POLYUNSATURATED FATTY-ACID METABOLISM IN THE MARINE DINOFLAGELLATE CRYPTHECODINIUM-COHNII

The rates of assimilation of C-14-labelled 18:0 and 18:1 (n-9) fatty acids into cellular triacylglycerols and polar lipids by batch cultures of Crypthecodinium cohnii were directly related to their concentration in the medium. A comparison of the incorporation of C-14-labelled acetate, 18:0 and 18:1(n-9) into lipids over a growth cycle of the algae showed that both preformed exogenous fatty acids and those formed de novo were incorporated at higher initial rates into polar lipids than into triacylglycerols. After three days growth in the presence of labelled acetate, 48% of the radioactivity incorporated into total polar lipids was located in 22:6(n-3). The corresponding values for C-14-18:0 and C-14-18:1(n-9) were 2% and 4%. Pulse-chase studies with the three labelled substrates showed that the amounts of radioactivity present in triacylglycerols increased during the three days following the initial labelling period. With C-14-18:0 and 18:1 substrates, the labelling patterns in fatty acids of lipid classes did not change with time whereas the amount of label from C-14-acetate recovered in 22:6(n-6) of triacylglycerols increased four-fold. Triacylglycerols from stationary phase cultures were richer in saturated fatty acids than those from cultures containing actively dividing cells. The results are discussed in relation to changes in the pattern of lipids synthesized during the growth cycle and potential substrates for polyunsaturated fatty acid formation.