INCREASE IN COLD RESISTANCE OF ELECTROGENESIS AS A BASIS FOR ADAPTIVEREPOLARIZATION IN HIGHER-PLANT CELLS DURING CHILLING

Electrogenesis in pumpkin (Cucurbita pepo L.) stems was examined in or der to find out whether pumpkin adaptation to cooling (from 21 to 5 de grees C) was due to an increase in either cold resistance or the inten sity of electrogenesis. Changes in the electrical potential difference in the region of cooling were measured with extracellular Ag/AgCl mac roelectrodes. Based on experiments with two consecutive chillings appl ied at an interval of 30-40 min, it was found that the second chilling induces an electrical response of a specific pattern, because the col d resistance of electrogenesis increased during adaptation to the prev ious chilling. Inhibition of protein synthesis by cycloheximide had no effect on the adaptive potential changes evoked by chilling. The adap tive increase in the cold resistance of electrogenesis forms the basis for the spontaneous repolarization of cells cooled to a temperature o f 5-6 degrees C. A decrease in the K+ permeability of plasma membranes was found to occur during adaptive repolarization, which suggests tha t the increase in the cold resistance of electrogenesis was related to an alteration in the state of the membranes. It is concluded that ele ctrogenesis in higher plant cells adapts to low temperatures by means of increasing its cold resistance rather than its intensity.