Monoenoic fatty acids, biosynthesis

As mentioned earlier, many seed oils produce a fatty acid that is different from the usual leaf fatty acids and which is characteristic of the plant family (Table II) (Smith, 1970 Hitchcock and Nichols, 1971). In general this makes a useful marker for seed oil development (Fig. 7). Caution is needed, since the characteristic fatty acid is not always exclusive to the oil. Appelqvist (1975) has demonstrated the presence of the monoenoic acid in the hypocotyls and testa ofB. napus, as well as in the cotyledons. It should be noted, however, that the structure of the major C22 monoenoic acid in the testa is not that of erucic acid (cis-13-docosenoic acid) but of an isomer, cis-15-docosenoic acid (Table VIII). Thus, if whole seeds are used in tracer studies of erucic acid biosynthesis or compartmentation, care must be taken in the interpretation of results if anjdysis is made only of the whole C22 monoene fraction (Appelqvist, 1975). Again it is emphasized that, although the subcellular compartmentation of erucic acid may not be exclusive to the major sites of oil storage, the compartmentation within lipid classes is absolutely exclusive to the triacyigiycerols as opposed to the polar lipids (Table III). 

The information about FA biosynthesis and/or uptake obtained from determining the location of double bonds can be clearly exemplified with the case of 18 1 FA. There are three major isomers of 18 1 FA in the majority of the biological samples, i.e., n-7, n-9, and n-12 18 1 FA isomers with minimal amount of others, particularly with a double bond in an even-numbered position [9]. The 18 1 (n-9) FA isomer (commonly called oleic acid ) is by far the most abundant monoenoic FA in both plant and animal tissues. This isomer also serves the biosynthetic precursor of a family of fatty... 

---