ABSTRACT
Glutamine synthetase (GS) is an important enzyme in nitrogen assimilation, photorespiration, and carbon balance in plants (see Chap. 2). Consequently, inhibitors of GS can have dramatic effects on plants. Both natural and synthetic GS inhibitors have been identified. Although few new GS inhibitors have been discovered since the comprehensive reviews of Lea and Ridley (1989) and Lea (1991), infonnation on the physiological and biochemical effects of GS inhibitors on plants continues to emerge. The commercial herbicides bialaphos (Hcmiace, Meiji Seika Kaisha. Japan) and glufosinate (Liberty and Basta. Hoechst AG, Gennany) are GS inhibitors. Genes for resistance to GS inhibitors have been used to develop herbicide-resistant crops (MUllner et al. 1993; Vasil 1996; also see Chap. 17). Furthermore, genes for the production of natural GS inhibitors have been isolated, and pathogens modified with these gene clusters are being developed as biological control agents of agriculturally important weeds (see Lydon 1996). This chapter will discuss the present state of knowledge of the physiological and biochemical effects of GS inhibitors. In addition, the biosynthesis and molecular genetics of the natural GS inhibitors and the resistance mechanisms to them will be discussed.
