Photosynthetic maintenance and heat shock protein accumulation relating to γ-aminobutyric acid (GABA)-regulated heat tolerance in creeping bentgrass (Agrostis stolonifera)

Abstract γ-Aminobutyric acid (GABA) is a non-protein amino acid involved in regulating various environmental adaption in plants. Twenty-six-day-old creeping bentgrass plants were treated with or without GABA (0.5 mM) and then exposed to heat stress (35/30 °C, day/night) for 25 days. Results showed that exogenous GABA application significantly increased endogenous GABA accumulation and alleviated heat-caused growth inhibition and water loss during heat stress. GABA-treated creeping bentgrass maintained significantly lower carbonyl content, malondialdehyde content, and electrolyte leakage, but exhibited higher total antioxidant capacity and antioxidant enzyme activities (SOD, CAT, POD, APX, and DR) than untreated plants under heat stress. Heat stress significantly decreased chlorophyll content, stomatal conductance, transpiration rate, net photosynthesis, and water use efficiency. However, GABA application effectively alleviated these heat-induced negative effects in creeping bentgrass. In addition, exogenous GABA further increased the expression of heat-induced HSPs (HSP12, HSP17.8, HSP26.7, HSP70, HSP82, HSP90.1-A1, HSP90.1-B1, and HSP90-5) and HSFs (HSFA-2c, HSFA-2d, HSFA-6a, HSFB-2b, and HSFC-2b) and also further increased the abundance of HSP70, HSP90-1, and HSP101 in leaves of creeping bentgrass under heat stress. These results indicated that GABA alleviated heat-induced oxidative damage and chlorophyll loss through enhancing antioxidant capacity. GABA-treated creeping bentgrass maintained higher photosynthesis in leaves contributing to higher accumulation of water soluble carbohydrates for osmotic balance and energy supply under heat stress. GABA-regulated thermotolerance could be involved in upregulating HSF pathways in creeping bentgrass.