ABSTRACT: Drought stress is one of the most prevalent environmental factors limiting faba bean (Vicia faba L.) crop productivity. β-aminobutyric acid (BABA) is a non-protein amino acid that may be involved in the regulation of plant adaptation to drought stress. The effect of exogenous BABA application on physiological, biochemical and molecular responses of faba bean plants grown under 18% PEG-induced drought stress were investigated. The results showed that the application of 1 mM of BABA improved the drought tolerance of faba bean. The application of BABA increased the leaf relative water content, leaf photosynthesis rate (A), transpiration rate (E), and stomatal conductance (gs), thereby decreased the water use efficiency. Furthermore, exogenous application of BABA decreased production of hydrogen peroxide (H2O2), malondialdehyde and electrolyte leakage levels, leading to less cell membrane damage due to oxidative stress. Regarding osmoprotectants, BABA application enhanced the accumulation of proline, and soluble sugars, which could improve the osmotic adjustment ability of faba bean under drought challenge. Interestingly, mended antioxidant enzyme activities like catalase, guaiacol peroxidase, ascorbate peroxidase and superoxide dismutase and their transcript levels may lead to counteract the damaging effects of oxidative stress and reducing the accumulation of harmful substances in BABA-treated faba bean plants. In addition, exogenous BABA significantly induced the accumulation of drought tolerance-related genes like VfMYB, VfDHN, VfLEA, VfERF, VfNCED, VfWRKY, VfHSP and VfNAC in leaves and roots, suggesting that BABA might act as a signal molecule to regulate the expression of drought tolerance-related genes.
