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Metabolism of Lipids Containing Arachidonic and Eicosapentaenoic Acids in Race-Specific Interactions Between Phytophthora infestans and Potato. R. M. Bostock, Associate professor, Department of Plant Pathology, University of California, Davis 95616; Phytopathology 79:898-902. Accepted for publication 28 April 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-898.

Lipids containing the radioisotope-labeled elicitors arachidonic (AA) and eicosapentaenoic (EPA) acids were extracted from Phytophthora infestans and applied to potato disks (cv. Kennebec), which were subsequently inoculated with spores of an incompatible (race 0) or compatible (race 1,4) isolate of P. infestans. Lipids were extracted from the disks at various times after inoculation and analyzed. Inoculation with either race resulted in a significant decline in the proportion of radioactivity recovered in triglycerides within 24 hr after inoculation and concomitant increases in polar lipid and free fatty acid pools. Between 6 and 48 hr after inoculation, the pattern was similar in both interactions. From 24 to 72 hr after inoculation, acyl esterase, phospholipase, and lipase activities were similarly affected in both interactions. However, between 6 and 12 hr after inoculation, phospholipase and lipase activities in the incompatible interaction exceeded the activities in disks inoculated with the compatible race. Lipoxygenase activity was similar in all treatments and declined slightly during this same period. These results indicate that inoculation with P. infestans stimulates degradation of lipids containing AA and EPA, and during the initial stages of infection the activities of lipolytic enzymes capable of releasing these elicitors are slightly higher in the incompatible interaction than in the compatible interaction.

Additional keywords: hypersensitive response, lipase, lipolytic acyl hydrolase, lipoxygenase.