Metabolic Inhibitors Block ABA-Induced Stomatal Closure

Closure of stomata of Commelina communis L. leaf epidermis caused by abscisic acid (ABA) was inhibited by sodium azide, potassium cyanide and hypoxic conditions. Azide was more effective than cyanide at low concentrations, but the cyanide effect could be enhanced by addition of salicylhydroxamic acid, providing indirect evidence for cyanide-resistant respiration in epidermal tissue. Azide also inhibited ABA-induced closure of ‘ isolated’ stomata and shrinkage of guard cell protoplasts. The results indicate that metabolic energy is required for ABA action involving solute loss from the guard cells. Possible mechanisms of action are discussed.