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 ²²Na⁺ within 1 h of exposure to isotope. Cytoplasmlc Na⁺ concentration and Na⁺ influx were greater in C. corallina than in C. longifolla 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 218% in C. coralllna and 320% in C. longifolia. In both species externally applied Li⁺ inhibited Na⁺ efflux at pH 5 but not at pH 7. Na⁺ etflux was not significantly inhibited by amiloride.