Delta 5-olefinic acids in the seed lipids from four Ephedra species and their distribution between the alpha and beta positions of triacylglycerols. Characteristics common to Coniferophytes and Cycadophytes

The fatty acid compositions of the seed lipids from four Ephedra species, E . nevadensis, E. viridis, E. przewalskii, and E. gerardiana (four gymnosper m species belonging to the Cycadophytes), have been established with an emp hasis on Delta 5-unsaturated polymethylene:interrupted fatty acids (Delta 5 -UPIFA). Mass spectrometry of the picolinyl ester derivatives allowed chara cterization of 5,9- and 5,11-18:2; 5,9,12-18:3; 5,9,12,15-18:4; 5,11-20:2; 5,11,14-20:3; and 5,11,14,17-20:4 acids. Delta 5-UPIFA with a Delta 11-ethy lenic bond (mostly C-20 acids) were in higher proportions than Delta 5-UPIF A with a Delta 9 double bond (exclusively C-18 acids) in all species. The t otal 5-UPIFA content was 17-31% of the total fatty acids, with 5,11,14-20:3 and 5,11,14,17-20:4 acids being the principal Delta 5-UPIFA isomers. The r elatively high level of cis-vaccenic (11-18:1) acid found in Ephedra spp. s eeds, the presence of its Delta 5-desaturation product, 5,11-18:2 acid (pro posed trivial name: ephedrenic acid), and of its elongation product, 13-20: 1 acid, were previously shown to occur in a single other species, Ginkgo bi loba, among the approximately 170 gymnosperm species analyzed so far. Conse quently, Ephedraceae and Coniferophytes (including Ginkgoatae), which have evolved separately since the Devonian period (similar to 300 million yr ago ), have kept in common the ability to synthesize C-18 and C-20 Delta 5-UPIF A. We postulate the existence of two Delta 5-desaturases in gymnosperm seed s, one possibly specific for unsaturated acids with a Delta 9-ethylenic bon d, and the other possibly specific for unsaturated acids with a Delta 11-et hylenic bond. Alternatively, the Delta 5-desaturases might be specific for the chain length with C-18 unsaturated acids on the one hand and C-20 unsat urated acids on the other hand. The resulting hypothetical pathways for the biosynthesis of Delta 5-UPIFA in gymnosperm seeds are only distinguished b y the position of 11-18:1 acid. Moreover, C-13 nuclear magnetic resonance s pectroscopy of the seed oil from two Ephedra species has shown that Delta 5 -UPIFA are essentially excluded from the internal position of triacylglycer ols, a characteristic common to all of the Coniferophytes analyzed so far ( more than 30 species), with the possibility of an exclusive esterification at the sn-3 position. This structural feature would also date back to the D evonian period, but might have been lost in those rare angiosperm species c ontaining Delta 5-UPIFA.