Effect of Partial Shading Treatments on Anthocyanin Synthesis in the Hypocotyls of Soybean Sprouts Under UV-A irradiation

Abstract

To evaluate the effects of different partial shading treatments on the synthesis of anthocyanins under UV-A irradiation in soybean sprouts, we examined the anthocyanin content, transcript levels of key genes related to anthocyanin biosynthesis (CRY1, CRY2, PAL, CHS, CHI, DFR, ANS and UFGT), and the activity of phenylalanine ammonia-lyase (PAL). The results showed that UV-A radiation could significantly increase the content of anthocyanins in the epidermal layer of hypocotyls in soybean sprouts. This trend was consistent with the pattern of anthocyanin biosynthesis-related gene expressions, which were significantly up-regulated by UV-A. Different partial shading treatments significantly reduced the content of anthocyanins and the expression of DFR, ANS, and UFGT in response to the UV-A irradiation. Cotyledon-shading treatment lowered the content of anthocyanin due to the down-regulation of the expression of anthocyanin biosynthesis-related genes, but this effect is limited. Compared with the cotyledon and the upper part of hypocotyls, the lower part of hypocotyls was the predominant site of anthocyanin synthesis in soybean sprouts. These findings imply that anthocyanins in hypocotyls are biosynthesised locally, and there is no systemic biosynthesis, which was further supported by the PAL activity and the transcripts of the genes responsible for anthocyanin biosynthesis.