Interaction of Gamma-Aminobutyric Acid and Ca2+ on Phenolic Compounds Bioaccumulation in Soybean Sprouts under NaCl Stress

Abstract

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.

Figure 1

Content of phenolic compounds (mg GAE/100 g DW) in soybean sprouts (n = 3). Treatments were as follows: N: NaCl; C: NaCl + CaCl₂; L: NaCl + LaCl₃; CL: NaCl + CaCl₂ + LaCl₃; GL: NaCl + GABA + LaCl₃; CM: NaCl + CaCl₂ + 3-mercaptopropionate (3-MP). Values bearing different letters in each form are significantly different (p < 0.05).

Figure 2

Activities of PAL (A), C4H (B), and 4CL (C) in soybean sprouts (n = 3). N: NaCl; C: NaCl + CaCl₂; L: NaCl + LaCl₃; CL: NaCl + CaCl₂ + LaCl₃; GL: NaCl + GABA + LaCl₃; CM: NaCl + CaCl₂ + 3-mercaptopropionate (3-MP). Values bearing different letters in each line are significantly different (p < 0.05).

Figure 3

(A) Content of Ca²⁺ (mg/sprout) and (B) calmodulin (CaM; ng/sprout) in soybean sprouts (n = 3). Sprouts in all treatments had a dry weight at around 0.12 g. Treatments were as follows: N: NaCl; C: NaCl + CaCl₂; L: NaCl + LaCl₃; CL: NaCl + CaCl₂ + LaCl₃; GL: NaCl + GABA + LaCl₃; CM: NaCl + CaCl₂ + 3-mercaptopropionate (3-MP). Values bearing different letters are significantly different (p < 0.05).