Nitrate reductase: a target for molecular and cellular studies in higher plants.

Nitrate reductase (NR) is a key enzyme in the assimilation of nitrate by plants. NR expression can be selected either for or against, both at the cellular level and at the level of the whole plant, and numerous mutants affected at the locus for the nia structural gene--which encodes the NR apoenzyme--have been identified. The nia gene, which has now been cloned, is a useful tool for molecular genetic studies in higher plants; furthermore, a combined genetic and biochemical approach to studying NR should allow an insight into the catalytic process of a multicenter redox enzyme.