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  • 11
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Guanine-nucleotide exchange factors on ADP-ribosylation factor GTPases (ARF-GEFs) regulate vesicle formation in time and space by activating ARF substrates on distinct donor membranes. Mammalian GBF1 (ref. 2) and yeast Gea1/2 (ref. 3) ARF-GEFs act at Golgi membranes, ...
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Planta 104 (1972), S. 234-246 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The plasmalemma of Oocystis apiculata, W. West when freezeetched has been shown to bear granules of several sizes. At the earliest stage of development the outer face of the plasmalemma of the naked autospore has small (8.5 nm diameter) granules aligned in rows, in pairs. These rows are stacked together forming extensive “granule-bands” over the plasmalemma surface. The orientation of these “granule-bands” corresponds exactly to one of the major microfibril directions. Occasionally, the bands are reduced to patches, some of which are at right angles to each other. Banding of granules on the inner plasmalemma face of naked autospores is also seen. During development the plasmalemma is seen to change so that in the final stages it bears reticulate invaginations, the granule bands occurring within them. The significance of the “granulebands” in terms of cellulose microfibril biosynthesis is discussed.
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  • 13
    ISSN: 1432-2048
    Keywords: Coated vesicle ; Cucurbita ; 1,3-β-Glucan synthase ; N-1-naphthylphthalamic acid binding ; Plasma membrane ; Vesicle, coated
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The two plasma-membrane (PM) markers: 1,3-β-glucan synthase and naphthylphthalamic-acid-binding capacity are localized in two peaks of activity on isopycnic Ficoll/D2O gradients prepared from a zucchini (Cucurbita pepo L.) hypocotyl post-microsomal fraction. The denser peak overlaps with the major distribution of clathrin and represents a region of the gradient enriched in coated vesicles (cv). Further purification of the pooled cv-fractions has shown that these PM marker activities are not borne by the cv, but are instead carried by smooth membrane fragments also present in these fractions. As judged from the results of Western blotting with polyclonal antibodies prepared against the 100-kilodalton (kDa) subunit of a PM H+-ATPase and the 70-kDa subunit of a tonoplastic H+-ATPase, these contaminants are of both PM and endomembrane origin. The PM contaminants however, differ from phase-partitioning- and free-flow-electrophoresis-purified PM prepared from microsomal fractions of zucchini hypocotyls in terms of their bouyant density in Ficoll/D2O gradients. Moreover, they do not appear to be present as sealed, outside-out, vesicles. Highly purified cv fractions from zucchini hypocotyls cross-react with subunit antibodies from both vacuolar and PM H +-ATPases. These results are discussed in terms of recent findings on cv ATPases from bovine brain.
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  • 14
    ISSN: 1432-2048
    Keywords: V-ATPase-immunocytochemistry ; Pea cotyledon ; Plasma membrane ; Putative γ-TIP ; Pyrophosphatase ; Tonoplast markers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The tonoplast is usually characterized by the presence of two electrogenic proton pumps: a vacuolartype H+-ATPase and a pyrophosphatase, as well as a putative water-channel-forming protein (γ-TIP). Using a post-embedding immunogold labelling technique, we have detected the presence of these transport-protein complexes not only in the tonoplast, but also in the plasma membrane and trans Golgi elements of maturing pea (Pisum sativum L.) cotyledons. These ultrastructural observations are supported by Western blotting with highly purified plasma-membrane fractions. In contrast to the vacuolar-type H+-ATPase, whose activity was not measurable, considerable pyrophosphatase activity was detected in the plasma-membrane fraction. These results are discussed in terms of a possible temporary repository for tonoplast proteins en route to the vacuole.
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Planta 141 (1978), S. 83-92 
    ISSN: 1432-2048
    Keywords: Cell wall regeneration ; Chlamydomonas ; Protoplasts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Protoplasts from Chlamydomonas smithii prepared by the action of C. reinhardii gamete autolysine have been studied with respect to cell wall regeneration. “Natural” protoplasts within sporangia were also investigated for purposes of comparison. In both cases a new cell wall is completed within 2–3 h of the onset of regeneration. The first visible stages of wall regeneration are to be seen after 40–60 min as a fine fringe outside of the plasmalemma. The development of the typical “central triplet” follows within the next 1 h. Cell wall regeneration is reversibly inhibited by cycloheximide (10μg ml-1) and reversibly disturbed by concanavalin A (50 μg ml-1). Actinomycin D at concentration over 100μg ml-1 also inhibit but the inhibition is irreversible and peculiar membrane effects are observed. Chelators (ethylenediamine tetraacetic acid; ethyleneglycol-bis-aminoethyl ether) and 2-deoxyglucose slightly retard or have no effect on cell wall regeneration.
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Planta 107 (1972), S. 131-144 
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Naked swarmers of Cladophora have been collected and wall synthesis and development have been followed using the techniques of freeze-etching and sectioning. Swarmers frozen after 9 hours liberation have lost their flagella, developed the characteristic fibrous layer and show the initial stages of wall production. Both the first formed (randomly oriented) and the later (more ordered) microfibrils appear to have a distinct granular texture. Occasionally linear arrays of granules up to 4 μm long may be seen. After 5 days settling a thick wall composed of almost transversely oriented microfibrils is present and a rhizoid is pushed out. Also characteristic of this stage is the central localisation of cell components and peripheral vacuolar distribution. Longitudinally oriented microtubules also reappear at this stage having been absent during carlier wall formation. A possible relationship between the cortical microtubules of the motile swarmer and the development of the fibrous layer is suggested.
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  • 17
    Electronic Resource
    Electronic Resource
    Springer
    Naturwissenschaften 76 (1989), S. 15-23 
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
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  • 18
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Prior to fusion, gametes ofChlamydomonas reinhardii discard their cell walls. This naturally occuring phenomenon has provided the basis for a method of protoplast isolation from both gametes and vegetative cells within the genusChlamydomonas. When synchronized cultures of compatibleChlamydomonas gametes are mixed it is possible, after removal of the cells, to obtain a solution having a high cell wall lytic activity. That vegetative and gamete cells after treatment with this “gamete-autolysine” are indeed protoplasts has been proved by various light and electron microscopical methods. The species specifity of this autolysine, its difference to the previously described “sporangialautolysine” (Schlösser 1966) and furthermore its use in the large scale production of protoplasts is also described. Since this wall autolysine is a factor produced by the cells themselves at a particular stage in their life cycle it represents a non-foreign agent in contrast to all other enzymic methods previously employed for protoplast isolation.
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  • 19
    Electronic Resource
    Electronic Resource
    Springer
    Plant molecular biology 38 (1998), S. 49-76 
    ISSN: 1573-5028
    Keywords: clathrin-coated vesicles ; COP-coated vesicles ; dense vesicles ; endocytosis ; vacuolar protein targeting ; v/t-SNAREs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Secretion, endocytosis and transport to the lytic compartment are fundamental, highly coordinated features of the eukaryotic cell. These intracellular transport processes are facilitated by vesicles, many of which are small (100 nm or less in diameter) and ‘coated’ on their cytoplasmic surface. Research into the structure of the coat proteins and how they interact with the components of the vesicle membrane to ensure the selective packaging of the cargo molecules and their correct targeting, has been quite extensive in mammalian and yeast cell biology. By contrast, our knowledge of the corresponding types of transport vesicles in plant cells is limited. Nevertheless, the available data indicate that a considerable homology between plant and non-plant coat polypeptides exists, and it is also suggestive of a certain similarity in the mechanisms underlying targeting in all eukaryotes. In this article we shall concentrate on three major types of transport vesicles: clathrin-coated vesicles, COP-coated vesicles, and ‘dense’ vesicles, the latter of which are responsible for the transport of vacuolar storage proteins in maturing legume cotyledons. For each we will summarize the current literature on animal and yeast cells, and then present the relevant data derived from work on plant cells. In addition, we briefly review the evidence in support of the ‘SNARE’ hypothesis, which explains how vesicles find and fuse with their target membrane.
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  • 20
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 90 (1976), S. 369-379 
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Stem segments ofPisum sativum L. when plasmolyzed with mannitol show a continued secretion through the dictyosome-vesicle pathway. While incorporation into the cell wall is inhibited during plasmolysis, the secreted material, expressed as an ethanol insoluble fraction of the homogenate supernatant after removal of cell organelles and cell wall, apparently accumulates between the protoplast and cell wall. The inhibition of cell wall incorporation and the accumulation of ethanol insoluble material may be reversed upon removal of the mannitol. The relevance of this effect for nonplasmolyzing turgor changes is discussed.
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