Planta

, Volume 215, Issue 3, pp 424–429

Expression of the NH4+-transporter gene LEAMT1;2 is induced in tomato roots upon association with N2-fixing bacteria

  • Dirk Becker
  • Ruediger Stanke
  • Istvan Fendrik
  • Wolf B. Frommer
  • Jos Vanderleyden
  • Werner M. Kaiser
  • Rainer Hedrich
Original Article

DOI: 10.1007/s00425-002-0773-x

Cite this article as:
Becker, D., Stanke, R., Fendrik, I. et al. Planta (2002) 215: 424. doi:10.1007/s00425-002-0773-x

Abstract.

Plants growing in close association with N2-fixing bacteria are able to overcome growth limitations in N-depleted soils. The molecular mechanism by which free-living, N2-fixing bacteria promote plant growth is still a matter of debate. By inoculating N-depleted tomato (Lycopersicon esculentum Mill.) plants with Azospirillum brasilense or Azoarcus sp. we could demonstrate the induction of the root NH4+-transporter gene, LEAMT1;2 (L. esculentum ammonium transporter 1;2), indicating that bacterial NH4+ might be used as an N source under these conditions. Azospirillum brasilense (nif) mutants, which lack the structural nifDK genes, failed to induce LEAMT1;2 expression. This suggests that root-associated N2-fixing bacteria do excrete NH4+ to levels that can be sensed by tomato roots and is in agreement with the induction of expression of LEAMT1;2 with as low as ≥1 µM external NH4+. While peak expression was obtained with 2–5 µM NH4+, a further increase in NH4+ reduced LEAMT1;2-mRNA levels in a concentration-dependent manner. The inhibition of LEAMT1;2 expression by glutamine and the glutamine synthetase blocker L-methionine sulfoximine (MSX) provided evidence for the control of LEAMT1;2 expression by cytoplasmic NH4+ concentration or the plant N status. Since micromolar concentrations of NH4+ strongly increased the LEAMT1;2-mRNA levels, the transported NH4+ ion itself could represent a key signal in the associative interaction between higher plants and N2-fixing micro-organisms.

Ammonium transport Growth-promoting bacteria Lycopersicon-(N2 fixation) Nitrogen fixation Plant–microbe interaction 

Copyright information

© Springer-Verlag 2002

Authors and Affiliations

  • Dirk Becker
    • 1
  • Ruediger Stanke
    • 2
  • Istvan Fendrik
    • 2
  • Wolf B. Frommer
    • 3
  • Jos Vanderleyden
    • 4
  • Werner M. Kaiser
    • 1
  • Rainer Hedrich
    • 1
  1. 1.Julius von Sachs-Institut, Molekulare Pflanzenphysiologie & Biophysik, Julius-von-Sachs-Platz 2, 97082 Würzburg, Germany
  2. 2.Institut für Biophysik, Universität Hannover, Herrenhäuser Str. 2, 30419 Hannover, Germany
  3. 3.Botanisches Institut, Universität Tübingen, Auf der Morgenstelle 1, 72076 Tübingen, Germany
  4. 4.F.A. Janssens Laboratory of Genetics, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, 3001 Heverlee, Belgium

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