Detoxification of chlorotoluron in a chlorotoluron‐resistant biotype of Alopecurus myosuroides. Comparison between cell cultures and whole plants

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Abstract
The metabolism of chlorotoluron in whole plants and cell suspensions was investigated in a previously characterized chlorotoluron‐resistant biotype of Alopecurus myosuroides Huds. Both resistant plants and cell suspensions showed a greater capability to metabolize chlorotoluron to non‐phytotoxic compounds than the respective susceptible counterparts. Data revealed that although both biotypes degraded chlorotoluron by N‐dealkylation and ring‐methyl hydroxylation, the resistant biotype showed an enhanced capacity to hydroxylate the parent herbicide. The cytochrome (Cyt) P450 inhibitor 1‐aminobenzotriazole (ABT) inhibited the metabolism of chlorotoluron in both resistant and susceptible plants by reducing the formation of non‐toxic aryl‐hydroxylated derivatives and polar conjugates. N‐demethylations were less susceptible to ABT than the other oxidative reactions, but this does not necessarily imply that the second detoxification activity is not Cyt P450, as some P450 activities are more susceptible to ABT than others. Ring‐methyl hydroxylation inhibition affected the ability of resistant plants to recover photosynthetic activity after incubation in chlorotoluron, showing a similar fluorescence pattern to susceptible plants in the same conditions without ABT. Fluorescence and metabolism data strongly support the thesis of Cyt P450‐mediated 4‐methylphenyl hydroxylation as the main route of detoxification of chlorotoluron in the resistant biotype.