Mechanisms of arsenate tolerance in Cytisus striatus

Arsenate tolerance, uptake and arsenate-induced phytochelatin (PC) accumulation were compared at different phosphorus supply rates in two populations of the broom, Cytisus striatus, one from an arsenic-enriched gold mine and one from a nonmetalliferous site. After 7 d of exposure, arsenate tolerance was higher in the mine population. Arsenate uptake was phosphate-suppressible, and much lower in the mine plants. When compared at equal levels of stress, the mine plants and the nonmetallicolous plants exhibited similar arsenic accumulation, suggesting that reduced arsenate uptake is mainly responsible for superior tolerance. Arsenate-induced PC accumulation occurred in both plant types. The gamma-glutamylcysteine synthetase inhibitor, L-buthioninesulfoximine, caused arsenate hypersensitivity in both plant types, suggesting that PC-based arsenic sequestration is essential for both normal and enhanced arsenate tolerance. Mine plants produced longer PCs than the nonmetallicolous plants, possibly due to a differential temporal pattern of arsenate accumulation. Our results are consistent with a similar mechanism underlying arsenate hypertolerance in C. striatus and grasses, that is reduced arsenate uptake through suppression of phosphate transporter activity.