SODIUM-CHLORIDE COMPARTMENTATION IN LEAF VACUOLES OF THE HALOPHYTE SUAEDA-MARITIMA (L) DUM AND ITS RELATION TO TONOPLAST PERMEABILITY

Single channel properties, whole vacuole currents and proton pumping capacity were investigated in the intact vacuoles and membrane patches of leaf tonoplast from the halophyte Suaeda maritima. ATP-dependent proton pumping capacity was similar to non-halophytes whether the plants were or were not grown with added sodium chloride (200 mM). The most abundant ion channel was inward rectifying and had a single channel conductance of 58 pS in symmetrical KCl solutions (100 mM) to 170 pS using physiological conditions (50/150 mM KCl/NaCl cytoplasmic side, 50/450 mM KCl/NaCl vacuolar side). The channel showed all the characteristics of the SV type channel described in many other species. In the open state these channels caused tonoplast conductances in excess of 0.5 nS m-2 but conductances were much lower using physiological ion concentrations and membrane potentials. In spite of the poor selectivity and the potentially large tonoplast conductance it is calculated that compartmentation of NaCl in leaf vacuoles can be sustained by about 30% of ATP-dependent proton pumping capacity. The results do not indicate any special adaptation of the tonoplast ion channels in the halophyte.