The influx of arsenate, arsenite and dimethyl arsinic acid (DMA) were studied in 7-day-old excised maize roots (Zea mays L.), and then related to arsenate, arsenite and DMA toxicity. Arsenate, arsenite and DMA influx was all found concentration dependent with significant genotypic differences for arsenite and DMA. Arsenate influx in phosphate starved plants best fitted the four-parameter Michaelis–Menten model corresponding to an additive high and low affinity uptake system, while the uptake of phosphate replete plants followed the two parameter model of Michaelis–Menten kinetics. Arsenite influx was well described by the two parameter model of ‘Michaelis–Menten’ kinetics. DMA influx was comprised of linear phase and a hyperbolic phase. DMA influx was much lower than that for arsenite and arsenate. Arsenate and DMA influx decreased when phosphate was given as a pre-treatment as opposed to phosphate starved plants. The +P treatment tended to decrease influx by 50% for arsenate while this figure was 90% for DMA. Arsenite influx increasing slightly at higher arsenite concentrations in P starved plants but at lower arsenite concentrations, there was little or no difference in arsenite uptake. Low toxicity was found for DMA on maize compared with arsenate and arsenite and the relative toxicity of arsenic species was As(V) > As(III) >> DMA. |
