Oxylipin profiling reveals the preferential stimulation of the 9-lipoxygenase pathway in elicitor-treated potato cells

Lipoxygenases are key enzymes in the synthesis of oxylipins and play an imp ortant role in the response of plants to wounding and pathogen attack. In c ultured potato cells treated with elicitor from Phytophthora infestans, the causal agent of late blight disease, transcripts encoding a Linoleate 9-li poxygenase and a Linoleate 13-lipoxygenase accumulate. However, lipoxygenas e activity assays and oxylipin profiling revealed only increased 9-lipoxyge nase activity and formation of products derived therefrom, such as 9-hydrox y octadecadienoic acid and colneleic acid. Furthermore, the 9-lipoxygenase products 9(S),10(S),11(R)-trihydroxy-12(Z)-octadecenoic and 9(S),10(S),11(R )-trihydroxy-12(Z),15(Z)-octadecadienoic acid were identified as novel, eli citor-inducible oxylipins in potato, suggesting a role of these compounds i n the defense response against pathogen attack. Neither 13-lipoxygenase act ivity nor 13-lipoxygenase products were detected in higher amounts in potat o cells after elicitation. Thus, formation of products by the 9-lipoxygenas e pathway, including the enzymes hydroperoxide reductase, divinyl ether syn thase, and epoxy alcohol synthase, is preferentially stimulated in cultured potato cells in response to treatment with P. infestans elicitor. Moreover , elicitor-induced accumulation of desaturase transcripts and increased pho spholipase A(2) activity after elicitor treatment suggest that substrates f or the lipoxygenase pathway might be provided by de novo synthesis and subs equent release hom lipids of the endomembrane system.