Anacardic acids, alkyl phenolic acids excreted by tall glandular trichomes of the garden geranium, Pelargonium xhortorum, confer small-pest resistance. Up to 90% of the trichome exudate from mite-resistant P. xhortorum inbreds consists of an unusual anacardic acid with an unsaturated omega-5 (ω5) alkyl chain. As fatty acids are biochemical precursors to anacardic acids, we examined by GC the fatty acid composition of leaves, pedicels, petals, sepals, mature seeds, and glandular trichomes from pest-resistant and pest-susceptible Pelargonium inbred lines to determine the localization of ω5-fatty acids within plant tissues. The fatty acid composition of lipid classes (galactolipids, phospholipids, and neutral lipids) extracted from glandular trichomes from mite-resistant pedicels were also examined. ω5-Fatty acids (16:1Δ11 and 18:1Δ13) were found only in the glandular trichomes from pest-resistant geraniums (27.2% in trichomes of pedicels) and were localized predominantly in the phospho- and galactolipids (phosphatidylinositol, 25.9%; phosphatidylcholine, 18.2%; monogalactosyldiglyceride, 15.5%; and diglactosyldiglyceride, 14.0%).
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