Plasmalemma redox activity and h extrusion in roots of fe-deficient cucumber plants.
Cucumber plants (Cucumis sativus L.) with incipient Fe deficiency showed increased root capacity to reduce chelated Fe(3+) compared to Fe-sufficient plants. When Fe-ethylenediaminete-traacetate was added to the root medium of the Fe-deficient plants, the reductase activity was associated with acidification of the medium and an increase in the net apparent K(+) efflux. In the presence of the H(+)-ATPase inhibitor N,N'-dicyclohexylcarbodiimide the net apparent H(+) efflux was completely suppressed, though some reductase activity was preserved, and the net apparent K(+) efflux was significantly increased. The inhibition of the reductase activity by N,N'-dicyclohexylcarbodiimide was similar whether the pH of the medium was buffered or not. Anoxia and the protonophore carbonyl cyanide m-chlorophenyl hydrazone also caused a similar inhibition of the reductase activity. It is proposed that this redox system transports electrons only and that its activity is inhibited by plasmamembrane depolarization and anoxia. The H(+) and K(+) efflux associated with the reductase activity may be a result of the plasmamembrane depolarization it causes.
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Department of Agronomy, Escuela T.S. Ingenieros Agrónomos, University of Córdoba, Apdo. 3048, 14080 Córdoba, Spain.
de la Guardia
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Romera
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