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

Transgenic tobacco lines expressing the borage Delta(6)-fatty acid desaturase were characterized for the accumulation of novel Delta(6)-unsaturated fatty acids, Two such fatty acids, gamma-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. Delta(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 Delta(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 Delta(6)-desaturated fatty acids in the storage triacylglycerols of seeds. As the borage Delta(6)-desaturase is most probably located in the endoplasmic reticulum, the present data suggest that Delta(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.