ABSTRACT
To be successful, commercial herbicides must control weeds, display crop safety, and have low toxicity toward other organisms. The sulfonylurea herbicides fulfill these requirements admirably, and, in addition, are applied at very low use rates and are available for use in several crops. This chapter summarizes the previous work on sulfonylurea herbicide resistance in crops and reviews the progress since 1989 in developing new resistant crops through selection and transformation. The molecular target of the sulfonylurea herbicides is the enzyme acetolactate synthase (ALS), also known as acetohydroxyacid synthase (AHAS). The quaternary structure of ALS is apparently different between prokaryotes and eukaryotes. Sulfonylurea herbicide resistance has been introduced into crops using two methods. One method involves the selection of mutant cells or seeds on sulfonylurea-impregnated media, and the other method involves the introduction of genes encoding insensitive forms of ALS through transformation. The relationship between ALS gene expression and whole-plant resistance was examined in detail with transgenic tobacco.
