Effects of Gamma-Aminobutyric Acid on Seed Germination, Ion Balance, and Metabolic Activity in Perennial Ryegrass Under Salinity Stress

Gamma-aminobutyric acid (GABA) can mediate plant stress tolerance. The objective of this study was to examine the effects of GABA on seed germination, seedling growth, ion elements, and carbohydrate and antioxidant metabolism in perennial ryegrass (Lolium perenne L.) cultivar ‘Inspire’ exposed to salinity stress. Seed germination percentage was significantly reduced by 175 mM NaCl, but 1 mM GABA added to the salinity treatment (GABA + NaCl) substantially improved germination (78%) compared to the NaCl treatment alone (46%). Compared to the non-stressed control, seedling length, shoot fresh weight, shoot dry weight, shoot carbon, and shoot nitrogen concentrations decreased under 175 mM NaCl, but such reductions were significantly lower in seedlings treated with GABA + NaCl. Salinity stress increased Na+ and did not alter K+ concentrations in the shoots, but GABA had no effect on both ions under the stress condition. The increased shoot glucose and fructose and unchanged sucrose concentrations were shown in the seedlings under the NaCl stress, and NaCl + GABA treatment had significantly higher glucose and lower sucrose but the same fructose concentrations, compared to the NaCl treatment alone. Salinity stress increased the activity of shoot superoxide dismutase (SOD) and decreased catalase (CAT) and ascorbate peroxidase (APX) activities, but higher CAT activity and unchanged SOD and APX activities were observed in the NaCl + GABA treatment, compared to the NaCl treatment alone. The results indicated that GABA ameliorated salinity tolerance by improving seed germination, seedling growth, and C and N status and altering carbohydrate and antioxidant metabolism.