GABA and Proline Application Induce Drought Resistance of Oilseed Rape

This study aims to investigate whether γ -aminobutyric acid (GABA) and proline, alone and in combination, can influence the growth of oilseed rape under drought stress and after the resumption of irrigation, and to determine whether the exogenous application of these acids improves the response of oilseed rape to prolonged water deficit, and, if so, which biochemical processes are involved in the plant tissue. The research was carried out under controlled laboratory conditions. After 21 days of plant cultivation, at the 3–4 leaf stage aqueous solutions of GABA (0.1 mM) and proline (0.1 mM) were used to spray seedlings and then subjected to prolonged drought stress for 8 days to achieve a severe water deficit, next, irrigation was resumed, and recovery was assessed after 4 days. According to the results, both amino acids effectively alleviated the drought-induced stress as reflected by higher relative water content (RWC) levels, endogenous proline and photo-synthetic pigment content in leaves, and survival capacity to resume growth after drought. Plants exposed to the GABA improved membrane integrity and maintained PM ATPase activity during long-term drought stress while decreasing ethylene, H2O2, and MDA levels. Proline affected these biochemical reactions during simulated drought but to a lesser degree. The combined treatment of GABA and proline stimulated oilseed rape recovery compared with drought control after resumed watering. A significant increase in gene expression was observed upon GABA treatment compared to untreated control. Molecular studies of drought-responsive genes revealed that the gene expression level of plants treated with proline and GABA simultaneously was almost always intermediate between gene expression in proline-treated and GABA-treated plants. Based on these findings, we proposed that application of GABA is an alternative to proline technique for improving oilseed rape tolerance to drought and could be used to increase the amount and quality of crops.