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Carbon Metabolism and Bacteroid Functioning Are Involved in the Regulation of Nitrogen Fixation in Medicago truncatula Under Drought and Recovery

December 2009 , Volume 22 , Number  12
Pages  1,565 - 1,576

Estíbaliz Larrainzar,1 Stefanie Wienkoop,2 Christian Scherling,3 Stefan Kempa,3 Rubén Ladrera,1 Cesar Arrese-Igor,1 Wolfram Weckwerth,2 and Esther M. González1

1Dpto. Ciencias del Medio Natural, Universidad Pública de Navarra, 31006 Pamplona, Spain; 2Department of Molecular Systems Biology, University of Vienna, 1090 Vienna, Austria; 3Max Planck Institute of Molecular Plant Physiology, 14424 Potsdam-Golm, Germany

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Accepted 27 July 2009.

Regulation of symbiotic nitrogen fixation (SNF) during drought stress is complex and not yet fully understood. In the present work, the involvement of nodule C and N metabolism in the regulation of SNF in Medicago truncatula under drought and a subsequent rewatering treatment was analyzed using a combination of metabolomic and proteomic approaches. Drought induced a reduction of SNF rates and major changes in the metabolic profile of nodules, mostly an accumulation of amino acids (Pro, His, and Trp) and carbohydrates (sucrose, galactinol, raffinose, and trehalose). This accumulation was coincidental with a decline in the levels of bacteroid proteins involved in SNF and C metabolism, along with a partial reduction of the levels of plant sucrose synthase 1 (SuSy1). In contrast, the variations in enzymes related to N assimilation were found not to correlate with the reduction in SNF, suggesting that these enzymes do not have a role in the regulation of SNF. Unlike the situation in other legumes such as pea and soybean, the drought-induced inhibition of SNF in M. truncatula appears to be caused by impairment of bacteroid metabolism and N2-fixing capacity rather than a limitation of respiratory substrate.

© 2009 The American Phytopathological Society