THE METABOLISM OF HERBICIDES*

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Abstract
Summary. A knowledge of the metabolism of herbicides within plants is of importance in a number of ways. Thus, whilst governmental control of the toxicity of potential herbicides is being exercised by fixing acceptable levels of residues, information may also be required an the toxicity of their possible metabolites. This aspect is not pursued but metabolism of chemicals by plants is divided into that which: (1) militates against their efficiency (deactivation), (2) introduces useful biological properties, (3) is essential to their biological activity (activation).The metabolism of the important herbicides of each class is reviewed briefly and its effect on their use in the field described where possible. Emphasis, however, is given to the unique mode of action of the bipyridylium quaternary ammonium compounds—diquat and paraquat—as herbicides in the last class, depending for their activity on a reduction by the plant In toxic free radicals. Evidence for the participation of free radicals in their herbicidal activity is presented, and their physical and biological properties described. Physiological processes involved in this free radical production are discussed and also hypotheses concerning their mode of action.Le métabolisme des herbicides