NaCl stress can enhance the accumulation of phenolic compounds in soybean during germination. In the present study, effects of gamma-aminobutyric acid (GABA) and Ca2+ on the biosynthesis of phenolic compounds in soybean sprouts germinated with NaCl stress were investigated. Results showed that addition of Ca2+ increased the content of total phenolics, phenolic acids, and isoflavonoids in soybean sprouts by ca. 15%, 7%, and 48%, respectively, through enhancing the activities of three key enzymes involved in the biosynthesis. On the other hand, addition of LaCl3, a calcium channel blocker, inhibited the synthesis of phenolic compounds, indicating that Ca2+ plays an important role in the synthesis of these compounds in soybean sprouts. Addition of GABA can increase the content of Ca2+ in soybean sprouts by ca. 20% and alleviate the inhibition of LaCl3 on phenolics biosynthesis in soybean sprouts. Similarly, addition of Ca2+ can reverse the inhibition of 3-mercaptopropionate, an inhibitor of endogenous GABA synthesis, on the biosynthesis of phenolic compounds in soybean sprouts under NaCl stress. To conclude, both GABA and Ca2+ can enhance the biosynthesis of phenolic compounds in soybean sprouts and there was an interaction between their effects on the promotion of phenolic compounds biosynthesis.
Keywords: Ca2+; GABA; NaCl stress; phenolic compounds; soybean sprout.