Study On Physiological And Molecular Mechanism Of AsA Accumulation During The Fruit Growth Of Sweet Cherry

L-Ascorbic acid (AsA), also known as vitamin C. is a small molecular substance in the process of plant metabolism, one of the most abundant antioxidants and cofactor for several enzymes, and also well known to have an important role in scavenging oxygen free radicals ande maintaining photosynthesis. Moreover, it is the main source of natural AsA to human due to humans are incapable of synthesizing AsA and must secure it by means of dietary food such as vegetables and fruits. Sweet cherry (Rosaceae, Cerasus) is delicious, nutritious, and rich of antioxidant substances such as AsA, which is a well loved fruit by curing for many diseases. However, studies on the regulation of AsA are mostly focused on a few model plants, the researches on fruit of AsA content are concentrated on the determination and comparison. Results from the present study can't find the mechanism of AsA accumulation during the growth and development of sweet cherry. To understand it, we performed on sweet cherry'Hongdeng'and'Sato Nishiki', the changes in the contents of AsA and glutathione (GSH), and related metabolites, the gene expression and activity of enzymes involved in AsA biosynthesis and recycling during fruit development were systematically investgated and analyzed.This study obtained the following results:1.The changes of AsA concentration in sweet cherry 'Hongdeng' and 'Sato Nishiki' during fruit development were determination. Quite similar among 'Hongdeng' and 'Sato Nishiki' in fruit AsA, total AsA, DHA concentrations, with the highest in 0 day after anthesis, then declined steady the next 10 days, the rapidly decreased in 10-40 days of anthesis, and rapidly growth during fruit ripening (40-50 d). The AsA content in'Hongdeng' was lower than 'Sato Nishiki' at early stage but higher than 'Sato Nishiki' in maturation, AsA concentration in ripe fruit of 'Hongdeng' and 'Sato Nishiki' were 34.27 mg/100g FW and 29.43 mg/100g FW. The accumulation of AsA occurred during the growth of sweet cherry fruit, but the main acuumulaion stages were 10-30 and 40-50 days after anthesis.2.The content of total GSH and GSH in different sweet cherry were diverse which down in'Hongdeng' and up in 'Sato Nishiki' during 0 to 10 days after anthesis, then the changes were the same with increased (10-20 d), rapidly decreased (20-30 d), slowly declining (30-40 d), finally increased slowly during maturation period (40-50 d). The total GSH, GSH contents in'Hongdeng" were higher than'Sato Nishiki'at early stage (0 d) but lower than'Sato Nishik' in maturation. The GSH accumulation of'Hongdeng" was contribution to 10-20, 40-50 days after anthesis, which of the'Sato Nishiki'was the whole growth and development period.3. The changes of total GSH and GSH in the sweet cherry fruit were not consistent, the GSH and AsA content showed no significant correlation, indicated that GSH may not a key substance for the accumulation of AsA during the growth and development of sweet cherry fruit.4. The contents of AsA, GSH, and the activities of L-galactose dehydrogenase (GalDH), L-galactono-1,4-lactone dehydrogenase (GalLDH), monodehydroascorbate reductase (MDHAR). dehydroascorbate reductase (DHAR), glutathione reductase (GR), ascorbic acid peroxidase (APX) were investigated during the development of sweet cherry fruit 'Hongdeng'and'Sato Nishiki'. Different enzymes involved in metabolism of AsA showed different patterns during the development of sweet cherry fruit, but only the activity changes of GalLDH, MDHAR and DHAR were similar to that of AsA.5.Totally 17 genes were cloned in sweet cherry including seven genes involved in AsA L-galacrose biosynthetic pathway, GDP-mannose pyrophosphorylase (GMP), GDP-3',5'-epimerase (GME); GDP-L-galactose phosphorylase (GGP), L-galactose-a-phosphate phosphatase (GPP), GalDH, GalLDH and eleven genes involved in recycling pathway, ascorbate oxidase (AO), MDHAR, APX, DHAR, GR.6.The changes in expression of these genes during fruit development of sweet cherry were analyzed in two genotypes respectively. Among the 17 genes, the expression pattern of L-galactose pathway gene GPP2, GalLDH, DHAR1 showed the highest similarity with the changes of AsA content among all the biosynthetic genes, with the correlation analysis showed they had a significantly positive correlation with the content of AsA, which indicated that they may be key enzymes of AsA accumulation in sweet cherry. During the development of sweet cherry fruit, the accumulation of AsA was demonstrated by the biosynthetic pathway and recycling pathway.