Repression of the K^+ Uptake and Cation-Stimulated ATPase Activity Associated with the Plasma Membrane-Enriched Fraction of Cucumber Roots Due to Ca^<2+> Starvation

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The uptake of K^+ by cucumber plants decreased markedly during Ca^<2+> starvation. A plasma membrane-enriched fraction, judged from the distribution of marker enzymes, was prepared from control and Ca^<2+>-starved roots. The Mg^<2+>- and K^+-Mg^<2+>-ATPase activities associated with the plasma membrane-enriched fraction of control roots were maxima at pH 6.5. Various monovalent catioris and potassium salts of monovalent anions stimulated Mg^<2+>-ATPase activity. Vanadate, DES and DCCD inhibited K^+-Mg^<2+>-ATPase activity. Of the divalent cations and phosphate esters tested, Mg^<2+> and ATP were most effective for the stimulation of ATPase by K^+ whereas Ca^<2+> was ineffec-tive in replacing Mg^<2+>. Mg^<2+>- and K^+-Mg^<2+>-ATPase activities associated with the plasma membrane-enriched fraction of Ca^<2+>-starved roots were much lower than those of control roots. K_m values of K^+-Mg^<2+>-ATPase for ATP were comparable for control and Ca^<2+>-starved roots. The K^+-stimulated activity of Mg^<2+>-ATPase in Ca^<2+>-starved roots was approxi-mately one fourth that of the control, whereas the rate of stimulation was only slightly lower in Ca^<2+>-starved roots.
日本植物生理学会の論文