Abstract
The effects of KC1 concentration in the incubation medium on stomatal opening and starch and malate metabolism in isolated abaxial and adaxial epidermis of Commelina communis were investigated. Increasing KC1 produced progressively wide apertures, reduced starch hydrolysis and malate synthesis, but failed to eliminate the normal disparity in abaxial and adaxial opening. The fusicoccin stimulated wide opening was accompanied by a dramatic enhancement of malate formation and starch hydrolysis at zero KC1, but not at 200 mol m-3 KC1, indicating a controlling influence of KC1 concentration on carbohydrate and malate metabolism. Accordingly, malate and CI appear to compete for K+, and the one assumes an increasingly decisive role as the other becomes limiting. However, starch hydrolysis and malate production must play a central role in stomatal opening in intact leaves because they are unlikely to have such high CI regimes as 200 mol m~3, though not necessarily in isolated epidermis incubated in media enriched with inorganic ions. The restricted adaxial opening is attributed to limited K+ accumulation, starch hydrolysis and malate production in the guard cells, but the primary cause is not known.
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