In Vivo Pathway of Oleate and Linoleate Desaturation in Developing Cotyledons of Cucumis sativus L. Seedlings.

Exogenous [1-(14)C]oleic acid and [1-(14)C]linoleic acid were taken up and esterified to complex lipids by greening cucumber (Cucumis sativus L.) cotyledons. Both (14)C-labeled fatty acids were initially esterified to phosphatidylcholine prior to eventual accumulation in triacylglycerols and galactolipids. Kinetic data suggest that esterification occurs prior to desaturation and that phosphatidylcholine is the initial site of both [(14)C]-oleate and [1-(14)C]linoleate esterification and of [1-(14)C]oleate desaturation to [1-(14)C]linoleate. [1-(14)C]Linoleic acid was esterified more rapidly than [(14)C]oleic acid and its desaturation product, [1-(14)C]alpha-linolenate, occurred mainly on monogalactosyl diacylglycerol, although some was also observed on the other major acyl lipids, including phosphatidylcholine.