Inhibition of the Stomatal Blue Light Response by Verapamil at High Concentration

Blue light-dependent proton pumping in guard cell protoplastsand light-induced stomatal opening in the epidermis were inhibitedby 1 mM verapamil, a Ca²⁺ channel blocker. Proton pumping andstomatal opening induced by fusicoccin, an activator of plasmamembrane proton pump, were not inhibited by verapamil. Theseresults suggest that verapamil inhibits blue light signalingin guard cells without inhibiting the pump. (Received January 6, 1997; Accepted March 26, 1997)