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  • 1
    Electronic Resource
    Electronic Resource
    Kinetics of amyloplast sedimentation in gravistimulated maize coleoptiles (1984)
    Springer
    Planta 161 (1984), S. 459-464 
    Details
    ISSN: 1432-2048
    Keywords: Amyloplast sedimentation ; Coleoptile (gravistimulation) ; Graviperception ; Zea (graviperception)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Inner mesophyll cells from coleoptiles of Zea mays L. cv. Merit were fixed after varying periods of gravistimulation. A statistically significant amount (17–21%) of amyloplast sedimentation occurred in these cells after 30 s of gravistimulation. The presentation time is approx. 40 s or less. The accumulation of amyloplasts near the new lower wall shows a linear relationship to the logarithm of the gravistimulation time (r=0.92 or higher). The intercept of this line with the baseline value of amyloplasts in vertical coleoptiles indicates that the number of amyloplasts on the new lower wall begins increasing 11–15 s after the onset of gravistimulation. Direct observations of living cells confirm that many amyloplasts sediment within less than 15–30 s. These rapid kinetics are consistent with the classical statolith hypothesis of graviperception involving the sedimentation of amyloplasts to the vicinity of the new lower wall.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00394578
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  • 2
    Electronic Resource
    Electronic Resource
    Surface charge on isolated maize-coleoptile amyloplasts (1983)
    Springer
    Planta 157 (1983), S. 511-517 
    Details
    ISSN: 1432-2048
    Keywords: Amyloplast ; Ferritin, cationised ; Graviperception and statolith charge ; Starch ; Zeta potential ; Zea (amyloplasts, surface charge)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Whole amyloplasts were isolated from Zea mays L. coleoptiles. Electron microscopy confirmed that their envelopes consisted of two intact membranes. Their surface charge was quantified through electrokinetic measurements employing a vertically oriented cataphoresis cell. Amyloplasts from coleoptiles of different ages (5–9 d) and degree of exposure to light (0–9 d) all had negative zeta potentials (mean of -19.4 mV). Isolated starch granules had comparable values. The net negative surface charge was confirmed ultrastructurally by the binding of cationised ferritin to both amyloplasts and starch grains. Cationised ferritin tagged with a fluorescent label (fluorescein isothiocyanate) showed binding to some amyloplasts but not to starch grains. These results are discussed in the context of a hypothesized role for statolith charge in plant graviperception.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396881
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  • 3
    Electronic Resource
    Electronic Resource
    Divergent regulation of stomatal initiation and patterning in organ and suborgan regions of the Arabidopsis mutants too many mouths and four lips (1998)
    Springer
    Planta 205 (1998), S. 522-530 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Arabidopsis (mutants) ; Cell differentiation ; Epidermis ; Mutant (Arabidopsis ; stoma) ; Stoma (development ; patterning)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Stomata are consistently patterned so that they are not in contact. This patterning is violated in the too many mouths (tmm) and four lips (flp) mutations of Arabidopsis thaliana (L.) Heynh. which have stomatal clusters in the first-formed leaves. To clarify the function of both genes in stomatal initiation and patterning, the phenotypes of many different organs were quantified. The flp mutation affects dorsiventral and cylindrical organs differentially with respect to the frequency of clustering. The tmm mutation has a more complex region-specific phenotype in that some regions lack stomata entirely, other regions have excess stomata, and the flower stalk exhibits an apex-to-base gradient from excess to no stomata. This suggests that TMM represents an unusual type of gene regulating plant cell development in that it can either influence stomatal initiation in a positive or negative fashion depending on region. Since the frequencies of initiation and clustering can be uncoupled in tmm, these two functions are under separate region-specific control. Analysis of double mutants shows that tmm and flp in some cases show region-specific interactions in both cluster formation and initiation, and that there may be subpopulations of stomata under different genetic control.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050351
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  • 4
    Electronic Resource
    Electronic Resource
    Cytoplasmic streaming affects gravity-induced amyloplast sedimentation in maize coleoptiles (1985)
    Springer
    Planta 164 (1985), S. 56-62 
    Details
    ISSN: 1432-2048
    Keywords: Amyloplast sedimentation ; Coleoptile (amyloplasts) ; Cytoplasmic streaming ; Graviperception ; Zea (graviperception)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Living maize (Zea mays L.) coleoptile cells were observed using a horizontal microscope to determine the interaction between cytoplasmic streaming and gravity-induced amyloplast sedimentation. Sedimentation is heavily influenced by streaming which may (1) hasten or slow the velocity of amyloplast movement and (2) displace the plastid laterally or even upwards before or after sedimentation. Amyloplasts may move through transvacuolar strands or through the peripheral cytoplasm which may be divided into fine cytoplasmic strands of much smaller diameter than the plastids. The results indicate that streaming may contribute to the dynamics of graviperception by influencing amyloplast movement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00391025
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  • 5
    Electronic Resource
    Electronic Resource
    The density of apical cells of dark-grown protonemata of the mossCeratodon purpureus (2000)
    Springer
    Protoplasma 211 (2000), S. 225-233 
    Details
    ISSN: 1615-6102
    Keywords: Cell density ; Ceratodon purpureus ; Protoplasts ; Stereology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Determinations of plant or algal cell density (cell mass divided by volume) have rarely accounted for the extracellular matrix or shrinkage during isolation. Three techniques were used to indirectly estimate the density of intact apical cells from protonemata of the mossCeratodon purpureus. First, the volume fraction of each cell component was determined by stereology, and published values for component density were used to extrapolate to the entire cell. Second, protonemal tips were immersed in bovine serum albumin solutions of different densities, and then the equilibrium density was corrected for the mass of the cell wall. Third, apical cell protoplasts were centrifuged in low-osmolarity gradients, and values were corrected for shrinkage during protoplast isolation. Values from centrifugation (1.004 to 1.015 g/cm3) were considerably lower than from other methods (1.046 to 1.085 g/cm3). This work appears to provide the first corrected estimates of the density of any plant cell. It also documents a method for the isolation of protoplasts specifically from apical cells of protonemal filaments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01304490
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  • 6
    Electronic Resource
    Electronic Resource
    Stomatal pore and cuticle formation inFunaria (1983)
    Springer
    Protoplasma 116 (1983), S. 1-13 
    Details
    ISSN: 1615-6102
    Keywords: Cuticle ; Peristomatal transpiration ; Stomata ; Ultrastructure ; Funaria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cuticle and pore development in the guard cells ofFunaria were investigated with the electron microscope. Pore cuticle formation is simultaneous with the creation of the pore itself. The morphology of the pore cuticle is unlike that of any cuticle described in the literature. It has many lamellae which are penetrated by electron dense fibrils. Three different cuticular morphologies exist from the pore to the subsidiary cell walls. The cuticles on the pore and outer walls contain fibrils that sometimes reach to the surface. The subsidiary cell cuticle lacks fibrils altogether. It is hypothesized that (1) cuticularization of the middle lamella contributes to ventral wall separation and (2) differences in extent of cuticular fibrils are related to greater water loss from stomata than from subsidiary cells (peristomatal transpiration).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01294225
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Microtubule distribution in gravitropic protonemata of the mossCeratodon (1990)
    Springer
    Protoplasma 159 (1990), S. 60-69 
    Details
    ISSN: 1615-6102
    Keywords: Gravity ; Microtubules ; Protonema ; Ceratodon ; Gravitropism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Tip cells of dark-grown protonemata of the mossCeratodon purpureus are negatively gravitropic (grow upward). They possess a unique longitudinal zonation: (1) a tip group of amylochloroplasts in the apical dome, (2) a plastid-free zone, (3) a zone of significant plastid sedimentation, and (4) a zone of mostly non-sedimenting plastids. Immunofluorescence of vertical cells showed microtubules distributed throughout the cytoplasm in a mostly axial orientation extending through all zones. Optical sectioning revealed a close spatial association between microtubules and plastids. A majority (two thirds) of protonemata gravistimulated for 〉20 min had a higher density of microtubules near the lower flank compared to the upper flank in the plastid-free zone. This apparent enrichment of microtubules occurred just proximal to sedimented plastids and near the part of the tip that presumably elongates more to produce curvature. Fewer than 5% of gravistimulated protonemata had an enrichment in microtubules near the upper flank, whereas 14% of vertical protonemata were enriched near one of the side walls. Oryzalin and amiprophos-methyl (APM) disrupted microtubules, gravitropism, and normal tip growth and zonation, but did not prevent plastid sedimentation. We hypothesize that a microtubule redistribution plays a role in gravitropism in this protonema. This appears to be the first report of an effect of gravity on microtubule distribution in plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01326635
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  • 9
    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
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  • 10
    Electronic Resource
    Electronic Resource
    Ultrastructural analysis of cell component distribution in the apical cell ofCeratodon protonemata (1995)
    Springer
    Protoplasma 189 (1995), S. 238-248 
    Details
    ISSN: 1615-6102
    Keywords: Tip growth ; Stereology ; Protonemata ; Moss ; Ceratodon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A distinctive feature of tip-growing plant cells is that cell components are distributed differentially along the length of the cell, although most ultrastructural analyses have been qualitative. The longitudinal distribution of cell components was studied both qualitatively and quantitatively in the apical cell of dark-grown protonemata of the mossCeratodon. The first 35 μm of the apical cell was analyzed stereologically using transmission electron microscopy. There were four types of distributions along the cell's axis, three of them differential: (1) tubular endoplasmic reticulum was evenly distributed, (2) cisternal endoplasmic reticulum and Golgi vesicles were distributed in a tip-to-base gradient, (3) plastids, vacuoles, and Golgi stacks were enriched in specific areas, although the locations of the enrichments varied, and (4) mitochondria were excluded in the tipmost 5 μm and evenly distributed throughout the remaining 30 μm. This study provides one of the most comprehensive quantitative, ultrastructural analyses of the distribution of cell components in the apex of any tip-growing plant cell. The finding that almost every component had its own spatial arrangement demonstrates the complexity of the organization and regulation of the distribution of components in tip-growing cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01280178
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