INDUCTION OF PATHOGENESIS-RELATED PROTEINS IN SUGAR ACCUMULATING TOBACCO-LEAVES

Tobacco plants accumulating high levels of soluble sugars due to the c ytosolic expression of an inorganic pyrophosphatase from Escherichia c oli were used to study adaptation to the osmotic stress that these pla nts are continuously faced with. In the course of differential RNA scr eening between wild type and transgenic plants three cDNA clones could be isolated, which after sequencing were identified as pathogenesis-r elated proteins (PR-proteins). Two cDNAs, PR1b and PR-P, belong to the acidic PR1 and PR3 groups of PR-proteins, and the third cDNA, SAR8.2, has so far been associated with systemic acquired resistance in tobac co plants. The expression of PR-proteins transcripts in general was we ll correlated with the steady-state level of total soluble sugars pres ent in the tobacco plants. The induction of PR protein transcripts res ulted in an accumulation of corresponding proteins. Moreover, the comp lete set of acidic PR-proteins induced by potato virus Y was also pres ent in the sugar-accumulating transgenic plants. The induction of PR-p roteins might be a general response to the osmotic stress in tobacco p lants.