Guard-cell chloroplasts provide ATP required for H(+) pumping in the plasma membrane and stomatal opening.

To elucidate the role of guard-cell chloroplasts (GCCs) in stomatal movement, we investigated the effects of oligomycin, an inhibitor of oxidative phosphorylation, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosystem II, on fusicoccin (FC)-induced H(+) pumping and stomatal opening. FC was found to induce H(+ )pumping in guard-cell protoplasts (GCPs) from Vicia faba and stomatal opening in the epidermis of Commelina benghalensis; and, red light (RL) slightly stimulated these responses. Oligomycin strongly inhibited the pumping and stomatal opening in the dark. RL partially reversed the inhibitions, and DCMU decreased the effect of RL. FC activated the plasma membrane H(+)-ATPase (EC 3.6.1.35) in GCPs similarly irrespective of these treatments, indicating that the H(+)-ATPase activity was not the limiting step in H(+) pumping. Oligomycin significantly decreased the ATP content in GCPs in the dark. RL partially reversed this effect, and DCMU eliminated the effect of RL. A significant part of the ATP produced by photophosphorylation to H(+) pumping was indicated under RL. These results suggest that GCCs supply ATP to the cytosol under RL, and that the ATP is utilized by the plasma membrane H(+)-ATPase for H(+) pumping.