Occurrence of gamma-linolenic acid in compositae: a study of Youngia tenuicaulis seed oil.

Seeds of Youngia tenuicaulis and other species from the plant family Compositae (Asteraceae) were studied for their oil content and fatty acid composition. The seed oil of Y. tenuicaulis growing in Mongolia was found to contain 5.6% gamma-linolenic acid (18:3delta6cis,9cis,12cis) in addition to common fatty acids. The oil was analyzed using chromatographic [capillary gas-liquid chromatography (GLC), thin-layer chromatography] and spectroscopic (infrared, gas chromatography-mass spectrometry) techniques. Seed oil fatty acids of Saussurea amara (containing gamma-linolenic acid) and of Arctium minus (containing 18:3delta3trans,9cis,12cis), as well as delta5cis- and delta5trans-18:3 were used as GLC reference substances. The evolution in this plant family of a large number of different 18:3 acids as well as the corresponding evolution of unusual desaturases should be investigated. On the other hand, the delta6cis-desaturase required for the biosynthesis of gamma-linolenic acid may have evolved independently several times in unrelated families of the plant kingdom.