title: Stomatal Opening in Isolated Epidermal Strips of Vicia faba. II. Responses to KCl Concentration and the Role of Potassium Absorption.
abstract: The stimulation by KCl of stomatal opening in isolated epidermal strips of Vicia faba was examined. In dark + normal air the opening response was maximal at 100 mm KCl while in light + CO(2)-free air it was maximal at about 10 mm KCl. CO(2)-free air was more influential than light in reducing the KCl concentration required for maximal opening. K(+) was essential while Cl(-) seemed to be of secondary importance in these processes.The use of (86)Rb(+) as a tracer for K(+) showed that the increase in stomatal aperture under various conditions was well correlated with K(+) uptake. The estimated amount of K(+) taken up by guard cells, along with a counter ion, was sufficient to account for the changes in solute potential associated with opening. It is suggested that the absorption of extracellular solutes, such as K(+), may be the primary mechanism of stomatal opening. Both opening and K(+) absorption are stimulated by light + CO(2)-free air.The increase in stomatal aperture was also well correlated with the decrease in stainable starch in guard cells under all conditions. It is suggested that this is a secondary change, although perhaps closely linked to K(+) absorption.
authors.affiliation: Laboratory of Plant-Water Relations, Department of Water Science and Engineering, University of California, Davis, California 95616.
authors.forename: R A
authors.initials: RA
authors.lastname: Fischer
authors.forename: T C
authors.initials: TC
authors.lastname: Hsiao