Woodfield, unpublished data. In addition, evidence has suggested the cholinephosphotransferase and ethanolaminephosphotransferase enzymes catalysing the final step in the CDP-base pathway have been shown to have distinct characteristics in soybean  ,  ,  , although an isolated gene codes for both activities .
On the other hand, two yeast enzymes which both show equal similarity to the deduced amino acid sequence of the soybean gene  have distinct characteristics . For the rapid period of oil accumulation, we used samples of 20—35 DAF which we determined were appropriate in the cultivar used and in agreement with other studies of B. Although the major species of TAG and DAG remained broadly constant, there were significant changes in their percentage distribution from early to late oil accumulation Fig.
Table 8. This was not reflected in the DAG species Fig. In contrast to the non-polar lipids, all three of the phosphoglycerides showed significant changes in the relative distribution of their molecular species during oil accumulation. Although PA, PC and PE each had a distinct distribution of molecular species, there were some consistent changes in major species with maturation. As remarked before, PA, PC and PE all had distinct differences in their distribution of molecular species, despite their metabolic connections  , .
There were also differences in the changes to their molecular species during maturation. All this points to the subtle distinctions in metabolism for phosphoglycerides which undoubtable reflects their different functions in plant cells .
Although there are significant differences in the molecular species of PC and PE, and indeed in their proportional changes in amounts during maturation Fig. These changes are likely to reflect the parallel alterations in DAG species Fig. Indeed, overexpression or knockout of Arabidopsis PDAT1 resulted in significant changes in oil content and fatty acid composition in leaves but not in seeds .
Nevertheless, it has been shown that DGAT and PDAT have overlapping function for oil accumulation in plants  ,  and, depending on the crops, their relative contribution may be quite different  ,  , . Evidence is accumulating that PDAT may be particularly important for incorporation of unusual e.
Efforts to address the question of the relative importance of DGAT and PDAT for TAG synthesis in oil crops have included measurements of enzyme activity in vitro  ,  ,  ,  and genomic manipulation  , . Even when measurements in vitro have been carried out very carefully and in detail  there is always the problem that enzyme specificity determinations in vitro may not reflect the selectivity and, hence, activity at the substrate concentrations in vivo.
Another method that has been applied to soybean in particular in to use radiolabelling from different precursors .
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Although previous studies with in vitro enzyme measurements  and transcription levels  suggested that DGAT was more important for overall flux into TAG in oilseed rape, we were interested to see whether our molecular species measurements could add useful information. This was particularly important in view of the current uses of genetic manipulation to enhance oil production  ,  ,  ,  , . As discussed in Section 3.
These assumptions included the availability of all acyl-CoAs in the proportions detected Fig. For the latter, recent experiments for safflower and sunflower suggest that fatty acids at the sn-1 position can also be used at a quarter of the rate for the sn-2 position . For B. Again, this agreed with measurements of ESTs in B.
The differences noted in Table 1 are obviously due in a major part to substrate selectivity. Unfortunately, we have no information for the oilseed rape enzymes but experiments in other plant tissues revealed substrate specificity for PDAT  and, especially, for DGAT  ,  , . Further experiments in this area, especially for major oil crops, would be timely.
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The data reported here describe lipidomic analysis of major lipids involved in TAG formation in the major oil crop, B. They are one of the first such analyses of a developing plant tissue — the maturing oilseed. The results show quite distinct molecular species distributions in the various lipid classes and demonstrate the complex nature of metabolism during oil accumulation. However, the actual pattern of TAG molecular species shows clearly that enzyme selectivity has major importance in forming the accumulating oil.
Our experiments contribute significantly towards understanding how the final storage lipid is formed within the world's third most important oil crop. The Transparency document associated with this article can be found, in online version. National Center for Biotechnology Information , U. Sponsored Document from. Biochim Biophys Acta. Helen K. Haslam , d Irina A.
Guschina , a Markus R. Richard P. Irina A. Markus R. John L. Author information Article notes Copyright and License information Disclaimer. Wenk: gs.
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Harwood: ku. This article has been cited by other articles in PMC. Supplementary Table 2 MRM list for phosphoglycerides. Abstract With dwindling available agricultural land, concurrent with increased demand for oil, there is much current interest in raising oil crop productivity.
Materials and methods 2. Materials Brassica napus cv. Results 3. Analysis of lipid molecular species at a midpoint of lipid accumulation In order to evaluate the lipidomic methodology we analysed molecular species of major lipid classes at a mid-point of lipid accumulation in oilseed rape. Open in a separate window. Changes to molecular species during lipid accumulation The development of an oil seed typically occurs in three main stages — cell division, oil accumulation and dehydration .
Measurement of the acyl-CoA pool during seed development A diverse variety of acyl-CoAs were detected in the developing oilseed rape seeds ranging from the medium-chain myristoyl-CoA up to very long chains of thirty carbons Fig. Can lipidomics inform judgements about enzymes used for triacylglycerol accumulation? Discussion With recent discoveries of new enzymes involved in lipid accumulation in oil crops, it is clear that our understanding of metabolism and particularly its regulation, is incomplete  ,  ,  ,  ,  , . Conclusions The data reported here describe lipidomic analysis of major lipids involved in TAG formation in the major oil crop, B.
The following are the supplementary data related to this article. Click here to view. Supplementary Table 2: MRM list for phosphoglycerides. Supplementary tables Click here to view. Transparency document Transparency document. References 1. Chen G. Acyl-trafficking during plant oil accumulation.
Gunstone F. The Lipid Handbook. McKeon T. Industrial Oil Crops. AOCS Press; Introduction to industrial oil crops; pp. Bates P. Biochemical pathways in seed oil synthesis. Plant Biol. Weselake R. Increasing the flow of carbon into seed oil. New frontiers in oilseed biotechnology: meeting the global demand for vegetable oils for food, feed, biofuel, and industrial applications. Harwood J. Regulation of lipid synthesis in oil crops. FEBS Lett. The significance of different diacylglycerol synthesis pathways on plant oil composition and bioengineering.
Introduction to lipidomics; from bacteria to man.
Chapman K. Compartmentation of triacylglycerol accumulation in plants. Ramli U. Control analysis of lipid biosynthesis in tissue cultures from oil crops shows that flux control is shared between fatty acid synthesis and lipid assembly.
Use of metabolic control analysis to give quantitative information on control of lipid biosynthesis in the important oil crop, Elaeis guineensis oilpalm New Phytol. Tang M. Metabolic control analysis of developing oilseed rape Brassica napus cv Westar embryos shows that lipid assembly exerts significant control over oil accumulation.
New Phytol. Guschina I.
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Studies on the regulation of lipid biosynthesis in plants: application of control analysis to soybean. Understanding the control of acyl flux through the lipid metabolic network of plant oil biosynthesis. The pathway of triacylglycerol synthesis through phosphatidylcholine in Arabidopsis produces a bottleneck for the accumulation of unusual fatty acids in transgenic seeds.