Active chloride transport in the leaf epidermis of Commelina communis in relation to stomatal activity.

A chloride selective micro-electrode has been used to determine vacuolar chloride concentrations in individual cells of the leaf epidermis of Commelina communis. When the stomata were open a gradient in chloride concentration across the stomatal complex was observed with the highest concentration in the guard cells. On stomatal closure the chloride gradient was reversed. Calculation of the driving forces on chloride indicated that active transport of chloride was occurring during both stomatal opening and closure. This transport appeared to be energetically independent of the transport of potassium. These results are discussed in relation to the behaviour of other anions during stomatal movements.

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.

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

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.