Differential Abaxial and Adaxial Stomatal Responses to Indole‐3‐acetic Acid Incommelina Communisl.

S ummary The responses of abaxial and adaxial stomata to indole‐3‐acetic acid (IAA) were examined on isolated epidermis of Commelina communis. IAA was remarkably effective in producing wide adaxial apertures accompanied by a massive increase in the stomatal K + content, and, therefore, eliminating the normal disparity in both the opening and K + accumulation between abaxial and adaxial stomatal cells; it also reversed the suppressive effect of abscisic acid. IAA may affect the transport of K + either directly or indirectly through its control of the proton pump. If the IAA‐induced adaxial opening and K + accumulation is a result of a stimulation of proton extrusion, then, under normal conditions, the proton pump should operate at a lower capacity in adaxial than in abaxial guard cells. Alternatively, the lack of stomatal sensitivity to IAA in the presence of Na + ions suggests a possibility that it might have a direct effect on the K + transport. In either case, as reported here, an external supply of IAA would enhance K + accumulation in adaxial guard cells. The inherent disparity in opening and accompanied K + accumulation between abaxial and adaxial stomatal cells is postulated to be a result of differences in endogenous auxin level between the two epidermes and/or of differential adaxial and abaxial sensitivity to auxin. Thus, the results indicate a hormonal basis for the differential adaxial and abaxial opening.