ABSTRACT
Detoxification is an important mechanism by which many plants as well as bacteria develop natural tolerance to a variety of herbicides. This chapter describes how metabolic inactivation has been used as a powerful and effective tool in engineering tolerance to the nonselective, broad-spectrum, postemergent, contact herbicide DL-phosphinothricin. L-phosphinothricin (PPT) is a potent inhibitor of the biosynthetic enzyme glutamine synthetase (GS), which is involved in general nitrogen metabolism in plants, including the assimilation of ammonia accumulated as a result of photorespiration and nitrate reduction. Varying levels of phosphinothricin-N-acetyl-transferase (PAT) activity were found in independently transformed plants, but even plants with low levels of PAT activity were found be herbicide resistant. The performance of transgenic PPT-resistant tobacco and potato plants in field trials in Europe was similar to nontransformed plants. A novel use of resistance to PPT has been made for hybrid seed production in oilseed rape by linking it to a male sterility gene.
