title: Light-dependent Influx and Efflux of Potassium of Guard Cells during Stomatal Opening and Closing.
abstract: 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.
authors.affiliation: Laboratory of Plant-Water Relations, Department of Water Science and Engineering, University of California, Davis, California 95616.
authors.forename: G D
authors.initials: GD
authors.lastname: Humble
authors.forename: T C
authors.initials: TC
authors.lastname: Hsiao