INDUCTION OF PR-1 PROTEINS AND POTENTIATION OF PATHOGEN SIGNALS BY SALICYLIC-ACID EXHIBIT THE SAME DOSE-RESPONSE AND STRUCTURAL SPECIFICITYIN PLANT-CELL CULTURES

Based on the marked difference in both dose response and structural sp ecificity, it has been recently proposed that the induction of acquire d resistance and pathogenesis-related (PR) proteins in intact plant le aves and the potentiation of pathogen signals in plant cell cultures b y salicylic acid (SA) and its analogues are mediated by different SA s ignaling pathways initiated from different SA receptor systems, We sho w here, however, that the induction of PR-1 proteins, the most widely used marker of acquired resistance, by SA and its analogues in tobacco cell cultures exhibits the same dose response and structural specific ity as the potentiation of pathogen signals demonstrated in soybean ce ll cultures. The different dose response and structural specificity fo r the induction of PR-I proteins by SA between intact tobacco leaves a nd cell cultures appear to be caused largely by the difference in upta ke and/or metabolism of these chemical inducers by different types of plant cells, These results suggest that the potentiation of pathogen s ignals by SA, which may contribute greatly to SA function, does not in volve a different, more potent signaling pathway from the one(s) respo nsible for the induction of acquired resistance and PR protein accumul ation.