Biochemistry of the Target and Resistance

Herbicidal sulfonylureas have a unique mode of action they interfere with a key enzyme required for plant cell growth - acetohydroxyacid synthase (AHAS, EC 2.2.1.6) [1, 2, 3] (see also Mark E. Thompson in this volume, Chapter 2.1 Biochemistry of the Target and Resistance ). AHAS is the enzyme responsible for the synthesis of the branched-chain amino acids valine, leucine and isoleucine. Inhibition of this enzyme disrupts the plant s ability to manufacture proteins, and this disruption subsequently leads to the cessation of all cell division and eventual death of the plant. 

With the introduction of Be 1 complex inhibitors (Chapter 13.2) in 1996, which act on the electron transport of fungi cells, the most important new compound class called strobilurins, derived from the natural compound Strobilurin A, was introduced in the reference period to the market. Chapter 13 describes the biochemistry of oxidative phosphorylation and of the related compounds and compound classes acting at different sites, reflecting the importance of these targets for the fungicide market nowadays. At the same time it became evident that resistance development, e.g., in the compound class of strobilurins must not lead necessarily to the abandonment of the marketing, research and development of such chemistry. 

Devine, M.D. and C.V. Eberlein (1997). Physiological, biochemical and molecular aspects of herbicide resistance based on altered target sites, pp. 295-348. In Roe, R.M. J.D. Burton, and R.J. Kuhr, eds., Herbicide Activity Toxicology, Biochemistry and Molecular Biology. Amsterdam, The Netherlands I. O. S. Press, Inc. 

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