Summary Subapical segments from maize roots took up Cs+, Rb+ and K+. At low external concentrations (up to 0.5 mM) the kinetics of Cs+, Rb+ or K+ influxes were very similar and competition experiments suggested that the three cations use the same transport system. At higher concentrations Cs+ was discriminated. Up to 0.5 mM, the net H+ efflux was similarly stimulated by the presence of Cs+, Rb+ or K+, at higher concentration the net H+ efflux was higher in K+. Potassium induced at 5 mM a depolarisation of the transmembrane electric potential difference <Em) higher than that induced by Rb+ and particularly by Cs+. JEA+, a K+- channel blocker, strongly hyperpolarized Em in the presence of K+, but had slight or no effect in Rb+ or Cs+, respectively. Cs+ influx was accompanied by a C02 dark fixation lower than that induced by K+ and Rb+. These results are consistent with the activity of a cation-H+ co- uptake mechanism, showing low selectivity between Cs+, Rb+ and K+, primarily operating at low external concentrations, and of a channel- mediated system more selective for K+, operating at higher concentrations; these two systems differently involve H+ transport activity and metabolic pH- stat mechanism. An effect of Cs+ on outward directed K+ channels, mediating the efflux of the cation from the cells, is also reported. These results are discussed in term of inhibition of K+ xylem loading
Transmembrane K+ transport system : selectivity, reciprocal integration and metabolic implications in maize roots / A. Rivetta, N. Negrini, M. Cocucci - In: Annual meeting of ESNA : jointly organized with UIR / [a cura di] M.H. Gerzabek. - [s.l] : Division of Life Sciences. Orterreichisches Forschungszentrum Seibersdorf Ges.m.b.h., 1995. - pp. 58-64 (( Intervento presentato al 25. convegno Annual Meteeng of ESNA /UIR tenutosi a Castel Nuovo Fogliani Piacenza nel 1995.
Transmembrane K+ transport system : selectivity, reciprocal integration and metabolic implications in maize roots
A. Rivetta;N. Negrini;M. Cocucci
1995
Abstract
Summary Subapical segments from maize roots took up Cs+, Rb+ and K+. At low external concentrations (up to 0.5 mM) the kinetics of Cs+, Rb+ or K+ influxes were very similar and competition experiments suggested that the three cations use the same transport system. At higher concentrations Cs+ was discriminated. Up to 0.5 mM, the net H+ efflux was similarly stimulated by the presence of Cs+, Rb+ or K+, at higher concentration the net H+ efflux was higher in K+. Potassium induced at 5 mM a depolarisation of the transmembrane electric potential differencePubblicazioni consigliate
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