Studies On Ascorbic Acid Diversity And Metabolism In Leaves Of Persimmon Germplasm

Ascorbic acid (ASA, vitamin C) is one of the most abundant low molecular weight antioxidants present in plant tissues, and also an important function composition of fruits and others food. In association with other components of the antioxidant system, it can protect plants against oxidative damage. It is well-known that plants can adjust ASA contents by modulating ASA recycle and biosynthesis. L-galactose pathway is the main ASA biosynthesis pathway in plants, L-galactono-1,4-lactone dehydrogenase(L-GLDH) is the last key enzyme for ascorbic acid biosynthesis in this way. Ascorbate-Glutathione cycle is the main ASA recycle pathway. In this cycle, ascorbate peroxidase (APX) utilizes ASA as electron donor for reduction of H2O2, monodehydroascorbate was reduced by monodehydroascorbate reductase (MDHAR) and dehydroascorbate was reduced by dehydroascorbate reductase (DHAR). Oxidized glutathione (GSSG) produced in this cycle is reduced to GSH by glutathione reductase (GR), so they can accomplish the process of ASA recycle in plant. In the world, China is a mainly country for producting persimmon (Diospyros kaki L). Except its fruits hold the high value of economy, Leaf, flower, bark, root and pedicel of persimmon all could be used as a drug. Especially the leaf is becoming increasingly concerned because having the function of health care for human. It was reported leaf of persimmon was very high in ASA content and reached several tens of some fruits. In this paper,In order to further research, exploit use persimmon germplasms,diversities of ASA and GSH content and the relation between both were studyed in leaves of 75 persimmon germplasms. Additionally, the relationship between ASA levels and enzymes related with ASA biosynthesis and recycle were also investigated in leaves of 22 acerbity varieties grown widely in china.The results were as follows:(1) Ascorbate and glutathione content and their redox state were assayed in leaves of 75 persimmon genotypes which grow in National Persimmon Germplasm Repository in China. Obvious diversity of total ascorbate content(from 27.17 to 147.20μmol/g) and total glutathione content(from 0.215 to 1.030μmol/g) and their redox state were detected amongst 75 persimmon genotypes,especially amongst 53 acerbity varieties grown widely in China. Moreover, negative correlation between T-ASA content and the percent of DHA was also discovered in leaves of persimmon genotypes and R2=0.527, but no significant correlation between T-GSH content and the percent of GSSG , T-ASA content and T-GSH content were found. These results suggested that persimmon, especially acerbity varieties grown widely in China, may be the good candidates in exploring and developing high ASA products and studying mechanizes for ASA formation in plants.(2) Through investigatede ASA levels and enzymes activities involved in ASA boisynthesis and recycle in 22 persimmon varieties grown widely in China, it was shown that not only Obvious diversity of ascorbate and glutathione levels were detected amongst leaves of22 china persimmon cultivars, there were the diversities in L-GLDH activity which was a key enzyme of ASA biosynthesis as well as APX,MDAHR,DHAR and GR activities which all involved in ASA recycle.(3) In order to investigate the relations between ASA content and enzymes and substances related with ASA metabolism, the correlations were anlysized between ASA levels and them.it was discovered that the correlation was extremely remarkable between T-ASA content and L-GLDH activity, but the correlations were observed with enzyme activity of APX, MDHAR and DHAR in leaves of 22 persimmon varieties grown widely in China. Moreover, at individual relations, diversities of relations with the enzymes were also found in leaves of 22 persimmon varieties grown widely in China.(4) Multivariate regressive analysis was used to further anlysize the relatinship between ASA levels and the enzymes, and line regressive equations were got. The results shown ASA content in leaves of chinese persimmons was mainly dependent on self biosynthesis, especielly L-GLDH activity. Meanwhile MDHAR and DHAR activities also played a important role in maitaining ASA content and redox state by influencing on redox balance. But APX activity and GSH leves were no obvious relationwith ASA levels.