Abstract
The triacylglycerol of Crambe abyssinica seeds consist of 95 % very long chain (>18 carbon) fatty acids (86 % erucic acid; 22:1∆13) in the sn-1 and sn-3 positions. This would suggest that C. abyssinica triacylglycerols are not formed by the action of the phospholipid:diacylglycerol acyltransferase (PDAT), but are rather the results of acyl-CoA:diacylglycerol acyltransferase (DGAT) activity. However, measurements of PDAT and DGAT activities in microsomal membranes showed that C. abyssinica has significant PDAT activity, corresponding to about 10 % of the DGAT activity during periods of rapid seed oil accumulation. The specific activity of DGAT for erucoyl-CoA had doubled at 19 days after flowering compared to earlier developmental stages, and was, at that stage, the preferred acyl donor, whereas the activities for 16:0-CoA and 18:1-CoA remained constant. This indicates that an expression of an isoform of DGAT with high specificity for erucoyl-CoA is induced at the onset of rapid erucic acid and oil accumulation in the C. abyssinica seeds. Analysis of the composition of the acyl-CoA pool during different stages of seed development showed that the percentage of erucoyl groups in acyl-CoA was much higher than in complex lipids at all stages of seed development except in the desiccation phase. These results are in accordance with published results showing that the rate limiting step in erucic acid accumulation in C. abyssinica oil is the utilization of erucoyl-CoA by the acyltransferases in the glycerol-3-phosphate pathway.Electronic supplementary materialThe online version of this article (doi:10.1007/s11745-014-3886-7) contains supplementary material, which is available to authorized users.
Highlights
Crambe (Crambe abyssinica Hochst.) is an annual herbaceous plant belonging to the Brassicaceae family
In the work presented here, we investigated the activity of phospholipid:diacylglycerol acyltransferase (PDAT) in a microsomal preparation of developing seeds from Crambe to evaluate if a lack of this enzyme activity could explain the near absence of PtdCho-derived acyl groups in the outer positions of seed TAG
Analyses of the acyl-CoA profile in Crambe seed during seed development revealed that the proportion of 22:1-CoA was much higher than that of the 22:1 acid found in lipids
Summary
Crambe (Crambe abyssinica Hochst.) is an annual herbaceous plant belonging to the Brassicaceae family. The polyunsaturated fatty acids, linoleic (18:2) and linolenic (18:3) acids, are produced as precursor fatty acids are esterified to PtdCho [5] These fatty acids are transferred to TAG by three major pathways: (i) transferred from PtdCho into the acylCoA pool where they can be acylated at all three positions of the glycerol molecule by the glycerol-3-phosphate pathway [5]; (ii) enter the diacylglycerol (DAG) pool by interconversion of PtdCho with DAG synthesized by glycerol-3-phosphate pathway, a reaction catalyzed by phosphatidylcholine:diacylglycerol cholinephosphotransferase (PDCT) [6]. Crambe offers a unique example of an oil seed that has TAG with fatty acids at the sn-1 and sn-3 position that are nearly exclusively synthesized outside PtdCho and are at very low in levels in this lipid. The data are discussed in relation to the rather unique fatty acid composition of the TAG molecules in Crambe oil
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