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Involvement of Salicylic Acid in the Establishment of the Rhizobium meliloti-Alfalfa Symbiosis

February 1998 , Volume 11 , Number  2
Pages  153 - 155

F. Martínez-Abarca , 1 J. A. Herrera-Cervera , 1 P. Bueno , 2 J. Sanjuan , 1 T. Bisseling , 3 and J. Olivares 1

1Departamento de Microbiología del Suelo y Sistemas Simbióticos; 2Departamento de Bioquímica y Biología Molecular y Celular de Plantas, Estación Experimental del Zaidín, CSIC, Profesor Albareda, 1. 18008 Granada, Spain; 3Department of Molecular Biology, Wageningen Agricultural University, 67034A Wageningen, The Netherlands

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Accepted 15 October 1997.

Inoculation of alfalfa plants with either incompatible Rhizobium or a Rhizobium mutant blocked in Nod factor synthesis led to an accumulation of salicylic acid in roots, in contrast to plants inoculated with a wild-type (compatible) R. meliloti strain. When salicylic acid was exogenously applied prior to inoculation of alfalfa plants with either purified Nod factor or compatible Rhizobium strains, a significant inhibition of nodule primordia formation and a reduction of the number of emerging nodules, respectively, as well as a delay in nodule visualization, were observed. These results suggest an involvement of Rhizobium-synthesized Nod factors in the inhibition of salicylic acid-mediated defense in legumes.

Additional keywords: hypersensitive response, plant defense, systemic acquired resistance.

© 1998 The American Phytopathological Society