The effect of divalent cations on Na⁺ tolerance in Charophytes. II: Chara corallina

Abstract The freshwater Charophyte Chora corallina dies when subjected to 70 molm⁻³ NaCl if the Ca²⁺ concentration is 0.1 mol m ⁻³. This stress is accompanied by a depolarization of the cell to a membrane potential more positive than E_K, a net influx of Na⁺ into the vacuole, and a net loss of K⁺ from the vacuole. Raising the Ca²⁺ concentration to 7 mol m ⁻³ in the presence of elevated Na⁺ restores the Na⁺ to Ca²⁺ ratio to 10: 1 as in the control solution, and results in enhanced survival even though turgor is not regulated. Mg²⁺ is not a good substitute for Ca²⁺. It is suggested that the main reason that C. corallina fails to occupy saline habitats is its failure to regulate turgor, not sensitivity to Na ⁺, since the latter is similar to that seen in C. buckellii, which is found in saline habitats.