title: N-feedback regulation is synchronized with nodule carbon alteration in Medicago truncatula under excessive nitrate or low phosphorus conditions.
abstract: The aim of the present study was to test the hypothesis that the higher nodule amino acid content induced under certain treatments may play a role in the N-feedback regulation of nitrogenase (EC 1.18.6.1) activity by restricting the carbon supply to the functioning nodules. Growing Medicago truncatula plants under sub-optimal phosphorus conditions or upon exposure to large supply of nitrate caused significant asparagine accumulation in nodules of the treated plants. In addition, there was a remarkable decline in the nodule succinate content under phosphorus deprivation while malate was tended to increase. Interestingly, the relative share of succinate in the symbiotic tissues was totally inhibited, i.e. reached zero, by excessive nitrate application. These results provide evidence that succinate might be greatly affected by asparagine content of the nodule fraction, thereby restricting cellular carbon supply to the functioning bacteroids which leads to down-regulation of nodule metabolism and nitrogenase activity.
authors.affiliation: Signaling Pathway Research Unit, RIKEN Center for Sustainable Resource Science (CSRS), 1-7-22, Suehiro-cho, Tsurumi, Yokohama 230-0045 Japan; Department of Agronomy, Faculty of Agriculture, University of Khartoum, 13314 Shambat, Khartoum North, Sudan. Electronic address: s.sulieman@psc.riken.jp.
authors.forename: Saad
authors.initials: S
authors.lastname: Sulieman
authors.affiliation: Department für Nutzpflanzenwissenschaften Abteilung Pflanzenernährung, Georg-August-Universität Göttingen, Carl-Sprengel-Weg 1, 37075 Göttingen, Germany. Electronic address: jschulz2@gwdg.de.
authors.forename: Joachim
authors.initials: J
authors.lastname: Schulze
authors.affiliation: Signaling Pathway Research Unit, RIKEN Center for Sustainable Resource Science (CSRS), 1-7-22, Suehiro-cho, Tsurumi, Yokohama 230-0045 Japan. Electronic address: son.tran@riken.jp.
authors.forename: Lam-Son Phan
authors.initials: LS
authors.lastname: Tran
mesh_terms: D001216:Asparagine / Q000378:metabolism; D002244:Carbon / Q000378:metabolism; D015536:Down-Regulation; D025461:Feedback, Physiological; D018506:Gene Expression Regulation, Plant; D018527:Hydroponics; D046913:Medicago truncatula / Q000201:enzymology / Q000382:microbiology / Q000502:physiology*; D008954:Models, Biological; D009566:Nitrates / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000378:metabolism*; D052585:Phloem / Q000201:enzymology / Q000382:microbiology / Q000502:physiology; D010758:Phosphorus / Q000378:metabolism*; D018517:Plant Roots / Q000201:enzymology / Q000382:microbiology / Q000502:physiology; D018520:Plant Shoots / Q000201:enzymology / Q000382:microbiology / Q000502:physiology; D053204:Root Nodules, Plant; D016962:Sinorhizobium meliloti / Q000502:physiology*; D019802:Succinic Acid / Q000378:metabolism; D013559:Symbiosis
chemical_list: D009566:Nitrates; D010758:Phosphorus; D001216:Asparagine; D002244:Carbon; D019802:Succinic Acid; D009591:Nitrogenase; D009584:Nitrogen
keywords: Asparagine; Carbon metabolism; Medicago truncatula; N feedback; Succinate