Induction of lipoxygenase activity in immunized cucumber plants

Lipoxygenase (LOX) activity increased in cucumber leaves (leaf 1) inoculated with either Colletotrichum lagenarium or tobacco necrosis virus (TNV) or sprayed with dipotassium phosphate. LOX activity also increased in noninoculated leaves above inoculated or treated leaves (leaf 2, systemic). The increase in LOX activity in leaf 1 and leaf 2 was evident at the time when systemic induced resistance became apparent, i.e. 2, 3 and 4 days after induction with dipotassium phosphate, TNV and C. lagenarium, respectively. Detection of LOX after electrophoretic separation in native gels indicated that inoculation or treatment with dipotassium phosphate caused the accumulation of a major LOX isozyme which was not apparent in noninoculated control leaves. The increase in LOX activity correlated with a decrease in the amount of LOX substrates, linoleic and linolenic acids, and in the total fatty acid fraction in cucumber leaves. The possible involvement of LOX and fatty acid metabolism in the induction of systemic resistance is discussed.