Nitric oxide mediates γ-aminobutyric acid signaling to regulate phenolic compounds biosynthesis in soybean sprouts under NaCl stress

Abstract

Salt stress is an effective way to enhance the accumulation of phenolic compounds in soybean sprouts. In the present study, the effects of nitric oxide (NO) and γ-aminobutyric acid (GABA) on the biosynthesis of phenolic compounds in soybean sprouts under NaCl stress were investigated. Results showed that activities of three key enzymes involved in the biosynthesis of phenolic compounds increased by 27%–55% when the exogenous donor of NO was applied. As a result, the concentration of total phenolic compounds, phenolic acids and isoflavones in sprouts under NaCl stress increased by 26.64%, 10.91% and 19.14%, respectively. In addition, both N-nitro-L-arginine methyl ester (L-NAME) and sodium tungstate treatment inhibited the synthesis of NO in soybean sprouts under NaCl stress, which lead to the decrease of phenolics content. Treatment of GABA can alleviate the inhibition of L-NAME on phenolics biosynthesis by enhancing the production of NO. On the other hand, NO treatment can also alleviate the inhibition of 3-mercaptopropionic acid, the inhibitor of GABA synthesis, on the biosynthesis of phenolic compounds. To conclude, both NO and GABA can enhance the biosynthesis of phenolic compounds in soybean sprouts and NO can mediate the promoting effect of GABA.