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. 1976 Nov;58(5):608–613. doi: 10.1104/pp.58.5.608

Turgor Pressure Regulation in Valonia utricularis

Effect of Cell Wall Elasticity and Auxin 1

Ulrich Zimmermann a, Ernst Steudle a, Peter I Lelkes a
PMCID: PMC542267  PMID: 16659728

Abstract

The electrical membrane resistance ρ0 of the marine alga Valonia utricularis shows a marked maximum in dependence on the turgor pressure. The critical pressure, Pc, at which the maximum occurs, as well as its absolute value, ρ0max, are strongly volume-dependent. Both Pc and ρ0max, increase with decreasing cell volume. It seems likely, that these relationships reflect the elastic properties of the cell wall, because the volumetric elastic modulus, ε, is also volume-dependent, increasing hyperbolically with cell volume. Both Pc and ρ0max can be affected by external application of indole-3-acetic acid at concentrations of 2·10−7m to 2 ·10−5m. The critical pressure is shifted by 1.2 to 6 bars toward higher pressures and the maximum membrane resistance increased up to 5.6-fold. During the course of the experiments (up to 4 hours), however, IAA had no effect on the volumetric elastic modulus, ε.

The maximum in membrane resistance is discussed in terms of a pressure-dependent change of potassium fluxes. The volume dependence of Pc and ρ0max suggests that not only turgor pressure but also ε must be considered as a regulating parameter during turgor pressure regulation. On this basis a hypothesis is presented for the transformation of both, a pressure signal and of changes in the elastic properties of the cell wall into alterations of ion fluxes. It is assumed that the combined effects of tension and compression of the membranes as well as the interaction between membrane and cell wall opposingly change the number of transport sites for K+ providing a turgor-sensing mechanism that regulates ion fluxes. The IAA effects demonstrated are consistent with this view, suggesting that the basic mechanisms for turgor pressure regulation and growth regulation are similar.

Any relation connecting growth rate with turgor pressure should be governed by two parameters, i.e. by a yielding pressure, at which cell growth starts, and by the critical pressure, at which it ceases again.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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