The identification and quantification of arsenic-induced phytochelatins -: comparison between plants with varying As sensitivities

The results presented in this paper provide evidence for the role of phytochelatins (PCs) in the detoxification of arsenic in six nonhyperaccumulating plant species, Agropyron repens, Glecoma hederacea, Leonurus marrubiastrum, Lolium perenne, Urtica dioica and Zea mays, in a pot experiment with high phosphate treatment. These plants differed in their arsenic sensitivities and were selected to investigate whether PCs with longer chains in roots of arsenic-tolerant species are synthesized. Raised concentrations of total PCs were measured in plant species with a range of sensitivities to arsenic at equivalent levels of arsenic exposure, determined as the inhibition of root biomass. In addition, the production of PCs as a function of accumulated arsenic was studied. Long-term PC synthesis (over a 5-week period) was positively, but non-linearly correlated with arsenic, suggesting that probably not all As is bound by PCs. Moreover, it could be shown that the synthesis of different chain lengths of PCs is associated with differences in As tolerance. In the more tolerant grasses A. repens and L. perenne it was chiefly the dithiol PC2 which was measured. In contrast, the dominant PC species in the less tolerant plants U. dioica, G. hederacea, L. marrubiastrum and Z. mays was PC3, while PC2 and PC3 were detected as well.