Tobacco plants accumulating high levels of soluble sugars due to the cytosolic expression of an inorganic pyrophosphatase from Escherichia coli were ušed to study adaptation to the osmotic stress that these plants are continuously faced with. In the course of differential RNA screening between wild type and transgenic plants three cDNA dones could be isolated, which after sequencing were identified as pathogenesis-related proteins (PR-proteins). Two cDNAs, PRlb and PR-P, belong to the acidic PRl and PR3 groups of PR-proteins, and the third cDNA, SAR8.2, has so far been associated with systemic acquired resistance in tobacco plants. The expression of PR-proteins transcripts in generál was well correlated with the steady- state level of total soluble sugars present in the tobacco plants. The induction of PR protein transcripts resulted in an accumulation of corresponding proteins. Moreover, the complete set of acidic PR-proteins induced by potato virus Y was also present in the sugar-accumulating transgenic plants. The induction of PR-proteins might be a generál response to the osmotic stress in tobacco plants.