Abstract
Internodal cells of a brackish water charophyte, Lamprothanium succinctum regulate their turgor pressure against changes in external osmotic pressure (turgor regulation). Vacuolar osmotic pressure is maintained by Na+, K+ and Cl- and modified by those ions during the turgor regulation. It was studied whether or not the modified vacuolar ionic concentrations were regulated after the recovery of turgor pressure. Upon hypotonic treatment, only a concentration of vacuolar KCl decreased during the turgor regulation. Then the vacuolar concentration of K+ increased with a concomitant decrease in vacuolar Na+ concentration under constant turgor pressure. Upon hypertonic treatment, both K+ and Na+ increased with Cl- during the recovery of turgor pressure and the increased concentrations of both K+ and Na+ did not change under constant turgor pressure. These results suggest that internodal cells can regulate the vacuolar concentration of K+ against its decrease, maintaining constant turgor pressure with releasing vacuolar Na+.
