High salt‐treatment‐induced Na⁺ extrusion and low salt‐treatment‐induced Na⁺ accumulation in suspension‐cultured cells of the mangrove plant, <i>Bruguiera sexangula</i>

Abstract

Abstract A suspension‐cultured cell strain of the mangrove plant ( Bruguiera sexangula ) was established from a callus culture and maintained in an amino acid medium in the absence of NaCl. NaCl non‐adapted cells were transferred to media containing 0–200 m m NaCl. The initial growth rate decreased gradually with increasing salt concentrations. However, at up to 150 m m NaCl, cell number growth at the highest point was almost the same as that at lower salt concentrations. Cells even continued to grow in the presence of 200 m m NaCl. Cells incubated in a medium containing 50 m m NaCl for 3 weeks accumulated Na + , while those incubated in 150 m m NaCl for 2 d showed only a transient increase in Na + and Cl – concentrations. In the latter treatment, the intracellular concentration of Na + returned to the original low level within 2 weeks. It took a longer time for Cl – to return to its original level. As a result, the Na + and Cl – concentrations in cells cultured with 50 m m NaCl were much larger than those in cells cultured with 150 m m NaCl. The intracellular distribution of ions after transfer to the medium containing 150 m m NaCl was analysed by isolating the vacuoles. Treatment with amiloride, an inhibitor of the Na + /H + antiporter, suppressed the recovery of Na + to the original level in the cells. Treatment with 150 m m NaCl for 3 d stimulated the activities of both the vanadate‐dependent H + ‐ATPase and the Na + /H + antiporter in the plasma membrane fraction.