Effects of exogenous melatonin on drought stress in celery (Apium graveolens L.): unraveling the modulation of chlorophyll and glucose metabolism pathways.

Drought, a prevalent abiotic stressor, significantly impacts plant yield and quality. Melatonin (MT), a potent and economical growth regulator, plays a pivotal role in augmenting crop resilience against stress. This study investigated the efficacy of exogenous MT on drought-stressed celery seedlings by comprehensively analyzing phenotypic, physiological, and molecular attributes. The results revealed that exogenous MT mitigated celery seedling damage under drought stress, lowered malondialdehyde (MDA) concentrations, elevated oxidase activities, osmolyte levels, chlorophyll content, and augmented light energy conversion efficiency. Transcriptomic analysis demonstrated that MT could regulate chlorophyll synthesis genes (AgPORA1 and AgDVR2), contributing to heightened photosynthetic potential and increased drought tolerance in celery. Moreover, MT was found to modulate glycolytic pathways, upregulate pyruvate synthesis genes (AgPEP1 and AgPK3), and downregulate degradation genes (AgPDC2 and AgPDHA2), thereby promoting pyruvate accumulation and enhancing peroxidase activity and drought tolerance. The RNA-seq and qRT-PCR analyses demonstrated similar results, showing the same general expression trends. The study elucidates the physiological and molecular mechanisms underlying MT's stress-alleviating effects in celery seedlings, offering insights into MT-based strategies in plant cultivation and breeding for arid environments.