Accumulation of Δ6-unsaturated fatty acids in transgenic tobacco plants expressing a Δ6-desaturase from Borago officinalis

Transgenic tobacco lines expressing the borage Δ 6 -fatty acid desaturase were characterized for the accumulation of novel Δ 6 -unsaturated fatty acids. Two such fatty acids, γ-linolenic acid and octadecatetraenoic acid, were found to be present in a range of seed and non-seed tissues, though accumulation in seed tissues was low. The distribution of these novel fatty acids amongst the various lipid classes of the tobacco leaf was examined. Δ 6 -Unsaturated fatty acids were found in both plastidic and microsomal lipids and positional analysis revealed that the novel fatty acids accumulated predominantly at the sn-2 position of the glycerolipid backbone. These data indicate that Δ 6 -desaturated fatty acids are readily incorporated into a range of membrane lipids, unlike other unusual plant fatty acids. However, it may be that a number of different factors regulate the accumulation of Δ 6 -desaturated fatty acids in the storage triacylglycerols of seeds. As the borage Δ 6 -desaturase is most probably located in the endoplasmic reticulum, the present data suggest that Δ 6 -unsaturated fatty acids present in the plastid lipids are likely to have arisen as a result of import into this organelle after desaturation in the ER.