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Effects of Cr on proton extrusion, potassium uptake and transmembrane electric potential in maize root segments
Author(s) -
ZACCHEO P.,
COCUCCI M.,
COCUCCI S.
Publication year - 1985
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/1365-3040.ep11611843
Subject(s) - fusicoccin , depolarization , proton transport , proton , membrane potential , chemistry , incubation , potassium , extrusion , membrane transport , biophysics , nuclear chemistry , electrochemical gradient , membrane , atpase , biochemistry , biology , materials science , organic chemistry , physics , quantum mechanics , metallurgy , enzyme
Proton extrusion of maize root Zea mays segments, was inhibited by the presence of Cr (o.n. + 6; present in solution as CrO 4 2‐ , Cr 2 O 7 2‐ ) 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.