The role of 1-methylcyclopropene in sulfur accumulation and assimilation in Ziziphus jujuba Mill.

Sulfur dioxide (SO2), sulfites, and related sulfur derivatives are widely present in air, water, and food systems, where excessive exposure can lead to respiratory irritation, oxidative stress, hypersensitivity reactions, and micronutrient depletion, threatening human health and ecological safety. Nevertheless, unavoidable residues and sulfur assimilation in plants can cause phytotoxicity and leave harmful sulfur species in edible tissues. In this study, we explore the role of 1-methylcyclopropene (1-MCP) in regulating sulfur accumulation and assimilation, using Ziziphus jujuba Mill. as a model. Quantitative analysis revealed distinct tissue-specific sulfur distribution in untreated fruits: sulfite levels in the peel reached 60.47 μg/g and 69.69 μg/g at days 3 and 6, which were 2.93- and 3.40-fold higher than those in the pulp; by day 6, the peel still contained nearly twice the sulfite content of the pulp. Sulfates also accumulated predominantly in the peel, reaching 706.13 μg/g and 736.69 μg/g at days 3 and 6. Fruits with active sulfur conversion exhibited stronger redox maintenance, with ascorbic acid reaching 4.04 g/kg and 3.82 g/kg, and glutathione levels better preserved. 1-MCP markedly decreased free sulfite and total extractable sulfur residues, alleviated oxidative injury, and enhanced ascorbate-glutathione homeostasis. Mechanistically, 1-MCP promoted sulfur assimilation via the canonical pathway, redirected cysteine towards glutathione synthesis, and inhibited ethylene-linked routes, enhancing in vivo sulfur detoxification and sequestration while minimizing harmful residue buildup. These findings indicate that a 1-MCP-guided practical and eco-friendly approach to reduce sulfur residues, offering potential applications for food health and environmental safety.