Role of Potassium in Stomatal Opening in the Leaf of Vicia faba

With isolated epidermal strips of Vicia faba, the intensity of potassium-staining in the guard cells of stomata was calibrated against the uptake of radioactively labeled potassium. By using this calibration, the quantity of potassium that had accumulated in the guard cells, as stomata of leaves of Vicia open in the light, was estimated. Results support the hypothesis that in leaves, as well as in isolated epidermal strips, potassium and an accompanying anion comprise the major, osmotically active solutes in the guard cells of open stomata.