Utilization of petroselinate (C 18:1 Δ6 ) by glycerol acylation enzymes in microsomal preparations of developing embryos of carrot ( Daucus carota L.), safflower ( Carthamus tinctorius L.) and oil rape ( Brassica napus L.)

Abstract

Glycerol 3-phosphate acyltransferase (E.C. 2.3.1.15), lysophoshatidic acid acyltransferase (E.C. 2.3.1.51) and lysophosphatidylcholine acyltransferase (E.C. 2.3.1.23) activities with acyl substrates containing petroselinate (18:1 Δ6 ) or oleate (18:1 Δ9 ) were compared in microsomal preparations from developing zygotic embryos of carrot and safflower, microspore-derived embryos from rape and somatic embryos from carrot. In the glycerol 3-phosphate acylation step, 18:1 Δ9 -CoA was used at a higher rate than 18:1 Δ6 -CoA in active preparations from all species but the enzyme from the zygotic carrot embryos showed higher rates with 18:1 Δ6 -CoA substrate than the safflower and rape enzymes. Acylation of sn-1 -18:1 Δ9 -glycerol 3-phosphate (18:1 Δ9 -LPA) or 18:1 Δ6 -LPA with 18:1 Δ9 -CoA showed similar rates with all species studied and was much higher than with 18:1 Δ6 -CoA as acyl donor. The preparations from carrot zygotic embryos acylated 18:1 Δ6 -LPA with 18:1 Δ6 -CoA at a substantial rate whereas this combination of substrates was only poorly utilized in preparations of carrot somatic embryos and not at all in safflower and rape. Microsomes from carrot zygotic embryos acylated both 18:1 Δ6 -CoA and 18:1 Δ9 -CoA to exogenous lysophosphatidylcholine, when presented as single acyl-CoA substrates, but 18:1 Δ9 -CoA utilization was greatly inhibited by the presence of 18:1 Δ6 -CoA. This preparation also acylated sn-[ 14 C] glycerol 3-phosphate with both 18:1 Δ9 -CoA and 18:1 Δ6 -CoA in the formation of radioactive phosphatidic acid, diacylglycerols and triacylglycerols. The amount and distribution of label between different lipid classes was similar with the two acyl-CoAs and with very little [ 14C]glycerol entering phosphatidylcholine. Fatty acid analysis of various lipids in developing carrot seed are also presented. The results of the present study are discussed in terms of specializations of lipid synthesizing enzymes in tissues accumulating high amounts of 18:1 Δ6 .