Effects of Osmotic Stress, Ionic Stress and IAA on the Cell-Membrane Resistance of Vigna Hypocotyls

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The cell-membrane resistance (R_m) of Vigna hypocotyls was examined, and the effects of osmotic stress, ionic stress and IAA on R_m were investigated. R_m decreased by 64 to 77% under osmotic stress in the presence of absorbable solutes (40 mM sorbitol, 15 mM KCl, 30 mM sucrose; or 40 mM sorbitol, 15 mM KCl, 30 mM sucrose plus 10^<-4> M IAA) or under ionic stress (50 mM NaCl or 50 mM KCl). R_m was not changed by perfusion with 10^<-4>M IAA. Therefore, the hyperpolarizations of the membrane potential observed in both cases should be ascribed totally to the activation of the electrogenic proton pump. Although R_m showed an increase of 1.6 fold when the hypocotyls were subjected to osmotic stress (100 mM sorbitol or 100 mM sorbitol plus 10^<-4> M IAA), 83.6% or 92.4% of the hyperpolarization of the membrane potential (V_<px> was also the result of the activation of the pump. The results, calculated on the basis of the current source model, support the viewpoint that the hyperpolarization of the cell membrane potential of Vigna hypocotyls under osmotic stress, ionic stress or in the presence of IAA is an expression of the activation of the proton pump, and is not caused by an increase in R_m.
日本植物生理学会の論文