Malfunction of Enzyme Systems Involved in the Regeneration of Glutathione in Perennials at Low Temperatures

When frozen flower buds of apple trees started to thaw, an abrupt decrease of levels of reduced glutathione and glucose-6-phosphate occurred, even without freezing injuries. With freezing injuries, a steep decrease in the levels of the above substrates was observed, suggesting that the level of generating peroxide depends on freezing temperatures. Enzyme systems involved in the regeneration of reduced glutathione also do not seem to function properly in poplar twigs in a frozen milieu. At about - 10°C, a decrease in levels of reduced glutathione was detected and this decrease was followed by a decrease in levels of glucose 6-phosphate. When twigs that contained depressed levels of reduced glutathione and glucose-6-phosphate were transferred to 4°C, overcompensation for the decrease in reduced glutathione and glucose-6-phosphate occurred and the resultant surplus appeared to reflect the metabolic dysfunction in the supply and demand for reduced glutathione and glucose-6-phosphate that occurs under frozen conditions. These results suggest that the sequence of reactions which starts from the reaction catalyzed by hexokinase, through reactions catalyzed by glucose-6-phosphate dehydrogenase and glutathione reductase, does not function properly under frozen conditions in perennial plants.