Inhibition of the stomatal blue light response by verapamil at high concentration

Blue light-dependent proton pumping in guard cell protoplasts and light-induced stomatal opening in the epidermis were inhibited by 1 mM verapamil, a Ca2+ channel blocker. Proton pumping and stomatal opening induced by fusicoccin, an activator of plasma membrane proton pump, were not inhibited by verapamil. These results suggest that verapamil inhibits blue light signaling in guard cells without inhibiting the pump.