Protection Induced by Protein‐Lipopolysaccharide Complexes in Tobacco Leaves: Role of Protected Tissue Free‐space Solutes

Hypersensitive confluent necrosis in tobacco leaves, caused by Pseudomonas syringae pv. aptata, is prevented by an intercellular injection of protein‐lipopolysaccharide (pr‐LPS) complexes 48 h earlier. An increase (48 %) in the peroxidase activity and a new low molecular weight protein (ε 17.5 kD) were found in the intercellular fluid of protected tissue (treated fluid) 48 h after pr‐LPS infiltration. Up to 24 h after pr‐LPS infiltration the treated fluid did not inhibit the in vitro growth of heterologous bacteria. Injected into tobacco leaves 30 min before the bacteria, the treated fluid retarded the rate of intercellular bacterial growth between 8 and 12 h after infiltration of the bacteria compared with the control fluid. Up to 4 h after injection, the attachment of live and dead bacteria to the cell walls occurred in both the protected tissue and in the control; 4 h after injection, however, the dead bacteria were only weakly attached in the protected tissue. Within 20 min after the intercellular infiltration, there was a decrease in the heterologous bacterial number in the protected tissue, 33 % less than that in the control tissue. Protected tissue free‐space solutes did not have a direct antibacterial effect but activated an antibacterial response in the leaf tissue. Attachment of bacteria to the cell walls did not in itself trigger hypersensitive confluent necrosis. The protected tissue was initially more favourable for the survival of heterologous bacteria. Copyright © 1989, Wiley Blackwell. All rights reserved