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 M 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.