| Abstrakt: |
The fatty acid compositions of the seeds from three Taxus(yew) species and one Torreyaspecies belonging to the Taxaceae family [Taxus cuspidata(Japanese yew), T. chinensis(Chinese yew), T. baccata(English yew), and Torreya grandis(Chinese nutmeg yew)] have been established. These compositions were compared with those previously published for T. canadensis(Canadian yew) and Torreya nucifera. In Taxusspecies, as well as in Torreyaspecies, Δ5-olefinic acids are present in the seed lipids from all species analyzed. In Taxus, 5,9-18:2 (taxoleic) acid is the prominent Δ5-olefinic acid. It represents between 9.5 and 16.2% of total fatty acids. Other Δ5-olefinic acids that occur in low amounts are 5,9,12-18:3 (<3.5%), 5,11-20:2 (<0.3%), 5,11,14-20:3 (<2.2%), and 5,11,14,17-20:4 (<0.3%) acids. In Torreyaspecies, the major Δ5-olefinic acid is 5,11,14-20:3 (sciadonic) acid (between 6.7 and 11.2%). In contrast to Taxusspecies, the 5,9-18:2 and 5,9,12-18:3 acids are scarce in Torreyaspecies: less than 0.1%. Also, the 9,12,15-18:3 acid content is significantly lower in Torreyathan in Taxus. The prominence of taxoleic acid among Δ5-olefinic acids in the seed lipids is a unique characteristic of the genus Taxusthat isolates it from all other Coniferophytes analyzed so far. However, this feature is not shared by other Taxaceae species, such as Torreya, and with regard to their seed fatty acid compositions, the family Taxaceae appears particularly heterogeneous. Our observations favor the hypothesis that in Gymnosperm seeds, there might exist two Δ5-desaturases, one specific for unsaturated acids with a Δ9-ethylenic bond (active in Taxusbut not in Torreya), and the other specific for unsaturated acids with a Δ11-ethylenic bond (active in Torreyabut not in Taxus). Our data also highlight the importance of the elongase(s) in the metabolism of fatty acids in Gymnosperm seeds. 14-Methylhexadecanoic acid, a habitual component of Pinaceae and Ginkgo bilobaseed lipids, could not be detected in the Taxaceae studied here. 13C nuclear magnetic resonance spectroscopy of the oils from both genera has confirmed that Δ5-olefinic acids are apparently excluded from the internal position of triacylglycerols, which is a characteristic common to all Gymnosperm species analyzed so far, and consequently of great antiquity in their life history. |
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