Integrated physiological and transcriptomic analyses reveal MT-mediated aluminum tolerance mechanisms in celery

Aluminum toxicity is one of the primary stresses limiting plant growth in acidic soils, mainly through the induction of oxidative damage and disruption of hormone-mediated developmental pathways. Melatonin (MT), a critical endogenous plant regulator, has been demonstrated to enhance plant tolerance to various abiotic stresses; however, its molecular mechanisms in alleviating aluminum stress remain to be further elucidated. In this study, celery (Apium graveolens L.) was used as the experimental material, and physiological phenotype analysis combined with transcriptome sequencing was performed to systematically explore the alleviative role of MT under aluminum stress and its molecular basis. The results showed that aluminum stress significantly inhibited the growth and development of celery, whereas melatonin treatment markedly promoted biomass accumulation and root growth, thereby effectively alleviating the growth inhibition caused by aluminum toxicity. Specifically, MT treatment significantly increased plant height (by 6.7%) and root activity (by 250.9%) while reducing oxidative damage, as evidenced by decreased H₂O₂ content (by 25.1% and 21.9%, respectively). Transcriptome analysis revealed that aluminum stress markedly induced phenylpropanoid and flavonoid biosynthesis pathways, whereas MT treatment enhanced the expression of genes involved in glutathione metabolism, particularly with the significant upregulation of GST family genes. In addition, MT treatment affected multiple plant hormone signaling pathways (such as auxin, brassinosteroid, and salicylic acid), accompanied by changes in the expression of key genes, including ARF, GH3, SAUR, TCH4, CYCD3, and PR-1. Overall, melatonin treatment is closely associated with the regulation of antioxidant metabolism and plant hormone signaling pathways and may alleviate the inhibitory effects of aluminum toxicity on celery growth. This study provides a theoretical basis for the further application of melatonin to enhance aluminum tolerance in crops.