Journal Article

Cs<sup>+</sup> Uptake in Subapical Maize Root Segments: Mechanism and Effects on H<sup>+</sup> Release, Transmembrane Electric Potential and Cell pH

Gian Attilio Sacchi, Luca Espen, Fabio Nocito and Maurizio Cocucci

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 38, issue 3, pages 282-289
Published in print January 1997 | ISSN: 0032-0781
Published online January 1997 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/oxfordjournals.pcp.a029164
Cs+ Uptake in Subapical Maize Root Segments: Mechanism and Effects on H+ Release, Transmembrane Electric Potential and Cell pH

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Subapical segments from maize (Zea mays) root took up Cs+; at low external concentrations (≦0.25 mM) the kinetic constants for the influx of this cation were similar to those for the uptake of Rb+ and K+ (Km=26, 26 and 22 μM and Vmax = 2.62, 3.94 and 4.09μmol h–1 (gFW)–1 respectively). Competition experiments suggested that the three cations use the same transport system. At higher concentrations (>0.25mM) the discrimination between Cs+ and Rb+ increased. At low external concentrations, the release of H+ into the medium was promoted similarly by Cs+, Rb+ or K+; at higher concentration (5 mM) the H+ release was higher in the presence of K+ than with Rb+ or Cs+. The transmembrane electrical potential difference (Em) was depolarised when Cs+, Rb+ or K+ were present in the incubation media; this depolarisation was greater in the presence of K+ and was particularly evident at higher concentrations: the Em was –85 mV, –105 mV and –119 mV in 5 mM K+, Rb+ or Cs+, respectively. Tetraethylam-monium-chloride, a K+-channel blocker, strongly hyper-polarized Era in the presence of K+ but had little or no effect with Rb+ or Cs+, respectively. The influx of Cs+ was accompanied by less dark fixation of CO2 than was that of K+ or Rb + . These results are consistent with the activity of a system showing low selectivity between Cs+, Rb+ and K+, operating primarily at low external concentrations, which possibly uses a cation-H+ co-uptake mechanism, and of a channel-mediated system more selective for K+, operating at higher concentrations; these systems differ in their involvement of H+ transport activity and the metabolic pH-stat mechanism.

Keywords: Cesium transport; Potassium transport; Uptake selectivity; Zea mays

Journal Article.  0 words. 

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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