Synthesis and function of 9,12,15-octadecatrien-6-ynoic acid in the moss ceratodon purpureus

Biosynthesis of all-cis-9,12,15-octadecatrien-6-ynoic acid in the moss, Ceratodon purpureus, was studied using protonemata cultures with labeled 9,12,15-octadecatrienoic (linolenic) and 6,9,12,15-octadecatetraenoic acids as substrates. Both acids were efficiently converted into the acetylenic and into 5,8,11,14,17-eicosapentaenoic acids. Accordingly, the introduction of a triple bond in position 6 of linolenic acid involves formation of a double bond as a discrete step. Acetylenic acid triglycerides are reserve lipids in the moss. Under suitable growth conditions the acetylenic acids are catabolized and partly reused via acetate for de novo synthesis of fatty acids. They are not used for more direct syntheses of the common polyunsaturated fatty acids.