GABA Regulates Phenolics Accumulation in Soybean Sprouts under NaCl Stress

Abstract

NaCl stress causes oxidative stress in plants; γ-aminobutyric acid (GABA) could alleviate such abiotic stress by enhancing the synthesis of phenolics, but the underlying mechanism is not clear. We investigated the effects of GABA on phenolics accumulation in soybean sprouts under NaCl stress by measuring changes in the content of physiological biochemicals and phenolic substances, in the activity and gene expression of key enzymes, and in antioxidant capacity. GABA reduced the oxidative damage in soybean sprouts caused by NaCl stress and enhanced the content of total phenolics, phenolic acids, and isoflavones by 16.58%, 22.47%, and 3.75%, respectively. It also increased the activities and expression of phenylalanine ammonia lyase, cinnamic acid 4-hydroxylase, and 4-coumarate coenzyme A ligase. Furthermore, GABA increased the activity of antioxidant enzymes and the antioxidant capacity. These events were inhibited by 3-mercaptopropionate (an inhibitor for GABA synthesis), indicating that GABA mediated phenolics accumulation and antioxidant system enhancement in soybean sprouts under NaCl stress.

Keywords: GABA; NaCl stress; accumulation; phenolics components.

Figure 1

Effects of γ-aminobutyric acid (GABA) treatment on morphological status (A), length (B), weight (C), and phenolics content (D) of soybean sprouts under NaCl stress (n = 3). CK indicates distilled water treatment, N indicates 40 mM NaCl treatment, NG indicates 40 mM NaCl + 5 mM GABA treatment, NM indicates 40 mM NaCl + 0.2 mM 3-MP treatment, and NGM indicates 40 mM NaCl + 0.2 mM 3-MP + 5 mM GABA treatment. Error bars represent the standard deviation. Values in the same measured category bearing different uppercase letters (A–E) or lowercase letters (a–d) are significantly different (p < 0.05).

Figure 2

Effects of GABA treatment on phenylalanine ammonia lyase (PAL; A), cinnamic acid 4-hydroxylase (C4H; C), 4-coumarate coenzyme A ligase (4CL; E) activity and their mRNA levels (B,D,F) in soybean sprouts under NaCl stress (n = 3). CK, N, NG, NM, and NMG indicate distilled water treatment, 40 mM NaCl treatment, 40 mM NaCl + 5 mM GABA treatment, 40 mM NaCl + 0.2 mM 3-MP treatment, and 40 mM NaCl + 0.2 mM 3-MP + 5 mM GABA treatment, respectively. Error bars represent standard deviation. Values in the same measured category bearing different letters (a–e) are significantly different (p < 0.05).

Figure 3

Effects of GABA treatment on 2,2’-azinobis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS; A) and1,1-Diphenyl-2-picrylhydrazyl radical 2,2-Diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl (DPPH; B) Super oxide dimutese (SOD; C), CAT, and peroxidase (POD; D) activity in soybean sprouts under NaCl stress. CK, N, NG, NM, and NMG indicate distilled water treatment, 40 mM NaCl treatment, 40 mM NaCl + 5 mM GABA treatment, 40 mM NaCl + 0.2 mM 3-MP treatment, and 40 mM NaCl + 0.2 mM 3-MP + 5 mM GABA treatment, respectively. Error bars represent standard deviation. Values in the same measured category bearing different uppercase letters (A–E) or lowercase letters (a–e) are significantly different (p < 0.05).