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  • 1
    Electronic Resource
    Electronic Resource
    Macromolecular differentiation of Golgi stacks in root tips ofArabidopsis andNicotiana seedlings as visualized in high pressure frozen and freeze-substituted samples (1990)
    Springer
    Protoplasma 157 (1990), S. 75-91 
    Details
    ISSN: 1615-6102
    Keywords: Cryofixation ; Golgi ; Root cap ; Secretion ; Slime
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The plant root tip represents a fascinating model system for studying changes in Golgi stack architecture associated with the developmental progression of meristematic cells to gravity sensing columella cells, and finally to “young” and “old”, polysaccharideslime secreting peripheral cells. To this end we have used high pressure freezing in conjunction with freeze-substitution techniques to follow developmental changes in the macromolecular organization of Golgi stacks in root tips ofArabidopsis andNicotiana. Due to the much improved structural preservation of all cells under investigation, our electron micrographs reveal both several novel structural features common to all Golgi stacks, as well as characteristic differences in morphology between Golgi stacks of different cell types. Common to all Golgi stacks are clear and discrete differences in staining patterns and width of cis, medial and trans cisternae. Cis cisternae have the widest lumina (∼30 nm) and are the least stained. Medial cisternae are narrower (∼20 nm) and filled with more darkly staining products. Most trans cisternae possess a completely collapsed lumen in their central domain, giving rise to a 4–6 nm wide dark line in cross-sectional views. Numerous vesicles associated with the cisternal margins carry a non-clathrin type of coat. A trans Golgi network with clathrin coated vesicles is associated with all Golgi stacks except those of old peripheral cells. It is easily distinguished from trans cisternae by its blebbing morphology and staining pattern. The zone of ribosome exclusion includes both the Golgi stack and the trans Golgi network. Intercisternal elements are located exclusively between trans cisternae of columella and peripheral cells, but not meristematic cells. In older peripheral cells only trans cisternae exhibit slime-related staining. Golgi stacks possessing intercisternal elements also contain parallel rows of freeze-fracture particles in their trans cisternal membranes. We propose that intercisternal elements serve as anchors of enzyme complexes involved in the synthesis of polysaccharide slime molecules to prevent the complexes from being dragged into the forming secretory vesicles by the very large slime molecules. In addition, we draw attention to the similarities in composition and apparent site of synthesis of xyloglucans and slime molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01322640
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Comparison of the ultrastructure of conventionally fixed and high pressure frozen/freeze substituted root tips ofNicotiana andArabidopsis (1990)
    Springer
    Protoplasma 157 (1990), S. 64-74 
    Details
    ISSN: 1615-6102
    Keywords: Cryofixation ; Tobacco ; Ultrarapid freezing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary To circumvent the limitations of chemical fixation (CF) and to gain more reliable structural information about higher plant tissues, we have cryofixed root tips ofNicotiana andArabidopsis by high pressure freezing (HPF). Whereas other freezing techniques preserve tissue to a relatively shallow depth, HPF in conjunction with freeze substitution (FS) resulted in excellent preservation of entire root tips. Compared to CF, in tissue prepared by HPF/FS: (1) the plasmalemma and all internal membranes were much smoother and often coated on the cytoplasmic side by a thin layer of stained material, (2) the plasmalemma was appressed to the cell wall, (3) organelle profiles were rounder, (4) the cytoplasmic, mitochondrial, and amyloplast matrices were denser, (5) vacuoles contained electron dense material, (6) microtubules appeared to be more numerous and straighter, with crossbridges observed between them, (7) cisternae of endoplasmic reticulum (ER) were wider and filled with material, (8) Golgi intercisternal elements were more clearly resolved and were observed between both Golgi vesicles and cisternae, and (9) larger vesicles were associated with Golgi stacks. This study demonstrates that HPF/FS can be used to successfully preserve the ultrastructure of relatively large plant tissues without the use of intracellular cryoprotectants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01322639
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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