Abstract
The native lipid composition and the capacity of cell-free extracts to biosynthesize acyl lipids in vitro were determined for the first time using the recently reported microspore-derived (MD) embryo system from the Brassica campestris low erucic acid line BC-2 (Baillie et al. 1992). The total lipid fraction isolated from midcotyledonary stage MD embryos (21 days in culture) was composed primarily of triacylglycerol (76%) with an acyl composition quite similar to that of mature BC-2 seed. When incubated in the presence of glycerol-3-phosphate, 14C 18∶1-CoA, and reducing equivalents, homogenates prepared from 21-day cultured MD embryos were able to biosynthesize glycerolipids via the Kennedy pathway. The maximum in vitro rate of triacylglycerol biosynthesis could more than account for the known rate of lipid accumulation in vivo. The homogenate catalyzed the desaturation of 18∶1 to 18∶2 and to a lesser extent, 18∶3. The newly-synthesized polyunsaturated fatty acids initially accumulated in the polar lipid fraction (primarily phosphatidic acid and phosphatidylcholine) but began to appear in the triacylglycerol fraction after longer incubation periods. As expected for a low erucic acid cultivar, homogenates of MD embryos from the BC-2 line were incapable of biosynthesizing very long chain monounsaturated fatty acyl moieties (20∶1 and 22∶1) from 18∶1-CoA in vitro. Nonetheless, embryo extracts were still capable of incorporating these fatty acyl moieties into triacylglycerols when supplied with 14C 20∶1-CoA or 14C 22∶1-CoA. Collectively, the data suggest that developing BC-2 MD embryos constitute an excellent experimental system for studying pathways for glycerolipid bioassembly and the manipulation of this process in B. campestris.
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Abbreviations
- CPT:
-
sn-1,2-diacylglycerol cholinephosphotransferase
- DAG:
-
diacylglycerol
- DGAT:
-
diacylglycerol acyltransferase
- DGDG:
-
digalactosyldiacylglycerol
- G-3-P:
-
glycerol-3-phosphate
- G-3-PAT:
-
glycerol-3-phosphate acyltransferase
- LPA:
-
lyso-phosphatidic acid
- LPAT:
-
lyso-phosphatidic acid acyltransferase
- LPC:
-
lyso-phosphatidylcholine
- LPCAT:
-
acyl-CoA: lyso-phosphatidylcholine acyltransferase
- LPE:
-
lyso-phosphatidylethanolamine
- MGDG:
-
monogalactosyldiacylglycerol
- PA:
-
phosphatidic acid
- PA:
-
Phosphatase, phosphatidic acid phosphatase
- PC:
-
phosphatidylcholine
- PE:
-
phosphatidylethanolamine
- PG:
-
phosphatidylglycerol
- TAG:
-
triacylglycerol
- 18∶1-CoA:
-
oleoyl-Coenzyme A
- 18∶1:
-
oleic acid, cis-9-octadecenoic acid
- 18∶2:
-
linoleic acid, cis-9,12-octadecadienoic acid
- 18∶3:
-
α-linolenic acid, cis-9,12,15-octadecatrienoic acid
- 20∶1:
-
cis-11-eicosenoic acid
- 22∶1:
-
erucic acid, cis-13-docosenoic acid; all other fatty acids are designated by number of carbon atoms: number of double bonds
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Communicated by F. Constabel
National Research Council of Canada Publication No. 35896
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Taylor, D.C., Ferrie, A.M.R., Keller, W.A. et al. Bioassembly of acyl lipids in microspore-derived embryos of Brassica campestris L.. Plant Cell Reports 12, 375–384 (1993). https://doi.org/10.1007/BF00234696
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DOI: https://doi.org/10.1007/BF00234696