Planta

, Volume 211, Issue 4, pp 587–595

Negative regulation of nitrate reductase gene expression by glutamine or asparagine accumulating in leaves of sulfur-deprived tobacco

  • Andrea Migge
  • Christiane Bork
  • Rüdiger Hell
  • Thomas W. Becker

DOI: 10.1007/s004250000322

Cite this article as:
Migge, A., Bork, C., Hell, R. et al. Planta (2000) 211: 587. doi:10.1007/s004250000322
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Abstract.

 Tobacco (Nicotiana tabacum L.) plants were subjected to a prolonged period of sulfur-deprivation to characterize molecular and metabolic mechanisms that permit control of primary N-metabolism under these conditions. Prior to the appearance of chlorotic lesions, sulfur-deprived tobacco leaves showed a strong decrease in the sulfate content and changes in foliar enzyme activities, mRNA accumulation and amino-acid pools. The basic amino acids glutamine, asparagine and arginine accumulated in the leaves of sulfur-deprived plants, while the foliar concentrations of aspartate, glutamate, serine or alanine remained fairly unchanged. Maximal extractable nitrate reductase (NR; EC 1.6.6.1) activity decreased strongly in response to sulfur-deprivation. The decrease in maximal extractable NR activity was accompanied by a decline in NR transcripts while the mRNAs of the plastidic glutamine synthetase (EC 6.1.3.2) or the β-subunit of the mitochondrial ATP synthase were much less affected. Nitrate first accumulated in leaves of tobacco during sulfur-deprivation but then declined. An appreciable amount of nitrate was, however, present in severely sulfur-depleted leaves. The repression of NR gene expression is, therefore, not related to the decrease in the leaf nitrate level. However, glutamine- and/or asparagine-mediated repression of NR gene transcription is a possible mechanism of control in situations when glutamine and asparagine accumulate in leaves and provides a feasible explanation for the reduction in NR activity during sulfur-deprivation. The removal of reduced nitrogen from primary metabolism by redirection and storage as arginine, asparagine or glutamine combined with the down-regulation of nitrate reduction via glutamine- and/or asparagine-mediated repression of NR gene transcription may contribute to maintaining a normal N/S balance during sulfur-deprivation and indicate that the co-ordination of N- and S-metabolism is retained under these conditions.

Key words: Amino acid – Glutamine synthetase – Nitrate assimilation – Nitrate reductase –Nicotiana (sulfur-deprivation) – Sulfur-deprivation 

Copyright information

© Springer-Verlag Berlin Heidelberg 2000

Authors and Affiliations

  • Andrea Migge
    • 1
  • Christiane Bork
    • 2
  • Rüdiger Hell
    • 3
  • Thomas W. Becker
    • 1
  1. 1.Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Postfach 10 01 31, 33501 Bielefeld, GermanyDE
  2. 2.Lehrstuhl für Pflanzenphysiologie, Ruhr-Universität-Bochum, 44801 Bochum, GermanyDE
  3. 3.Institut für Pflanzengenetik und Kulturpflanzenforschung, Abteilung Molekulare Zellbiologie, 06466 Gatersleben, GermanyDE

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