Arachidonic, eicosapentaenoic, and biosynthetically related fatty acids in the seed lipids from a primitive gymnosperm, Agathis robusta

Abstract

The fatty acid composition of the seeds from Agathis robusta, an Australian gymnosperm (Araucariaceae), was determined by a combination of chromatographic and spectrometric techniques. These enabled the identification of small amounts of arachidonic (5,8,11,14-20:4) and eicosapentaenoic (5,8,11,14,17-20:5) acids for the first time in the seed oil of a higher plant. They were apparently derived from gamma-linolenic (6,9,12-18:3) and stearidonic (6,9,12,15-18:4) acids, which were also present, via chain elongation and desaturation, together with other expected biosynthetic intermediates [bis-homo-gamma-linolenic (8,11,14-20:3) and bishomo-stearidonic (8,11,14,17-20:4) acids]. Also present were a number of C20 fatty acids, known to occur in most gymnosperm families, i.e., 5,11-20:2, 11,14-20:2 (bishomo-linoleic), 5,11,14-20:3 (sciadonic), 11,14,17-20:3 (bishomo-alpha-linolenic), and 5,11,14,17-20:4 (juniperonic) acids. In contrast to most other gymnosperm seed lipids analyzed so far, A. robusta seed lipids did not contain C18 delta5-desaturated acids [i.e., 5,9-18:2 (taxoleic), 5,9,12-18:3 (pinolenic), or 5,9,12,15-18:4 (coniferonic)]. These structures support the simultaneous existence of delta6- and delta5-desaturase activities in A. robusta seeds. The delta6-ethylenic bond is apparently introduced into C18 polyunsaturated acids, whereas the delta5-ethylenic bond is introduced into C20 polyunsaturated acids. A general metabolic pathway for the biosynthesis of unsaturated fatty acids in gymnosperm seeds is proposed. When compared to Bryophytes, Pteridophytes (known to contain arachidonic and eicosapentaenoic acids), and species from other gymnosperm families (without such acids), A. robusta appears as an "intermediate," with the C18 delta6-desaturase/C18-->C20 elongase/C20 delta5-desaturase system in common with the former subphyla, and the unsaturated C18-->C20 elongase/C20 delta5-desaturase system specific to gymnosperms. The following hypothetical evolutionary sequence for the C18 delta6/delta5-desaturase class in gymnosperm seeds is suggested: delta6 (initial)-->delta6/delta5 (intermediate)-->delta5 (final).

Arachidonic and eicosapentaenoic acids in Araucariaceae, a unique feature among seed plants

“…All other chromatographic data supported these structural characterizations [GLC on capillary columns with different polarities, i.e., DB-Wax, CP-Sil 88, and Silar 5CP, fractionation by argentation thin-layer chromatography (Ag-TLC), and by reversed-phase high-performance liquid chromatography]. Experimental details are given elsewhere [2]. As an example, we show in figure 3 the fractionation of A. araucana seed fatty acids by Ag-TLC and analyses of the fractions by GLC on a 30-m DB-Wax column.…”

“…In contrast, plants of lower phyletic rank (microalgae, algae, bryophytes, pteridophytes) have the capability to synthesize arachidonic and eicosapentaenoic acids. In the course of systematic studies of gymnosperm lipids, we observed that a species (Agathis robusta) of the Araucariaceae family (gymnosperms of the division Coniferophytina) contains in low amounts arachidonic and eicosapentaenoic acids in its seeds, as well as all intermediate metabolites that are necessary for their biosynthesis [2]. We give here evidence that the presence of arachidonic acid is not limited to A. robusta seeds among Araucariaceae, as it also occurs in Araucaria spp.…”

Structures, practical sources (gymnosperm seeds), gas-liquid chromatographic data (equivalent chain lengths), and mass spectrometric characteristics of all-cis Δ5-olefinic acids

“…AA and EPA are well known components of animal lipids. However, these acids also commonly occur in the plant kingdom in (micro) algae, and in some higher plants, e.g., bryophytes and pteridophytes [25], but more seldom in gymnosperms (i.e., in low amounts in the seed and leaf lipids from Agathis and Araucaria, of the primitive Araucariaceae family [26,27]). This is why we include these fatty acids in the present review.…”

LC/ESI-MS/MS detection of FAs by charge reversal derivatization with more than four orders of magnitude improvement in sensitivity

“…An alternative strategy for enhanced sensitivity is to improve the ionization effi ciency of FAs via specifi c derivatization with reagents that introduce either readily chargeable or fi xed charge groups such as tertiary or quaternary amines, respectively. Many derivatives of this nature have been reported including: pyrolidides (19)(20)(21), picolinyl esters ( 22,23 ), dimethyloxazolines (24)(25)(26)(27)(28), benzofurazans ( 29 ), pyridiniums ( 30 ), and cholines ( 31 ). The advantages of these derivatives include improved MS sensitivity and reproducible chromatography profi les.…”