EVIDENCE THAT ARSENIC TOLERANCE IN HOLCUS LANATUS L. IS CAUSED BY AN ALTERED PHOSPHATE UPTAKE SYSTEM.

The uptake of arsenate by arsenic tolerant and non-tolerant plants of Holcus lanatus L., and the interaction of this uptake with phosphate level, was studied. The tolerance of the different plants, as measured by root growth, was also investigated. Arsenate inhibited the root growth of non-tolerant plants much more than that of tolerant ones, but at low levels of arsenate, the high phosphate treatment reduced the toxicity of arsenate in non-tolerants but not in tolerants. Tolerant plants took up less arsenate than non-tolerants. The effect of phosphate on arsenate uptake was very small in the tolerant plants, but in non-tolerants phosphate inhibited arsenate uptake when the phosphate was at a higher concentration than arsenate. These results are compatible with the hypothesis that arsenate is taken up by the phosphate uptake system in non-tolerant plants, but in tolerant plants this system has become altered so that it no longer recognizes arsenate.