GABA enhances physio-biochemical metabolism and antioxidant capacity of germinated hulless barley under NaCl stress.

The effects of exogenous γ-aminobutyric acid (GABA) on the endogenous GABA metabolism and antioxidant capacity of germinated hulless barley (Hordeum vulgare L.) under NaCl stress were investigated. The results showed that all of the GABA treatments could alleviate the growth inhibition and oxidative damage by NaCl stress, with 0.5 mM being the most effective concentration. The GABA-treated barley seedlings exhibited a significantly higher content of endogenous GABA and other free amino acids, especially proline, which resulted from the changes in corresponding enzyme activity. The phenylalanine ammonia lyase (PAL), cinnamic acid 4-hydroxylase (C4H), and 4-coumarate coenzyme A ligase (4CL) activities also increased in GABA-treated barley, which led to higher total phenolic content and antioxidant capacity than that of the control barley. These results indicate that GABA treatment may be an effective way to relieve salt stress as it induces the accumulation of endogenous GABA and proline and total phenolic content, thus enhancing the antioxidant capacity.