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Retroconversion of Docosapentaenoic Acid (n‐6): an Alternative Pathway for Biosynthesis of Arachidonic Acid in Daphnia magna
Author(s) -
Strandberg Ursula,
Taipale Sami J.,
Kainz Martin J.,
Brett Michael T.
Publication year - 2014
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/s11745-014-3902-y
Subject(s) - daphnia magna , daphnia , docosapentaenoic acid , biology , linoleic acid , arachidonic acid , biochemistry , fatty acid , algae , food science , zoology , botany , polyunsaturated fatty acid , docosahexaenoic acid , chemistry , toxicity , crustacean , organic chemistry , enzyme
Abstract The aim of this study was to assess metabolic pathways for arachidonic acid (20:4n‐6) biosynthesis in Daphnia magna . Neonates of D. magna were maintained on [ 13 C] enriched Scenedesmus obliquus and supplemented with liposomes that contained separate treatments of unlabeled docosapentaenoic acid (22:5n‐6), 20:4n‐6, linoleic acid (18:2n‐6) or oleic acid (18:1n‐9). Daphnia in the control treatment, without any supplementary fatty acids (FA) containing only trace amounts of 20:4n‐6 (~0.3 % of all FA). As expected, the highest proportion of 20:4n‐6 (~6.3 %) was detected in Daphnia that received liposomes supplemented with this FA. Higher availability of 18:2n‐6 in the diet increased the proportion of 18:2n‐6 in Daphnia, but the proportion of 20:4n‐6 was not affected. Daphnia supplemented with 22:5n‐6 contained ~3.5 % 20:4n‐6 in the lipids and FA specific stable isotope analyses validated that the increase in the proportion of 20:4n‐6 was due to retroconversion of unlabeled 22:5n‐6. These results suggest that chain shortening of 22:5n‐6 is a more efficient pathway to synthesize 20:4n‐6 in D. magna than elongation and desaturation of 18:2n‐6. These results may at least partially explain the discrepancies noticed between phytoplankton FA composition and the expected FA composition in freshwater cladocerans. Finally, retroconversion of dietary 22:5n‐6 to 20:4n‐6 indicates Daphnia efficiently retain long chain n‐6 FA in lake food webs, which might be important for the nutritional ecology of fish.