Rice can potentially pose serious health risks due to its higher arsenic (As) uptake. Sulfur (S) is not only an essential macronutrient, but it also has the ability to decrease As accumulation. In the present study, a hydroponic experiment was conducted to investigate the mechanisms underlying the effects of S on the As uptake and transport at different S (pre-)treatments and additional supply levels. It was found that additional S supply decreased As content by 20%-50% in both S-deficient and S-normal pre-treated shoots compared to the no S supply throughout the treatment; As root-to-shoot translocation factors was reduced by 7%-46% with S supply. On the one hand, additional S supply could elevate levels of thiol compounds (by 15%-280%) and increase the As percentage in soluble cytosol of roots. Additional S supply also enhanced the casparian strip development of rice roots, which could block As transfer in roots apoplast pathway. Moreover, additional S supply lead to the down-regulation of OsLsi2 expression (e.g., reduced by 71% by S at 2 mmol L-1 with the S-normal pre-treatment). Sulfur also promoted the biotransformation of As(III) in shoots into less toxic As species; reducing the As(III) proportion by 25% by 2 mmol L-1 of S under S-normal pre-treatment. These results suggest that S could play an important role in the inhibition of As transfer and the detoxification of As in rice by enhancing root retention (the vacuole sequestration), impeding transportation pathway of root apoplast, and regulating As-related gene expression. Thus, providing a basis for the potential application of S in rice production in As-contaminated paddy soil.
Keywords: Arsenic; As speciation; Casparian strip; Gene expression; Sulfur; Thiol compounds.
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