Effect Of High Temperature On Anthocyanin Metabolism In ‘Red Beauty’ Plum(Prunus Salicina Lindl.) Fruit

Anthocyanin is a kind of water-soluble pigment and antioxidant, and abundant in plant. Some Chinese plum cultivars fruit contain high concentration of anthocyanin. Anthocyanin plays an important role in resisting abiotic and biotic stresses. The present study focuses on the mechanism of anthocyanin synthesis and degradation in ‘red beauty’ plum fruit under high temperature. The main results are as follows:1. Concentrations of phenolic compound increased in plum fruit at 20oC and 35oC treatments. At day 5 after treatment, anthocyanin concentration was significantly higher at 35oC compared to 20oC in either fruit peel or flesh. At day 9, flavonol and anthocyanin concentrations were both significantly lower while that of chlorogenic and neochlorogenic acid were significantly higher at 35oC. Meanwhile, for the key genes involved in anthocyanin synthesis, the transcription levels of PpPAL, PpCHS and PpDFR were significantly lower at 35oC than 20oC, especially at day 9. The expressions of PpANS and PpUFGT were similar at the two temperatures at day 5, but were lower at 35oC treatment at day 9. The enzyme activities of phenylalanine ammonialyase(PAL), chalconesynthase(CHS) and dihydroflavono-4-reductase(DFR) were similar after 20oC and 35oC treatments when assayed at 20oC, whereas anthocyaninsynthase(ANS)and flavonoid-3-O-glucosyltransferase(UFGT) activities were higher at 35oC treatment than that at 20oC. The enzyme activities of PAL, CHS, DFR and ANS were higher when assayed at 35oC compared to that at 20oC, while UFGT activity was similar at the two assayed temperatures. Respiration rate and ethylene production of plum fruit were accelerated by high temperature treatment. Exogenous malate, citrate, ATP, and ethylene accelerated, whereas low O2 and 1-MCP treatment significantly inhibited anthocyanin synthesis and the expressions of key genes involved in plum peel. These results indicate that 35oC enhanced anthocyanin synthesis in ‘Red Beauty’ plum fruit. This might relate to the enhancement of TCA cycle at high temperature, which may produce more ATP and then improve the ethylene production.2. Compared to that at 20oC, concentrations of total ascorbate, total and reduced glutathione were similar while concentration of reduced ascorbate was lower at 35oC in plum fruit. Enzymatic antioxidant system was enhanced in plum fruit by 35oC. However, the concentration of hydrogen peroxide was higher at 35oC than 20oC. Meanwhile, high hydrogen peroxide concentration and peroxidase activity were found in the inner vacuolar membrane of plum fruit. The experiments in vitro demonstrated that anthocyanin was prior to be used to scavenge hydrogen peroxide among the ten detected phenolic compounds, and this reaction could be catalyzed by peroxidase. In addition, one of the products of the reaction of anthocyanin and hydrogen peroxide was identified, i.e. protocatechuic acid. The concentration of protocatechuic acid at 20oC hardly changed in plum fruit during the treatment, but significantly increased at 35oC treatment at day 9. The activity of peroxidase at the two treatment temperatures was similar when assayed at 20oC. When the assayed temperature increased to 35oC, the activity of peroxidase also increased significantly. These results indicate that anthocyanin was degraded at day 9 at 35oC treatment, which might relate to the excess accumulation of hydrogen peroxide and peroxidase. Though simulation analysis, we suggest that about 16.5% of anthocyanin in plum fruit were degraded self-chemically directly induced by high temperature, and more than 60% of anthocyanin was degraded physiologically induced by excess accumulation of hydrogen peroxide, respectively.In general, high temperature enhances anthocyanin synthesis and degradation, and the anthocyanin concentration in plum fruit depends on the counterbalance between its synthesis and degradation.