An altered phosphate uptake system in arsenate‐tolerant Holcus lanatus L.

The mechanism of phosphate and arsenate uptake was investigated in arsenate‐tolerant and non‐tolerant genotypes of Holcus lanatus L. It appeared that arsenate and phosphate were taken up by the roots by the same uptake system in both genotypes, although the uptake system had a much greater affinity for phosphate than arsenate. In non‐tolerant plants the uptake of both anions was much greater than for tolerant plants at low phosphate and arsenate concentrations. High‐affinity uptake appeared to be absent in the tolerant plants for both arsenate and phosphate. The absence of this high‐affinity uptake is discussed in terms of arsenate tolerance in this species. The identification of a mutant with only one phosphate uptake system provides further evidence that ‘normal’ uptake of ions occurs via two distinct transport systems. The theoretical and ecological implications of this altered phosphate uptake mechanism are considered.