Thiol metabolism and antioxidant systems complement each other during arsenate detoxification in Ceratophyllum demersum L.

Ceratophyllum demersunt L. is known to be a potential accumulator of arsenic (As), but mechanisms of As detoxification have not been investigated so far. In the present study, we analyzed the biochemical responses of Ceratophyllum plants to arsenate (As-v; 0-250 mu M) exposure to explore the underlying mechanisms of As detoxification. Plants efficiently tolerated As toxicity up to concentrations of 50 mu M As-v and durations of 4 d with no significant effect on growth by modulating various pathways in a coordinated and complementary manner and accumulated about 76 mu g As g(-1) dw. Significant increases were observed in the levels of various thiols including phytochelatins (PCs), the activities of enzymes of thiolic metabolism as well as arsenate reductase (AR). These primary responses probably enabled plants to detoxify at least some part of Asv through its reduction and subsequent complexation. The maximum proportion of As chelated by PCs was found to be about 30% (at 50 mu M As-v after 2 d). Simultaneously, a significant increase in the activities of antioxidant enzymes was observed and hence plants did not experience oxidative stress when exposed to 50 mu M As-v for 4 d. Exposure of plants to higher concentrations (250 mu M As-v) and/or for longer durations (7 d) resulted in a significant increase in the level of As (maximum 525 mu g g(-1) dw at 250 mu M after 7 d) and an inverse relationship between As accumulation and various detoxification strategies was observed that lead to enhanced oxidative stress and hampered growth. (c) 2007 Elsevier B.V. All rights reserved.