Abstract：Vitamin C, also known as L-ascorbic acid (AsA), plays an important role in plant growth and development, stress response, signal transduction and so on. Its synthesis and accumulation is regulated by many biological and non-biological factors. In order to explore the mechanism of plant growth regulators regulating the accumulation of AsA in fruit, the fruits of Rosa roxburghii Tratt 'Guinong 5' were used to investigate the effects of exogenous plant growth regulators on AsA accumulation and expression of metabolite genes using the methods of incubation in vitro and spraying in vivo. The three exogenous plant growth regulators included brassinolide (BR), methyl jasmonate (MeJA) and gibberellin 3 (GA3). The results indicated that the content of AsA in the fruit of Rosa roxburghii treated by BR, including exogenous feeding and field spraying, was significantly increased, while it showed the opposite situation in the MeJA and GA3 treatment and the AsA content decreases with the lapse of time. Furthermore, different influence patterns were obtained on the expression of AsA metabolic genes by qRT-PCR analysis after three exogenous plant growth regulators treatment. The expression of genes involved in AsA biosynthesis including GDP-L-galactose phosphatase(GGP), L-galactose phosphatase(GPP), L-galactose dehydrogenase(GDH), L-galactono-1,4-lactone dehydrogenase(GalLDH), D-galacturonic acid reductase(GalUR), Myo-inositol oxygenase(MIOX), and the reduction process including Dehydroascorbate reductase(DHAR), Monodehydroascorbate reductase(MDHAR) had different degrees of upregulation when the fruits of Rosa roxburghii were treated with BR in vitro incubation, especially the effect on GGP (about 5 times after 24 h). This effect was consistent with that of the field spraying experiment. It was inferred that exogenous BR treatment could promote the accumulation of AsA in Rosa roxburghii by increasing the expression of genes of AsA synthesis and reduction process. In vitro experiment, the expression of GGP, GalLDH and DHAR was up-regulated after 24 h treatment of exogenous GA3, and the other metabolic genes showed a decreasing trend. At the same time, the expression of GDP-mannose-3′,5′-epimerase (GME), GalUR and Ascorbate peroxidase (APX) had a certain degree of upregulation after 24 h treatment of exogenous MeJA and the expression of remaining metabolic genes was different; Field spray verification experiments showed that exogenous GA3 treatment down-regulated the expression of synthetic pathway genes, meanwhile, up-regulated the expression of Ascorbate oxidase (AAO). On the other hand, the accumulation of AsA in exogenous MeJA treatment was significantly inhibited in the fruit of Rosa roxburghii. And the gene expression pattern in the synthetic pathway was different, moreover, genes in oxidation ways had no differences after MeJA treatment. In general, it did not show a consistent pattern between the expression of genes and AsA accumulation after the two exogenous plant growth regulators treatment. This study show that different exogenous growth regulators have different effects on AsA accumulation in fruits of Rosa roxburghii and would provide a theoretical basis for exploring the mechanism of plant hormones involved in AsA synthesis or accumulation.
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