title: Rhizobial strains exert a major effect on the amino acid composition of alfalfa nodules under NaCl stress.
abstract: Specific amino acids have protective functions in plants under stress conditions. This study assessed the effects of rhizobial strains on the amino acid composition in alfalfa under salt stress. Two alfalfa cultivars (Medicago sativa L. cv Apica and salt-tolerant cv Halo) in association with two Sinorhizobium meliloti strains with contrasting growth under salt stress (strain A2 and salt-tolerant strain Rm1521) were exposed to different levels of NaCl (0, 20, 40, 80 or 160 mM NaCl) under controlled conditions. We compared root and shoot biomasses, as well as root:shoot ratio for each association under these conditions as indicators of the salt tolerance of the symbiosis. Amino acid concentrations were analyzed in nodules, leaves and roots. The total concentration of free amino acids in nodules was mostly rhizobial-strain dependent while in leaves and roots it was mostly responsive to salt stress. For both cultivars, total and individual concentrations of amino acids including asparagine, proline, glutamine, aspartate, glutamate, γ-aminobutyric acid (GABA), histidine and ornithine were higher in Rm1521 nodules than in A2 nodules. Conversely, lysine and methionine were more abundant in A2 nodules than in Rm1521 nodules. Proline, glutamine, arginine, GABA and histidine substantially accumulated in salt-stressed nodules, suggesting an enhanced production of amino acids associated with osmoregulation, N storage or energy metabolism to counteract salt stress. Combining the salt-tolerant strain Rm1521 and the salt-tolerant cultivar Halo enhanced the root:shoot ratios and amino acid concentrations involved in plant protection which could be in part responsible for the enhancement of salt tolerance in alfalfa.
authors: Soils and Crops Research and Development Centre, Agriculture and Agri-Food Canada, Québec, G1V 2J3, QC, Canada. Electronic address: Annick.Bertrand@agr.gc.ca.
authors: Annick
authors: A
authors: Bertrand
authors: Departement de phytologie, 2425 rue de l'agriculture, Université Laval, Québec, G1V 0A6, QC, Canada. Electronic address: marie.bipfubusa.1@ulaval.ca.
authors: Marie
authors: M
authors: Bipfubusa
authors: Departement de phytologie, 2425 rue de l'agriculture, Université Laval, Québec, G1V 0A6, QC, Canada. Electronic address: Catherine.dhont.1@ulaval.ca.
authors: Catherine
authors: C
authors: Dhont
authors: Departement de phytologie, 2425 rue de l'agriculture, Université Laval, Québec, G1V 0A6, QC, Canada. Electronic address: Francois-p.chalifour@fsaa.ulaval.ca.
authors: François-P
authors: FP
authors: Chalifour
authors: Université du Québec en Abitibi-Témiscamingue (UQAT), Rouyn-Noranda, J9X 5E4, QC, Canada. Electronic address: pdrouin@lallemand.com.
authors: Pascal
authors: P
authors: Drouin
authors: Departement de phytologie, 2425 rue de l'agriculture, Université Laval, Québec, G1V 0A6, QC, Canada. Electronic address: Chantal.Beauchamp@fsaa.ulaval.ca.
authors: Chantal J
authors: CJ
authors: Beauchamp
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000455:Medicago sativa / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism* / Q000382:microbiology*; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology; D011392:Proline / Q000378:metabolism; D053204:Root Nodules, Plant / Q000378:metabolism* / Q000382:microbiology*; D055049:Salt Tolerance / Q000502:physiology; D016962:Sinorhizobium meliloti / Q000502:physiology*; D012965:Sodium Chloride / Q000494:pharmacology; D013312:Stress, Physiological; D013559:Symbiosis
chemical_list: D000596:Amino Acids; D012965:Sodium Chloride; D011392:Proline
keywords: Amino acids; Forage; Legume; Medicago sativa L.; Proline; Salt tolerance; Sinorhizobium meliloti