Persistence and detoxification of Pretilachlor and Fenclorim in rice (Oryza sativa)

The contents and persistence of pretilachlor (P) and of the safener fenclorim (F) in rice treated with P, F and their mixture were investigated in relation to the expression of glutathione-S-transferase (GST) activity in response to treatments. F failed to reduce the accumulation of P, however it was able to reduce its persistence in rice shoots. On the other hand, while P did not reduced F persistence, it determined a greater than two-fold F accumulation in plants. Therefore, a detoxification mechanism common to the two compounds but favourable to P was hypothesised. This mechanism consists in an activation of GST activity toward P as substrate [GST(P)] in response to all treatments. The activation levels were found to be proportional to the amount of persistent P and F, and to be additive following the P-F mixture treatment. The kinetic parameters V-max and K-m of GST(P) were increased and decreased, respectively, in rice shoots treated with P, F and particularly with P-F mixture. Therefore, a defence mechanism toward P, consisting in an increased expression of GST(P) in rice plant, both as the global amount of the enzyme in the protein pull and the induction of the enzyme isoforms more sensitive to P, in response to all treatments, especially the P-F mixture treatment, is confirmed. This finding is consistent with the observed effect of F on P persistence and detoxification in the rice shoots.