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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Planta 161 (1984), S. 459-464 
    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
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Planta 164 (1985), S. 56-62 
    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.
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  • 3
    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.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 189 (1995), S. 238-248 
    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.
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