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

摘要

The cell-membrane resistance (Rm) ofVignahypocotyls was examined, and the effects of osmotic stress, ionic stress and IAA onRmwere investigated.Rmdecreased by 64 to 77under osmotic stress in the presence of absorbable solutes (40 mM sorbitol, 15 mM KC1, 30 mM sucrose; or 40 mM sorbitol, 15 mM KC1, 30 mM sucrose plus 10−4M IAA) or under ionic stress (50 mM NaCl or 50 mM KC1).Rmwas not changed by perfusion with 10−4M IAA. Therefore, the hyper-polarizations of the membrane potential observed in both cases should be ascribed totally to the activation of the electrogenic proton pump. AlthoughRmshowed an increase of 1.6 fold when the hypocotyls were subjected to osmotic stress (100 mM sorbitol or 100 mM sorbitol plus 10−4M IAA), 83.6or 92.4of the hyperpolarization of the membrane potential (Vpxwas 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 ofVignahypocotyls 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