Exploring Phylogenetic Relationships between Hundreds of Plant Fatty Acids Synthesized by Thousands of Plants. more details ...
Abstract The fatty acid compositions of the seed lipids from four Ephedra species, E. nevadensis, E. viridis, E. przewalskii, and E. gerardiana (four gymnosperm species belonging to the Cycadophytes), have been established with an emphasis on Δ5-unsaturated polymethylene-interrupted fatty acids (Δ5- UPIFA). Mass spectrometry of the picolinyl ester derivatives allowed characterization 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. Δ5-UPIFA with a Δ11 -ethylenic bond (mostly C20 acids) were in higher proportions than Δ5-UPIFA with a Δ9 double bond (exclusively C18 acids) in all species. The total A5-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 Δ5-UPIFA isomers. The relatively high level of cis-vaccenic (11-18:1) acid found in Ephedra spp. seeds, the presence of its Δ5:desaturation product, 5, 11-18:2 acid (proposed trivial name: ephedrenic acid), and of its elongation product, 13- 20:1 acid, were previously shown to occur in a single other species, Ginkgo biloba, among the approximately 170 gymnosperm species analyzed so far. Consequently, Ephedraceae and Coniferophytes (including Ginkgoatae), which have evolved separately since the Devonian period (~300 million yr ago), have kept in common the ability to synthesize C18 and C20 Δ5-UPIFA. We postulate the existence of two A5-desaturases in gymnosperm seeds, one possibly specific for unsaturated acids with a Δ9-ethylenic bond, and the other possibly specific for unsaturated acids with a Δ11-ethylenic bond. Alternatively, the Δ5-desaturases might be specific for the chain length with C18 unsaturated acids on the one hand and C20 unsaturated acids on the other hand. The resulting hypothetical pathways for the biosynthesis of Δ5-UPIFA in gymnosperm seeds are only distinguished by the position of 1118:1 acid. Moreover, 13C nuclear magnetic resonance spectroscopy of the seed oil from two Ephedra species has shown that Δ5-UPIFA are essentially excluded from the internal position of triacylglycerols, 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 Devonian period, but might have been lost in those rare angiosperm species containing Δ5-UPIFA.

Authors: Wolff, R. L.; Christie, W. W.; Pédrono, F.; Marpeau, A. M.; Tsevegsüren, N.; Aitzetmüller, K.; Gunstone, F. D.

Journal: Lipids

Year: 1999

Volume: 34

Page: 855-864

UID: None

URL: http://www.scopus.com/inward/record.url?eid=2-s2.0-0032589485&partnerID=40&md5=5e6715169fb5d44f662a9f5d31c71673

DOI: 10.1007/s11745-999-0433-1

Plants View All 3 Datasets
Genus Species Data Points
Agathis robusta 26
Ephedra nevadensis 25
Ephedra viridis 25