Molecular Control of Nitrate Reductase and Other Enzymes Involved in Nitrate Assimilation

  • Wilbur H. Campbell
Part of the Advances in Photosynthesis and Respiration book series (AIPH, volume 12)


Nitrate acts as both a nutrient and a signal in plants. Nitrate induces gene expression of enzymes for its metabolism into amino acids but also has other effects on plant metabolism and development. Familiar nitrate-induced enzymes are nitrate and nitrite reductases, nitrate transporters, glutamine synthetase, glutamate synthase, ferredoxin and ferredoxin NADP+ reductase. Microarray analysis of nitrate-stimulated gene expression has identified 40 transcripts including hemoglobin, transaldolase, regulatory and stress proteins, several protein kinases and several methyltransferases. Coordinated expression of these nitrate-stimulated genes is probably due to a single ‘nitrate-transacting factor’ and a ‘nitrate’ box has been elucidated for nitrate and nitrite reductase genes with constitutively expressed nuclear proteins which bind to the box. A MADS transcription factor is nitrate-induced in roots and involved in development of lateral roots. However, accumulation of nitrate overcomes this signal and halts lateral root development. Post-translational inhibition of nitrate reductase activity illustrates a complex control mechanism involving protein phosphorylation and binding of the ubiquitous binding protein called 14-3-3. Protein kinases catalyzing phosphorylation have been identified and 14-3-3 binding elucidated, which includes activation of 14-3-3 by polycations such as polyamines. Using molecular modeling, it was shown that one 14-3-3 binding site can bind to the nitrate reductase dimer. Nitrate reductase-14-3-3 complexes could bind via the second binding site on 14-3-3 to another enzyme/protein with a 14-3-3 binding site or nitrate reductase aggregation could result in rapid degradation. Two types of protein kinases are involved in nitrate reductase phosphorylation: calcium-dependent protein kinases and SnRKs (enzymes related to yeast sucrose non-fermenting (SNF1) protein kinases). Calcium-dependent protein kinases are activated by environmental and development signals via changes in intracellular calcium level, which impacts many plant metabolic pathways. SnRKs are less well understood and may be responding to more general metabolic signals.


BPB — bromophenol blue CbR — Cyt b reductase fragment of NR CDPK — calcium-dependent protein kinase Cyt — cytochrome GOGAT — glutamate synthase GS — glutamine synthetase MADS — MCM1, AGAMOUS, DEFICIENS, and serum response factor genes Mo-MPT — molybdenum-molybdopterin cofactor MoR — molybdenum reductase fragment of NR MV — methyl viologen NiR — nitrite reductase NR — nitrate reductase SNF1 — sucrose non-fermenting control gene encoding a protein kinase SnRK1 — plant protein kinases related to yeast SNF1 protein kinase 


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Copyright information

© Kluwer Academic Publishers 2002

Authors and Affiliations

  • Wilbur H. Campbell
    • 1
  1. 1.Department of Biological SciencesMichigan Technological UniversityHoughtonUSA

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