G. Kohn et al., BIOSYNTHESIS OF ACETYLENIC FATTY-ACIDS IN THE MOSS CERATODON PURPUREUS (HEDW) BRID, Journal of plant physiology, 144(3), 1994, pp. 265-271
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.