Reduction of nitrate in higher plants

This paper summarises the mechanism of the reduction of nitrate to nitrite as the key process in the assimilation of nitrate, The role of the enzyme n itrate reductase in higher plants is discussed, The structure of the enzyme is presented and an idea is given of its Function and regulation. On entering the plant cell, nitrate is utilised after a number of reduction steps in the form of ammonium, which is used for creating N-containing int ermediaries, mainly amino acids. The key enzyme of the reaction is nitrate reductase (NR), which consists of three domains: three polypeptide units li nking a coenzyme FAD, a hem unit and a molybdenum cofactor, respectively Th e molybdenum cofactor (MoCo) connected to the N-terminal of the polypeptide chain performs the actual reduction of nitrate to nitrite. The function of NR is well controlled at the transcriptional, translational and posttranslational levels. Its most important activator is nitrate, but light, sucrose and its metabolites, and cytokinins also affect the functio ning of the enzyme too. Its repressors are nitrogen metabolites, especially glutamine. The regulation of the enzyme activity is achieved by postsyntet ic phosphorylation.