γ-Aminobutyric acid-mediated regulation of osmolytes, nitrogen metabolism, and antioxidant defense confers dose-dependent drought tolerance in mungbean.

BACKGROUND: Drought severely limits mungbean (Vigna radiata) growth by disrupting physiological and metabolic processes. Although γ-aminobutyric acid (GABA) enhances abiotic stress tolerance, its dose-dependent effects across different drought intensities in mungbean remain unclear. RESULTS: This study evaluated the effects of exogenous GABA (0, 0.5, 1, and 2 mmol L-1) on growth, osmolyte accumulation, nitrogen assimilation, and antioxidant defense in mungbean under well-watered (WW), moderate drought (MD), and severe drought (SD). Both drought stress levels significantly reduced shoot-root growth and biomass, leaf relative water content, photosynthetic pigments, and NO₃-, NH₄+, and the activities of nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT). Oxidative stress increased, as evidenced by higher levels of H2O2, malondialdehyde (MDA), dehydroascorbate, and oxidized glutathione. Drought also increased proline, glycine betaine, total phenols, and antioxidant enzymes (SOD, CAT, APX), but reduced ascorbate (AsA), glutathione (GSH), and the activities of MDHAR and DHAR, indicating disruption of the AsA-GSH cycle. Exogenous GABA, particularly at 2 mmol L-1, markedly alleviated these adverse effects by improving osmotic adjustment, enhancing antioxidant defense, and restoring nitrogen assimilation. GABA treatment increased proline, glycine betaine, NR, GS, GOGAT, and antioxidant enzyme activities (SOD, CAT, APX, GR), while improving AsA-GSH recycling and reducing H2O2 and MDA accumulation. The protective effects of GABA were more pronounced under MD than SD conditions. CONCLUSION: GABA enhances drought tolerance in mungbean through coordinated regulation of osmotic adjustment, antioxidant defense, and nitrogen metabolism, highlighting its potential as a priming agent for sustaining productivity under water-limited conditions. Future molecular studies are needed to elucidate the mechanisms through which GABA regulates drought tolerance in mungbean. © 2026 Society of Chemical Industry.