关键词: 黑穗醋栗, 果实, 抗坏血酸, 合成, L-半乳糖-1, 4-内酯脱氢酶

Abstract:

【Objective】 The changes in the ascorbic acid (AsA) contents and the enzymatic activities during the anabolic process of different cultivars and growth stages of black currant fruits were studied to determine the relationship between AsA contents and anabolic enzymes during the growth and development of fruits, so as to provide a theoretical basis for comprehensively revealing the accumulation rule of AsA in black currant fruits. 【Method】 Three different cultivars of black currant fruits (Adelinia, Brodtrop and Heifeng) were studied and determined the contents of reduced AsA, oxidized ascorbic acid (DHA), reduced glutathione (GSH) and oxidized glutathione (GSSG) and anabolic enzymatic activities of young, expansion, half-veraison, veraison and maturity stages. 【Result】 There were significant diversities in fruit sizes, AsA contents and AsA metabolites of different cultivars of black currant fruits. The Adelinia had the largest weight of single fruit (1.97 g). During the growth and development process of fruits, the changes in the total ascorbic acid (T-AsA) and AsA contents of fruits were consistent among the three cultivars, and the young fruits had the highest contents. The AsA content of young Adelinia fruit was the highest (83.17 μmol?g ^-1 FW) and then sharply decreased rapidly to the maturity stage with the growth of the fruit, which decreased to 21.28 μmol?g ^-1 FW at maturity stage. The contents of GSH and T-GSH in the three cultivars increased with the development of fruits, but the different cultivars increased in different stages and degrees. The content of GSSG was quite different among different cultivars. For the mature fruits, the GSSG content of Heifeng was the lowest, which was 0.008 μmol?g ^-1 FW and only accounted for 10.2% of Adelinia. In AsA-GSH recycling regeneration metabolism, the activities of dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) showed the highest level at expansion period, and finally decreased to the lowest level at maturity stage. The DHAR and MDHAR activities of Brodtrop fruits showed slightly higher than those of Adelinia and Heifeng fruits. The activity of glutathione reductase (GR) was the highest level at young stage. The GR activity of Adelinia young fruits was the highest (0.06 μmol?min ^-1?g ^-1 FW), and then decreased with the growth of fruits. The changes in the activities of ascorbate peroxidase (APX) were similar to the changes in the activities of GR. The changes in the activities of L-galactose-1,4-lactone dehydrogenase (GalLDH), a key enzyme of L-galactose pathway, were consistent with the changes in AsA contents. The GalLDH activity of Adelinia young and mature fruits showed higher than that of Heifeng and Brodtrop young and mature fruits, respectively. According to the correlation analysis, the GalLDH activity showed a highly significant positive correlationship with T-AsA, AsA, DHA, DHAR and MDHAR. The correlation coefficient was above 0.91. The higher GalLDH activity was found in the fruits, the higher AsA contents of fruits also was found. There was a highly significant positive correlationship between DHAR and MDHAR, T-AsA and AsA. The APX had a high correlation with T-GSH and GSH. 【Conclusion】 The AsA content of black currant young fruits was the highest and there were significant differences among the three cultivars. The GalLDH, MDHAR and DHAR might be the key enzymes for AsA anabolism in black currant fruits. The accumulation of AsA content of black currant fruits resulted from the activity of GalLDH, which indicated that the anabolic pathway played a more important role and were found to be a dominant position. The related enzymes of AsA-GSH recycling regeneration pathway also contributed to the AsA anabolism. The accumulation of high AsA content in black currant fruits resulted from the combined effects of anabolic and recycling pathways.

Key words: Ribes nigrum L., fruit, ascorbic acid, anabolism, L-galactose-1, 4-lactone dehydrogenase