A study of potassium gradients in the epidermis of intact leaves of Commelina communis L. in relation to stomatal opening

Abstract

Potassium sensitive microelectrodes have been used to determine the potassium content of individual epidermal cells in intact leaves of C. communis L. Large gradients of potassium across the stomatal complex were observed. When the stomata were open a stepwise decrease in vacuolar potassium content from the guard cells outwards was found. With the stomata closed a gradient in the opposite direction was observed, with the potassium content of the guard cells much lower than that of the surrounding cells. Electrical potential differences between the cells were determined enabling driving forces on potassium to be calculated. The results indicate that the potassium gradients are maintained against the electrochemical gradient and that potassium transport both into and out of the guard cells is an active process. Potassium transport between the subsidiary cells also appears to be active. Potassium fluxes into the guard cell during stomatal opening were calculated and found to be relatively high. The implications of this are discussed.