ACTIVATION OF THE ELECTROGENIC PLASMALEMMA H-PUMP IN THE ADAPTATION OF HIGHER-PLANTS TO MODERATE LOW-TEMPERATURE STRESS()

A study was made of the role of K+ efflux from precooled (from 22 to 6 -degrees-C) pumpkin (Cucurbita pepo L.) stem cells and of the cooling- induced increase in plasma membrane lipid fluidity in the processes of activating the electrogenic plasma membrane H+-pump (H+-ATPase) and o f adaptive plasma membrane repolarization. Inhibition with ethacrinic acid (a blocker of Cl- channels) and tetraethylammonium (a blocker of K+ channels) demonstrated that it is the K+ efflux, occurring mostly d uring the generation of the cooling-induced action potential(s), that was primarily responsible for the H+-pump activation at 6-degrees-C; t his was tentatively called the ''potassium'' mechanism. Very early (wi thin 15 - 30 min of cell exposure to 6-degrees-C) changes in the plasm a membrane lipid fluidity related to an increase in fatty acid unsatur ation were detected. We concluded that both the K+ efflux and the chan ge in plasma membrane lipid fluidity following a downward temperature shift are the principal mechanisms for initiating and developing the a daptive plasma membrane repolarization associated with the activation of the electrogenic H+-pump.