Abstract
This study investigates the effects of γ-aminobutyric acid (GABA) and proline, both individually and in combination, on the growth of oilseed rape under drought stress and following the resumption of irrigation. The goal was to determine whether the exogenous application of these compounds enhances the plants response to prolonged water deficit and, if so, to identify the biochemical processes involved in the plant tissue. The experiment was conducted under controlled laboratory conditions. After 21 days of plant cultivation, at the 3-4 leaf stage, seedlings were sprayed with aqueous solutions of GABA (0.1 mM) and proline (0.1 mM). The plants were then subjected to 8 days of severe drought stress, after which irrigation was resumed, and recovery was assessed over 4 days. The results showed that both amino acids alleviated the drought-induced stress as indicated by higher relative water content (RWC), increased levels of endogenous proline and photosynthetic pigments in leaves, and enhanced survival and growth recovery after drought. GABA-treated plants maintained membrane integrity and preserved plasma membrane (PM) ATPase activity during prolonged drought stress while reducing ethylene, H(2)O(2), and MDA levels. Proline also influenced these biochemical responses, though to a lesser extent. The combination of GABA and proline facilitated better recovery of oilseed rape compared to the drought control group following rewatering. Notably, GABA treatment resulted in a significant increase in gene expression compared to the untreated control. Molecular analysis of drought-responsive genes revealed that the gene expression in plants treated with both proline and GABA was typically intermediate between those treated with proline alone and those treated with GABA alone. Based on these findings, we propose that GABA application could serve as an alternative to proline for improving oilseed rape's drought tolerance, potentially increasing both crop yield and quality.