Rice is more efficient in arsenite uptake and translocation than wheat and barley

Rice is efficient at arsenic (As) accumulation, thus posing a potential health risk to humans and animals. Arsenic bioavailability in submerged paddy soil is enhanced due to mobilisation of arsenite, but rice may also have an inherently greater ability to take up and translocate arsenite than other cereal crops. To test this hypothesis, rice, wheat and barley were exposed to 5 A mu M arsenate or arsenite for 24 h. Arsenic uptake and distribution, and As speciation in the xylem sap and nutrient solution were determined. Regardless of the As form supplied to plants, rice accumulated more As in the shoots than wheat or barley. Arsenite uptake by rice was double of that by wheat or barley, whereas arsenate uptake was similar between rice and wheat and approximately a third smaller in barley. The efficiency of As translocation from roots to shoots was greater when plants were supplied with arsenite than with arsenate, and in both treatments rice showed the highest translocation efficiency. Arsenite was the main species of As (86-97%) in the xylem sap from arsenite-treated plants of all three species. In the arsenate-treated plants, 84%, 45% and 63% of As in the xylem sap of rice, wheat and barley, respectively, was arsenite. Arsenite efflux to the external medium was also observed in all three plant species exposed to arsenate. The results show that rice is more efficient than wheat or barley in arsenite uptake and translocation, probably through the highly efficient pathway for silicon.