Genetics and Molecular Biology of Higher Plant Nitrate Reductases

Abstract

Nitrate assimilation is the primary pathway through which most reduced nitrogen is accumulated in plants. The pathway consists of two well characterized enzymes, nitrate and nitrite reductases. Poorly characterized nitrate uptake and transport mechanisms are also involved. Nitrate reductase (NR) catalyzes the reduction of nitrate to nitrite which is then reduced to ammonium ion by nitrite reductase. Incorporation of ammonium ion into amino acids is carried out by the glutamine synthetaseglutamate synthase pathway. The first step in the nitrate assimilation pathway, nitrate reductase, is highly regulated and is believed to be rate limiting. There has been a great deal of research concerning the biochemistry, genetics and physiology of NR which has recently been reviewed.1–3 Also a recent comprehensive conference was held on the topic of nitrate assimilation, and the proceedings will be published.4 Readers are referred to these works and the references therein for a detailed review. Here we will concentrate on NR, especially the recent accomplishments.