Decreasing As accumulation in lettuce (Lactuca sativa L.) with exogenous sulfur in terms of As uptake, conversion, complexation, and transfer

Background and Aims Sulfur (S) decreases arsenic (As) accumulation in crops, yet its mechanism and applicability to other plants remain unclear. This study investigated the role of S in As behavior in lettuces ( Lactuca sativa L.) and evaluated S application in leafy plants, focusing on As complexation. Methods Plants were stressed with arsenate (AsV) and dimethylarsinic acid (DMA) under three different S supplementation (0, 1, and 3 mM) in hydroponic culture. As species, As-phytochelatins, ascorbate–glutathione (AsA-GSH) cycle enzymes and mineral elements in plants were analyzed. Results The effect of S was As-species-dependent. Specifically, under AsV stress, 3 mM S significantly decreased As content by 20.8% in leaves and As translocation factor (TF) by 17.4%, while root As (230–252 mg/kg, dry weight) and As-phytochelatins (1.02–1.27 mg/kg, fresh weight) remained unaffected, which is contrary to other reports. In terms of As species, leaf arsenite (AsIII) content and TF-AsIII were decreased, but AsV and root AsIII content were not significantly changed. Under DMA stress, 3 mM S significantly decreased As content by 17.7% in roots but did not alter leaf As content. The root DMA was significantly decreased, while monomethylarsonic acid (MMA) and leaf DMA content were unchanged. Additionally, exogenous S regulated root AsA-GSH cycle over leaves under both As stresses and increased leaf Fe and Zn accumulation. Conclusions Exogenous S inhibited AsV and DMA uptake, suppressed AsV-to-AsIII conversion and AsIII transfer to leaves, and facilitated DMA-to-MMA conversion, highlighting its potential applications in agriculture to restrict As in leaves on contaminated lands.