Development from acetolactate synthase

A great number of herbicides that work through the inhibition of acetolactate synthase (ALS) have been commercialized. They belong to four chemical groups sulfonylureas (23), triazolopyrimidines (2), imidazolinones (5), and pyrimidinyloxybenzoic analogues (3). (The number of active ingredients in parentheses is taken from The Pesticide Manual.) Also in this case, potent herbicides were developed (e.g., chlorsulfuron) before the site of action was found. 

Some groups of herbicides depend upon phloem translocation to reach their sites of action. For example, the phenoxyalkanoic acid herbicides, which act on cell growth and development, and glyphosate, which inhibits the biosynthesis of aromatic amino acids, are translocated from leaves to all sites of active growth within the plant. Similarly, the sulfonylureas and imidazolinones, which inhibit acetolactate synthase, are, when applied postemergence, translocated in the phloem to all parts of the plant. 

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