Effects of Cr on proton extrusion, potassium uptake and transmembrane electric potential in maize root segments |
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Authors: | P ZACCHEO M COCUCCI S COCUCCI |
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Institution: | Istituto di Chimica Agraria, Universitàdi Milano, Via Celoria 2, Milano, Italy |
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Abstract: | Abstract Proton extrusion of maize root Zea mays segments, 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?3 mol m?3 and 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?3 lower (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 carbonylcyanide m-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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Keywords: | Zea mays Maize roots chromium o n +6 proton extrusion K+ uptake PD |
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