Identification of Compatible and Incompatible Interactions Between Arabidopsis thaliana and Xanthomonas campestris pv. campestris and Characterization of the Hypersensitive Response. M. Lummerzheim. Laboratorium voor Genetica, Universiteit Gent, B-9000 Gent, Belgium. D. de Oliveira(2), C. Castresana(1), F. C. Miguens(3), E. Louzada(2), D. Roby(4), M. Van Montagu(1), and B. Timmerman(2). (1)Laboratorium voor Genetica, Universiteit Gent, B-9000 Gent, Belgium, (2)Laboratório de Genética Molecular Vegetal, and (3)Laboratório de Microscopia Electrônica e Ultrastructura Cellular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil. (4)Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, F-31326 Castanet - Tolosan, France.. MPMI 6:532-544. Accepted 22 April 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993.

Both compatible and incompatible interactions between Arabidopsis thaliana and Xanthomonas campestris have been identified and, for the first time, a strong hypersensitive response has been characterized. A highly reproducible mass spray inoculation protocol has been established and was used together with the more commonly used infiltration inoculation procedure to study the defense responses occurring in mature A. thaliana plants. A series of bacterial strains have been tested on A. thaliana ecotype Columbia (Col-O). X. c. pv. campestris was the most effective pathogen in these tests and was used for further detailed analysis. Several X. c. pv. campestris isolates were tested on A. thaliana Col-O, and one particular X. c. pv. campestris strain (147) was tested on 27 Arabidopsis ecotypes. Symptom development of compatible and incompatible interactions, including the hypersensitive response, was extensively characterized in A. thaliana Col-O. Lesion structure, bacterial distribution, accumulation of polyphenolic compounds, and the deposit of callose in inoculated leaves were documented by microscopic analysis. Activation of the defense-associated genes coding for phenylalanine ammonia lyase (PAL), Beta-1, 3-glucanases, chitinases, and peroxidases was evaluated by Northern blot analysis.