Melatonin enhances drought tolerance in Myrtus communis via antioxidant defense and osmotic regulation

Drought stress is a major constraint on plant growth and metabolic stability, particularly in medicinal species. This study investigated the effects of foliar-applied melatonin (0, 50, 100, and 200 μM) on drought tolerance in Myrtus communis at three field-capacity levels (100%, 70%, and 40%). Drought significantly reduced growth, relative water content, and photosynthetic pigments, while increasing oxidative damage, as indicated by elevated H₂O₂, malondialdehyde, and ion leakage. Melatonin application, particularly at 200 µM, mitigated these effects by enhancing antioxidant defense and osmotic regulation. Increased activities of superoxide dismutase and catalase were associated with reduced oxidative stress, while higher accumulation of soluble carbohydrates, proline, and glycine betaine improved cellular water balance. In addition, melatonin stimulated the synthesis of phenolic and flavonoid compounds, thereby enhancing antioxidative capacity. Correlation analysis revealed strong associations among physiological and biochemical traits, indicating coordinated regulation of drought responses. Overall, melatonin acts as an effective modulator of drought tolerance in M. communis by integrating antioxidant and osmotic mechanisms. These findings highlight its potential for improving plant performance under water-limited conditions. Further studies are required to elucidate the molecular mechanisms and gene regulatory networks underlying melatonin-mediated drought tolerance.