Changes in ethanol, lactate and malate content in Acer pseudoplatanus cells: effects of fusicoccin and O2 availability

Changes in the contents of ethanol, lactate and malate were determined at different activities of the plasma membrane H+ pump [in the presence and absence of fusicoccin (FC)] and at different O2 availability in cultured cells of Acer pseudoplatanus L. FC induced acidification of the medium under all tested conditions of O2 availability. At low O2 concentrations both ethanolic and lactic fermentations occurred, and FC markedly stimulated lactate production but had no effect on ethanol production. There was also a small, stimulating effect of FC on malate production. At high O2 concentrations no ethanol production was observed and lactate production was reduced. Under these conditions the stimulating effect of FC on lactate production decreased, while that on malate production increased. FC‐induced synthesis of lactate and malate is interpreted as depending on the activation of lactate dehydrogenase (EC 1.1.1.27) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) (alkaline pH optima), respectively, due to the alkalinization of the cytoplasmic pH resulting from the stimulation of the H+ pump by FC. These results suggest that the balance between the two pH stat systems depends on the availability of O2.