Effect of exogenous γ-aminobutyric acid on the antioxidant defense system and phytohormones metabolism under high temperature stress in perennial ryegrass

In order to elucidate the effects of exogenous γ-aminobutyric acid on the high temperature stress tolerance, plant growth, root activity, leaf membrane stability, chlorophyll content, reactive oxygen species metabolism, antioxidant enzyme activities and gene expression, endogenous hormones were investigated in a heat sensitive cultivar ‘Pinnacle’ of perennial ryegrass (Lolium perenne) under high temperatures (35 ℃/30 ℃) in growth chambers for 21 d. The results showed that heat stress decreased plant growth, root activity and chlorophyll content, and increased leaf electrolyte leakage, reactive oxygen species and antioxidant enzyme activities. The inhibiting hormone abscisic acid (ABA) content increased while the growth-promoting hormones auxin (IAA), gibberellin (GA₃) and cytokinin (ZR)decreased under high temperature stress. Exogenous application of γ-aminobutyric acid (GABA) remarkably promoted plant growth, increased turf quality, chlorophyll content and root activity under heat stress. In addition, the growth-promoting hormones IAA, GA₃ and ZR, and the gene expression levels of antioxidant enzymes and the enzyme activities were also enhanced by GABA application when compared to the non-GABA treatment under high temperature stress. These results suggested that the enhanced high temperature stress tolerance by exogenous application of GABA may contribute to the induced higher antioxidant systems and the growth-promoting hormone IAA, GA₃ and ZR levels.