Presence of Chloride Reduces Malate Production in Epidermis during Stomatal Opening

When stomata of isolated epidermis of Vicia faba are allowed to open in the presence of K⁺ and iminodiacetate (an impermeant zwitterion), malate is formed in the epidermis; the increases in malate content follow a nearly linear relationship with stomatal aperture. Stomata of leaf sections of V. faba floated on water during opening also exhibit this relationship. When isolated epidermis is offered KCI, this relationship is not observed and less malate is detected at comparable stomatal apertures. The data indicate that Cl⁻, if present at concentrations ≥ 10⁻⁵ eq liter⁻¹, can partially satisfy the anion requirement of guard cells of V. faba during stomatal opening. Discrepancies between earlier reports on the relative roles Cl⁻ and malate play as counterions for K⁺ in guard cells of V. faba could now be explained as resulting from variations in the availability of Cl⁻ to guard cells.