UV-B- triggered H₂O₂ production mediates isoflavones synthesis in germinated soybean

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.