Abstract
AbstractProton extrusion of maize rootZea mayssegments, was inhibited by the presence of Cr (o.n. + 6; present in solution as CrO42‐, Cr2O72‐) in the incubation medium: the minimum inhibiting concentration was 2 × 10−3mol m−3and the inhibition progressively increased with Cr concentration. Cr inhibited proton extrusion. Also, when this activity was stimulated by the presence of K+or fusicoccin (FC) in the incubation medium, the K+and FC stimulating effect was still present when proton extrusion was inhibited by Cr. In addition, Cr inhibited K+uptake. This inhibition was higher (50%) at K+concentrations up to 1 mol m−3lower (15%) at higher K+concentrations. This result indicates that the system responsible for K+uptake operating at low K+concentrations is more sensitive to Cr inhibition. Cr had no effect on transmembrane electric potential (PD). The depolarizing and hyper‐polarizing effect of K+ and FC, respectively, were not affected by Cr; but Cr enhances the depolarizing effect of the uncoupler carbonylcyanidem‐chlorophenylhydrazone (CCP). These results indicate that Cr inhibited the proton translocating mechanism coupled with K+uptake, but did not change the net transport of charges through the plasmalemma. The Cr effect is discussed, taking into account the possibility of a direct effect of Cr at the membrane level or, alternatively, of an effect on some metabolic processes controlling membrane function.
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