IN-VIVO DESATURATION OF CIS-DELTA-9-MONOUNSATURATED TO CIS-DELTA-9,12-DIUNSATURATED ALKENYLETHER GLYCEROLIPIDS

Plants convert lipid-bound cis-n-9 monoenoic to polyenoic fatty acid r esidues without involvement of corresponding CoA-thioesters. To provid e additional evidence for this type of lipid-linked desaturation we in cubated sn-1-O- and 2-O-(cis-9)octadecenylglycerol isomers with photoa utotrophic cell cultures from tomato. After 14 days the fractions of p hosphatidylcholine and monogalactosyldiacylglycerol were isolated and the incorporated glycerol ether backbones released by treatment with L iAlH4 (reduction of ester bonds) and short acid hydrolysis (cleavage o f enol ether bonds). High performance liquid chromatography and mass s pectroscopy of the products in appropriately derivatized form showed t hat the (cis-9)octadecenyl group in the sn-1 position of the phospholi pid was nearly completely desaturated to a (cis-9,12)octadecadienyl re sidue having the same double bond arrangement as linoleic acid. In the galactolipid fraction the desaturation had progressed to octadecatrie nyl residues. Similarly, the octadecenyl residue in the sn-2 position of the phospholipid was nearly completely desaturated to an octadecadi enyl group. These results are unambiguous proof for lipid-linked desat uration by both microsomal and plastidial desaturase systems of plants .