Evidence for amino acid-hydrogen (H) cotransport in Lemna gibba given by effects of fusicoccin
1981
Luettge, U. | Jung, K.-D. | Ullrich-Eberius, C.I. (Technische Hochschule Darmstadt (Germany, F.R.). Inst. fuer Botanik)
The fungal toxin fusicoccin (FC, 0,015-0,03 mol m(-3)) considerably hyperpolarizes the membrane of energy deficient Lemna gibba plants where delta phi initially is low, and to a lesser extent the higher delta phi of non-deficient plants. In both cases similar delta phi values are attained in the presence of FC. L-alanine uptake is enhanced by FC in relation to the FC-induced increase of delta phi, i.e., the effect is larger in deficient plants than in non-deficient ones. FC does not significantly affect the substrate constant (K(S)) of amino acid uptake by Lemna. It decreases the amplitude of L-alanine triggered transient membrane depolarizations and inhibits repolarization in the presence of L-alanine. FC effects on membranes are not readily reversible by washing FC-treated plants with FC-free medium. It is known from the literature that FC is a specific stimulatory effector of an adenosine triphosphatase in the plasmalemma of higher plants, which actively extrudes protons. Therefore, the present results allow the conclusion that electrogenicity in Lemna is due to active H(+) extrusion. The proton pump of Lemna binds FC rather tightly and works near its maximum possible rate in the presence of FC. The H(+)-electrochemical gradient established by the pump drives amino acid uptake via cotransport with H(+)
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