Two effects of combined nitrogen on the adhesion of Rhizobium etli to bean roots
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Combined forms of nitrogen negatively influence rhizobia-legume symbiosis. The effects of combined nitrogen are known for nodulation and dinitrogen (N2) fixation, but little is known about the effect on preinfection events. Here, we studied the effects of combined nitrogen on the adhesion of Rhizobium etli to common bean (Phaseolus vulgaris L.) roots. When potassium nitrate (KNO3) or sodium glutamate was added to an incubation mixture of rhizobia and plants that were previously grown in nitrogen-free solution, rhizobial adhesion to roots was stimulated. However, the rhizobial adhesion to bean roots that were previously grown with 10 mM KNO3 was reduced by half. A fraction of the bean root exudates, which is thermolabile and has molecular mass larger than 12 kDa stimulated rhizobial adhesion, but this stimulatory activity was lost in root exudates obtained with 10 mM KNO3. Thus, the inhibition of symbiosis in response to combined nitrogen may be controlled by the plant at the preinfection stage as well.
KeywordsNitrate Root exudate Adhesion Rhizobium
This work was supported by Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT, Argentina). JPG is researcher at Universidad Nacional de La Plata and ARL is member of the Scientific Career of Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), both of Argentina. The authors are grateful to Paula Giménez, Silvana Tongiani, Abel Bortolameotti and Bernabé Castillo for their excellent technical assistance.
- Caetano-Anollés G, Favelukes G (1986) Quantitation of adsorption of rhizobia in low numbers to small legume roots. Appl Environ Microbiol 52:371–376Google Scholar
- Calderón-Flores A, Du Pont G, Huerta-Saquero A, Merchant-Larios H, Servín-González L, Durán S (2005) The stringent response is required for amino acid and nitrate utilization, nod factor regulation, nodulation, and nitrogen fixation in Rhizobium etli. J Bacteriol 187:5075–5083PubMedCrossRefGoogle Scholar
- Quelas JI, Mongiardini EJ, Casabuono A, López-García SL, Althabegoiti MJ, Covelli JM, Pérez-Giménez J, Couto A, Lodeiro AR (2010) Lack of galactose or galacturonic acid in Bradyrhizobium japonicum USDA 110 exopolysaccharide leads to different symbiotic responses in soybean. Mol Plant-Microbe Interact 23:1592–1604PubMedCrossRefGoogle Scholar
- Robledo M, Jiménez-Zurdo JI, Velázquez E, Trujillo ME, Zurdo-Piñeiro JL, Ramírez-Bahena MH, Ramos B, Díaz-Minguez JM, Dazzo F, Martínez-Molina E, Mateos PF (2008) Rhizobium cellulase CelC2 is essential for primary symbiotic infection of legume host roots. Proc Natl Acad Sci USA 105:7064–7069PubMedCrossRefGoogle Scholar
- Smit G, Logman TJJ, Boerrigter M, Kijne JW, Lugtenberg BJJ (1989) Purification and partial characterization of the Rhizobium leguminosarum biovar viciae Ca2+-dependent adhesin, which mediates the first step in attachment of cells of the family Rhizobiaceae to plant root hair tips. J Bacteriol 171:4054–4062PubMedGoogle Scholar
- Vincent JM (1970) A manual for the practical study of the root nodule bacteria. IBP Handbook No. 15. Blackwell Scientific Publications, OxfordGoogle Scholar