Fig. 7.

Model proposed for the effect of NO on nitrate reductase activity (NRA). In low-level nitrate supply conditions, NRA was stimulated by the basal endogenous NO or the NO induced by chemical compounds via a post-translational regulatory pathway. However, in high-level nitrate supply conditions, the NRA was inhibited by the basal endogenous NO also via a post-translational regulatory pathway. The role of the physiological processes on nitrate assimilation and NO synthesis in conditions of low and high levels of nitrate supply speculated on above should be further studied. A red ‘ × ’ in the figure denotes that the pathway is not acted on by NO, and ‘NR’ denotes the enzyme protein of nitrate reductase.