Regulatory function of light quality on anthocyanin synthesis in blood orange peel

【Objective】To explore the role of light quality in the regulation of anthocyanin biosynthesis in blood orangepeel,so as to provide scientific basis for uncovering the coloring regularity of anthocyanin in blood orange peel and developing the method of improving the blood orange fruit quality and production efficiency.【Method】Blood orange was treated with shading treatment. Visible light(VL,390-780 nm),partial UV and visible light(UV + VL,300-780 nm),long-wave ultraviolet(UVA,365 nm)and medium wave ultraviolet(UVB,311 nm)were used to irradiate the fruit during color-changing period. The fruits shaded without light irradiating treatment were used as the control group. The content of total anthocyanin and soluble sugar in blood orange peel of different treatment groups were determined dynamically,and the dynamic expressions of 7 genes related to anthocyanin synthesis were detected by real-time fluorescence quantitative PCR(qRT-PCR).【Result】In the color-changing period,the shaded blood orange peel,the control and the groups irradiated by VL or UVA did not showed purplish-red colorof anthocyanin under shading condition.After 46 days irradiation with UV+VL and UVB supplementary light,the fruit peel of two experimental groups showed the color of anthocyanin,and the contents of anthocyanin in the peel were 1.78 and 1.75 mg/kg,respectively. After 61 days irradiation,the contents of anthocyanin in peel were increased to 8.78 and 6.15 mg/kg,respectively. During the experiment,the fructose and glucose contents in the peel of blood orange were continuously accumulated,especially under the irradiation of UV+VL,UVA and UVB. The fructose and glucose contents of these three treatment groups were obviously higher than those of other treatment groups. The expressions of 7 genes(4CL,CHS,DFR,ANS,UFGT,GST and Ruby)involved in anthocyanin biosynthesis showed an increasing trend in all the treatment groups. Under UV+VL and UVB irradiation treatments,the expressions of these 7 genes in the peel were significantly higher than those of other treatment groups at each sampling stage.After 61 days of UV+VL and UVB supplementary irradiation,the expression of 4CL,CHS,DFR,ANS,UFGT,GST and Ruby in the peel were at least 2.42 and 2.76 times,26.46 and 23.91 times,46.68 and 44.24 times,10.94 and 9.70times,2.09 and 2.09 times,42.84 and 36.28 times,5.58 and 4.99 times higher than other treatment groups,respectively.【Conclusion】UVB is the light that can induce anthocyanin synthesis in blood orange peel. UVB enhances the expression of most genesrelated toanthocyanin biosynthetic,promotes the rapid accumulation of fructose and glucose,and finally induces the biosynthesis and accumulation of anthocyanins in the peel during blood orange ripening.