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Nanogram Amounts of Salicylic Acid Produced by the Rhizobacterium Pseudomonas aeruginosa 7NSK2 Activate the Systemic Acquired Resistance Pathway in Bean

May 1999 , Volume 12 , Number  5
Pages  450 - 458

Geert De Meyer , 1 Kristof Capieau , 1 Kris Audenaert , 1 Antony Buchala , 2 Jean-Pierre Métraux , 2 and Monica Höfte 1

1Lab of Phytopathology, Faculty of Agricultural and Applied Biological Sciences, University Gent, Coupure links, 653, B-9000 Gent, Belgium; 2Institut de Biologie Végétale, Rue Albert-Gockel 3, Université de Fribourg, CH-1700 Fribourg, Switzerland

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Accepted 3 February 1999.

Root colonization by specific nonpathogenic bacteria can induce a systemic resistance in plants to pathogen infections. In bean, this kind of systemic resistance can be induced by the rhizobacterium Pseudomonas aeruginosa 7NSK2 and depends on the production of salicylic acid by this strain. In a model with plants grown in perlite we demonstrated that Pseudomonas aeruginosa 7NSK2-induced resistance is equivalent to the inclusion of 1 nM salicylic acid in the nutrient solution and used the latter treatment to analyze the molecular basis of this phenomenon. Hydroponic feeding of 1 nM salicylic acid solutions induced phenylalanine ammonia-lyase activity in roots and increased free salicylic acid levels in leaves. Because pathogen-induced systemic acquired resistance involves similar changes it was concluded that 7NSK2-induced resistance is mediated by the systemic acquired resistance pathway. This conclusion was validated by analysis of phenylalanine ammonia-lyase activity in roots and of salicylic acid levels in leaves of soil-grown plants treated with Pseudomonas aeruginosa. The induction of systemic acquired resistance by nanogram amounts of salicylic acid is discussed with respect to long-distance signaling in systemic acquired resistance.

Additional keywords: Botrytis cinerea, induced systemic resistance.

© 1999 The American Phytopathological Society