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  • 1
    Electronic Resource
    Electronic Resource
    Dehydroepiandrosterone Sulphate (DHEAS) in the Oldest Old, Aged 85 and Over (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 719 (1994), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1994.tb56858.x
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  • 2
    Electronic Resource
    Electronic Resource
    Fimbriae and flagella of methanogenic bacteria (1979)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 5 (1979), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1979.tb03264.x
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  • 3
    Electronic Resource
    Electronic Resource
    Organization of actin filaments in regenerating and outgrowing subprotoplasts from pollen tubes ofNicotiana tabacum L. (1990)
    Springer
    Planta 180 (1990), S. 471-479 
    Details
    ISSN: 1432-2048
    Keywords: Actin ; Nicotiana (action in protoplasts) ; Pollen tube ; Protoplast regeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The dynamics of actin-filament organization in pollen-tube subprotoplasts ofNicotiana tabacum L. cv. Samsun during regeneration and outgrowth was examined using phalloidin probes and a non-fixation method. A succession of actin arrays was examined during subprotoplast regeneration that strongly resembled the actin dynamics described for developing microspores by Van Lammeren et al. (1989, Planta178, 531–539) and activated pollen by Tiwari and Polito (1988, Protoplasma147, 5–15). At the end of the succession the actin filaments often became extended between two opposite polar foci. The ordering of the cortical actin filaments reflected a polarity in the subprotoplasts which determined the plane of outgrowth. The site of outgrowth was often marked by a ring of actin filaments. As growth proceeded and tube-like structures were formed, the arrangement of cortical actin filaments was found to be transverse to the elongation axis. Since the patterns of actin distribution were identical in both caryoplasts and cytoplasts, it was concluded that the pollen-tube cytoplasm has the intrinsic capacity of reorganizing actin filaments and imposing polarity on the spherical subprotoplasts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02411443
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  • 4
    Electronic Resource
    Electronic Resource
    The symplasmic coupling of L2-cells diminishes in early floral development of Iris (1997)
    Springer
    Planta 203 (1997), S. 245-252 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Cell lineage ; Floral development ; Iris (floral development) ; Meristem (floral ; inflorescence) ; Plasmodesma (distribution) ; Symplasm (mapping)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The transition from vegetative to reproductive development involves extensive revisions of cellular collaboration at the apical meristem and results in the production of novel appendages. In Dutch Iris (Iris xiphium) the transition from vegetative apical meristem to inflorescence meristem was morphologically signalled by the appearance of a `spathe leaf '. After enlargement of the inflorescence meristem, a second spathe leaf and a double floral meristem were formed. The then undulated surface corresponded to general topological changes and a beginning of altered cell division patterns. Throughout, all cells produced in the meristem remained in contact via plasmodesmata (Pd), thus maintaining the symplasmic unity of the meristem. Since the symplasm harbours part of the signal network that coordinates the activities of the meristem cells, we investigated if alterations in Pd numbers could underlie meristem transitions. Prior to Pd counting, potentially important borders inside the meristem, representing primary and secondary cell contacts, were identified by the construction of a symplasmetric map. During the transition, significant alterations did take place at some of the borders defined by the map. Within the second tunica layer (L2), and between the L2 and adjacent cells, Pd numbers were strongly reduced. Within the first tunica layer (L1) and within the corpus they remained the same. The reduction was 25% between L2-cells, and between L2- and L1-cells; it was 40% between the L2 and the outer corpus layer. The reductions appeared to be due to a lowered production of primary and secondary Pd by L2-cells towards each other and towards adjacent cells. As a result of this the integration of all L2-cells and, as a consequence, of the L1 as a whole in the symplasmic network of the meristem was reduced. The implied gain in autonomy of the individual L2-cells and of the L1-layer may reflect their new functions in the floral meristem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050188
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  • 5
    Electronic Resource
    Electronic Resource
    Methanotrophic symbionts provide carbon for photosynthesis in peat bogs (2005)
    [s.l.] : Nature Publishing Group
    Nature 436 (2005), S. 1153-1156 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Wetlands are the largest natural source of atmospheric methane, the second most important greenhouse gas. Methane flux to the atmosphere depends strongly on the climate; however, by far the largest part of the methane formed in wetland ecosystems is recycled and does not reach the atmosphere. ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature03802
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  • 6
    Electronic Resource
    Electronic Resource
    Evidence for complete denitrification in a benthic foraminifer (2006)
    [s.l.] : Nature Publishing Group
    Nature 443 (2006), S. 93-96 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Benthic foraminifera are unicellular eukaryotes found abundantly in many types of marine sediments. Many species survive and possibly reproduce in anoxic habitats, but sustainable anaerobic metabolism has not been previously described. Here we demonstrate that the foraminifer Globobulimina ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature05070
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  • 7
    Electronic Resource
    Electronic Resource
    Pollen tubes of flavonol-deficient Petunia show striking alterations in wall structure leading to tube disruption (1999)
    Springer
    Planta 207 (1999), S. 575-581 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Cell wall ; Fertilization ; Flavonol ; Petunia ; Pollen tube ; Transformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Despite the vital role that flavonols play in fertilization and pollen tube growth of a number of species such as petunia and maize, their function is still unclear. Pollen tubes of the flavonol-deficient transformant T17.02 of Petunia hybrida L. are able to germinate and start growing in vitro, but eventually disrupt at the tip approximately 2 h after germination. In order to establish the possible role of flavonols in this process, wild-type and flavonol-deficient pollen tubes were subjected to cytological and ultrastructural analyses and screened for differences. The results showed that before disruption of the flavonol-deficient pollen tubes, the structure of the primary wall at the tip dramatically changed from layered to granular. Secretory vesicles at the tip still fused with the wall but lost their capacity to melt into the wall and to form layers. Instead they remained as dark, electron-dense granular structures surrounded by an electron-translucent matrix. Apparently the matrix is not able to sustain the wall's coherence and as a consequence the tube disrupts. No other remarkable cytological or ultrastructural differences between the transformant and the wild-type pollen tubes could be found before tip disruption. Even a morphometric analysis of abundance and distribution of endoplasmic reticulum, dictyosomes and mitochondria did not reveal any significant difference. However, for the first time, obvious morphological differences were observed in the wall of the flavonol-deficient pollen tubes. We conclude that flavonols act on precursors of the pollen tube wall of petunia and interfere with a cross-linking system in the wall, possibly via extensins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050520
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  • 8
    Electronic Resource
    Electronic Resource
    Development and cellular organization ofPinus sylvesfris pollen tubes (1996)
    Springer
    Sexual plant reproduction 9 (1996), S. 93-101 
    Details
    ISSN: 1432-2145
    Keywords: Cytoskeleton ; Microscopy ; Pinus sylvestris ; Pollen ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The organization ofPinus sylvestris pollen tubes during growth was studied by video microscopy of living cells and by electron microscopy after freeze-fixation and freeze-substitution (FF-FS). Pollen germinated and the tubes grew slowly for a total period of about 7 days. Some of the grains formed two tubes, while 10–50% of the tubes ramified. These features are in accordance with development in vivo. The cytoplasmic hyaline cap at the tip disappeared during the 2nd or 3rd day of culture. Aggregates of starch grains progressively migrated from the grain into the tube and later into the branches. Vacuoles first appeared at day 2 and eventually filled large parts of the tube. The tube nucleus was located at variable distances from the tip. Some of the organelles showed linear movements in a mostly circulatory pattern, but the majority of the organelles showed brownian-like movements. Rhodamine-phalloidin-stained actin filaments had a gross axial orientation and were found throughout the tube including at the tip. The ultrastructure of pollen tubes was well preserved after FF-FS, but signs of shrinkage were visible. The secretory vesicles in growing tips were not organized in a vesicle cone, and coated pits had a low density with only local accumulations, which is in accordance with slow growth. The mitochondria contained small cristae and a darkly stained matrix and were located more towards the periphery of the tube, indicating low respiratory activity and low oxygen levels. The dictyosomes carried typical trans-Golgi networks, but some contained less than the normal number of cisternae. Other elements of the cytoplasm were irregularly spaced rough endoplasmic reticulum, many multivesicular bodies, lipid droplets and two types of vacuoles. The typical organization associated with tip growth in angiosperm pollen tubes, e.g.Nicotiana tabacum, was not present inP. sylvestris pollen tubes. The different morphology may relate to the growth rate and not to the type of growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02153056
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  • 9
    Electronic Resource
    Electronic Resource
    The wall ofPinus sylvestris L. pollen tubes (1999)
    Springer
    Protoplasma 208 (1999), S. 26-36 
    Details
    ISSN: 1615-6102
    Keywords: Callose ; Cell wall ; Cellulose ; Pinus sylvestris ; Pectin ; Pollen tube ; Tip growlh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The wall ofPinus sylvestris pollen and pollen tubes was studied by electron microscopy after both rapid-freeze fixation and freeze-substitution (RF-FS) and chemical fixation. Fluorescent probes and antibodies (JIM7 and JIM5) were used to study the distribution of esterified pectin, acidic pectin and callose. The wall texture was studied on shadow-casted whole mounts of pollen tubes after extraction of the wall matrix. The results were compared to current data of angiosperms. TheP. sylvestris pollen wall consists of a sculptured and a nonsculptured exine. The intine consists of a striated outer layer, that stretches partly over the pollen tube wall at the germination side, and a striated inner layer, which is continuous with the pollen tube wall and is likely to be partly deposited after germination. Variable amounts of callose are present in the entire intine. No esterified pectin is detected in the intine and acidic pectin is present in the outer intine layer only. The wall of the antheridial cell contains callose, but no pectin is detectable. The wall between antheridial and tube cell contains numerous plasmodesmata and is bordered by coated pits, indicating intensive communication with the tube cell. Callose and esterified pectin are present in the tip and the younger parts of the pollen tubes, but both ultimately disappear from the tube. Sometimes traces in the form of bands remain present. No acidic pectin is detected in either tip or tube. The wall of the pollen tube tip has a homogenous appearance, but gradually attains a fibrillar character at aging, perhaps because of the disappearance of callose and pectin. No secondary wall formation or callose lining can be seen wilh the electron microscope. The densily of the cellulose microfibrils (CMF) is much lower in the tip than in the tube. Both show CMF in all but axial and nontransverse orientations. In conclusion,P. sylvestris and angiosperm pollen tubes share the presence of esterified pectin in the tip, the oblique orientations of the CMF, and the gradual differentiation of the pollen tube wall, indicating a possible relation to tip growth. The presence of acidic pectin and the deposition of a secondary-wall or callose layer in angiosperms but not inP. sylvestris indicales that these characteristics are not related to tip growth, but probably represent adaptations to the fast and intrastylar growth of angiosperms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01279072
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  • 10
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    The symplasmic coupling of L 2 -cells diminishes in early floral development of Iris (1997)
    Springer
    Details
    Publication Date: 1997-09-26
    Print ISSN: 0032-0935
    Electronic ISSN: 1432-2048
    Topics: Biology
    Published by Springer
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