GENERATION OF ACTION-POTENTIAL INDUCES PREADAPTATION OF CUCURBITA-PEPO L STEM TISSUES TO FREEZING-INJURY

Electrophysiology of pumpkin (Cucurbita pepo L.) stem was investigated in order to assess the effect of action potential (AP) generation, ca used by short (5-10 s) local cooling of the stem to 5-9 degrees C, on the resistance of stem tissue to freeze treatment (-2 degrees C). The experiments were performed on hypocotyls of intact seedlings and on sp ecially prepared hypocotyls. The bioelectric responses to cooling from 18 to 8 degrees C evoked 24 h after the freeze treatment were indicat ive of the transient increase in cold resistance of hypocotyl tissues in a 12- to 60-min interval after AP generation in intact seedlings an d a 5- to 25-min interval in hypocotyl preparations. It is concluded t hat AP generation induced by moderate cooling initiates physiological preadaptation to possible severe stresses in those tissues and organs where AP was generated or propagated.