Ascorbate levels and activities of enzymes related to the glutathione-ascorbate cycle in fruits of Chinese persimmon cultivars

Abstract

We evaluated differences in ascorbic acid (AsA) and glutathione (GSH) contents and activities of enzymes involved in the AsA metabolism in fruits of 20 cultivars of Chinese persimmon (Diospyros kaki). The total AsA content ranged from 3.85 (cv. Yangshuohuoshi) to 83.02 μmol·g−1 FW (cv. Wangmoshuishi), with an average of 36.69 μmol·g−1 FW across the 20 cultivars. The total GSH content ranged from 0.205 (cv. Yangshuohuoshi) to 0.815 μmol·g−1 FW (cv. Mimiguan) with an average 0.533 μmol·g−1 FW. There were significant differences in activities of dehydroascorbate reductase (DHAR, EC 1.8.5.1), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), ascorbate peroxidase (APX, EC 1.11.1.11), and glutathione reductase (GR, EC 1.6.4.2) in fruits among the 20 cultivars. The AsA content was significantly positively correlated with MDHAR and DHAR activities, but not with GSH and hydrogen peroxide (H2O2) contents or APX activity. These results indicated that both MDHAR and DHAR, especially MDHAR, play important roles in maintaining the AsA redox state by reducing oxidized AsA back to AsA and the AsA level mainly depends on biosynthesis, rather than recycling.