Mechanism of paraquat action: inhibition of the herbicidal effect by a copper chelate with superoxide dismutating activity.

The treatment of flax cotyledons (Linium usitatissimum) with paraquat was shown to decrease the levels of chlorophyll and carotenoid pigments. The fatty acid content of chloroplast fragments isolated from treated tissue was determined and shown to be greatly decreased by paraquat treatment. The superoxide radical was demonstrated to play an important role in the phytotoxic action of paraquat by the use of a copper chelate of D-penicillamine, which has a high superoxide is discussed with reference to the generation of more toxic species, such as singlet oxygen.