DEGRADATION PATTERNS OF PECTIC SUBSTRATES RELATED TO THE LOCALIZATIONOF BACTERIAL PECTATE-LYASES IN THE MODEL ERWINIA-CHRYSANTHEMI SAINTPAULIA-IONANTHA

Erwinia chrysanthemi is a bacterium which macerates host plant tissues by secreting at least five major pectate-lyases (PLa-e) which depolym erize the homogalacturonans of the cell walls. Immunocytochemical stud ies were carried out on Saintpaulia ionantha leaves inoculated with E. chrysanthemi to localize both the homogalacturonans of the plant cell walls and the PLs a/d secreted by the bacterium. Different degradatio n patterns of pectic substrates were observed by following the loss of immunolabelling: several cell walls were highly degraded whereas some areas were still highly labelled, giving the walls a dotted appearanc e. The first attachment sites of PLa/d were on the side of the wall fa cing the intercellular spaces. In more degraded walls the enzymes were more regularly distributed throughout the walls. Local domains were e videnced where the substrate was not accessible for the PLs a/d. The i nvolvement of the battery of PLs secreted by E. chrysanthemi in host-p lant interactions is discussed. (C) 1997 Academic Press Limited.