The mechanisms of arsenate tolerance in Deschampsia cespitosa (L.) Beauv. and Agrostis capillaris L.

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Abstract
Arsenate influx isotherms in Deschampsia cespitosa (L.) Beauv. and Agrostis capillaris L. showed that tolerance to arsenate in these grasses is achieved at least in part by adaptation of the arsenate uptake system, which leads to reduced influx of arsenate in arsenate-tolerant plants. In D. cespitosa, this reduction in arsenate ioflux was by suppression of the Vmax of the high-affinity uptake system and by an increase in the Km of the low-affinity uptake system. In A. capillaris the reduction in arsenate uptake in arsenate-tolerant plants was by a decrease in the Vmax of both uptake systems and by an increase in the Km of the high-affinity uptake system. The differences in the rates of arsenate influx between tolerant and non-tolerant plants was much greater for D. cespitosa than for A. capillaris. The mechanism of arsenate tolerance in D. cespitosa and A. capillaris was the same mechanism of tolerance that had been demonstrated in arsenate-tolerant Holcus lanatus L. Reduced arsenate influx by adaptation of the arsenate uptake mechanism is a mechanism of tolerance that has evolved in three separate species.