Specific Requirement of Potassium for Light-Activated Opening of Stomata in Epidermal Strips

Abstract

The effect of various ions on stomatal opening was studied in isolated epidermal strips of Vicia faba L. Stomata in strips floating on 10 mm KCl and in CO₂-free air opened in light, closed in subsequent darkness, then opened fully again when illuminated. A light-activated highly specific effect of K^- (and Rb⁺) on opening was found. When strips were floated on high concentrations (50 or 100 meq/liter) of Li⁺, Na⁺ or Cs⁺, stomata opened but light had very little effect on the concentrations required for opening. With K⁺, the opening produced in the dark was the same as with the other alkali ions. Light, however, lowered more than 100-fold the concentration of K⁺ required for maximal opening. Thus only the effect of K⁺ (and Rb⁺) was greatly accentuated by light. NH₄⁺ and Mg²⁺ did not produce opening.