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Gentisic Acid As a Pathogen-Inducible Signal, Additional to Salicylic Acid for Activation of Plant Defenses in Tomato

March 1999 , Volume 12 , Number  3
Pages  227 - 235

José María Bellés , 1 Rafael Garro , 1 Joaquín Fayos , 1 Pilar Navarro , 1 Jaime Primo , 2 and Vicente Conejero 1

1Instituto de Biología Molecular y Celular de Plantas, and 2Instituto de Tecnlogía Química, Universidad Politécnica de Valencia-Consejo Superior de Investigaciones Científicas, Camino de Vera s/n, 46022 Valencia, Spain

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Accepted 1 December 1998.

Citrus exocortis viroid (CEVd) and tomato mosaic virus (ToMV), which produce a systemic non-necrotizing infection in tomato (Lycopersicon esculentum cv. Rutgers), strongly induced the accumulation of a phenolic compound that we have characterized as 2,5-dihydroxybenzoic acid (gentisic acid, GA) by nuclear magnetic resonance, following purification by high-performance liquid chromatography. Levels of free and total GA increased more than 150-fold in response to CEVd and ToMV infections. Unlike these non-necrotizing infections, the necrotizing reaction elicited by Pseudomonas syringae pv. syringae in this host did not produce any accumulation of GA. It is also shown that, in healthy leaf tissues, benzoic acid (BA) and salicylic acid (SA) were rapidly converted to GA, SA being the immediate precursor of GA, according to radiolabeling studies. Interestingly, exogenous GA elicited accumulation of the previously described CEVd-induced antifungal pathogenesis-related (PR) proteins P23, P32, and P34. These proteins were not induced by exogenous SA, which is able to elicit other CEVd-induced PR proteins in tomato. These results suggest that GA acts as a pathogeninduced signal, additional to SA, for activation of plant defense genes in tomato.

Additional keywords: antifungal proteins, phenolics.

© 1999 The American Phytopathological Society