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. R-L 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 R-L. These results suggest that GCCs supply ATP to the cytosol under R-L, and that the ATP is utilized by the plasma membrane H+-ATPase for H+ pumping.