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Selectivity of Alkali Cation Influx Across the Plasma Membrane of Oat Roots

Cation Specificity of the Plasma Membrane ATPase ¹

^a Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907

Influx of alkali cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) across plasma membranes of cells of excised roots of Avena sativa cv. Goodfield was selective, but different, in the absence and in the presence of 1 mM CaSO₄. Ca²⁺ reduced the influx rates of all of the alkali cations—especially Na⁺ and Li⁺. Transport selectivity changed as the external concentrations of the alkali cations increased.

Plasma membrane ATPase, purified from Avena sativa roots, was differentially stimulated by alkali cations. This specificity, however, was not altered by Ca²⁺ or the external cation concentrations. A close correspondence existed between the relative influx rates of K⁺, Rb⁺, and Cs⁺ and the relative stimulation of the ATPase by these cations. A similar correspondence did not occur for Na⁺ and Li⁺.

Selective cation transport in oat roots could result, in part, from the specificity of the plasma membrane ATPase, but other factors such as specific carriers or porters or differential diffusion rates must also be involved.

¹ Supported by National Science Foundation Grant BMS 75-02471. Purdue Agricultural Experiment Station Journal Paper No. 6418.

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