Redox Activity and Alcohol-mediated Energization of the Plasma Membrane of Plant Cells

Abstract

Summary Medium acidification accompanying ferricyanide-induced plasma membrane redox activity of leaves of the fresh-water plant Egeria densa was shown to be indirectly and not stoichiometrically coupled with the ferricyanide reduction rate. The ATPase inhibitors DCCD and erythrosine B had no effect on the ferricyanide reduction rate whereas they essentially inhibited medium acidification. Ethanol (0.1-1% = 17-170 mol m -3 ) caused the energization of the plasma membrane in darkadapted Egeria leaves. This became evident by the strong ethanol-induced hyperpolarization of the plasma membrane and the stimulated net proton efflux out of leaves measured as medium acidification. Also, the ferricyanide-reducing activity (FRA) as well as the uptake of a aminoisobutyric acid (Affi) and sucrose by Egeria leaves were significantly enhanced in the presence of ethanol. Ethanol-induced energization was, at least partly, inhibited by the alcohol dehydrogenase inhibitor, pyrazol. Furthermore, alcohols that are substrates of alcohol dehydrogenase (1-propanol, 1-butanol) exhibit similar effects on membrane energization as ethanol, whereas alcohols that are hardly metabolized (methanol, 2-propanol) do only to a lesser extent. In epidermal strips of the monocot, Commelina communis , ethanol (1 %) significantly stimulated stomatal opening whereas no effect of the same concentration of methanol could be found. Using the example of fusicoccin, the significance of these results for the use of alcohols as solvents for phytoeffectors is discussed.