リンゴ樹における耐凍性と過酸化物分解機能の季節変化

Abstract

Seasonal changes in peroxide-scavenging enzyme systems were studied with special reference to seasonal variations in cold hardiness of apple trees (Malus pumila MILL.). The activity of glucose-6-phosphate dehydrogenase increased as the resistance to freezing increased, and the activity decreased in early spring when the resistance to freezing decreased. The activities of hexokinase, glucosephosphate isomerase, glyceraldehyde-3-phosphate dehydrogenase, glutathione reductase, dehydroascorbate reductase and ascorbate peroxidase changed in parallel with changes in the activity of glucose-6-phosphate dehydrogenase, and the changes in these enzymatic activities occurred simultaneously. Glutathione peroxidase activity was low but stable throughout the year. In contrast to the activities of the above-mentioned eight enzymes, peroxidase showed different profiles of activity in various tissues and organs. Furthermore, catalase activity began to increase in the fall, but the activity decreased in the winter. The levels of glucose-6-phosphate, fructose-6-phosphate, glucose-1-phosphate, reduced glutathione and oxidized glutathione were high during the winter. The level of ascorbate remained constant throughout the winter. These results clearly show that cold hardiness is closely related to increases in the activities of the peroxide-scavenging systems of glutathione and ascorbate metabolism, in conjunction with the activities of enzymes in the pentose phosphate cycle.