Increase in voltage sensitivity of plasmalemma ATPase after cold hardeningof wheat seedlings

ATPase activity was determined in the plasma membranes (inside-out vesicles , 5 mM K+ inside) isolated from 5-day-old wheat (Triticum aestivum L.) seed lings. The cultivars Zarya and Moskovskaya 35 represented winter and spring wheat, respectively. Plasma membrane (PM) vesicles were prepared before an d after the cold hardening of plants (acclimation for 2 days at 4 degrees C ) and were incubated in the following media: (1) K+ free medium, (2) medium with 50 mM K+, and (3) medium with 50 mM KC and 5 mu M valinomycin. After cold hardening of winter wheat, the ATPase activity of PM in medium 1 incre ased by 19%, and the stimulating effect of valinomycin on ATPase activity ( medium 3) increased twofold. ATPase activity of PM incubated in medium 2 wa s 16% higher than in medium 1 for both unhardened and hardened seedlings. I n similar experiments with PM from spring wheat, there was no significant e ffect of cold hardening on ATPase activity. It is proposed that cold harden ing of winter wheat not only stimulates ATPase activity but also causes an adaptive elevation of PM ATPase sensitivity to the modulating action of mem brane potential Delta psi, the generation of which was most prominent in th e presence of valinomycin. The possible significance of this phenomenon for plants enduring the effects of very low temperature during growth is discu ssed.