NA+ FLUXES IN CHARA UNDER SALT STRESS

The influx and efflux of Na+ across the plasma membrane of Chara corallina and Chara longifolia were examined under mild salt stress conditions. Na+ influx was found to be rapid in both species with the freely exchangeable cytoplasmic Na+ coming into isotopic equilibrium with external Na-22(+) within 1 h of exposure to isotope. Cytoplasmic Na+ concentration and Na+ influx were greater in C. corallina than in C. longifolia under the same conditions. Na+ influx across the tonoplast was much lower than the flux across the plasma membrane. Na+ efflux was stimulated at pH 5 relative to pH 7 by 216% in C. corallina and 320% in C. longifolia. In both species externally applied Li+ inhibited Na+ efflux at pH 5 but not at pH 7. Na+ efflux was not significantly inhibited by amiloride.