The effect of Cl(-) upon the sensitivity of starch-containing and starch-deficient stomata and guard cell protoplasts towards potassium ions, fusicoccin and abscisic acid.

Chloride ions are necessary to compensate for the positively charged potassium ions imported into guard cells of Allium cepa L. during stomatal opening. Therefore an external Cl(-) supply of intact Allium plants is important. But high levels of chloride have been found to reduce the sensitivity of the starch-lacking stomata and isolated guard cell protoplasts (GCPs) from Allium to potassium ions, fusicoccin and abscisic acid. Furthermore, with high levels of chloride, malate anions disappear from the guard cells of Allium, a finding which contrasts with situation in Vicia where the stomatal sensitivity to K(+) ions, fusicoccin and ABA is not influenced by Cl(-) ions and malate levels are unaffected. It is suggested that the absence of malate as a proton yielding primer inhibits the mechanism of H(+)/K(+) exchange in Allium.