Nitrogen uptake and assimilation process in plants.

<p>The uptake of nitrate (NO₃^-) and ammonium (NH₄⁺) ions is mediated by nitrate (NRT) and ammonium transporters (AMT), respectively. The NO₃^- entered into the cell is reduced to nitrite ions (NO₂^-) by an enzyme nitrate reductase (NR). The nitrite ion then moves to plastid and reduced to ammonium ion by nitrite reductase (NiR) enzyme. The ammonium is then incorporated into amino acid by glutamine synthetase and glutamate synthase via GS/GOGAT cycle. The ammonium ion transported by ammonium transporters directly enters into GS/GOGAT cycle. The two additional enzymes glutamate dehydrogenase (GDH) and asparagine synthetase (ASN) also participates in ammonium assimilation. The GS, GDH and ASN are the key enzymes involved in synthesis of glutamine (Gln), Glutamate (Glu) and Asparagine (Asn).