Ethanol-Induced Activation of ATP-Dependent Proton Extrusion in Elodea densa Leaves.
In Elodea densa leaves, ethanol up to 0.17 m stimulates H(+) extrusion activity. This effect is strictly dependent on the presence of K(+) in the medium and is suppressed by the presence of the plasmalemma H(+)-ATPase inhibitor vanadate. Stimulation of H(+) extrusion is associated with (a) a decrease in cellular ATP level, (b) a marked hyperpolarization of transmembrane electrical potential, and (c) an increase in net K(+) influx. These results suggest that ethanol-induced H(+) extrusion is mediated by an activation of the plasma membrane ATP-dependent, electrogenic proton pump. This stimulating effect is associated with an increase of cell sap pH and of the capacity to take up the weak acid 5,5-dimethyloxazolidine-2,4-dione, which is interpretable as due to an increase of cytosolic pH. This indicates that the stimulation of H(+) extrusion by ethanol does not depend on a cytosolic acidification by products of ethanol metabolism. The similarity of the effects of ethanol and those of photosynthesis on proton pump activity in E. densa leaves suggests that a common metabolic situation is responsible for the activation of the ATP-dependent H(+)-extruding mechanism.
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Centro di Studio del Consiglio Nazionale delle Ricerche sulla Biologia Cellulare e Molecolare delle Piante c/o Dipartimento di Biologia, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy.
Venegoni
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Moroni
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