Biochemistry, Molecular Genetics and Regulation of Nitrate Reductase in Nicotiana Plumbaginifolia, Tobacco and Tomato

The nitrate assimilation pathway is known to be tightly controlled in plants by many endogenous and environmental factors (Beevers and Hageman 1983), the most important being the nature and availability of the nitrogen source, and light. Nitrate compartmentalization and flux between plant tissues and inside plant cells are clearly the first critical steps in that control, but are, as yet, refractory to molecular analysis. The second step, nitrate reduction into ammonium, is catalysed by two enzymes, a likely cytosolic nitrate reductase (NR), and a plastidial nitrite reductase, both induced by nitrate. Interestingly, each factor known to control the overall pathway appears to control NR, which is thus thought to play a central role in regulation of the nitrate assimilation pathway.