Effect of melatonin on seed germination of Cichorium glandulosum under drought stress.

Cichorium glandulosum, a valuable medicinal herb in Uyghur traditional medicine, mainly reproduces via seeds. Drought stress severely restricts its seed germination and threatens yield stability in the major growing areas. Although melatonin is known to protect seeds against drought in many crops, its roles in this medicinal species remain unclear. In this study, seed priming with 200 μM melatonin was applied to alleviate the adverse effects of drought simulated by 10% PEG-6000, followed by physiological, transcriptomic, and metabolomic analyses. Melatonin significantly improved seed germination performance and seedling growth under drought conditions. Physiologically, melatonin relieved drought-induced oxidative injury and promoted the accumulation of protective substances, while maintaining normal photosynthetic activity. Transcriptomic and metabolomic analyses demonstrated that melatonin reshaped gene expression and metabolic profiles and further improved the overall stress adaptability of plants. We also identified a melatonin-responsive metabolite-fucose-that can independently alleviate drought stress. This study elaborates the holistic regulatory mechanism of melatonin-enhanced drought tolerance across physiological, transcriptional, and metabolic levels. The findings provide a theoretical basis for drought-resistant cultivation and refined field management of medicinal plants in drought environments.