Exogenous melatonin stimulated isoflavone biosynthesis in NaCl-stressed germinating soybean (Glycine max L.)

Melatonin (MT) has gained increasing attention due to its pleiotropic effects. In this study, the function of exogenous MT on the response to NaCl stress and isoflavone biosynthesis in germinating soybeans was investigated. Results showed the exogenous MT (100 μM) application neutralised the negative effects of NaCl stress (60 mM), induced sprout growth, biomass and fluorescence intensity of intracellular free calcium, decreased malondialdehyde, H₂O₂ content and fluorescence intensity of O₂^•-, and enhanced superoxide dismutase, catalase and peroxidas activities of germinating soybeans. Meanwhile, total flavonoids and different forms of isoflavone content were enhanced by MT application, not only companied by the up-regulated relative gene expression of cinnamic acid 4-hydroxylase chalcone reductase, chalcone isomerase 1A, isoflavone reductase and isoflavone synthase 1 that involved in isoflavone biosynthesis, but also increased activities of phenylalanine ammonia lyase and 4-coumarate coenzyme A ligase. Given the evidence from the present study, it's proposed that the exogenous MT could relieve NaCl stress and stimulate isoflavone biosynthesis in germinating soybeans.