Direct Determination of pH in the stomatal complex of Commelina.

The vacuolar pH of individual cells of the epidermis of intact leaves of Commelina communis L. has been determined using pH sensitive microelectrodes. The results show that the pH of the guard cells increases by approximately 0.5 units during stomatal opening. The changes in vacuolar pH mirror the changes in vacuolar potassium concentration that occur during stomatal movements.