IDENTIFICATION OF COMPATIBLE AND INCOMPATIBLE INTERACTIONS BETWEEN ARABIDOPSIS-THALIANA AND XANTHOMONAS-CAMPESTRIS PV CAMPESTRIS AND CHARACTERIZATION OF THE HYPERSENSITIVE RESPONSE

Both compatible and incompatible interactions between Arabidopsis thal iana and Xanthomonas campestris have been identified and, for the firs t time, a strong hypersensitive response has been characterized. A hig hly reproducible mass spray inoculation protocol has been established and was used together with the more commonly used infiltration inocula tion procedure to study the defense responses occurring in mature A. t haliana plants. A series of bacterial strains have been tested on A. t haliana ecotype Columbia (Col-O). X. c. pv. campestris was the most ef fective pathogen in these tests and was used for further detailed anal ysis. Several X. c. pv. campestris isolates were tested on A. thaliana Col-O, and one particular X. c. pv. campestris strain (147) was teste d on 27 Arabidopsis ecotypes. Symptom development of compatible and in compatible interactions, including the hypersensitive response, was ex tensively characterized in A. thaliana Col-O. Lesion structure, bacter ial distribution, accumulation of polyphenolic compounds, and the depo sit of callose in inoculated leaves were documented by microscopic ana lysis. Activation of the defense-associated genes coding for phenylala nine ammonia lyase (PAL), beta-1, 3-glucanases, chitinases, and peroxi dases was evaluated by Northern blot analysis.