Pathogen attacks and treatment of many plant species by various chemicals induce the synthesis of pathogenesis-related (PR) proteins. These host-encoded, low molecular mass proteins have been well studied in tobacco reacting hypersensitively to infection by TMV. A partial cDNA clone encoding for β-1,3-glucanase was used as a probe to study the kinetics of accumulation of the corresponding mRNAs in tobacco leaves infiltrated with water or with compatible (K60), incompatible (GMI1000), and avirulent (GMI1178) isolates of a phytopathogenic bacterium, Pseudomonas solanacearum. A nonspecific accumulation of these transcripts, independent of the nature of the inoculum, was observed. Similar results were obtained with pCHN50, a chitinase-encoding cDNA clone. In addition, antibodies directed against several PR proteins were used to estimate the accumulation of these proteins in tobacco leaves infiltrated for 18 hr with the same P. solanacearum isolates or with water: no qualitative or quantitative difference could be detected. These data show that the stress provoked by our technique of infiltration of bacteria in leaves induces a nonspecific accumulation of these PR proteins. In addition, our results indicate that these polypeptides are not sufficient to provoke the appearance of necrotic lesions associated with the hypersensitive reaction.
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Laurence Godiard (1990) studied this question.