Calcium Inhibits Ion-Stimulated Stomatal Opening in Epidermal Strips ofCommelina communisL.

Abstract

Inoue, H. and Katoh, Y. 1987. Calcium inhibitsion-stimulated stomatal opening in epidermal strips of Commelina communis L.—J. exp. Bot. 38: 142–149. Ca²⁺ suppressed both the ion-stimulated stomatal opening and H⁺ extrusion of pre-illuminated epidermal strips isolated from Commelina communis L. In the absence of Ca²⁺, the rate of H⁺ release was 18 nmol H⁺ cm^–2 h^–1 per epidermal strip unit area in 150 mol m^–3 KCL at pH 7·4. Half-maximum inhibition of stomatal opening was observed with 220 mmol m^–3 of Ca²⁺. The hexavalent dye, ruthenium red, showed concentration-dependent prevention of the inhibition by Ca²⁺ of the ion-stimulated stomatal opening. The effect of ruthenium red was non-competitive, and the K₁ for the calcium inhibition was found to be 3·6 mmol m^–3. The calcium inhibition of H⁺ extrusion was also prevented by ruthenium red. These results suggest that Ca²⁺ inhibits the activity of electrogenic H⁺ translocating ATPase of the guard cell plasma membrane and leads to the suppression of stomatal opening.