Enhanced arsenic sensitivity with excess phytochelatin accumulation in shoots of a SULTR1;2 knockout mutant of Arabidopsis thaliana (L.) Heynh

One mechanism of arsenic detoxification in plants is synthesis of phytochelatins from glutathione in a sulfur-dependent manner. This study examined the contribution of a sulfate transporter, SULTR1;2, in arsenic tolerance in terms of sulfur metabolism in Arabidopsis thaliana (L.) Heynh. Comparative analysis of SULTR mutants showed that defective mutations of SULTR1;2 resulted in an increased arsenic sensitivity, in both shoots and roots, establishing that SULTR1;2 is required for arsenic tolerance. We subsequently quantified total sulfur content and levels of sulfur compounds (phytochelatins, glutathione, cysteine) in a SULTR1;2 mutant, sel1-8. Arsenic treatments increased sulfur uptake of sel1-8, but the mutant was unable to maintain the proper basal level of sulfur. Despite drastic reduction of total sulfur content, the mutant accumulated substantial or rather excess phytochelatins in shoots under arsenic stress conditions. The levels of glutathione and cysteine in shoots were lower in sel1-8 than in the wild type, possibly representing partial disorder of sulfur nutrition under limited sulfur supply. Taken together, we propose that SULTR1;2 contributes to arsenic tolerance by maintaining proper sulfur nutrient status at high demand for sulfur by phytochelatins-synthetic pathway, and/or optimal level of phytochelatin synthesis in shoots.