Light-dependent Influx and Efflux of Potassium of Guard Cells during Stomatal Opening and Closing

Stomata in epidermal strips of Vicia faba opened in light and closed in darkness when floated on dilute K(+) solutions. Opening and closing, respectively, paralleled the fluxes of labeled K(+) into and out of the strips. The gain and loss of K(+) by the strips were shown by colbaltinitrite stain to be centered at guard cells. Intact epidermal cells, however, appeared to take up K(+), complicating interpretation of the data.The specific requirement of K(+) for stomatal opening in light appeared to be related to the specific uptake of K(+). There was little or no light stimulation of opening in strips on Na(+), nor was there stimulation of Na(+) uptake. The marked light stimulation of opening on K(+) was generally matched by stimulation of K(+) uptake.Anaerobiosis markedly reduced opening in leaf discs but not in strips. Under anaerobic conditions, opening in strips was not appreciably affected by 3(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) but was completely inhibited by carbonyl cyanide m-chlorophenylhydrazone plus diuron. Inhibition of opening was generally correlated with inhibition of K(+) uptake by the strips. Also stomata in strips opened well under far red light (>700 nanometers). These data suggest that photosystem I and cyclic electron flow can supply the necessary energy for K(+) uptake and stomatal opening.