title: Growth and nodulation of symbiotic Medicago truncatula at different levels of phosphorus availability.
abstract: Medicago truncatula is an important model plant for characterization of P deficiency on leguminous plants at the physiological and molecular levels. Growth optimization of this plant with regard to P supply is the first essential step for elucidation of the role of P in regulation of nodulation. Hence, a study was carried out to address the growth pattern of M. truncatula hydroponically grown at different gradual increases in P levels. The findings revealed that M. truncatula had a narrow P regime, with an optimum P level (12 μM P) which is relatively close to the concentration that induces P toxicity. The accumulated P concentration (2.7 mg g(-1) dry matter), which is normal for other crops and legumes, adversely affected the growth of M. truncatula plants. Under P deficiency, M. truncatula showed a higher symbiotic efficiency with Sinorhizobium meliloti 2011 in comparison with S. meliloti 102F51, partially as a result of higher electron allocation to N2 versus H(+). The total composition of free amino acids in the phloem was significantly affected by P deprivation. This pattern was found to be almost exclusively the result of the increase in the asparagine level, suggesting that asparagine might be the shoot-derived signal that translocates to the nodules and exerts the down-regulation of nitrogenase activity. Additionally, P deprivation was found to have a strong influence on the contents of the nodule carbon metabolites. While levels of sucrose and succinate tended to decrease, a higher accumulation of malate was observed. These findings have provided evidence that N2 fixation of M. truncatula is mediated through an N feedback mechanism which is closely related to nodule carbon metabolism.
authors.affiliation: Signaling Pathway Research Unit, RIKEN Center for Sustainable Resource Science, 1-7-22, Suehiro-cho, Tsurumi, Yokohama 230-0045, Japan.
authors.forename: Saad
authors.initials: S
authors.lastname: Sulieman
authors.forename: Chien Van
authors.initials: CV
authors.lastname: Ha
authors.forename: Joachim
authors.initials: J
authors.lastname: Schulze
authors.forename: Lam-Son Phan
authors.initials: LS
authors.lastname: Tran
mesh_terms: D046913:Medicago truncatula / Q000254:growth & development* / Q000378:metabolism* / Q000382:microbiology; D009586:Nitrogen Fixation; D010758:Phosphorus / Q000378:metabolism*; D055170:Plant Root Nodulation; D053204:Root Nodules, Plant / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology; D016962:Sinorhizobium meliloti / Q000502:physiology*; D013559:Symbiosis
chemical_list: D010758:Phosphorus
keywords: Asparagine; Medicago truncatula; carbon and nitrogen metabolites; feedback; nitrogen fixation; nitrogenase activity; nodulation; phloem; phosphorus availability; plant growth; symbiosis capacity; translocation.