Arsenic metabolism in litchi chinensis and its effects on fruit quality

This study investigates the impact of different arsenic (As) species (arsenite (As³⁺), arsenate (As⁵⁺), and their mixture) on Litchi chinensis Sonn. fruit quality and underlying mechanisms through foliar spray treatments on 3-year-old litchi trees. The results revealed that As accumulation and distribution vary significantly across tissues, with leaves and peels exhibiting 40 times higher As levels than those in the flesh. As³⁺ treatment resulted in the highest total As accumulation in fruits by the end of ripening, whereas mixed treatments prolonged the persistence of bioavailable As (particularly As³⁺), leading to sustained stress. As exposure reduced yields by an average of 36 % (As³⁺) and moderately inhibited fruit development (As⁵⁺ and mixed treatment). Mechanistically, As speciation reshaped the sugar-acid metabolic network primarily by modulating the PPC-MDH axis. The analysis revealed that As exposure upregulated PPC and MDH pathways, redirecting carbon flux toward ascorbate-derived organic acid accumulation (e.g., tartaric acid), while increased TCA cycle activity negatively regulated sugar accumulation. Mixed treatments induced complex shifts in gene expression, reflecting the combined effects of oxidative stress and metabolic perturbations. Notably, As³⁺ exhibited 10-fold higher toxicity than As⁵⁺ due to stronger thiol group binding and enzymatic inhibition. These findings underscore the risks of As contamination in litchi production, underscoring the need for monitoring As species in fertilizers and mitigating their accumulation to ensure food safety and sustainability.