for metallochromic indicator characterization (1986)
    Springer
    Microchimica acta 88 (1986), S. 73-85 
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    ISSN: 1436-5073
    Keywords: arsenazo ; calcium ; titration ; tristimulus-colorimetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ca(II) ions react with arsenazo, 2-(4-arsonophenyl)-azo-7-(4-antipyril)azo-l,8-dihydroxy-3,5-naphtalene disulphonic acid, at pH 10.0 to produce a blue complex, with stoichiometry 1∶1, and stability constant of 6.64×105. Its molar absorptivity is 3.78×1041·mol−1 cm−1. This reagent has been used as metallochromic indicator in the complexometric titration of Ca. Its colour transition has been specified by tristimulus colourimetry. New parameters are defined and compared to Ringbom's parameters.
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    Involvement of a Ca2+-calmodulin interaction in the yeast-mycelial (Y-M) transition of Candida albicans (1989)
    Springer
    Mycopathologia 108 (1989), S. 47-54 
    Details
    ISSN: 1573-0832
    Keywords: Candida albicans ; dimorphism ; yeast-mycelium transition ; calcium ; calmodulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A yeast-mycelium (Y-M) transition of Candida albicans (3153A) was induced by 1.5 mM CaCl2 · 2H2O in defined liquid medium, pH 7, at 25 °C. Germ tube formation was detected after approximately 8 h and peaks of maximum germination occurred at approximately 20 h in all experimental treatments. Non-toxic concentrations of the calmodulin inhibitor R24571 almost completely suppressed germ tube formation whereas trifluoperazine (TFP) and the Ca2+ ionophore A23187 were only about half as effective. Further Ca2+ addition failed to reverse the inhibitory effect of R24571 and induced only about 10% of the cells inhibited by TFP or A23187 to germinate.
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    The ultrastructure of the zygospore in Endogone flammicorona Trappe & Gerdemann (1976)
    Springer
    Mycopathologia 59 (1976), S. 117-123 
    Details
    ISSN: 1573-0832
    Keywords: Ultrastructure ; Zygospore ; Mycorrhizal fungus ; Flaming crown
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The ultrastructural organization of the spores of the sporocarp of Endogone flammicorona was studied. Two types of organization are described. Initially the spore possessed a vacuolate protoplasm and was bound by two cell wall layers. The spore was surrounded by a hyphal mantle formed of a sheet of vacuolized hyphae with uniformly thin walls. Secondly, although the ultrastructural features of the spore appeared the same, it was now surrounded by a hyphal mantle with unevenly thickened walls (i. e., the so-called flaming crown) due to the gradual and irregular deposition of granules and lamellae. This crown gives the spore its most commonly observed morphological feature and is the preminent character employed taxonomically to speciate Endogone flammicorona Trappe & Gerdemann.
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    Guayule seedling response to nitrogen fertilizers (1987)
    Springer
    Nutrient cycling in agroecosystems 11 (1987), S. 113-121 
    Details
    ISSN: 1573-0867
    Keywords: ammonium sulfate ; urea ; calcium nitrate ; nitrogen-calcium interaction ; leaching ; subirrigation ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Slow growth and high seedling mortality limit direct seeding establishment of guayule (Parthenium argentatum G.). This study was conducted to assess seedling growth enhancement by the addition of different rates and forms of N fertilizers and Ca salts. Experiments were conducted in a greenhouse with cultivar 593 under both surface and subirrigated conditions using water low in salts (salinity of 0.8 dSm−1, SAR of 5.0 and 10 mg Ca L−1). Under surface-irrigated conditions, seedling height and fresh plant weight increased with N application to the irrigation water to 70 mg L−1. The best seedling growth was observed when (NH4)2SO4 was added in combination with CaCl2 or CaSO4. Progressively less growth was observed by addition of (NH4)2SO4 alone, CO(NH2)2 plus CaSO4, CO(NH2)2 alone and Ca(NO3)2. When seedlings were subirrigated, however, the best growth was observed with Ca(NO3)2. Intermediate growth was obtained with (NH4)2SO4 plus CaSO4 and lowest growth rates with (NH4)2SO4 alone. These differential responses may be explained by the differences in leaching and volatile characteristics of the N forms. Growth enhancement from N and Ca additions increased with time with significant increases 45 days after seeding. Nitrogen application with Ca may be effective amendment in promoting subsequent growth of direct seeded guayule.
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    The variation of element contents in triticale during vegetative growth (1987)
    Springer
    Nutrient cycling in agroecosystems 13 (1987), S. 155-159 
    Details
    ISSN: 1573-0867
    Keywords: triticale ; contents of nitrogen ; phosphorus ; potassium ; calcium ; magnesium ; trace elements ; heavy metals ; stage of growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Description / Table of Contents: Zusammenfassung Es wurden die Schwankungen in den Konzentration von N, P, K, Ca, Mg, Fe, Mn, Zn, Cu, B, Ba, Be, Bi, Sn, Sr, Sb, Ti, Te, V, Se, As und Hg in Triticale unter Feldbedingungen untersucht. Von der Bestockung bis zur Vollreife wurden alle 10 Tage von je 0.5 m2 pro Parzelle Pflanzenproben genommen. In allgemeinen haben die Konzentrationen von Frühjar bis zur Ernte abgenommen. Der elementengehalt in Triticale war demjenigen der übrigen Getreidearten verschieden, aber der Trend der Änderungen war ähnlich.
    Notes: Abstract The variation of N, P, K, Ca, Mg, Fe, Mn, Zn, Cu, B, Ba, Be, Bi, Sn, Sr, Sb, Ti, Te, V, Se, As and Hg concentrations was studied under field conditions in triticale. The samples were collected every 10 days from tillering to full ripening stage using plant material from 0.5 m2 per plot. The concentrations generally decreased from early growth to harvest. The elemental concentrations in triticale differed from the other cereals, but the variation's trend was similar.
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    Effect of cation exchange on the distribution and movement of cations in soils with variable charge. I. Effect of lime on potassium and magnesium exchange equilibria (1988)
    Springer
    Nutrient cycling in agroecosystems 17 (1988), S. 21-30 
    Details
    ISSN: 1573-0867
    Keywords: Potassium ; magnesium ; calcium ; aluminium ; exchange coefficient ; equilibrium activity ratio ; organic matter ; bonding strength
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The influence of Ca(OH)2 on K and Mg exchange equilibria in three New Zealand soils was studied. Calcium hydroxide was mixed with each soil to raise the pH to about 6 or 7. For each Ca(OH)2 treatment, K and Mg exchange isotherms were determined, from which the equilibrium activity ratios were derived. Exchange coefficients and solution activity ratios were calculated according to the Gapon convention. The addition of Ca(OH)2 produced varying effects in the Gapon exchange coefficient for both K and Mg. The magnitude and direction of change in the exchange coefficient were related to the cation initially dominating the exchange sites, rate of Ca(OH)2 addition, soil colloids contributing to the CEC and specific interactions of Ca with these soil colloids. Addition of Ca(OH)2 reduced the equilibrium activity ratio of all soils. Changes in the bonding strength of K and Mg with increasing CEC were suggested as a possible mechanism for this decrease.
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    Effects of gypsum on growth and mineral content of Brussels sprouts, and soil properties of Orthic Podzols (1990)
    Springer
    Nutrient cycling in agroecosystems 24 (1990), S. 77-84 
    Details
    ISSN: 1573-0867
    Keywords: Brussels sprouts ; calcium ; calcite ; elemental sulphur ; gypsum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Studies of crop response to Ca fertilizers are generally few as well as information concerning the Ca nutrition of Brussels sprouts (Brassica oleracea var.gemmifera). Six field studies were conducted, over three years, to determine yield response of Brussels sprouts to soil applied gypsum (CaSO4.2H2O), lime (calcite), and elemental S on sandy loam to loamy sand Orthic Podzols in Prince Edward Island. Relative yield of marketable (0–32mm) Brussels sprouts were related to soil ammonium acetate extractable Ca (r = 0.71). The highest yields (11 to 13 t ha−1) were associated with an extractable Ca of above 400µg g−1 soil, while a Ca level below 400µg reduced yield by 20%. Highest marketable yields were associated with a Ca level in the leaf tissue (in upper mature leaves at sprout formation) of above 2.2% (w/w) (r = 0.55), this in turn was associated (r = 0.87) with an extractable soil Ca above 400µg g−1 soil. Calcite and elemental S did not influence yield or mineral content. Gypsum, as expected increased leaf S content, but leaf tissue S levels were not related to marketable yield. Slight decreases in soil pH due to increasing gypsum rate (0.5–4.3 t ha−1) were associated with changing accumulations of B, Mn, Fe, Ca, and Zn in the leaf tissue. Gypsum had little effect on soil porosity and structure indices, but changing pH (in both gypsum and lime treatments) significantly influenced soil microbial biomass.
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    Leaching loss of calcium, magnesium, potassium and nitrate derived from soil, lime and fertilizers as influenced by urea applied to undisturbed lysimeters in south-east Nigeria (1992)
    Springer
    Nutrient cycling in agroecosystems 31 (1992), S. 281-289 
    Details
    ISSN: 1573-0867
    Keywords: Leaching ; calcium ; magnesium ; potassium ; nitrate ; tropical soils ; 15N ; urea ; shifting cultivation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Calcium hydroxide was applied to monolith lysimeters at Onne in south-east Nigeria. Eight lysimeters were cropped with maize followed by upland rice and four were uncropped. The cropped and two uncropped lysimeters received Mg, K and urea in the first season. Two uncropped lysimeters received no fertilizers. Drainage water was collected during the two growing seasons and analyzed for calcium, magnesium, potassium, sodium, nitrate and chloride. The fertilizer applied in the second season was not leached during the year of application. The cropped lysimeters lost 27 percent of the sum of the exchangeable Ca in the soil profile and the calcium added, and 29 percent of the corresponding sum for Mg. With no crop, the losses increased to 34 and 37 percent, respectively, but with no crop or fertilizer, the losses were similar to those from the cropped lysimeters. The loss of potassium ranged from 6 percent from the unfertilized lysimeters to 10 percent in the cropped lysimeters. The amounts of sodium leached ranged from 29 to 35 kg Na ha−1. The bulk of the calcium and magnesium leached from calcium hydroxide and fertilizers occurred in the second season when the loss was in good agreement with the amount of nitrate lost giving (Ca + Mg)/NO3 charge ratios of approximately one. Urea increased the amount of nitrate leached and led to a corresponding increase in the amounts of calcium and magnesium lost in the drainage water. The charge ratio remained unchanged when the cations were leached only with nitrate derived from the mineralization of soil organic matter. In the cropped lysimeters, this source accounted for about four times more nitrate in the drainage water than the fertilizer.
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    Fertilization of millet cv. Souna III in Senegal: dry matter production and nutrient uptake (1993)
    Springer
    Nutrient cycling in agroecosystems 35 (1993), S. 217-226 
    Details
    ISSN: 1573-0867
    Keywords: calcium ; dry matter distribution ; fertilizer ; harvest index ; magnesium ; manure ; millet ; nitrogen ; nutrient uptake ; phosphorus ; potassium ; Senegal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In a fertilizer and manure experiment, millet was grown under four treatments (no fertilizer or manure, farmyard manure, chemical fertilizer, and both). Grain yield and total aboveground biomass production of the unfertilized plot were relatively high. The observed differences in total dry matter production must be attributed to differences in nutrient availability, as amount of rainfall and its distribution were favourable. Results show only small differences in distribution of dry matter among the various plant organs between the best and the non-fertilized treatments. Nutrient supply from natural sources, defined as crop content of N, P, and K at maturity without fertilizer application, amounted to 104, 16 and 103 kg ha−1, respectively, which are very high values. Total uptake of calcium and magnesium is related to that of potassium, as the combined content of these three elements is linearly related to total aboveground biomass production. Minimum removal of nitrogen and phosphorus per ton grain dry matter amounts to 29 and 4kg, respectively, and 9 kg potassium per ton total aboveground dry matter. A possible double function of phosphorus as element of structural biomass and for maintenance of electro-neutrality is discussed.
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    Ammonia volatilization losses from different fertilizers and effect of several urease inhibitors, CaCl2 and phosphogypsum on losses from urea (1990)
    Springer
    Nutrient cycling in agroecosystems 23 (1990), S. 147-150 
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    ISSN: 1573-0867
    Keywords: Ammonium sulphate ; diammonium phosphate ; urease inhibitors ; hydrolysis ; pH ; calcium ; phosphogypsum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The extent of ammonia volatilization losses from urea, ammonium sulphate (AS), and diammonium phosphate (DAP) were determined in soil incubation studies. The effects of some urease inhibitors (thiourea, hyroquinone, 2–4 dinitro phenol and boric acid) and CaCl2 and phosphogypsum additions on ammonia loss from urea were also studied. Total ammonia volatilization losses were 32.6%, 3.1% and 2.3% of the N applied to the soil as urea, AS and DAP, respectively. Among the chemicals examined in the study, 500 mg H3BO3 in 1 kg of the soil decreased the ammonia loss from urea by 21% in comparison with the control. When 50 mg/kg soil of thiourea, 2–4 dinitro phenol or hydroquinone were applied, ammonia volatilization losses were found to be 10%, 3% and 0% less than urea applied alone, respectively. When 2500 mg CaCl2 was applied to 1 kg of soil with urea, ammonia loss was decreased by 5%. The lowest hydrolysis rate (65%) occurred with the boric acid treatment. The differences between the hydrolysis rates of the other treatments were not statistically significant. Phosphogypsum was found the most effective agent in reducing ammonia losses from urea. When phosphogypsum was mixed at 2.3 times as much as the urea, ammonia loss was about 85% less than that of urea applied alone. Obviously, further work is needed to find out the potential of both boric acid and phosphogypsum as reducing agents of ammonia losses from urea.
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    Ultrastructural study ofCryptococcus neoformans by quick-freezing and deep-etching method (1993)
    Springer
    Mycopathologia 121 (1993), S. 133-141 
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    ISSN: 1573-0832
    Keywords: Capsule ; Cryptococcus neoformans ; Deep-etching ; Quick-freezing ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The three-dimensional ultrastructure ofCryptococcus neoformans was studied by quick-freezing and deep-etching (QF-DE) method.C. neoformans, strain CDC551, was cultured on agar. The viable yeast cells (107 cells) were inoculated into each mouse from the tail vein. Three weeks after the inoculation, the brains of the mice were perfused with fixatives, quickly frozen, freeze-fractured, deeply etched and rotary shadowed with platinum and carbon. In addition, the viable cells ofC. neoformans on agar were picked up and quickly frozen, and replica membranes were prepared as described above. The ultrastructure ofC. neoformans was three-dimensionally demonstrated by the QF-DE method. The capsule was composed of fine meshworks of microfibrils (10–13 nm in diameter), which were directly attached to the cell walls. The capsule of the in vivo yeasts (yeast cells in the brain lesion) was thicker than that of the in vitro yeasts (yeast cells on agar culture). At the outer part of the cell wall, a particle-accumulating layer was observed. This layer in vivo was thicker than that in vitro. Occasionally, the yeast cells were ingested by phagocytes in the mouse brain. Although the cytoplasm of such yeast cells was destroyed, the capsular meshworks were well preserved. The ultrastructure of the capsule was the same both in cultured and phagocytized yeasts in the cystic lesions of the brains. This lack of morphological changes of the capsular meshworks suggests that they are resistant to the digestion by phagocytes. This stability of capsular structures may provide one of the important pathogenic factors in cystic lesions byC. neoformans.
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    Aflatoxin B1-induced ultrastructural alterations in matureZea mays embryos (1994)
    Springer
    Mycopathologia 128 (1994), S. 181-192 
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    ISSN: 1573-0832
    Keywords: Aflatoxin B1 ; Embryo ; Mature ; Ultrastructure ; Zea mays L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Mature maize (Zea mays L.) embryos were exposed to aflatoxin B1 (AFB1) concentrations ranging from 0.1 to 25 µg/ml for 9 days. With increasing toxin concentration above 2 µg/ml, primary root elongation of germinated embryos was progressively inhibited, to reach a maximum value of 81% at 25 µ/ml toxin. An ultrastructural investigation of the subcellular alterations induced following toxin exposure provided evidence of deteriorative changes in several compartments of the plant cell. Alteration in membrane integrity (e.g., the tonoplast, plasmalemma and inner mitochondrial membrane) was a frequent feature of many cells. Apparent fusion of vacuoles, incorporation of cytoplasmic components into vacuoles and intravacuolar membrane whorls might be interpreted as deteriorative alterations. The results are discussed in the light of ultrastructural findings for other plant systems exposed to similar AFB1 concentrations, as well as findings for animal systems.
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    A rapid, reproducible method for processing human solid tumors for in vitro culture (1983)
    Springer
    Methods in cell science 8 (1983), S. 63-67 
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    ISSN: 1573-0603
    Keywords: human tumors ; tissue culture methods ; stem cell assay ; calcium ; growth factors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The described techniques permit rapid processing of solid human tumors. Resultant cell and tissue suspensions have high viability and can be readily propagated in vitro.
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    Cultivation, frozen storage, and clonal growth of normal human epidermal keratinocytes in serum-free media (1985)
    Springer
    Methods in cell science 9 (1985), S. 83-93 
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    ISSN: 1573-0603
    Keywords: keratinocytes ; human ; epidermis ; serum-free ; calcium ; differentiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Methods are described for serum-free culture of human epidermal keratinocytes derived from neonatal foreskin tissue. Cultures are initiated, stored frozen, and returned to active growth, all with bovine pituitary extract as the only undefined supplement. Clonal growth assays are then performed in a biochemically defined medium. The degree of stratification and differentiation in the defined medium (and also with pituitary extract) is controlled by the extracellular calcium ion concentration.
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    Calcium binding and induction of conidiation in protoplasts of Penicillium cyclopium (1990)
    Springer
    Antonie van Leeuwenhoek 57 (1990), S. 43-49 
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    ISSN: 1572-9699
    Keywords: calcium ; conidiation ; plasma membrane ; protoplast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cell wall-free protoplasts of P. cyclopium could regenerate a cell wall and form mycelia in liquid culture with high rates of viability. When calcium was added to the medium, protoplasts displayed biphasic accumulation with an immediate metabolism-independent adsorption phase, followed by slow metabolism-dependent uptake. Exposure of the protoplasts to Ca2+ for periods of 2 min, followed by incubation in calcium-free medium for 24 hours, was sufficient to induce conidiation with morphogenetic events parallel to those found in cultures containing calcium throughout the incubation period, and similar to those reported in cultures inoculated from conidia. The conidiation event caused by short exposure to calcium could be reversed, within 2 hours of Ca2+ addition, by a brief treatment with the specific calcium chelating agent BAPTA (100 μM), which removed 65 to 75% of the total cell calcium. The results implicate the membrane-bound calcium fraction in the process of conidiation induction.
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    Role of Calcium in the Evolution of Superconductivity in a (La2−xRx)Ba2(CayCu4+y)Oz (R = Y, Er, Gd) System (2000)
    Springer
    Journal of superconductivity 13 (2000), S. 37-40 
    Details
    ISSN: 1572-9605
    Keywords: LaBaCuO ; calcium ; superconductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract It has been reported that, by adding equal amounts of CaO and CuO to non superconducting La3Ba3Cu6O z (La-336), a series of superconductors with nominal compositions La3Ca y Ba3Cu6+y O z were prepared with maximum Ton c ∼ 80K. Similar studies on addition of CaO and CuO in nonsuperconducting LaBaCu2O z (La-112) resulted into superconducting LaCaBaCu3O z (La-1113). To date no attempt has been made to synthesize La2CaBa2Cu5O z (La-2125) superconducting phase by addition of CaO and CuO to non superconducting La2Ba2Cu4O z (La-224) system. Also no reports are published to study the effect of replacing larger La3+-ions (1.01Å) by smaller rare earth ions viz Y3+(0.89Å), Er3+(0.91Å), Gd3+(0.91Å) on the structural and superconducting properties of (La2−x R x )Ba2(Ca y Cu4+y )O z (LRBCaC); 0.0 ≤ x ≤ 0.5; y=2x system. In this paper, we report the method of synthesis, structural and superconducting property characterization using X-ray diffraction, oxygen content measurements using iodometry, resistivity measurements using d.c. four probe technique and a.c. susceptibility measurements in the temperature range RT to 15K. Also a comparative study, on the evolution of superconducting phase with Ca-concentration for different rare earth substitutions for LRBCaC system in the context of hole doping mechanism, is carried out.
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    URL: http://dx.doi.org/10.1023/A:1007765907530
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    The long-term influence of past land use on the Walker Branch forest (1990)
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    Landscape ecology 4 (1990), S. 211-224 
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    ISSN: 1572-9761
    Keywords: calcium ; forest ; insects ; land use ; landscape ecology ; soils ; succession
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Forest structure and composition influence patterns of insect outbreaks and can be explained on the Walker Branch watershed by past land use (timber harvest and agriculture), soils, aspect, and slope. In particular, pine bark beetles caused large losses of pine on sites that had been used for agriculture, on Fullerton silt loam soils, and on north-to-northeast and east-to-southeast exposures. Hickory bark beetles had a high impact on hickory biomass on Bodine soil areas that were forested in 1935 and sloped greater than 11%. Thus, prior land use can have an indirect effect on future disturbances. Because forest disturbances can affect nutrient distribution, land use can also indirectly affect nutrient availability. For example, locations of hickory bark beetle outbreaks experience a large flux of calcium from dead wood to soil because hickory accumulates large amounts of calcium in woody tissue. The research demonstrates a link between past land use, insect outbreaks, and calcium cycling.
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    Étude en microscopie électronique et par cytophotométrie à balayage de la structure et de la distribution de la chromatine dans les noyaux des cellules cartilagineuses deTriturus cristatus âgés au cours de la régénération (1978)
    Springer
    Development genes and evolution 184 (1978), S. 195-211 
    Details
    ISSN: 1432-041X
    Keywords: Ultrastructure ; Scanning cytophotometry ; Chromatin ; Chondrocytes ; Regeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Résumé Les cellules cartilagineuses des membres postérieurs deTriturus cristatus en régénération après amputation, ont été étudiées en microscopie électronique et par cytophotométrie à balayage. Nous nous sommes intéressés à la structure et à la distribution de la chromatine mais aussi à différents organites cytoplasmiques. Dans l'étude de cytophotométrie à balayage, la chromatine a été considérée à travers son constituant majeur, l'ADN, coloré par la réaction de Feulgen. Au cours de la régénération du membre, l'hétérochromatine initialement condensée, essentiellement accolée à la membrane nucléaire se décondense. Les vacuoles du cytoplasme, caractéristiques des animaux âgés par rapport aux animaux jeunes, disparaissent, les mitochondries et le reticulum endoplasmique rugueux deviennent plus abondants. Les caractéristiques nucléaires de l'activation cellulaire apparaissent précocement, précédent les modifications cytoplasmiques et conduisent à des cellules en tous points identiques aux cellules d'animaux jeunes en dehors de tout processus régénératif. Cette phase d'euchromatisation et de restructuration cytoplasmique est peut-être nécessaire à l'accroissement d'activité métabolique et à la division cellulaire qui suivent. Son déroulement peut expliquer tout au moins le ralentissement de la régénération observé chez les animaux âgés par rapport aux animaux jeunes.
    Notes: Summary Cartilaginous cells of aged newts (Triturus cristatus) were studied during hind limb regeneration. The electron microscope was used to study the structure and distribution of chromatin in the cell nuclei, while the DNA content of the chromatin was measured by means of a scanning cytophotometer. Changes in the ultrastructure of the cytoplasm during regeneration were also studied. It was observed that the structure and distribution of chromatin in the activated cell is greatly modified. In the non-activated cell of the aged newt, the chromatin is found highly condensed and distributed peripherally close to the nuclear membrane. In contrast, in the activated cells, the chromatin is much less condensed and is distributed throughout the nucleus. Moreover, cytoplasmic vacuoles, found only in the non-activated aged cells, disappear and an increase in the mitochondria and rough endoplasmic reticulum is also observed. Changes in the nuclear structure are observed prior to the cytoplasmic modifications. It is interesting to note that the process of activation induces structural changes in the aged cells which make these cells appear to be structurally identical to the young cells. This process of rejuvenation takes 3–5 days in the newt. We suggest that these structural changes of the chromatin and cytoplasm in the aged cells are necessary to increase the metabolic activity which precedes cell division. It may also explain why regeneration takes a longer time in the aged animals than in the young ones.
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    Ultrastructural localization of adenylate cyclase and cAMP phosphodiesterase in the gastrulating chick embryo (1983)
    Springer
    Development genes and evolution 192 (1983), S. 42-44 
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    ISSN: 1432-041X
    Keywords: Chick embryo ; Gastrulation ; Adenylate cyclase ; cAMP phosphodiesterase ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The ultrastructural localization of adenylate cyclase (E.C. 4.6.1.1.) and cAMP phosphodiesterase (PDE) (E.C. 3.1.4.17.) in the ectoderm of the developmental stage 4 chick embryo was studied. Adenylate cyclase was localized in the lateral surfaces of the ectodermal cells. In the primitive streak cells the enzymatic activity was observed on all the lateral surfaces, whereas in the periphery of the blastoderm the reaction product was localized in the apical parts of the lateral plasma membranes only. cAMP PDE localized in the apical cytoplasm of the ectodermal cells, with highest activity in the globular projections.
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    Are accessory nuclei involved in the establishment of developmental gradients in hymenopteran oocytes? (1991)
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    Development genes and evolution 199 (1991), S. 423-426 
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    ISSN: 1432-041X
    Keywords: Oogenesis ; Accessory nuclei ; Developmental gradients ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the oocytes ofTenthredo olivacea, accessory nuclei (AN) are formed by budding from the nuclear envelope of the oocyte nucleus. Newly formed AN contain electron-dense material of nuclear origin and are surrounded by a double envelope devoid of pores. Such structures are subsequently transported to the peripheral ooplasm (periplasm), where they grow to reach a final diameter of 5 µm. In the envelopes of advanced AN nuclear pores arise. Through these pores “nuage” material is extruded into the surrounding periplasm. These findings are discussed with respect to a possible involvement of AN in the establishment of developmental gradients in hymenopteran oocytes.
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    Release of calcitonin gene-related peptide from a human medullary carcinoma of the thyroid in vitro (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 829-830 
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    ISSN: 1420-9071
    Keywords: Calcitonin gene-related peptide ; calcitonin ; calcium ; perifusion ; medullary carcinoma of thyroid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The secretion of human calcitonin gene-related peptide was examined in perifusates of medullary carcinoma of the thyroid with a sensitive radioreceptor assay. Calcitonin gene-related peptide was released after the addition of calcium (25–100 mM), in a dose-dependent manner. The results indicate that human medullary carcinomas of the thyroid secrete the calcitonin gene-related peptide as well as calcitonin.
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    Modulation of calcium sensitivity in guinea pig taenia coli: skinned fiber studies (1985)
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    Cellular and molecular life sciences 41 (1985), S. 997-1001 
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    ISSN: 1420-9071
    Keywords: Myosin light chain kinase ; calcium ; c-AMP ; calmodulin ; smooth muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF01952120
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    Failure of calcium to stimulate Na, K-ATPase in the presence of EDTA (1985)
    Springer
    Cellular and molecular life sciences 41 (1985), S. 1048-1051 
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    ISSN: 1420-9071
    Keywords: Na, K-ATPase ; calcium ; calmodulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effect of calcium on Na, K-ATPase activity of rat brain homogenates and its modification by the chelating agent EDTA has been investigated. In the absence of EDTA, free calcium (approximately 10−6mol/l) stimulates Na,K-ATPase activity; in the presence of EDTA the same concentration of free calcium is without effect on the enzyme. In the absence of EDTA the stimulation by calcium of Na,-K-ATPase activity is enhanced by the additional presence of calmodulin but in the presence of EDTA, even when calmodulin is added to excess, calcium still fails to stimulate the enzyme. The possibility that EDTA interferes with an interaction between a calcium-calmodulin complex and Na,K-ATPase is discussed.
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    Mechanical and biochemical characterization of the contraction elicited by a calcium-independent myosin light chain kinase in chemically skinned smooth muscle (1985)
    Springer
    Cellular and molecular life sciences 41 (1985), S. 1002-1006 
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    ISSN: 1420-9071
    Keywords: Smooth muscle ; calcium ; myosin light chain kinase ; regulation of contraction ; ATPase ; mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The contraction induced by a Ca2+-independent myosin light chain kinase (MLCK-) was characterized in terms of isometric force (Fo), immediate elastic recoil (SE), unloaded shortening velocity (Vus), shortening under a constant load and ATPase activity of chemically skinned smooth muscle preparations. These parameters were compared to those measured in a Ca2+-induced contraction to assess the nature of cross bridge interaction in the MLCK-induced contraction. Fo developed in chicken gizzard fibers as well as SE were similar in contractions elicited by either agent. Vus in the contraction induced by MLCK-(0.36 mg/ml) was similar though averaged 39.3±8.9% less than Vus induced by Ca2+ (1.6x10−6M) in the control fibers. Addition of Ca2+ (1.6x10−6M) to a contraction induced by MLCK-resulted in small increases in both Fo and Vus. Shortening under a constant load was similar for both types of contractions. The contraction induced by MLCK-was accompanied by an increased rate of ATP hydrolysis. The MLCK-induced contraction is thus kinetically similar though not identical to a contraction induced by Ca2+. We conclude that with respect to actin-myosin interaction, MLCK- and Ca2+-induced contractions are similar.
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    Energetics and regulation of crossbridge states in mammalian smooth muscle (1985)
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    Cellular and molecular life sciences 41 (1985), S. 1020-1025 
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    ISSN: 1420-9071
    Keywords: Smooth muscle energetics ; light chain phosphorylation ; crossbridges ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Conclusion On the basis of measurements of the high energy phosphate usage associated with different mechanical states, as well as the degree of myosin light chain phosphorylation and mechanical properties, information has been gained concerning the existence and regulation of different crossbridge states in smooth muscle. Although incomplete, a general operational scheme is shown in figure 5. At very low intracellular calcium concentrations, actin and myosin are dissociated, as shown by a loss of resistance to stretch in resting muscles. At somewhat higher intracellular calcium concentrations in atonic, resting muscles, crossbridges can attach and be manifest mechanically as an increased resistance to stretch without ATP-driven crossbridge cycling and active force production. When the muscle is activated, intracellular calcium increases further, the light chains of myosin are phosphorylated through the calcium-calmodulin activation of myosin light chain kinase, actin-activated myosin ATPase activity increases and crossbridges cycle. Calcium also appears to modulate the ATPase activity and the rate of cycling of the phosphorylated crossbridge. The crossbridge cycling rate is highest during force development and slows with time as maximum isometric force is maintained reflecting a change in the rate at which phosphorylated crossbridges cycle. This may result from a decrease in the intracellular free calcium concentration with continued stimulation. During relaxation, the intracellular calcium concentration decreases, there is net dephosphorylation of the myosin light chains, the rate at which phosphorylated crossbridges cycle slows further with a gradual return to the attached, but non-cycling state or the detached state.
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    Effects of water acidification on the distribution pattern and the reproductive success of amphibians (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 495-503 
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    ISSN: 1420-9071
    Keywords: Acidication ; pH ; calcium ; (heavy) metals ; ammonium ; amphibians ; development of eggs ; hatching percentage ; mortality of larvae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Nine amphibian species were encountered in poorly buffered waters of The Netherlands (alkalinity ≦1 meq·l−1). These soft water systems are highly sensitive to acidifying precipitation. The number of species as well as the percentage of waters which harbour amphibian populations are strongly reduced in the extremely acid pH-class $$(\bar pH〈 4.0)$$ . The reproductive success of amphibians is negatively affected by low pH. The eggs become heavily infested with fungi (Saprolegniaceae). In acidifying systems many physico-chemical parameters are significantly correlated with the pH of the water. Strongly acidified waters are characterized by low alkalinity, conductivity and ionic content but high acidity and high concentrations of (heavy) metals and ammonium and a high relative sulphate concentration. Culture experiments with eggs and larvae ofRana arvalis. Rana ‘esculenta’, Rana temporaria andBufo bufo show that apart from the pH, elevated aluminium, cadmium and ammonium contents may also affect the reproductive success of amphibians.
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    Development of the myocardial contractile system (1988)
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    Cellular and molecular life sciences 44 (1988), S. 936-944 
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    ISSN: 1420-9071
    Keywords: Contractile system ; fetus ; premature myocardium ; calcium ; sarcoplasmic reticulum ; contractile protein ; sarcolemma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Recent studies regarding developmental changes in the myocardial contractile system from fetal, newborn, and adult animals are reviewed. From the data obtained so far, we conclude that in the early fetus myocardial contraction is mainly dependent on Ca which enters via the sarcolemma. Ca release from the sarcoplasmic reticulum is minimal. The role of the sarcoplasmic reticulum as a source of contractile Ca increases and the role of Ca influx across the sarcolemma in contractile system decreases with development.
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    Effect of feeding cereal-legume diets to rats on in vitro absorption of45Ca (1990)
    Springer
    Cellular and molecular life sciences 46 (1990), S. 1016-1017 
    Details
    ISSN: 1420-9071
    Keywords: In vitro absorption ; calcium ; wheat ; Bengal gram
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The in vitro absorption of calcium from the duodenum was significantly less in a group of rats fed on a wheat diet than in a group fed a wheat and Bengal gram (70∶30) diet.
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    URL: http://dx.doi.org/10.1007/BF01940659
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    Endothelial cells as part of a vascular oxygen-sensing system: Hypoxia-induced release of autacoids (1990)
    Springer
    Cellular and molecular life sciences 46 (1990), S. 1175-1179 
    Details
    ISSN: 1420-9071
    Keywords: Prostacyclin ; EDRF ; $$P_{O_2 } $$ ; calcium ; vascular oxygen sensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Higher developed organisms are equipped with many central and local control mechanisms, which enable an adequate blood and oxygen supply to tissues over a wide range of demands. Global adaptive responses include changes in the circulatory and ventilatory system as well as increases in the oxygen carrying capacity of the blood. At the level of the specialized organs there exist additional control systems for the regulation of local blood flow. Most systems make use of highly specialized cells which are able to sense the oxygen partial pressure of the transport medium, blood, and within the tissues. In the past years, it has been shown that the vascular endothelium lining the entire circulatory system can actively modulate the vascular tone and platelet functions by the release of autacoids, among them prostacyclin and endothelium-derived nitric oxide (EDRF). Recent experiments demonstrate that the release of EDRF is $$P_{O_2 } $$ -dependent, which suggests that endothelial cells may act as functional local oxygen sensors within the vascular system.
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    URL: http://dx.doi.org/10.1007/BF01936931
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    Role of protein kinase C and Ca2+ in glucose-induced sensitization/desensitization of insulin secretion (1991)
    Springer
    Cellular and molecular life sciences 47 (1991), S. 1201-1208 
    Details
    ISSN: 1420-9071
    Keywords: Pancreatic islet ; β-cell ; calcium ; protein kinase C down-regulation ; sensitization ; desensitization ; insulin secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The role of protein kinase C and Ca2+ in glucose-induced sensitization/desensitization of insulin secretion was studied. A 22–24h exposure of mouse pancreatic islets to glucose (16.7 mmol/l) in TCM 199 culture medium, with 0.26 mmol/l or 1.26 mmol/l Ca2+, reduced total islet protein kinase C activity to approx. 85% and 60% of control values, respectively. At 0.26 mmol/l Ca2+ in TCM 199 medium, exposure to glucose (16.7 mmol/l) led to a potentiation of both phase 1 and phase 2 of glucose-induced insulin secretion, and caused a shift in the dose-response curve with 10 mmol/l and 16.7 mmol/l glucose exhibiting equipotent effects in stimulation of insulin secretion. In glucose-sensitized islets, the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (0.16 μmol/l) did not further potentiate induction of secretion by 10 mmol/l or 16.7 mmol/l glucose. At 3.3 mmol/l glucose, however, phorbol ester-induced secretion was augmented, and was characterized by a faster onset of secretion in glucose-sensitized islets relative to control islets. In contrast, a partial reduction in arachidonic acid (100 μmol/l)-induced insulin release was observed in glucose-sensitized islets in the absence of extracellular Ca2+. Increasing the Ca2+ concentration to 1.26 mmol/l in TCM 199 during the 22–24h exposure to glucose (16.8 mmol/l) led to inhibition of phase 1 and abolition of phase 2 of glucose (10 mmol/l, 16.7 mmol/l)-induced insulin secretion. In addition, this treatment abolished phorbol ester-induced and arachidonic acid-induced insulin secretion at 3.3 mmol/l glucose. Altogether, these data suggest that sensitization of insulin secretion is caused by a preferential down-regulation of the inhibitory effects of protein kinase C, leading to an increased first phase, and an increased coupling of glucose to the stimulatory effects of protein kinase C during the second phase of glucose-induced insulin secretion. Desensitization of insulin secretion appears to be a consequence of sustained Ca2+ influx, inducing extensive down-regulation of protein kinase C and also causing deleterious effects on islet cell function in protein kinase C-deprived islets.
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    Blockade by zinc ions of K+-induced contraction and calcium in guinea pigTaenia coli (1993)
    Springer
    Cellular and molecular life sciences 49 (1993), S. 865-869 
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    ISSN: 1420-9071
    Keywords: Zinc ions ; calcium ; ileal muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Preincubation with 0.3 mM Zn2+ markedly inhibited both the tonic response and Ca2+ binding at low affinity sites induced by K+ (60 mM), with smaller effects on the phasic response and the high affinity Ca2+ sites, inTaenia coli. However, when the muscle was kept in Zn2+-containing medium following the first stimulation with the K+, the phasic response and the high affinity Ca2+ sites were more severely inhibited during the second stimulation with K+. This probably indicates that Zn2+ reduced the tonic tension response to K+ mainly by inhibiting Ca2+ influx at the cell membranes ofTaenia coli. However, when Zn2+ is continuously present, Ca2+ is not supplied at the storage sites and is not available for the phasic response to a second stimulation with K+.
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    Towards an understanding of the role of glutamate in neurodegenerative disorders: energy metabolism and neuropathology (1993)
    Springer
    Cellular and molecular life sciences 49 (1993), S. 1064-1072 
    Details
    ISSN: 1420-9071
    Keywords: Aminooxyacetic acid ; 1-methyl-4-phenylpyridinium ion ; malonic acid ; 3-nitropropionic acid ; rotenone ; sodium azide ; nitric oxide ; N-methyl-D-aspartate ; oxidative phosphorylation ; calcium ; cell death
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract It is thought that impairment, of energy metabolism that results in deterioration of membrane function, leading to loss of the Mg2+ block on NMDA receptors, and allowing persistent activation of these receptors by glutamate, might be a cause of neuronal death in neurodegenerative disorders. Studies in rodents using mitochondrial respiratory chain toxins, such as aminooxyacetic acid, 1-methyl-4-phenylpyridinium, malonic acid and 3-nitropropionic acid, suggest that such processes may indeed be involved in neurotoxicity. Striatal and nigral degeneration induced by mitochondrial toxins in rodents resembles the neuropathology seen in humans suffering from Huntington's or Parkinson's disease, and can be prevented either by decortication or by NMDA receptor antagonists. Such experimental observations suggest that glutamate may be involved in neuronal death leading to neurodegenerative disorders in humans. If so, glutamate antagonists may offer a therapeutic approach for retarding the progression of these disabling disorders.
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    Lipid droplets of neuroepithelial cells are a major calcium storage site during neural tube formation in chick and mouse embryos (1992)
    Springer
    Cellular and molecular life sciences 48 (1992), S. 516-519 
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    ISSN: 1420-9071
    Keywords: Lipid ; neuroepithelial cells ; calcium ; neurulation ; neural tube ; chick embryo ; mouse embryo
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In situ precipitation of calcium (Ca2+) with fluoride and antimonate shows that Ca2+-specific precipitate is localized almost exclusively within lipid droplets of neuroepithelial cells during neural tube formation in chick and mouse embryos. The density of Ca2+ precipitate within lipid droplets is generally greater in the apical ends of cells situated in regions of the neuroepithelium that are actively engaged in bending. These findings suggest that lipid droplets, in addition to providing a source of metabolic fuel for developing neuroepithelial cells, also serve as Ca2+-storage and-releasing sites during neurulation.
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    The cytoplasmic architecture of the egg cell ofSmittia spec. (Diptera, Chironomidae) (1977)
    Springer
    Development genes and evolution 183 (1977), S. 233-248 
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    ISSN: 1432-041X
    Keywords: Cytoplasmic architecture ; Ultrastructure ; Insect egg ; Pattern formation ; Yolk ; Cytoplasma-Architektur ; Ultrastruktur ; Insekten-Ei ; Musterbildung ; Dotter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung 1. Das Ei der ZuckmückeSmittia spec. wurde licht- und elektronenmikroskopisch untersucht. Die vorliegende Arbeit beschreibt den Bau des Periplasmas und des Dotter-Endoplasma-Systems vor Bildung der Polzellen. 2. Das Periplasma, nach außen vom Oolemm und einer mehrschichtigen Eihülle begrenzt, besteht aus einer ribosomenreichen cytoplasmatischen Matrix, in die vor allem Mitochondrien und ER-Zisternen, wenig annulate lamellae und gelegentlich Golgi-Apparate eingelagert sind. Mikrotubuli wurden nur selten nachgewiesen. Öfters sind Anhäufungen einer dichten granulierten Substanz zu beobachten, die in ihrer Struktur dem Oosom-Material ähnelt. 3. Das Dotter-Endoplasma-System stellt ein Netzwerk aus Cytoplasma dar, in das Proteid-Dotterkugeln, Lipidtröpfchen sowie Glycogen-Anhäufungen eingelagert sind. Das Endoplasma, das sich zu 3–7 Plasma-Inseln erweitern kann und unmittelbar in das Periplasma übergeht, besteht wie dieses aus einer cytoplasmatischen Matrix und enthält die gleichen Zellelemente wie das Periplasma. Rosettenförmige Membran-Strukturen werden als “nuclear envelope organizing center” gedeutet. 4. Drei der sorgfältig analysierten Eier enthielten je 2 Kerne; sie lagen in Plasma-Inseln in der hinteren Eihälfte. 5. Sowohl im Periplasma wie im Dotter-Endoplasma-System sind alle Zellelemente unregelmäßig verteilt. Eine besondere Anordnung oder Zonierung ist nicht zu erkennen. 6. Die räumliche Verteilung der erfaßten Eikomponenten liefert keine Hinweise auf eine Funktion dieser Komponenten als Determinanten für die embryonale Musterbildung.
    Notes: Summary 1. Eggs of the midgeSmittia were investigated by light microscopy and transmission electron microscopy. This paper describes elements and architecture of periplasm and yolk endoplasm before the formation of pole cells. 2. The periplasm is coated externally by the oolemma and a multilayered egg shell. The periplasm consists of a cytoplasmic matrix rich in ribosomes; it contains mitochondria and ER cisternae, some annulate lamellae and an occasional Golgi complex. Microtubuli were demonstrated only rarely. Accumulations of a dense granulated substance resembling in its structure the oosome material were frequently observed. 3. The yolk endoplasm is a cytoplasmic network embodying proteid yolk particles, lipid droplets and accumulations of glycogen. The endoplasm is continuous with the periplasm and shows the same cell constituents. It may form between 3 and 7 cytoplasmic islands free of yolk particles. Rosette-shaped membranous structures in the yolk endoplasm are interpreted as nuclear envelope organizing centres. 4. Three carefully analysed eggs contained 2 nuclei each. both nuclei were situated in the posterior egg half. 5. Periplasm and yolk endoplasm are characterized by random distribution of cell elements. No zonation or special accumulations could be recognized. 6. The spatial distribution of the egg components studied did not indicate that any of these components could function as a determinant in embryonic pattern formation.
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    Ultrastructure of a fertilized barnacle egg (Pollicipes polymerus) with peristaltic constrictions (1977)
    Springer
    Development genes and evolution 181 (1977), S. 333-355 
    Details
    ISSN: 1432-041X
    Keywords: Barnacle eggs ; Constriction rings ; Microfilaments ; Ultrastructure ; Peristalsis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. The egg ofPollicipes polymerus, the common intertidal gooseneck barnacle, has been studied by electron microscopy. Constriction rings, similar to the contractile rings of cleaving cells and polar lobes, move unidirectionally from the animal to the vegetal pole of newly fertilized eggs. This is referred to as peristaltic constriction. The present paper describes the fine structure of the egg during first polar body formation and peristalsis. 2. During formation of the polar body, dense bodies are produced by the Golgi and extracellular plaques are observed. Thin microfilaments (40–60 Å) are in the egg adjacent to the polar body. 3. In eggs undergoing peristalsis, the appearance of extracellular spheres, flocculent material and filaments is observed. Intracellularly large numbers of multivesiculate bodies, glycogen granules, mitochondria and protein-carbohydrate and lipid yolk bodies are seen at the level of constriction. 4. Thin microfilaments are found in the cortical area of newly-fertilized eggs exclusively in peristaltic constriction rings. Filaments are oriented primarily in a meshwork, although circumferentially-oriented filaments are also found in rings near the vegetal pole. Microvilli extend into the space created between a constriction and the elevated egg membrane. 5. A model is proposed to explain the peristalsis in this species. It is suggested that information from a pacemaker region activates peristalsis by affecting filament polymerization and orientation. One function of peristalsis may be elongation of the egg from a sphere to an ovoid, although other possibilities such as elevation of the egg membrane, segregation of the lipid yolk to the vegetal pole and predetermination of the first cleavage plane are also discussed.
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    Ultrastructure of collagen in sea urchin embryos (1979)
    Springer
    Development genes and evolution 186 (1979), S. 65-70 
    Details
    ISSN: 1432-041X
    Keywords: Sea urchin ; Embryo ; Collagen ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Collagen fibrils with a main period banding of 610 Å and 220 Å in width were observed in the blastocoel of 72-h embryos of the sea urchin,Strongylocentrotus purpuratus. Non-striated fibrils of 50 Å diameter were also observed. The collagen is seen in highest concentration in the vicinity of mesenchyme cells which are richly endowed with endoplasmic reticulum and secretory vesicles. A role for collagen in cell attachment, orientation and spicule formation is discussed.
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    Electron microscopical study of self-differentiation potency in the chick embryonic endoderm cultured in vitro (1983)
    Springer
    Development genes and evolution 192 (1983), S. 171-178 
    Details
    ISSN: 1432-041X
    Keywords: Differentiation ; Digestive tract ; Endoderm ; Organ culture ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The self-differentiation potency of the endoderm of the chick embryo was investigated mainly by transmission electron microscopy. Endodermal fragments isolated from 4- to 6-day stomach or small intestine were cultured in the absence of mesenchyme and were able to differentiate in vitro into organ-specific epithelia. Endodermal fragments isolated from the stomach region differentiated into a pseudo-stratified epithelium with periodic acid Schiff-positive mucous granules in the apical cytoplasm, while those from the small intestinal region differentiated into a simple columnar epithelium with a striated border which was positive in alkaline phosphatase activity. These features are comparable with those of the mucous secretory epithelium of the normal embryonic stomach and the absorptive epithelium of normal embryonic small intestine, respectively. Next, the self-differentiation potencies were investigated of the upper and lower layers of the blastoderms, at stages 1–5 of Hamburger and Hamilton (H. and H.). Both stomach-type and small-intestine-type epithelia developed only when fragments of the lower layer isolated from the blastoderms older than stage 3 of H. and H. were cultured, suggesting that cells possessing the potency to differentiate into the stomach- and small-intestine-type epithelia exist in the definitive endoderm at the beginning of its formation.
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    Migration and division of cleavage nuclei in the gall midge,Wachtliella persicariae (1980)
    Springer
    Development genes and evolution 188 (1980), S. 65-73 
    Details
    ISSN: 1432-041X
    Keywords: Nuclear migration ; Cleavage ; Microtubules ; Ultrastructure ; Gall midge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the eggs ofWachtliella persicariae the cleavage nuclei move relative to the surrounding ooplasm. This ‘active’ migration is caused by an organelle whose ultrastructure was studied throughout the mitotic cycle. It consists of a greatly enlarged polar cytaster derived from the mitotic apparatus, linked to the nucleus by 100 Å filaments. The microtubules of the cytaster were found only during periods of active nuclear migration, i.e., from the onset of anaphase to the early prophase of the next mitotic cycle. They are always solitary and follow the course of the astral rays, which are known to temporarily adhere to peripheral structures of the egg cell and to exert tractive forces. In contrast to the cytaster microtubules, the microtubules in the spindle are bundled and persist from early metaphase through late telophase. During ontogenesis the first migration cytaster is built up between 3 and 12 min after oviposition near the anterior egg pole, in the vicinity of the sperm nucleus. In non-inseminated eggs time lapse films show a migration cytaster to develop autonomously in a region free from nuclei, but it does not follow the normal path of the male pronucleus. In several cases the female pronucleus, which remains without a cytaster of its own, was observed to move to the cytaster generated in the absence of the male pronucleus. Whether or not it is adhering to a nucleus, the cytaster divides into two at the correct time, i.e, corresponding to the first cleavage division in fertilized eggs. In some non-inseminated eggs this type of ‘pseudocleavage’ has been observed to occur repeatedly, giving rise to an increasing number of anucleate cytasters.
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    Morphogenesis in the embryo ofDrosophila melanogaster — Germ band extension (1980)
    Springer
    Development genes and evolution 188 (1980), S. 163-177 
    Details
    ISSN: 1432-041X
    Keywords: Yolk sac ; Ultrastructure ; Embryogenesis ; Drosophila
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Changes at the ultrastructural level during germ band extension in the embryo ofDrosophila melanogaster are described. Cytoplasmic connections between cells and the yolk sac are present during initial cellular movements. At this time, a continuous system of microfilaments is present adjacent to the membranes in the connections and at the periphery of the yolk sac. As germ band extension progresses, this system becomes discontinuous, and microfilaments are apparent only in the immediate vicinity of the connections. Cytoplasmic connections are disassembled at approximately the midpoint of extension; at the same time, extensive membrane associations develop between germ band cells and between these cells and adjacent yolk sac membranes. Positioning and orientation of cytoplasmic connections suggest that the yolk sac, via these connections, is actively involved in the cellular movements of early germ band extension.
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    Retention of the differentiated state by larvalXenopus liver cells in primary culture (1978)
    Springer
    Development genes and evolution 185 (1978), S. 235-248 
    Details
    ISSN: 1432-041X
    Keywords: Liver ; Primary culture ; Ultrastructure ; Albumin synthesis ; Xenopus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Electron microscopic analysis of primary cultures derived from larvalXenopus liver has shown that these cells, although they form only two-dimensional aggregates, retain and presumably also develop structural characteristics typical of liver parenchyma cells, such as bile canaliculi with microvilli and epithelial junctional complexes. As judged from structural criteria, primary cultures contain 80–90% hepatocytes. In contrast to the intact tissue, primary cultures showed excessive development of microfilaments, however. Incorporation of labeled amino acids has revealed further that the capacity for protein synthesis is maintained in culture and that synthesis of liverspecific protein albumin is maintained in vitro, even in liver cultures derived from thyrostatic tadpoles. This latter result suggests that initiation of albumin synthesis in the larval liver is probably not dependent upon thyroid hormones but rather reflects the protodifferentiated state of this tissue.
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    Mayflies (ephemeroptera), the most “primitive” winged insects, have telotrophic meroistic ovaries (1993)
    Springer
    Development genes and evolution 203 (1993), S. 18-27 
    Details
    ISSN: 1432-041X
    Keywords: Oogenesis ; Germ line cell cluster ; Oocyte determination ; Ultrastructure ; Mayflies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Germ line cell cluster formation in ovarioles of three different stages, each from a different mayfly species, was studied using ultra-thin serial sectioning. In the analysed ovariole of Cloeön sp., only one linear, zigzag germ line cell cluster was found, consisting of sibling cells connected by intercellular bridges which represent remnants of preceding synchronized mitotic cycles followed by incomplete cytokinesis. A polyfusome stretched through all sibling cells. At the tip of the ovariole, cytokinesis occurred without preceding division of nuclei; thus, intercellular bridges were lined up but the remaining cytoplasm between the bridges had no nuclei. The analysed Siphlonurus armatus vitellarium contained five oocytes at different stages of development. Each oocyte in the vitellarium was connected via a nutritive cord to the linear cluster of its sibling cells in the terminal trophic chamber. Each cluster had the same architecture as was found in Cloëon. The 3-dimensional arrangement and distribution of closed intercellular bridges strongly suggest that all five clusters are derived from a single primary clone. The position of oocytes within each cluster is random. However, each oocyte is embraced by follicular or prefollicular cells whilst all other sibling cells are enclosed by somatic inner sheath cells, clearly distinguishable from prefollicular cells. In the analysed ovariole of Ephemerella ignita, two small linear clusters were found in the tropharium beside two single cells, two isolated cytoplasmic bags with intercellular bridges but no nuclei, and some degenerating aggregates. One cluster was still connected to a growing oocyte via a nutritive cord. In all species the nurse cells remained small and no indications of polyploidization were found. We suggest that this ancient and previously unknown telotrophic meroistic ovary has evolved directly from panoistic ancestors.
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    The origin of the nascent blastocoele in preimplantation mouse embryos ultrastructural cytochemistry and effect of chloroquine (1991)
    Springer
    Development genes and evolution 200 (1991), S. 77-85 
    Details
    ISSN: 1432-041X
    Keywords: Lysosomes ; Ultrastructure ; Chloroquine ; Blastocyst ; Mouse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mouse morulae are known to undergo cavitation as soon as some external cells have entered the sixth cell cycle (Garbutt et al. 1987). Since the early cytological features of cavitation are still unclear, we undertook a careful ultrastructural analysis of late morulae-nascent blastocysts. In addition, since maturation of lysosomes might be involved in the first step of cavity formation, we focused our attention on these organelles by means of the cytochemical localization of trimetaphosphatase activity and by the study of the effects of chloroquine on precavitation embryos. Our results suggest that cavitation starts in a few external cells (presumably competent cells entering the sixth cell cycle), by the chloroquine-sensitive formation of degradative autophagic vacuoles engulfing lipid droplets and vacuoles containing osmiophilic material. These complex structures enlarge (as a result of lipid metabolism?) and so transform into intrablastomeric cavities which, by means of a membrane fusion process, very rapidly become extracellular cavities that coalesce. The abembryonic pole of the blastocyst is determined in this way. Moreover, we suggest that the juxtacoelic cytoplasmic processes covering the inner cell mass (ICM) cells, which are known to restrict the expression of their totipotency during early cavitation (Fleming et al. 1984), are the latest remnants of the walls of the growing intrablastomeric cavities.
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    Ultrastructural changes in the distal wing bud of the chick embryo after removal of the apical ectodermal ridge (1979)
    Springer
    Development genes and evolution 185 (1979), S. 333-346 
    Details
    ISSN: 1432-041X
    Keywords: Chick embryo ; Limb bud ; Ultrastructure ; Cell death
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The ultrastructural changes in the wing bud afterapical ectodermal ridge (A.E.R.) removal was studied to re-examine the issue of distal mesenchymal cell death. The A.E.R. of the right wing bud was removed microsurgically from chick embryos of stages 18 to 22 (HH 1951). The wing buds were examined at three hour intervals up to twelve hours after the operation with light, transmission and scanning electron microscopy. The main findings were: (1) Immediate and temporary shrinkage of the mesenchymal extracellular space 100 to 150 μm and chromatin condensation in the cells 50 to 75 μm from the wound. (2) Death of ectodermal and mesenchymal cells in the immediate vicinity of the wound. (3) Formation of a single squamous-like layer of mesenchymal cells to cover the wound. (4) Occasional evidence of cell death in the distal mesenchyme at later times after the operation. The pattern of cell death observed suggests only a traumatic etiology, and gives little evidence for the postulated developmental significance of cell death following A.E.R. removal.
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    Membranes during yolk-platelet development in oocytes of the toad Bufo marinus (1987)
    Springer
    Development genes and evolution 196 (1987), S. 367-371 
    Details
    ISSN: 1432-041X
    Keywords: Vitellogenesis ; Bufo marinus oocyte ; Yolk-platelet membrane ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Oocytes of the toad Bufo marinus have been studied by means of thin section and particularly freeze-fracture electron microscopy to characterize the cytoplasmic membranes around the yolk organelle, and the storage of yolk material in precursors and platelets. This appears to be a previously unknown type of yolk-platelet formation. During yolk-organelle development from the primordial precursor to the bi-partite fully grown yolk platelet, numerous lipoid droplets are attached to the periphery of the platelet, indicating an intense uptake of lipids. As is typical for amphibians, the fully grown yolk platelet has a crystalline internum covered by a dense osmiophilic externum, and the whole organelle is enveloped by a plasma membrane that shows no direct connection or fusion with endocytotic vesicles. The yolk membrane exhibits few intramembraneous particles (IMPs) at the core areas and some more where it borders fields of lipoid droplets. Here the IMPs show a net-like arrangement in the furrows between adjacent droplets.
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    Yolk organelles and their membranes during vitellogenesis ofXenopus oocytes (1989)
    Springer
    Development genes and evolution 198 (1989), S. 92-102 
    Details
    ISSN: 1432-041X
    Keywords: Vitellogenesis ; Xenopus oocyte ; Yolk-platelet membrane ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The yolk platelets ofXenopus laevis have been studied by thin-section and freeze-fracture electron microscopy to characterize the boundary membrane during yolk formation. Throughout vitellogenesis, large yolk platelets are in close contact with smaller nascent yolk organelles. Two types of primordial yolk platelets (I and II) have been discriminated. After membrane fusion these precursors can be completely incorporated into the main body of existing platelets, numerous yolk crystals then merge and form one uniformly stratified core. Lipid droplets are tightly attached to the membrane at all developmental stages of yolk platelets. A direct connection of endoplasmic reticulum to the membranes of yolk platelets was not observed. On freezeetching replicas, yolk-platelet membranes present fracture faces with intramembranous particles (IMP) of various sizes and a heterogeneous distribution of approximately 200–600 IMP/μm2 at the E face, and 1200–2100 IMP/μm2 at the P face. Again, this presentation of the membrane exhibits neither anastomoses to the endoplasmic reticulum, nor caveolae that exclude the uptake of yolk-containing vesicles into these yolk organelles. Proteinaceous yolk platelets tend to fracture along their periphery through the superficial layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02447744
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    The effects of acid deposition on benthic animals in lakes and streams (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 471-486 
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    ISSN: 1420-9071
    Keywords: Acidification ; benthic animals ; calcium ; invertebrates ; lakes ; pH ; streams ; fresh water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01946685
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    Ultrastructural localization of catalase and D-amino acid oxidase in ‘normal’ fetal mouse liver (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 144-147 
    Details
    ISSN: 1420-9071
    Keywords: Ultrastructure ; catalase ; D-amino acid oxidase ; fetal mouse liver ; hepatocytes ; peroxisomes ; muscular dysgenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In the hepatocytes of ‘normal’ fetal mice from mothers which were carriers of muscular dysgenesis, catalase and D-amino acid oxidase (DAAO) positive as well as negative peroxisomes were observed. DAAO reaction product was occasionally localized in patches around cell membranes and DAAO-positive peroxisomes were frequently observed near mitochondria.
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    URL: http://dx.doi.org/10.1007/BF01952437
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    Biological effects of lithium: Experimental analysis in plant cytokinesis (1987)
    Springer
    Cellular and molecular life sciences 43 (1987), S. 1025-1027 
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    ISSN: 1420-9071
    Keywords: Plant cytokinesis ; lithium ; caffeine ; calcium ; magnesium ; sodium and potassium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The biological effects of lithium ions have been studied, using plant cytokinesis in onion root meristems as the experimental model. Lithium induces binucleate cells by inhibiting cell plate formation. Moreover, lithium and caffeine have additive effects on the induction of binucleate cells. Na+, K+, Ca++ and Mg++ antagonize lithium-induced inhibition of cytokinesis.
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    URL: http://dx.doi.org/10.1007/BF01952228
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    Ultrastructure, histology, and innervation of the mantle edge of the freshwater pulmonate snailsLymnaea stagnalis andBiomphalaria pfeifferi (1978)
    Springer
    Calcified tissue international 26 (1978), S. 271-282 
    Details
    ISSN: 1432-0827
    Keywords: Shell formation ; Free nerve endings ; Ultrastructure ; Lymnaea stagnalis ; Biomphalaria pfeifferi
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The mantle edge of the freshwater pulmonate snailsLymnaea stagnalis andBiomphalaria pfeifferi was investigated with histochemical and ultrastructural methods. The mantle edge gland, which is involved in shell formation, consists of the periostracal groove and the belt. This belt appears to be composed of various regions. In the area of the periostracal groove a number of subepithelial gland cell types occur; these release their products into the groove. Between the groove cells ciliated free nerve endings terminate; the corresponding perikarya occur in the subepidermal connective tissue. Also in the posterior belt region free nerve endings were observed between the epithelial cells; in addition, a particular type of subepithelial gland cell was found in this area. The epithelial cells of this part of the belt have the ultrastructural characteristics of ion and water transporting cells; they are probably involved in calcium deposition and resorption. The possible role of the free nerve endings and of the subepithelial gland cells is discussed.
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    URL: http://dx.doi.org/10.1007/BF02013270
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    Ultrastructural localization and gradient of activity of alkaline phosphatase activity during rodent odontogenesis (1982)
    Springer
    Calcified tissue international 34 (1982), S. 273-279 
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    ISSN: 1432-0827
    Keywords: Odontogenesis ; Ultrastructure ; Alkaline phosphatase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The ultrastructural localization and gradient of activity of alkaline phosphatase were studied with respect to cell differentiation, matrix synthesis, and matrix mineralization in the incisor and molar teeth of 4-day-old Sprague-Dawley rats. The animals were perfused intracardially at room temperature with 2.5% glutaraldehyde in 0.1M sodium cacodylate (pH 7.4) with 3–4% sucrose. The jaws were dissected, immersion-fixed for 24 h, and the incisor and molar tooth germs removed. These were demineralized in 10% EDTA in NaOH (pH 7.4) with 7% sucrose. After reactivation of the enzyme with 0.1M MgCl in Tris-maleate buffer (pH 7.4) at 4°C, the teeth were incubated for alkaline phosphatase in a medium consisting of 6 ml 3% sodiumβ-glycerophosphate, 4 ml 0.2M Tris-HCl buffer (pH 9.2), 3 ml 1.6% MgSO4, 12 ml 0.5% lead citrate (pH⋍12), and 2.1 g sucrose. The pH was adjusted to 9.2 with 0.2M HCl, the volume made up to 30 ml, and the solution centrifuged for 10 min at 5000 rpm. Control teeth were incubated in medium minus the substrate. Finally, the specimens were routinely post-fixed and embedded for sectioning and examination with a Philips 300 electron microscope. A gradient of alkaline phosphatase activity was mapped along the developing teeth in the cells of the stratum intermedium, the proximal borders of the ameloblasts, the early dentine matrix, the predentine-dentine border, matrix vesicles, and the plasma membranes of odontoblasts and subodontoblast cells. The gradient of alkaline phosphatase activity was evident in the forming tooth from the cervical loop to the crown apex and was related to the cellular events, matrix synthesis, and matrix mineralization occurring during odontogenesis.
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    URL: http://dx.doi.org/10.1007/BF02411250
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    Ultrastructural study of apatites in human urinary calculi (1980)
    Springer
    Calcified tissue international 31 (1980), S. 93-108 
    Details
    ISSN: 1432-0827
    Keywords: Calculus ; Ultrastructure ; Apatite ; Transmission ; Scanning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Using transmission and scanning electron microscopy, we have studied the ultrastructure of a number of urinary calculi, mainly composed of calcium phosphate. Three fundamental kinds of calcium phosphates were detected: nonstoichiometric carbonate apatite, nonhexagonal octacalcium phosphate, and calcium-magnesium whitlockite. The influence that the organic matter, substitutions in the phosphate lattice of CO3 and Mg, and apatitic stoichiometry have on the ultrastructure of the calcium phosphate calculi has been detailed. An originating apatitic unity named U2 is assumed to be the responsible for all the different structures of calcium apatites appearing in renal calculi. On the basis of our observations, a mechanism whereby apatites grow is postulated; magnesium functions as an inhibitor for the growing mechanism.
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    URL: http://dx.doi.org/10.1007/BF02407170
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    Bone mineral status measured by direct photon absorptiometry in institutionalized adults receiving long-term anticonvulsant therapy and multivitamin supplementation (1980)
    Springer
    Calcified tissue international 31 (1980), S. 117-121 
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    ISSN: 1432-0827
    Keywords: Bone mineral ; osteopenia ; anticonvulsant ; multivitamin ; calcium ; alkaline phosphatase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The effects of long-term anticonvulsant drug therapy and multivitamin supplementation on bone mineral status were evaluated by direct photon absorptiometry in 53 adult residents of an institution for the mentally disturbed. Results demonstrated a similar amount of osteopenia for control subjects and those on anticonvulsant drugs. Average osteopenia was 8% for control subjects and 6% for subjects taking anticonvulsant drugs. Significant osteopenia was found in 25% of subjects taking anticonvulsant drugs and 20% of control subjects. Multivitamin supplementation had a beneficial effect on bone status in both subject groups. The use of anticonvulsant drugs had a significant effect on levels of alkaline phosphatase. Elevated alkaline phosphatase was found in 37% of subjects taking anticonvulsant drugs and 22% of control subjects. Hypocalcemia was found only in subjects taking anticonvulsant drugs (19%). Average calcium values were similar for both subject groups. Multivitamins were shown to have no significant effect on alkaline phosphatase or calcium values. Because both control subjects and those taking anticonvulsant drugs showed similar levels of osteopenia, factors other than anticonvulsant drug therapy appeared to adversely affect bone mineral status in this population. Conversely, multivitamin supplementation and the dietary control present in the institutionalized setting appear to have ameliorated the osteopenia commonly seen in anticonvulsant-treated populations without greatly modifying elevated alkaline phosphatase and hypocalcemia.
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    URL: http://dx.doi.org/10.1007/BF02407172
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    The loci of mineral in turkey leg tendon as seen by atomic force microscope and electron microscopy (1994)
    Springer
    Calcified tissue international 55 (1994), S. 180-189 
    Details
    ISSN: 1432-0827
    Keywords: Collagen ; Crystal habit ; Ultrastructure ; Turkey leg tendon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Transmission electron micrographs of fully mineralized turkey leg tendon in cross-section show the ultrastructure to be more complex than has been previously described. The mineral is divided into two regions. Needlelike-appearing crystallites fill the extrafibrillar volume whereas only platelike crystallites are found within the fibrils. When the speciment is tilted through a large angle, some of the needlelike-appearing crystallites are replaced by platelets, suggesting that the needlelike crystallites are platelets viewed on edge. If so, these platelets have their broad face roughly parallel to the fibril surface and thereby the fibril axis, where the intrafibrillar platelets are steeply inclined to the fibril axis. The projection of the intrafibrillar platelets is perpendicular to the fibril axis. The extrafibrillar volume is at least 60% of the total, the fibrils occupying 40%. More of the mineral appears to be extrafibrillar than within the fibrils. Micrographs of the mineralized tendon in thickness show both needlelike-appearing and platelet crystallites. Stereoscopic views show that the needlelike-appearing crystallites do not have a preferred orientation. From the two-dimensional Fourier transform of a selected area of the cross-sectional image, the platelike crystallites have an average dimension of 58 nm. The needlelike-appearing crystallites have an average thickness of 7 nm. The maximum length is at least 90 nm. Atomic force microscopy (AFM) of unstained, unmineralized turkey leg tendon shows collagen fibrils very much like shadow replicas of collagen in electron micrographs. AFM images of the mineralized tendon show only an occasional fibril. Mineral crystallites are not visible. Because the collagen is within the fibrils, the extrafibrillar mineral must be embedded in noncollagenous organic matter. When the tissue is demineralized, the collagen fibrils are exposed. The structure as revealed by the two modalities is a composite material in which each component is itself a composite. Determination of the properties of the mineralized tendon from the properties of its elements is more difficult than considering the tendon to be just mineral-filled collagen.
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    URL: http://dx.doi.org/10.1007/BF00425873
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    Bioactive glass-ceramic containing crystalline apatite and wollastonite initiates biomineralization in bone cell cultures (1994)
    Springer
    Calcified tissue international 55 (1994), S. 458-466 
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    ISSN: 1432-0827
    Keywords: In vitro ; Bioactive glass ceramic ; Mineralization ; Bone bonding mechanisms ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Rat bone cells were cultured in the presence of bioactive glass-ceramic containing crystalline apatite and wollaston te. Scanning electron microscopy observations of the surface of the seeded ceramic disks revealed that cells attached, spread, and proliferated on the material surface. Soaking in cell-free culture medium showed that no change occurred in the surface structure. However, when cultured with bone cells and observed under a transmission electron microscope, an electron-dense layer was noted initially at the surface of the material, before bone formation occurred. In addition, energy-dispersive X-ray microanalysis demonstrated the presence of calcium and phosphorus in this layer. Progressively, during the following days of culture, active osteoblasts synthetized and laid down an osteoid matrix composed of numerous collagen fibrils arranged either parallel or perpendicularly to the first-formed electron-dense layer. Mineralization initiated on the ceramic surface dispersed then along the collagenous fibrils, leading to a mineralized matrix which surrounded the ceramic particles. These results demonstrate the capacity of apatite-wollastonite glass ceramic to initiate biomineralization in osteoblast cultures and to achieve a direct bond between the surface apatite layer of the bioactive glass-ceramic and the mineralized bone matrix.
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    URL: http://dx.doi.org/10.1007/BF00298560
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    Calmodulin-like activity in a mineralising tissue: The rat molar tooth germ (1981)
    Springer
    Calcified tissue international 33 (1981), S. 545-548 
    Details
    ISSN: 1432-0827
    Keywords: calmodulin ; calcium ; mineralisation ; tooth germ
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Calmodulin, a calcium binding protein, has been implicated in the regulation of many calcium-dependent biological processes. Since calcium has an important role in hard tissue genesis, both at intra- and extracellular levels, we anticipate that calcium binding proteins may modulate this process. The present study investigated a mineralising tissue, the rat molar tooth germ, to determine the presence of calmodulin-like activity. A heat-treated cell-free extract of tooth germs provided enhancement of Ca2+-dependent Mg2+-ATPase and 3′:5′-nucleotide phosphodiesterase activity. No enhancement occurred in the absence of calcium or in the presence of trifluoperazine. SDS-polyacrylamide gel electrophoresis of this extract revealed a protein band of approximately 18,000 mol. wt. These findings indicate the presence of calmodulin-like activity in rat molar tooth germs and support the proposal that calcium and calcium binding proteins, in particular calmodulin, have a major regulatory role in the biology of mineralising tissues.
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    URL: http://dx.doi.org/10.1007/BF02409487
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    Ultrastructural localization of calcium in the mandibular condylar growth cartilage of the rat (1980)
    Springer
    Calcified tissue international 30 (1980), S. 27-34 
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    ISSN: 1432-0827
    Keywords: Ultrastructure ; Calcium ; Cartilage ; Vesicles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The potassium pyroantimonate technique was utilized for the selective subcellular localization of calcium in the mandibular condylar cartilage of 1-day-old rats. Electron dense calcium pyroantimonate precipitates were localized principally in mitochondria and at the cell membrane of the chondrocytes. In addition, small intracellular vesicles 0.1–0.2µm in diameter were observed in proximity to the cell membrane of chondrocytes of the mid-hypertrophic zone. The results suggest that these vesicles were being extruded from the cell into the extracellular matrix. Energy-dispersive analysis by X-rays confirmed that calcium is the principal cation of the electron-dense precipitates.
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    URL: http://dx.doi.org/10.1007/BF02408603
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    Length and shape of enamel crystals (1984)
    Springer
    Calcified tissue international 36 (1984), S. 550-555 
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    ISSN: 1432-0827
    Keywords: Enamel crystals ; Length ; Shape ; Apatite ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary An original method for fractionating and preparing isolated crystals of homogeneous size was developed. It was demonstrated that enamel apatite crystals are at least 100 µm long. The flexibility of the very long crystallites was demonstrated. Crystal curvatures, accounting for the irregular course of the prisms through the enamel thickness, were visualized and measured. It was shown that in the deep forming enamel layer, lateral branches may grow out of the crystals and crystal fusing often occurs, inducing the crystallites to assume pyramidal shapes with their wide bases pointing toward the dentino-enamel junction and one or two tops toward Tomes' processes. During the maturation process, the two tops of the still immature crystals also fuse so that the mature crystals acquire a rodlike aspect, with parallel faces and steplike graduations along thec axis, allowing a close contact between the crystals. These results support the hypothesis that the crystallites would be continuous from the dentino-enamel junction to the surface.
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    URL: http://dx.doi.org/10.1007/BF02405364
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    Electron microscopy of avian osteopetrosis induced by retrovirus MAV.2-O (1982)
    Springer
    Calcified tissue international 34 (1982), S. 382-390 
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    ISSN: 1432-0827
    Keywords: Avian osteopetrosis ; Avian oncornavirus ; Ultrastructure ; Calcification ; Bone cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Diaphyseal tibial bone of 12.5 – 13-day and 19-day-old embryos and 20-day-old hatched chicks infected with retrovirus MAV.2-O were examined by transmission electron microscopy. The viruses were associated with lining osteoblasts and osteocytes. Whereas the infection of the osteoblast layer seemed to be a transient stage, virus association with osteocytes was a constant and main ultrastructural feature. The viruses were found either in the osteoid or in the periosteocytic space of the bone lacunae. They arose from dense cytoplasmic areas located near the cell plasmalemma via a budding process. The newly budded virus particles often had a large tail or a fine stalk-like process lost in the extracellular space. The viruses underwent calcification by deposition of inorganic material and were incorporated in the bone trabeculae. No production of virus was observed in typical osteoclasts with well-differentiated ruffled borders. The viral-induced avian osteopetrosis seemed to result from increased bone deposition through stimulation of osteoblast and osteocyte activities, whereas osteoclastic bone resorption seemed to be undisturbed.
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    URL: http://dx.doi.org/10.1007/BF02411272
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    Ultrastructural damage due to freezing followed by thawing in shoot meristem and leaf mesophyll cells of tall fescue (Festuca arundinacea Schreb.) (1977)
    Springer
    Planta 134 (1977), S. 159-168 
    Details
    ISSN: 1432-2048
    Keywords: Festuca ; Frost damage ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Tillers of Festuca arundinacea Schreb. were subjected to-8°C in a bath of methylated spirits for three-quarters of an hour. They were thawed at room temperature and some material taken from the shoot apical meristem and leaf blade for electron microscopy. Similar material was taken from control plants for electron microscopy. Nine tillers subjected to-8°C and thawed subsequently failed to regrow. Nine control tillers regrew. All the treated meristem cells and about half the treated leaf mesophyll cells were extensively altered. Their nuclei were contracted, organelles were swollen or partly disrupted, plasmalemma and nuclear membranes were broken or absent and vacuoles were sometimes disrupted. Strongly osmiophilic material accumulated in the vicinity of membranes. About half the leaf mesophyll cells differed from the control mesophyll cells only in having more spherosomes and narrower thylakoids. Parallels with other ultrastructural studies of stress damage and the indications the results give of possible primary damaging events are discussed.
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    Early events during the establishment of the Gunnera/Nostoc symbiosis (1992)
    Springer
    Planta 188 (1992), S. 403-413 
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    ISSN: 1432-2048
    Keywords: Cyanobacterium ; Gunnera ; Infection process ; Nostoc ; Symbiosis ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The symbiosis between Gunnera and Nostoc was reconstituted using G. chilensis Lam. and G. manicata Linden, respectively, and three different Nostoc strains. Six stages characterised by specific modifications in both the cyanobiont and the host were recognised during the infection process. Mucilage-secreting stem glands developed on the Gunnera stems independent of the presence of cyanobacteria (Stage I). Soon after addition of the Nostoc isolates to the plant apices, an abundant differentiation of motile hormogonia commenced. The cyanobacteria accumulated in the mucilage on the surface of the gland (Stage II), and the hormogonia then proceeded into the stem tissue through intercellular channels (Stage III). At the channel bases, Nostoc was detected between the cell walls of small, densely cytoplasmic Gunnera cells and also in elaborate folds of these (Stage IV). The Gunnera cell walls subsequently dissolved adjacent to the cyanobacteria and Nostoc entered the host cells (Stage V). Once the intracellular association was formed, a high proportion of the vegetative Nostoc cells differentiated into heterocysts (Stage VI). Nostoc changed from being rich in inclusions (particularly cyanophycin) while on the gland surface into a comparatively “non-storing” form during penetration and the early intracellular stages. Bacteria were numerous on the gland surface, fewer in the channels, and were never detected within the Gunnera cells, indicating the existence of specific recognition mechanisms discriminating between conceivable microsymbionts. Mechanisms behind mutual adaptations and interactions between the two symbionts are discussed.
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    High-pressure freezing of soybean nodules leads to an improved preservation of ultrastructure (1992)
    Springer
    Planta 188 (1992), S. 155-163 
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    ISSN: 1432-2048
    Keywords: Bradyrhizobium ; Electron microscopy ; Glycine (root nodules) ; High-pressure freezing ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract High-pressure freezing of chemically untreated nodules of soybean (Glycine max (L.) Merr.), in sharp contrast to chemical fixation and prefixation, appears to preserve the ultrastructure close to the native state. This is supported by the observation that the peribacteroid membrane of high-pressure-frozen samples is tightly wrapped around the bacteroids, a finding that is fully consistent with the current views on the physiology of oxygen and metabolite transport between plant cytosol and bacteroids. In soybean root nodules, the plant tissue and the enclosed bacteria are so dissimilar that conventional aldehyde-fixation procedures are unable to preserve the overall native ultrastructure. This was demonstrated by high-pressure freezing of nodules that had been pre-fixed in glutaraldehyde at various buffer molalities: no buffer strength tested preserved all ultrastructural aspects that could be seen after high-pressure freezing of chemically untreated nodules.
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    An electron microscope study on in vitro parthenogenesis in sunflower (1989)
    Springer
    Sexual plant reproduction 2 (1989), S. 154-166 
    Details
    ISSN: 1432-2145
    Keywords: Helianthus annuus ; Unfertilized ovule culture ; Parthenogenesis ; Ultrastructure ; Proembryo
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Electron microscope studies have been conducted on the parthenogenesis induced by in vitro culture of unfertilized ovules of sunflower (Helianthus annuus). In comparison with the state of the egg prior to inoculation, some eggs 5 days after culture show striking ultrastructural changes, which include, among others, nuclear migration, an increase in the number and activity of the organelles, a loss of polarity and wall formation at the chalazal end of the cell. Most of these changes are similar to those that occur normally in the zygote, indicating that parthenogenic development has been triggered in these eggs. Such eggs have been termed activated and are presumed to be capable of undergoing parthenogenesis. The parthenogenic proembryos which result share some features in common with zygotic proembryos. In addition, some parthenogenic proembryos exhibit unique properties not found in zygotic proembryos. These include embryos that consist of two parts differing markedly in density, an inversion of polarity, the frequent occurrence of autophagic vacuoles, the thickening of cell walls, a centripetal growth mode of wall formation, the appearance of an incomplete cell wall, free nuclear division, amitosis and degeneration. We believe that these ultrastructural peculiarities are the effects of in vitro culture.
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    The ultrastructure of polymorphic pollen grains of Canna indica L. (1989)
    Springer
    Sexual plant reproduction 2 (1989), S. 193-198 
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    ISSN: 1432-2145
    Keywords: Polymorphism ; Ultrastructure ; Pollen grains ; Canna indica L ; Tannin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Our investigations on Canna indica L. indicate that the pollen of this species is polymorphic: there are two types of pollen — a larger type and a comparatively smaller type. Transmission electron microscopy (TEM) revealed the presence of small vacuoles containing tannic substances in the generative cell (GC) of the larger grains: the GC of the mature grain contained a higher quantity of tannins than the GC of the immature grain. Mitochondria, lipid bodies, rough endoplasmic reticulum (RER) and microtubular bundles were present in the cytoplasm of the GC. Numerous mitochondria, lipid bodies and plastids were also present in the vegetative cell (VC), with the mitochondria clustered around the vegetative nucleus. The plastids were observed to be associated with the RER cisterns. During the maturation process, the number of starch grains contained in the plastids decreased.
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    Secretory tapetum of Brassica oleracea L.: polarity and ultrastructural features (1991)
    Springer
    Sexual plant reproduction 4 (1991), S. 28-35 
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    ISSN: 1432-2145
    Keywords: Tapetal cells ; Brassica oleracea L ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The ultrastructure of the secretory, binucleate tapetum of Brassica oleracea in the micro spore mother cell (MMC) stage through to the mature pollen stage is reported. The tapetal cells differentiate as highly specialized cells whose development is involved in lipid accumulation in their final stage. They start breaking down just before anther dehiscence. Nuclei with dispersed chromatin, large nucleoli and many ribosomes in the cytoplasm characterize the tapetal cells. The wall-bearing tapetum phase ends at the tetrade stage. The dissolution of tapetal walls begins from the inner tangential wall oriented towards the loculus and proceeds gradually along the radial walls to the outer tangential one. The plasmodesmata transversing the radial walls between tapetal cells persist until the mature microspore, long after loss of the inner tangential wall. After wall dissolution, the tapetal protoplasts retain their integrity and position within the anther locule. The tapetal cell membrane is in direct contact with the exine of the microspores/pollen grains and forms tubular evaginations that increase its surface area and appear to be involved in the translocation of solutes from the tapetal cells to the microspores/ pollen grains. The tapetal cells exhibit a polarity expressed by spatial differentiation in the radial direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00194568
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  • 94
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    Brassica napus pollen development during generative cell and sperm cell formation (1991)
    Springer
    Sexual plant reproduction 4 (1991), S. 176-181 
    Details
    ISSN: 1432-2145
    Keywords: Pollen ; Brassica napus ; Mitoses ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Brassica napus pollen development during the formation of the generative cell and sperm cells is analysed with light and electron microscopy. The generative cell is formed as a small lenticular cell attached to the intine, as a result of the unequal first mitosis. After detaching itself from the intine, the generative cell becomes spherical, and its wall morphology changes. Simultaneously, the vegetative nucleus enlarges, becomes euchromatic and forms a large nucleolus. In addition, the cytoplasm of the vegetative cell develops a complex ultrastructure that is characterized by an extensive RER organized in stacks, numerous dictyosomes and Golgi vesicles and a large quantity of lipid bodies. Microbodies, which are present at the mature stage, are not yet formed. The generative cell undergoes an equal division which results in two spindle-shaped sperm cells. This cell division occurs through the concerted action of cell constriction and cell plate formation. The two sperm cells remain enveloped within one continuous vegetative plasma membrane. One sperm cell becomes anchored onto the vegetative nucleus by a long extension enclosed within a deep invagination of the vegetative nucleus. Plastid inheritance appears to be strictly maternal since the sperm cells do not contain plastids; plastids are excluded from the generative cell even in the first mitosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00190001
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  • 95
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    The microtubule cytoskeleton and the rounding of isolated generative cells ofNicotiana tabacum (1992)
    Springer
    Sexual plant reproduction 5 (1992), S. 64-71 
    Details
    ISSN: 1432-2145
    Keywords: Generative cell ; Isolation ; Microtubules ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Upon squashing of the pollen grain, the isolated generative cell ofNicotiana tabacum looses its spindle shape to become spherical; this phenomenon is independent of the sucrose concentration used. The time necessary for this change can vary from 1 min (0% sucrose) to 20 min (30% sucrose). The microtubular cytoskeleton was studied by means of immunofluorescence and electron microscopy. Just after isolation, 5 to 15 clearly visible bundles in microtubules organized in a basket-like structure are present. After 15 min in medium with 15% sucrose, the microtubular cytoskeleton disappears, and a diffusely spread tubulin can be observed. Neither the addition of 10–20 μM taxol to the medium, nor the omission of Ca2+ to the medium has any effect on the changes in cell shape and loss of microtubular bundles after isolation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00714559
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  • 96
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    Ultrastructural expression of cytoplasmic male sterility in sugar beet (Beta vulgaris L.) (1993)
    Springer
    Sexual plant reproduction 6 (1993), S. 22-32 
    Details
    ISSN: 1432-2145
    Keywords: Cytoplasmic male sterility ; Ultrastructure ; Mitochondria morphometry ; Beta vulgaris L
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The development of microspore mother cells (MMC) and tapetum in male-fertile and male-sterile anthers of Beta vulgaris L. was compared at the electron microscope level. These studies were complemented by morphometric analyses of mitochondria in both tissues through successive stages of microsporogenesis. The earliest irregularities in the ultrastructure of male-sterile anthers were noted within the tapetum at the tetrad stage. These disturbances were initially expressed by a slight reduction in mitochondrial size and the appearance of concentric configurations of endoplasmic reticulum. As development proceeded, a further decrease in mitochondrial size become more conspicuous and was accompanied by a reduction in ribosome population and a failure of the tapetum to produce Ubisch bodies. This failure to produce Ubisch bodies is reflected in the underdevelopment of sterile microspore exine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00227579
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  • 97
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    Megaspore development in Selaginella. I. “Wicks”, their presence, ultrastructure, and presumed function (1993)
    Springer
    Sexual plant reproduction 6 (1993), S. 98-107 
    Details
    ISSN: 1432-2145
    Keywords: Selaginella ; Megaspore ; Exospore ; Ultrastructure ; Tapetal cells ; Plasmodesmata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Structures have been found in the locular space between the tapetal cells and megaspores in Selaginella argentea and S. kraussiana that enter the megaspore wall and extend to the plasma membrane of the megaspore cytoplasm. We have called these structures “wicks”. Unless special fixation procedures are used wicks are either very poorly preserved or not apparent. Wicks appear to be routes for the transport of materials from the tapetum to developing megaspores. The entry of the wicks into the megaspore wall and their passage throughout the wall implies that the megaspore wall of Selaginella is a three-dimensional mesh-work of inter-connecting spaces. Wicks have several macromolecular-sized subunits, and the results of our histochemical reactions indicated the presence of glycoprotein and/or mucopolysaccharide. X-ray microanalysis of the S. convoluta exospore showed that silicon is present in rod-shaped structures between units of the exospore in mature megaspores. Because of the size and form of the structures between the exospore units we consider that they are remnants of wicks stabilized by silicon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00227654
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  • 98
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    Pre-fertilization degeneration of both synergids in Brassica campestris ovules (1988)
    Springer
    Sexual plant reproduction 1 (1988), S. 208-216 
    Details
    ISSN: 1432-2145
    Keywords: Megagametophyte ; Synergids ; Brassica campestris ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In Brassica campestris, both synergids of the ovule degenerate before the arrival of the pollen tube. Synergid degeneration does not depend on pollination. At the non-degenerated stage, the synergids are completely filled with a complexly organized cytoplasm containing numerous mitochondria with many cristae, a large number of dictyosomes with many associated vesicles, and a very extensive rough endoplasmic reticulum. The degenerative changes that occur in the cytoplasm of the synergids are characterized by a loss of visibility of the membranes of the endoplasmic reticulum and the simultaneous formation of dense deposits on the surrounding membranes of the mitochondria. Locally, the plasma membranes of the synergids disappear, and some ground plasma of the synergids penetrates into the space between the plasma membranes of the egg cell and the central cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00189154
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  • 99
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    Ultrastructure of the micropyle and its relationship to pollen tube growth and synergid degeneration in sunflower (1991)
    Springer
    Sexual plant reproduction 4 (1991), S. 166-175 
    Details
    ISSN: 1432-2145
    Keywords: Helianthus annuus ; Ultrastructure ; Micropyle ; Pollen tube ; Synergid degeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Ultrastructural studies made on the micropyle of sunflower before and after pollination resulted in the following observations. (1) The micropyle is closed instead of a hole or canal. The inner epidermis of the integument on both sides of the micropyle is in close contact at the apex of the ovule. The boundary between the two sides consists of two layers of epidermal cuticle. (2) The micropyle contains a transmitting tissue. The micropyle is composed of an intercellular matrix produced by the epidermal cells of the integument. (3) The micropyle is asymmetrical, and is much wider on the side proximal to the funicle. On the funicle side the cells adjacent to the micropyle are similar to those of the transmitting tissue: they have large amounts of intercellular matrix and contain abundant dictyosomes, rough ER, and starch grains, and provide an appropriate environment for growth of the pollen tubes. The cells distal to the funicle are rich in rough ER and lipid bodies; they lack large intercellular spaces. (4) The micropyle is variable in the axial direction, i.e., it is much larger and more asymmetric at the level distal to the embryo sac than at a level close to the embryo sac. After pollination, one to four pollen tubes are seen in a micropyle. During their passage through the micropyle, most pollen tubes are restricted to the side proximal to the funicle. There is a greater tendency (81%) for the degenerate synergid to be located toward the funicle, i.e., at the same side as the pollen tube pathway. The data indicate a close relationship between micropyle organization, orientation of pollen tube growth, and synergid degeneration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00190000
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  • 100
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    Sperm cells of the pollen tubes of Brassica: Ultrastructure and isolation (1991)
    Springer
    Sexual plant reproduction 4 (1991), S. 226-234 
    Details
    ISSN: 1432-2145
    Keywords: Male germ unit ; Sperm cells ; Isolation ; Pollen tubes ; Brassica napus ; Pollen-tube inner plasma membrane ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Sperm cells of pollen tubes grown both in vivo and in vitro form a male germ unit. Extensions from both sperm cells of each pollen tube are closely associated with the tube nucleus. A high yield (2.7 × 104. 20 mg−1 pollen grains germinated) of intact sperm cells was obtained following release by osmotic shock from pollen tubes grown in vitro. Structural integrity of isolated sperm was maintained by isolation at low temperature in an osmotically balanced medium. At 4° C many isolated sperm pairs were still enclosed within the pollentube inner plasma membrane. Sperm cells not enclosed within this membrane no longer remained connected as a pair. During isolation vesicles formed on the sperm cell surface from disruption of the fibrillar components bridging the periplasmic space. Both in the pollen tube and after isolation the sperm nucleus is in close association with at least one region of the sperm plasma membrane. Sperm isolated at room temperature showed the presence of nucleopores, and nuclei were euchromatic, instead of heterochromatic as in intact sperm in the pollen tube.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00190009
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