Research Institute of Modern Biological Techniques, University of Zanjan Journal of Medicinal Plants Biotechnology 2423-6039 11 2 2025 12 22 Effect of gamma-aminobutyric acid and proline on morphological and phytochemical traits of Matricaria chamomilla L. under water defecit stress condition Effect of gamma-aminobutyric acid and proline on morphological and phytochemical traits of Matricaria chamomilla L. under water defecit stress condition 736696 10.30470/jmpb.2026.2072887.1154 FA Azizollah Kheiry Associate Professor, Department of Horticultural Sciences, Faculty of Agriculture, University of Zanjan-Iran. 0000-0002-5527-6544 Fatemeh Mahya Pouryusef Master&#039;s student, Department of Horticultural Sciences, Faculty of Agriculture, University of Zanjan -Iran Mohsen Sanikhani Assistant Professor, Department of Horticultural Sciences, Faculty of Agriculture, University of Zanjan-Iran Journal Article 2025 09 27 To investigate the effect of proline and gamma-aminobutyric acid on the quantitative and qualitative traits of medicinal plant chamomile (Matricaria chamomilla L.) under water deficit stress, an experiment was conducted according to split plots design with a completely randomized block arrangement with four replications during the spring and summer of 2024 in the research greenhouse at the University of Zanjan. The main factor consisted of two irrigation levels (70 and 100% of field capacity) and the subplots included foliar applications of two levels of proline (0.5 and 1 mM), gamma-aminobutyric acid (0.5 and 1 mM) and control treatment (distilled water).<br>The results showed that the highest chlorophyll a content (1.40 mg/g fresh weight) was achieved under 100% field capacity irrigation combined with 1 mM proline. Foliar application of 0.5 mM proline under 70% irrigation level resulted in the highest phenolic content (4.78 mg gallic acid/g dry weight) and the greatest total antioxidant activity (51.75%). The maximum flavonoid content (1.49 mg quercetin/g dry weight) was observed with 0.5 M GABA treatment. Additionally, the highest thousand-seed weight (148 mg) was recorded under full irrigation (100% field capacity) with 1 mM proline, compared to the control. Overall, the combined application of 0.5 mM proline and GABA was most effective in mitigating the adverse effects of drought stress on chamomile. To investigate the effect of proline and gamma-aminobutyric acid on the quantitative and qualitative traits of medicinal plant chamomile (Matricaria chamomilla L.) under water deficit stress, an experiment was conducted according to split plots design with a completely randomized block arrangement with four replications during the spring and summer of 2024 in the research greenhouse at the University of Zanjan. The main factor consisted of two irrigation levels (70 and 100% of field capacity) and the subplots included foliar applications of two levels of proline (0.5 and 1 mM), gamma-aminobutyric acid (0.5 and 1 mM) and control treatment (distilled water).<br>The results showed that the highest chlorophyll a content (1.40 mg/g fresh weight) was achieved under 100% field capacity irrigation combined with 1 mM proline. Foliar application of 0.5 mM proline under 70% irrigation level resulted in the highest phenolic content (4.78 mg gallic acid/g dry weight) and the greatest total antioxidant activity (51.75%). The maximum flavonoid content (1.49 mg quercetin/g dry weight) was observed with 0.5 M GABA treatment. Additionally, the highest thousand-seed weight (148 mg) was recorded under full irrigation (100% field capacity) with 1 mM proline, compared to the control. Overall, the combined application of 0.5 mM proline and GABA was most effective in mitigating the adverse effects of drought stress on chamomile. https://jmpb.znu.ac.ir/article_736696_a86f9f8f6c3aa7775dbe9bfc705ca956.pdf