Target Sites For Herbicide Action

The development of chemicals to selectively control the growth of weeds has been a fascinating success story which has unfolded largely during the last four decades. The dramatic growth of herbicide research that followed the wartime discoveries of the auxin-type herbicides (phenoxyalkanoic acids) resulted in a whole range of compounds and mixtures which are used to eliminate broad-or narrow-leaved weeds from agricultural, horticul tural, or forestry crops. Today, the safe use of this armament of compounds requires our understanding of their mode of action, metabolism, and environmental persistence. The most recently developed herbicides are highly effective inhibitors of specific enzyme systems, and formulation may be an important factor determining their efficient delivery at specific target sites. In this book, the major target sites of herbicide action are discussed in Chapters 1-5, with particular reference to photosynthesis; amino acid, lipid, and carotenoid synthesis; and other primary target sites. The effects of synergists or antagonists as modifiers of herbicide action are described in Chapter 6. The importance of efficient target site delivery as a fundamental factor in herbicide activity and selectivity is generally recognized. Delivery of a potentially lethal dose of active ingredient may depend on a whole range of factors including the efficiency of application, retention, absorption, translocation, immobilization, and detoxification. These aspects are con sidered in the remaining chapters, with particular reference to the pathways and mechanisms involved in the uptake, translocation, and metabolism of soil-and foliage-applied herbicides.

This publication is based on the plant processes and reaction sites for which reliable knowledge on both their physiology and biochem-istry and the mode of herbicidal action is available. Targets of the agrochemical research, such as enzymes of biosynthetic pathways or herbicide-binding peptides in the photosynthetic membrane, are highlighted. Detailed knowledge about the target sites will allow bio-chemical model systems to evaluate the biological activity of newly synthesized compounds before their conventional screening in the greenhouse. Quantitative structure/activity relationships should be performed more reliably with simple biological species or enzymol-ogy assays, to aid in the rational design of pesticides. This text is highly valuable for plant physiologists, pathologists, and chemists in the agrochemical industry and universities.

This publication is based on the plant processes and reaction sites for which reliable knowledge on both their physiology and biochem-istry and the mode of herbicidal action is available. Targets of the agrochemical research, such as enzymes of biosynthetic pathways or herbicide-binding peptides in the photosynthetic membrane, are highlighted. Detailed knowledge about the target sites will allow bio-chemical model systems to evaluate the biological activity of newly synthesized compounds before their conventional screening in the greenhouse. Quantitative structure/activity relationships should be performed more reliably with simple biological species or enzymol-ogy assays, to aid in the rational design of pesticides. This text is highly valuable for plant physiologists, pathologists, and chemists in the agrochemical industry and universities.

An introduction to herbicide action; Reaching the target; Oxigen toxicity and herbicidal action; Microtubule disruptors; Herbicide effects on lipid synthesis; Nucleic acid and protein synthesis inhibitors; Inhibition of amino acid biosysnthesis; Herbicides with auxin activity; Other sites of herbicide action; Secondary physiological effects of herbicides; Herbicide interactions with herbicides, synergists, and safeners; Naturally occurring chemicals as herbicides.

This book presents the progress made in the study of the mode of action of phytotoxic compounds that have been developed as herbicides in the recent past. The 13 chapters are written by experts in herbicide research and development, chemists, biochemists, and plant physiologists. The biochemistry of the target enzymes is described together with model assays, molecular genetics and special reference to transgenic herbicide-resistant crops. Additional chapters deal with new synthetic chemical pathways, chirality effects found in certain herbicide classes, and transcuticular pesticide penetration.

Developments in the understanding of herbicide activity and toxicology have expanded tremendously in the past fifteen years. Research on the mechanism of action of most major classes of herbicide chemistry has provided scientists with excellent insight into enzyme targets. More recently, developments in molecular biology have provided information about herbicide action at the genetic level. Less well understood are the toxicological aspects of herbicide activity that culminate in plant injury or death. Toxicology, Biochemistry and Molecular Biology of Herbicide Activity is a review of the recent literature on most of the major classes of herbicide chemistry in commercial use. The chapters include information about different aspects of herbicide activity related to photosynthesis, inhibition of amino acid biosynthesis, disruption of cell division and microtubule assembly, activity of phytohormone (auxin) mimics, inhibition of fatty acid biosynthesis and some developments in the understanding of herbicide resistance.