Radiolabelling Studies of Lipids in the Marine Cryptomonad Chroomonas salina in Relation to Fatty Acid Desaturation

Cells of Chroomonas salina were exposed to ¹⁴C]acetate, ^l4C]16:0,¹⁴C]18:0, ¹⁴C]18:1(n-9), ¹⁴C]18:2(n–6) or ¹⁴C]18:3(n–3)for 1 h and then incubated for 24 h in non-radioactive medium.At the end of the pulse period, non-glycolipid polar lipidscontained the highest proportions of radioactivity incorporatedfrom ¹⁴C]acetate and ¹⁴C]18:3(n–3) whereas with ¹⁴C]16:0,¹⁴C]18:1 and ¹⁴C]18:2(n–6), triacylglycerols were mosthighly labelled. ¹⁴C-18:0 was recovered mainly as non-esterifiedfatty acid. Monogalactosyldiacylglycerol initially contained17% of label incorporated from ¹⁴C]acetate but less than 3%of that from ¹⁴C]fatty acids. With all substrates, excluding¹⁴C]18:0, a gradual transfer of label from polar lipids totriacylglycerols was observed during the chase period. Saturatesand monoenes synthesised from ¹⁴C]acetate were mostly transferedfrom phospholipids and glycolipids to neutral lipid withoutfurther desaturation. Most of the incorporated ¹⁴C-fatty acidsremained unchanged and only with ¹⁴C]18:3(n–3) was substantialamounts of label recovered in penta- and hexaenoic fatty acids.The results indicate that, under the conditions of the study,lipid synthesis in the algae was heavily dominated by triacylglycerolformation and that the mechanisms of fatty acid desaturationin this species may differ from those in higher plants. (Received December 10, 1991; Accepted March 6, 1992)