Suppression of arbuscular mycorrhizal colonization and nodulation in split‐root systems of alfalfa after pre‐inoculation and treatment with Nod factors

• Published in: Journal of experimental botany 2003-05, Vol.54 (386), p.1481-1487
• Main Authors: Catford, Jean‐Guy, Staehelin, Christian, Lerat, Sylvain, Piché, Yves, Vierheilig, Horst
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Alfalfa; Autoregulation; Biological and medical sciences; Carbon - metabolism; Crop harvesting; Economic plant physiology; Fundamental and applied biological sciences. Psychology; Glomales; Key words: Arbuscular mycorrhiza; Lipopolysaccharides - pharmacology; Medicago sativa; Medicago sativa - drug effects; Medicago sativa - growth & development; Medicago sativa - microbiology; Microbial colonization; Mycorrhizae - drug effects; Mycorrhizae - growth & development; Nod factors; Nodulation; Nodules; Parasitism and symbiosis; Plant physiology and development; Plant roots; Plant Roots - drug effects; Plant Roots - growth & development; Plant Roots - microbiology; Plants; RESEARCH PAPER; Root systems; Sinorhizobium meliloti; Sinorhizobium meliloti - drug effects; Sinorhizobium meliloti - growth & development; split‐root system; Symbiosis; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...); Symbiosis - drug effects; Symbiosis - physiology
• ISSN: 0022-0957; 1460-2431; 1460-2431
• DOI: 10.1093/jxb/erg156

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 14C 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.