BIOSYNTHESIS OF ACETYLENIC FATTY-ACIDS IN THE MOSS CERATODON PURPUREUS (HEDW) BRID

Protonema cells of the moss Ceratodon purpureus accumulate triacylglyc erols with two acetylenic acids, 9,12-octadecadien-6-ynoic acid (18:2A ) and 9,12,15-octadecatrien-6-ynoic acid (18:3A), as main components. By following the incorporation of the [C-14]-precursors (acetate, lino leate, gamma-linolenate, alpha-linolenate, stearidonate and 18:2A) int o 18:3A in triacylglycerol accumulating cells, the pathway for acetyle nic acids could be established. 18:2A and 18:3A could be synthesized b y a second desaturation of the Delta 6 double bond of linolenate and s tearidonate, respectively. However the major pathway for 18:3A synthes is was via a Delta 15 desaturation of 18:2A. Since 18:2A was found exc lusively in the triacylglycerols of the cell, the triacylglycerols in Ceratodon purpureus can act either as a direct substrate for the Delta 15 desaturation or, alternatively, the 18:2A has to be detached, desa turated and reincorporated into triacylglycerols. These results, as we ll as recent results from developing sunflower seeds by Garces et al. (1994, in press), present evidence that, in contrast to the general be lieve, plant triacylglycerols are not metabolic inert molecules during the cell stage of triacylglycerol deposition.