Abstract
In this study, the functions of Hydrogen peroxide (H2O2) on the synthesis of isoflavones in germinated soybean under UV-B radiation were investigated. Results showed that the activity, gene, and protein expression of NADPH oxidase were up-regulated by 1.46, 6.92, and 1.34 times with UV-B radiation, while endogenous H2O2 content was also significantly increased. UV-B radiation and exogenous H2O2 treatment significantly increased the activities, gene and protein expression of phenylalanine ammonia lyase (PAL), chalcone synthase (CHS), and isoflavone synthase (IFS) involved in isoflavones synthesis, and there was a synergistic effect with combining treatment. However, these up-regulation effects were suppressed by the supplementary diphenylene iodonium (DPI), which is the inhibitor of NADPH oxidase. Interestingly, the inhibition effect was largely reversed by exogenous H2O2, indicating that H2O2 was indispensable in regulating the isoflavones synthesis in germinated soybeans under UV-B radiation. Overall, H2O2 is an essential signaling molecule, mediating UV-B-induced isoflavone accumulation.