Bioassembly of acyl lipids in microspore-derived embryos of Brassica campestris L. |
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Authors: | D C Taylor A M R Ferrie W A Keller E M Giblin E W Pass S L MacKenzie |
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Institution: | (1) National Research Council of Canada, Plant Biotechnology Institute, 110 Gymnasium Place, S7N 0W9 Saskatoon, SK, Canada |
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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 181-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 181 to 182 and to a lesser extent, 183. 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 (201 and 221) from 181-CoA in vitro. Nonetheless, embryo extracts were still capable of incorporating these fatty acyl moieties into triacylglycerols when supplied with 14C 201-CoA or 14C 221-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.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
- 181-CoA
oleoyl-Coenzyme A
- 181
oleic acid, cis-9-octadecenoic acid
- 182
linoleic acid, cis-9,12-octadecadienoic acid
- 183
-linolenic acid, cis-9,12,15-octadecatrienoic acid
- 201
cis-11-eicosenoic acid
- 221
erucic acid, cis-13-docosenoic acid; all other fatty acids are designated by number of carbon atoms: number of double bonds
National Research Council of Canada Publication No. 35896 |
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Keywords: | Brassica campestris Microspore Derived Embryos Acyl Lipid Biosynthesis |
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