Effect of Na+ on Ca2+-Binding on the Plasma Membrane of Barley Mesophyll Cells: an Electrophoretic Study

Abstract

It is well known that Ca ions play an important role in mitigating the detrimental effects of high NaCl on plant growth (LaHaye and Epstein 1969, Greenway and Munns 1980, Kent and Lauchli 1985). Several reports suggest that external Na can displace Ca from the binding sites on the outer plasma membrane (PM) surface, which may be one of the primary responses to salt stress, leading to a disruption of membrane integrity and leakage of intracellular solutes; the mitigative effects of supplemental Ca may be related to the maintenance of membrane-associated Ca (LaHaye and Epstein 1969, Cramer et al. 1985, Lynch et al. 1987, Colmer et al. 1994). Cramer et al. (1985) and Lynch et al. (1987) attempted to determine whether Na displaced Ca from the plasma membrane of root cells of salt-sensitive glycophytes but failed to get any conclusive evidence, because they used an unsuitable fluorescent probe CTC for measurement of Ca bound to the cell surface (Lynch and Lauchli 1988). Recently, Yermiyahu et al. (1994), using Ca sorption technique, reported that Na ions reduced the amount of Ca sorbed to plasma membrane vesicles of salt-sensitive melon root cells. Our electrophoretic studies showed that Na ions could specifically (and nonspecifically) cause desorption of Ca from the outer plasma membrane surface of salt-sensitive tobacco cells (Murata et al. unpublished