Abstract
Changes in levels of hydrogen peroxide (H2O2) and metabolic activities of peroxide-scavenging systems in flower buds of apple, Malus domestica Borkh., were studied with special reference to freezing injury. In the flower buds frozen at -20°C, a lethal temperature, an increase in levels of H2O2 was observed within 30 min after thawing began. H2O2 then decreased gradually even though its concentration remained high. As H2O2 accumulated, the concentrations of glucose-6-phosphate (G6P) and reduced glutathione (GSH) decreased to very low levels and both glucose-6-phosphate dehydrogenase (EC 1. 1. 1. 49) and ascorbate peroxidase (EC 1. 11. 1. 11) were inactivated. Contrarily, during freezing, little change was observed in levels of H2O2. However, the levels of GSH and G6P decreased accompanied with quantitative increases in levels of GSSG, which suggest that H2O2 is generated during freezing. These results indicate that H2O2, produced during freezing and thawing, renders the peroxide-scavenging systems dysfunctional ; that the sequence of events, which starts from the generation of H2O2, resulting in the collapse of peroxide-scavenging systems and the accumulation of H2O2, are associated with the freezing injury.
