Under conditions of global warming and threats of more frequent and more severe draughts, it is highly important to search new ways how to increase plant tolerance to water deficit. Plant treatment with bioactive materials that perform a protective function is one of the most promising methods. The idea of the project is based on investigations of the impact of proteinogenic amino acid proline and non-proteinogenic amino acid γ-aminobutyric acid (GABA). Proline naturally accumulates in plant cells during abiotic stress, including drought, and plays an important role in plant defence against osmotic stress, elimination of reactive oxygen species (ROS) and in signal transmission. GABA also accumulates during droughts and can act as a signal molecule; however, its function in plants is still little investigated. Little is known about proline and GABA interaction. Seeking to fill this gap in knowledge, a complex analysis of molecular mechanisms conditioning the effect of these amino acids on plant tolerance is pursued, by using commercially important rape and a model plant Arabidopsis thaliana. This would enable development of new biotechnological methods for plant adaptation to water deficit.