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  • 1
    Electronic Resource
    Electronic Resource
    pH gradients and cell polarity inPelvetia embryos (1991)
    Springer
    Protoplasma 163 (1991), S. 43-50 
    Details
    ISSN: 1615-6102
    Keywords: Embryogenesis ; Metabolic acid secretion ; Pelvetia ; pH gradient ; pH sensitive microelectrode ; Polarity ; Tip growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Endogenous pH profiles were measured around single fertilized eggs of the brown algaPelvetia during the earliest stages of development. Profiles were constructed by measuring the pH near the cell surface at several positions using a pH sensitive microelectrode. Transcellular pH differences in the medium surrounding zygotes were detected soon after fertilization, as the developmental axis was being formed. The future rhizoid end of the cell was relatively alkaline and the presumptive thallus was acidic. At germination and throughout the first 5 d of embryogenesis, the apex of the elongating rhizoid was alkaline with respect to more distal regions. However, conditions that dissipated or reversed this extracellular pH gradient had little or no effect on polarization or growth, indicating that the gradient was not essential for early development. Inhibition of respiratory electron transport by cyanide and antimycin A eliminated the pH gradient, while uncouplers of oxidative phosphorylation [2,4-dinitrophenol (DNP) and carbonylcyanide m-chlorophenylhydrazone (CCCP)] stimulated acidification of the thallus regions. Proton ATPase inhibitors had no effect. Acidification, therefore, is not generated by ATP-dependent proton pumps in the plasma membrane, and instead probably reflects secretion of metabolic acids. Localized metabolism may establish an internal pH gradient that controls regional differentiation, and we are presently investigating this possibility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01323405
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  • 2
    Electronic Resource
    Electronic Resource
    Localized membrane-wall adhesions inPelvetia zygotes (1996)
    Springer
    Protoplasma 190 (1996), S. 39-52 
    Details
    ISSN: 1615-6102
    Keywords: F-actin ; Plasma membrane ; Cell wall ; Calcium ; Hydrogen ; Peptide RGD ; Tip growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Membrane-wall adhesions in zygotes of the brown algaPelvetia were visualized following plasmolysis. Strands of cytoplasm remained firmly attached to the cell wall at discrete adhesion sites during plasmolysis. Adhesion sites were uniformly distributed in ungerminated zygotes, but were concentrated in the apical 5 μm of the elongating rhizoid in germinated zygotes. Few adhesions were detected along the flanks of the rhizoid or in the thallus region of germinated zygotes. The structure, physiology and function of apical adhesions in the rhizoid were characterized. F-actin was found at adhesion sites in plasmolyzed zygotes labeled with rhodamine phalloidin, and disruption of cortical F-actin reduced the number of adhesions. Manipulation of cytosolic H+ and Ca2+ activities also disrupted adhesions. On the extracellular surface, the number of adhesions was reduced by inhibition of cellulose synthesis, protease cleavage of wall proteins, and changes in extracellular H+ and Ca2+ activities. Chronic treatment with the synthetic peptide RGDS, which prevents cell adhesion in fibroblasts, also reduced adhesion number. The number of adhesions per cell did not correlate with growth rate, but was inversely correlated with the ability to establish new rhizoid growth sites. The results indicate that membrane wall adhesions containing F-actin on the cytoplasmic face are localized in the growing rhizoid apex. The adhesions may be structurally related to focal adhesions in animal cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01281193
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  • 3
    Electronic Resource
    Electronic Resource
    Microtubule orientation and dynamics in elongating characean internodal cells following cytosolic acidification, induction of pH bands, or premature growth arrest (1997)
    Springer
    Protoplasma 197 (1997), S. 188-198 
    Details
    ISSN: 1615-6102
    Keywords: Acid bands ; Alkaline bands ; Characeae ; Internodes ; Microinjection ; Microtubule dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cortical microtubules (MTs) at indifferent zones in immatureNitella internodes were investigated by injection of fluorescently tagged sheep brain tubulin into living cells and by immunofluorescence on fixed material. Nearly identical MT patterns and numbers were detected with the two techniques, indicating that sheep brain tubulin incorporated into all cortical MTs. MTs were aligned transversely to the long axis of the cell and approximately one MT was present every micrometer of longitudinal cell distance. Treatment of internodes with propionic acid to acidify cytosolic pH caused depolymerization of MTs and an increase in the unpolymerized tubulin pool. Transfer of young, vigorously elongating cells to media inducing premature growth cessation resulted in a slight decrease in microtubule numbers but did not significantly alter microtubule orientation patterns or microtubule lifespans. MTs remained transverse for days following growth cessation before finally assuming a more random alignment characteristic of mature, non-growing internodes. No differences in MT numbers, orientation, or dynamics were detected between acid and alkaline bands in internodes incubated in a band-inducing medium. Thus, properties of cortical MT arrays were not closely coupled to growth status or to regional differences in cellular physiology associated with pH banding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01288028
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Division patterns in the thallus ofPelvetia compressa embryos and the effects of gravity (1998)
    Springer
    Protoplasma 203 (1998), S. 112-117 
    Details
    ISSN: 1615-6102
    Keywords: Brown alga ; Cleavage plane ; Embryogenesis ; Gravity ; Microtubules ; Spindle orientation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The pattern of divisions in the thallus ofPelvetia compressa embryos was determined with respect to the embryonic growth axis. To detect all possible division planes, embryos were viewed from two vantages which permitted observations of (1) the thallus pole and (2) the longitudinal embryonic profile. Following formation of rhizoid and thallus cells by any asymmetrical division transverse to the embryonic axis that is established prior to any divisions, the thallus cell divided twice along the embryonic axis (axial divisions) in orthogonal planes, and then divided transverse to the growth axis. This division pattern produced an eight-cell thallus with four cells in each of two layers. The spatial relation between gravity and the first axial division was investigated, and gravity was found to have little effect on the alignment of this division. The reproducible pattern of divisions in the thallus indicates spatial control of spindle positioning.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01280593
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    Paper (German National Licenses)
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