THE INTERACTION OF HARPIN(PSS), WITH PLANT-CELL WALLS

Erwinia amylovora and Pseudomonas syringae pv. syringae produce elicit ors of the hypersensitive reaction (HR), harpin(Ea) and harpin(Pss), r espectively. Harpin(Ea) causes K+ efflux and extracellular alkalinizat ion in suspension-cultured cells of tobacco. These responses are assoc iated with disease resistance. We treated living, fixed, and permeabil ized cells and protoplasts from tobacco suspension cultures with harpi n(Pss), antiharpin(Pss) antibody, and fluorochrome-tagged antibody and examined them with confocal laser microscopy. The fluorescent signal was localized in the outer part of the cell and was not observed in pr otoplasts. EGTA, a chelating agent that extracts Ca++ and pectins from cell walls, blocked harpin(Pss) binding, as evidenced by the absence of fluorescent signal. The pH of the external medium of suspension cul tures alkalinized in response to harpin(Pss) and P. s. syringae. Bacte ria and harpin(Pss)-induced alkalinization of the extracellular medium were also completely blocked upon EGTA treatment. Protoplasts alkalin ized the medium at much reduced levels in response to P. syringae pv. syringae and did not alkalinize the medium in response to harpin(Pss). These results suggest that the cell wall is crucial for RR induction in the suspension culture cell.