Arsenic uptake and speciation and the effects of phosphate nutrition in hydroponically grown kikuyu grass (Pennisetum clandestinum Hochst)

Background. This work focuses on the accumulation andmobility properties of arsenic (As) and the effects of phosphate(P) on its movement in Pennisetum clandestinumHochst (kikuyu grass), grown hydroponically under increasingarsenate (As(V)) concentrations. The uptake of both ionsand the relative kinetics show that phosphate is an efficientcompetitive inhibitor of As(V) uptake. The P/As uptake rateratios in roots indicate that P is taken up preferentially by P/Astransporters. An arsenite (As(III)) efflux from roots was alsofound, but this decreased when the arsenate concentration inthe solution exceeded 5 μM.Methods. Increases in both arsenite and arsenate concentrationsin roots were observed when the arsenate concentrationin the solution was increased, and the highest accumulation ofAs(III) in roots was found when plants were grown at 5 μMAs(V). The low ratios of As accumulated in shoots comparedto roots suggest limited mobility of the metalloid withinKikuyu plants.Results. The results indicate that arsenic resistance in kikuyugrass in conditions of moderate exposure is mainly dependenton the following factors: 1) phosphate nutrition: P is anefficient competitive inhibitor of As(V) uptake because ofthe higher selectivity of membrane transporters with respectto phosphate rather than arsenate; and 2) a detoxificationmechanism including a reduction in both arsenate and arseniteroot efflux.Conclusions The As tolerance strategy of Kikuyu limitsarsenate uptake and As translocation from roots to shoots;therefore, this plant cannot be considered a viable candidatefor use in the phytoextraction of arsenic from contaminatedsoils or water.