Research Institute of Modern Biological Techniques, University of Zanjan Journal of Medicinal Plants Biotechnology 2423-6039 11 2 2025 12 22 Investigation of physiological and biochemical mechanisms and modulation of the antioxidant defense system in caper (Capparis spinosa L.) in response to drought stress Investigation of physiological and biochemical mechanisms and modulation of the antioxidant defense system in caper (Capparis spinosa L.) in response to drought stress 736695 10.30470/jmpb.2026.2086857.1173 FA زهرا رادمنش Researcher in SPCRI Farid Shekari Department of Plant Production and Genetics, Faculty of Agriculture, University of Zanjan, Zanjan, Iran Mohammad Hasan Assareh Seed and Plant Certification and Registration Institute, Karaj - Iran Bernardo Pascual Espana 3Department of Plant Production- Universitat De Valencia, Valencia - Spain Journal Article 2026 02 27 In order to evaluate the physiological and biochemical responses of different ecotypes of caper (Capparis spinosa L.) seedlings to drought stress, an experiment was conducted under laboratory conditions in 2023 at the Seed Quality Analysis Laboratory of the Seed and Plant Certification and Registration Research Institute, Karaj, Iran, using a completely randomized design with three replications. In this study, seeds of nine native caper ecotypes collected from Ardabil Province (Moghan), Alborz (Karaj), Ilam Province (Mehran), North Khorasan Province (Bojnord), Kermanshah Province (Dalahoo), and Khuzestan Province (Ramhormoz, Hendijan, Mahshahr, and Ahvaz) were evaluated. Drought stress was imposed using polyethylene glycol (PEG 6000) at an osmotic potential of −6 bar. The results indicated that drought stress significantly increased malondialdehyde content from approximately 6.5 to 11.3 nmol g⁻¹ FW and hydrogen peroxide from 3.1 to 6.0 µmol g⁻¹ FW, while total chlorophyll content decreased from 0.35 to 0.21 mg g⁻¹ FW. In contrast, proline content (12.7–45.8 µg g⁻¹ FW), total phenolic content (2.6–3.6 mg gallic acid g⁻¹ FW), and antioxidant capacity (38–47% DPPH inhibition) showed significant increases under drought conditions. Comparison among ecotypes revealed that under non-stress conditions, the Karaj and Moghan ecotypes exhibited greater physiological stability, whereas under drought stress, the Mahshahr and Hendijan ecotypes showed the lowest oxidative damage indices and the highest accumulation of protective compounds, and were therefore identified as drought-tolerant ecotypes. Overall, the results highlight the key role of antioxidant defense mechanisms and osmotic adjustment in the adaptation of caper plants to drought stress conditions. In order to evaluate the physiological and biochemical responses of different ecotypes of caper (Capparis spinosa L.) seedlings to drought stress, an experiment was conducted under laboratory conditions in 2023 at the Seed Quality Analysis Laboratory of the Seed and Plant Certification and Registration Research Institute, Karaj, Iran, using a completely randomized design with three replications. In this study, seeds of nine native caper ecotypes collected from Ardabil Province (Moghan), Alborz (Karaj), Ilam Province (Mehran), North Khorasan Province (Bojnord), Kermanshah Province (Dalahoo), and Khuzestan Province (Ramhormoz, Hendijan, Mahshahr, and Ahvaz) were evaluated. Drought stress was imposed using polyethylene glycol (PEG 6000) at an osmotic potential of −6 bar. The results indicated that drought stress significantly increased malondialdehyde content from approximately 6.5 to 11.3 nmol g⁻¹ FW and hydrogen peroxide from 3.1 to 6.0 µmol g⁻¹ FW, while total chlorophyll content decreased from 0.35 to 0.21 mg g⁻¹ FW. In contrast, proline content (12.7–45.8 µg g⁻¹ FW), total phenolic content (2.6–3.6 mg gallic acid g⁻¹ FW), and antioxidant capacity (38–47% DPPH inhibition) showed significant increases under drought conditions. Comparison among ecotypes revealed that under non-stress conditions, the Karaj and Moghan ecotypes exhibited greater physiological stability, whereas under drought stress, the Mahshahr and Hendijan ecotypes showed the lowest oxidative damage indices and the highest accumulation of protective compounds, and were therefore identified as drought-tolerant ecotypes. Overall, the results highlight the key role of antioxidant defense mechanisms and osmotic adjustment in the adaptation of caper plants to drought stress conditions. https://jmpb.znu.ac.ir/article_736695_6319981c1d8755ccd4209a3c8837a6c1.pdf