Molecular Characterization Of Maize Nadh:Nitrate Reductase

Abstract

The long-term goals of research on higher plant nitrate reductase (NR) are: (1) to understand the structure of the enzyme in relation to its mechanism of action; and (2) to explain how NR is regulated in relation to plant metabolism. Both goals are highly complex, but when they are pursued simultaneously, the most rapid progress is achieved. We have pursued the biochemistry of NR in squash (Cucurbita maxima), since it has been easy to obtain large quantities of homogeneous enzyme from its cotyledons (Campbell 1989). At the same time, we have studied the physiology of NR in maize (Zea mays), since it is a plant with agronomic importance and has been studied for a long time (Campbell 1988). At first, we bridged the gap between NR in these plant systems using immunochemical methods and now, a much stronger bridge has been established with molecular biology methods. Cloning and sequencing of NR has provided new insight into the structure of the enzyme (Crawford and Davis 1988; Galangau et al. 1988). At the same time, the availability of molecular probes for NR has made it possible to study the regulation of NR at the level of its mRNA (Kleinhofs et al. 1988; Gowri and Campbell 1989). Here I describe our recent progress toward gaining a unified understanding of NR biochemistry and physiology in maize.