Hongyin Qi, Yan Zhang, Zhou Li
Salinity stress threatens global agriculture through three main synergistic effects: osmotic stress, ionic toxicity, and oxidative stress. γ-Aminobutyric acid (GABA) is recognized as a critical regulator of plant tolerance to multiple abiotic stresses, but its positive effects on mitigating salt damage to plants have not been fully elucidated. This study aimed to investigate beneficial effects of exogenous GABA pretreatment on physiological homeostasis in salt-stressed white clover (Trifolium repens) and further elucidate potential role of the GABA shunt in regulating lipid reprogramming for maintaining the stability and functionality of cell membrane systems under salt stress. Results demonstrated that salt stress exerted negative impacts on white clover, including oxidative damage, disruption to water balance, and inhibition of photosynthesis. However, exogenous GABA pretreatment significantly reduced reactive oxygen species level and membrane lipid peroxidation, while enhancing net photosynthetic rate, photochemical efficiency, and water balance via improved osmotic adjustment and water use efficiency in leaves of white clover when exposed to salt stress. Furthermore, exogenous GABA significantly improved endogenous GABA content and GABA transaminase (GABA-T) activity, thereby enhancing GABA branched metabolism to support tricarboxylic acid (TCA) cycle during salt stress. Additionally, lipidomic analysis found that salt stress altered the accumulation and composition of lipids, and both GABA-pretreated and untreated plants increased DGDG/MGDG and PC/PE ratios to adapt to high-salt conditions. More importantly, GABA-pretreated plants maintained significantly higher contents of phospholipids, glycolipids, and sphingolipids as well as lower unsaturation level of lipids contributing to the stability and functionality of membrane systems. In addition, the GABA could enhance the conversion of lipids and pyruvate into acetyl-CoA to feed the TCA cycle. These findings highlight protective role of GABA against salt stress by improving physiological homeostasis, optimizing energy metabolism, and remodeling membrane lipids.