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Changes in Cucumber Cotyledon Membrane Lipid Fatty Acids During Paraquat Treatment and a Bacteria-Induced Hypersensitive Reaction. L. Dale Keppler, University of Missouri, Department of Plant Pathology, Columbia 65211, Current address: USDA-ARS, Bldg. 010, HH5, Beltsville, MD 20705; Anton Novacky, University of Missouri, Department of Plant Pathology, Columbia 65211. Phytopathology 79:705-708. Accepted for publication 10 February 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-705.

There is evidence that lipid peroxidation initiated by O2 radicals may be involved in altered plant cell membrane permeability in a bacteria-induced hypersensitive reaction. Such alterations have also been reported for paraquat-treated plants. Likely membrane targets for lipid peroxidation are unsaturated fatty acyl groups. We monitored levels of different fatty acyl groups in cucumber cotyledons during paraquat treatment and during a hypersensitive reaction induced by Pseudomonas syringae pv. pisi. Fatty acyl groups from galactolipids (a lipid found specifically in plastids) and polar lipids (found in all cell membranes) were analyzed in a total lipid extract. We also analyzed fatty acyl groups from polar lipids of an enriched plasma membrane fraction. The results verified that paraquat treatment reduces fatty acid unsaturation in plastid lipids. Fatty acid unsaturation decreased in the enriched plasma membrane fraction during both paraquat treatment and the hypersensitive reaction. These changes were concurrent with the onset of tissue collapse. We suggest that O2-initiated lipid peroxidation produced the altered plant cell membrane permeability observed in both paraquat treatment and bacteria-induced hypersensitive reaction.