Peroxide Metabolism and Cold Hardiness in Apple Flower-buds during Spring Dehardening.

Abstract

The relationship between peroxide metabolism and cold hardiness in flower buds of the apple, Malus pumila Mill., was studied during natural spring dehardening and under controlled dehardening conditions. During the natural spring dehardening, there was an increase, as cold hardiness decreased, in the activities of NADH-Cyt c reductase and Cyt c oxidase, enzymes involved in the electron-transport chains that are a major site of production of H2O2. By con-trast, the activities of glucose-6-phosphate dehydrogenase, glucosephosphate isomerase, glutathione reductase, glutathione peroxidase, dehydroascorbate reductase, and ascorbate peroxidase, enzymes associated with peroxide-scavenging systems that are coupled with the pentose phosphate cycle, varied as the development of flower buds proceeded. Under con-trolled dehardening conditions, the activities of NADH-Cyt c reductase and Cyt c oxidase in-creased while those of the enzymes associated with peroxide-scavenging systems that are coupled with the pentose phosphate cycle tended to decrease.Both under natural and artificial dehardening conditions, the ratio of the activity of NADH-Cyt c reductase to that of glucose-6-phosphate dehydrogenase and the ratio of the activity of Cyt c oxidase to that of glucose-6-phosphate dehydrogenase, indices of oxidizability, in-creased as cold hardiness decreased. Thus, there was a significant correlation between the cold hardiness and the values of the oxidizability index. These results suggest that vernal decreases in cold hardiness may be interpreted as a process wherein the cells become sus-ceptible to freezing injury due to oxidative stress.