Cyclohexanediones (e.g., sethoxydim) are known to be inhibitors of plastid acetyl-CoA carboxylase (ACCase) of monocotyledonous plants and provoke plant death. When rape leaves were treated with 10(-3) M sethoxydim, growth rate, chlorophyll and lipid contents were reduced, but plant resisted to herbicide. [1-(14)C] Acetate labelling showed that lipid synthesis was affected by sethoxydim, probably through inhibition of chloroplast homomeric ACCase activity, and the fatty acid synthase activity (FAS) was reduced because of malonyl-CoA deficiency. In contrast, sethoxydim treatment provoked an increase in phenylalanine ammonia lyase (PAL) activity with an accumulation of cinnamic acid, naringenin and anthocyanins. The accumulation of anthocyanins seems to reduce the damaging effect of the herbicide stress. Thus, in plant cell, the flux of carbon seems to be oriented towards protective mechanisms, and the two ACCases could have an important role in this orientation.
Keywords: Acetyl-CoA carboxylase (ACCase); Cyclohexanediones; Fatty acid synthase (FAS); Flavonoid metabolism; Phenylalanine ammonia lyase (PAL); Sethoxydim.
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