The role of phytochelatins in arsenic tolerance in the hyperaccumulator Pteris vittata

Pteris vittata was the first identified arsenic (As) hyperaccumulator. Here we investigated whether phytochelatins (PCs) are involved in the hypertolerance of arsenic by P. vittata . P. vittata was exposed to 0-500 mum arsenate for 5 d, or to 50 mum arsenate for 0-7 d. In addition, l-buthionine-sulphoximine (BSO), an inhibitor of gamma-glutamylcysteine synthetase, was used in combination with different arsenate exposures. The relationships between As accumulation and the concentrations of PCs and glutathione (GSH) were examined. PC synthesis was induced upon exposure to arsenate in P. vittata , with only PC2 detected in the plant. The As concentration correlated significantly with PC2 concentration in both roots and shoots, but not with GSH. The molar ratio of PC-SH to As was c. 0.09 and 0.03 for shoots and roots, respectively, suggesting that only a small proportion (1-3%) of the As in P. vittata can be complexed with PCs. In the presence of arsenate, addition of BSO decreased PC2 concentrations in roots and shoots by 89-96% and 30-33%, respectively. BSO alone was found to inhibit root growth of P. vittata markedly. The results suggest that PCs play a limited role in the hypertolerance of As in P. vittata .