Changes in sodium and potassium in Nitellopsis cells treated with transient salt stress
Abstract.Nitellopsis cells grown in fresh water have a relatively low cytoplasmic Na+ (11 mol m−3) and high cytoplasmic K+ (90 mol m−3) content. A 30-min treatment with 100 mol m−3 external NaCl resulted in a high [Na+]c (90 mol m−3) and a low [K+]c (33 mol m−3), Subsequent addition of external Ca2+ (10 mol m−3) prevented Na+ influx and then [Na+]c decreased slowly. Changes in [K+]c were opposite to [Na+]c. During the recovery time vacuolar Na+ increased, while vacuolar K+ decreased. Since all these processes proceeded also under ice-cold conditions, the restoration of original cytoplasmic ion compositions is suggested to be a passive nature. The notion that the passive movement of ions across the tonoplast can act as an effective and economic mechanism of salt tolerance under transient or under mild salt stress conditions is discussed.