O2-Initiated Lipid Peroxidation in a Bacteria-Induced Hypersensitive Reaction in Tobacco Cell Suspensions

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Abstract
O2- Initiated lipid peroxidation was observed in a hypersensitive reaction induced in an incompatible plant/bacterium combination of tobacco cell suspension and the phytopathogenic bacterium Pseudomonas syringae pv. syringae. The earliest symptoms of this hypersensitive reaction are increases in extracellular pH and K+. A Tn5 insertion mutant of P. s. syringae which does not induce the hypersensitive reaction, and Pseudomonas syringae pv. tabaci, a pathogen of tobacco, were used as controls. Transient increases in lipid peroxidation and O2- production which preceded the initial increases in extracellular pH and K+ were observed. Recovery of P. s syringae was lower from cell suspensions undergoing a hypersensitive reaction than from those treated with bacteria that did not induce a hypersensitive reaction. O2- scavengers added with P. s. syringae inhibited initial transient O2- production and lipid peroxidation and increased recovery of bacteria. O2--Initiated lipid peroxidation seems to be involved in the hypersensitive reaction, on O2- radicals may be involved in reduced recovery of bacteria during the reaction.