title: Suppression of arbuscular mycorrhizal colonization and nodulation in split-root systems of alfalfa after pre-inoculation and treatment with Nod factors.
abstract: Roots of legumes establish symbiosis with arbuscular mycorrhizal fungi (AMF) and nodule-inducing rhizobia. The existing nodules systemically suppress subsequent nodule formation in other parts of the root, a phenomenon termed autoregulation. Similarly, mycorrhizal roots reduce further AMF colonization on other parts of the root system. In this work, split- root systems of alfalfa (Medicago sativa) were used to study the autoregulation of symbiosis with Sinorhizobium meliloti and the mycorrhizal fungus Glomus mosseae. It is shown that nodulation systemically influences AMF root colonization and vice versa. Nodules on one half of the split-root system suppressed subsequent AMF colonization on the other half. Conversely, root systems pre-colonized on one side by AMF exhibited reduced nodule formation on the other side. An inhibition effect was also observed with Nod factors (lipo-chito-oligosaccharides). NodSm-IV(C16:2, S) purified from S. meliloti systemically suppressed both nodule formation and AMF colonization. The application of Nod factors, however, did not influence the allocation of (14)C within the split-root system, excluding competition for carbohydrates as the regulatory mechanism. These results indicate a systemic regulatory mechanism in the rhizobial and the arbuscular mycorrhizal association, which is similar in both symbioses.
authors.affiliation: CRBF, Faculté de Foresterie et de Géomatique, Université Laval, Pavillon C-E. Marchand, Ste-Foy G1K 7P4, Québec, Canada.
authors.forename: Jean-Guy
authors.initials: JG
authors.lastname: Catford
authors.forename: Christian
authors.initials: C
authors.lastname: Staehelin
authors.forename: Sylvain
authors.initials: S
authors.lastname: Lerat
authors.forename: Yves
authors.initials: Y
authors.lastname: Piché
authors.forename: Horst
authors.initials: H
authors.lastname: Vierheilig
mesh_terms: D002244:Carbon / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D000455:Medicago sativa / Q000187:drug effects / Q000254:growth & development* / Q000382:microbiology; D038821:Mycorrhizae / Q000187:drug effects / Q000254:growth & development*; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development* / Q000382:microbiology; D016962:Sinorhizobium meliloti / Q000187:drug effects / Q000254:growth & development; D013559:Symbiosis / Q000187:drug effects / Q000502:physiology*
chemical_list: D008070:Lipopolysaccharides; C092082:Nod factor IV, Rhizobium meliloti; D002244:Carbon