Light promotes the synthesis of lignin through the production of H2O2 mediated by diamine oxidases in soybean hypocotyls

In order to analyze the relationship between polyamine oxidative degradation induced by light and the lignin synthesis in cell walls, the activities of diamine oxidases and peroxidase, the contents of H₂O₂ and lignin, and the growth of hypocotyls in soybean [Glycine max (Linn.) Merr.] grown under light or in darkness were investigated. In comparison with the dark treatment, light irradiation significantly inhibited the growth of soybean hypocotyls and promoted the activities of diamine oxidases and peroxidase as well as the accumulation of H₂O₂ and lignin. Treatments with the different concentrations of diamine oxidase inhibitors (2-hydroxyethylhydrazine and aminoguanidine) under the light condition inhibited diamine oxidase activity, and decreased the contents of H₂O₂ and lignin. The results provide evidence for the hypothesis that light irradiation could promote the accumulation of H₂O₂ and lignin in cell walls by activating polyamine oxidative degradation mediated by diamine oxidases.