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JXB Advance Access originally published online on August 13, 2008
Journal of Experimental Botany 2008 59(13):3509-3522; doi:10.1093/jxb/ern203
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© The Author [2008]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

RESEARCH PAPER

The model symbiotic association between Medicago truncatula cv. Jemalong and Rhizobium meliloti strain 2011 leads to N-stressed plants when symbiotic N2 fixation is the main N source for plant growth

Delphine Moreau, Anne-Sophie Voisin, Christophe Salon and Nathalie Munier-Jolain*

INRA – UMR Génétique et Ecophysiologie des Légumineuses, 17 rue Sully, BP 86510, F-21065 Dijon cedex, France

* To whom correspondence should be addressed. E-mail: munierjo{at}dijon.inra.fr

A better knowledge of the nitrogen nutrition of Medicago truncatula at the whole plant level and its modulation by environmental factors is a crucial step to reach a complete understanding of legume nitrogen nutrition. This study was based on the symbiotic system that is the most commonly used by the research community (M. truncatula cv. Jemalong A17xRhizobium meliloti strain 2011). Plant nitrogen nutrition was analysed in relation to carbon nutrition, under a range of nitrate concentrations in the nutrient solution and different light conditions. This study shows that this ‘model symbiotic association’ does not allow the plant to meet its nitrogen requirements, when dinitrogen fixation is the main nitrogen source for plant growth. A strong interaction between nitrogen and carbon nutrition was shown: when plant nitrogen requirements were not sustained, plant leaf area was much affected whereas photosynthesis per unit leaf area remained relatively stable. Both total nitrogen uptake and leaf area increased with increasing nitrate concentration in the nutrient solution; the magnitude of these responses varied according to the light conditions. Interestingly, the plant nitrogen nutrition level remained nearly unaffected by the light conditions. The observed nitrogen-limitation in this ‘model symbiotic association’ is an important finding for the research community. Based on practical recommendations regarding both the experimental conditions and the phenotypic traits to consider, a methodological framework was proposed to (i) help genomicists to assess plant nitrogen nutrition better, and (ii) assist in the detection of new genetic variants affected for nitrogen uptake in large-scale phenotyping studies.

Key words: Carbon, genetic variability, growth, leaf area, Medicago truncatula, nitrate assimilation, nitrogen, phenotyping, symbiotic dinitrogen fixation

Received 17 April 2008; Revised 30 June 2008 Accepted 7 July 2008


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