Do phosphorus nutrition and iron plaque alter arsenate (As) uptake by rice seedlings in hydroponic culture?

• A hydroponic experiment was conducted to investigate the effect of phosphorus (P) nutrition and iron plaque on root surfaces on arsenate uptake by, and translocation within, the seedlings of three cultivars of rice (Oryza sativa). • Supply of 0.5 mg As l-1 had no significant effects on dry weights of shoots or roots, but resulted in elevated concentrations of As in tissues, particularly in roots Rice roots appeared reddish after 24 h in -P solution (without P), indicating the formation of iron plaque. • Arsenic concentrations in iron plaque (determined in dithionite-citrate-bicarbonate (DCB)-extracts) were significantly higher in -P plants (up to 1180 mg kg-1 in cultivar CDR22) than in +P plants. Concentrations of arsenic in shoots were significantly lower in -P plants than in +P plants. This indicates that iron plaque might sequestrate As, and consequently reduce the translocation of arsenic from roots to shoots. • Values for the total uptake of As show that As in -P rice plants was mainly concentrated in the DCB-extracts or on the surface of rice roots, whereas most arsenic in +P plants was accumulated in the roots. Arsenic significantly decreased the concentrations of iron (Fe) in roots and shoots (P < 0.001) and slightly reduced P concentrations in shoots, except for the -P cultivar CDR22.