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Published on March 27, 2009; 10.1104/pp.109.137737

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Received February 24, 2009
Accepted March 24, 2009

Analysis of acyl fluxes through multiple pathways of triacylglycerol synthesis in developing soybean embryos

Philip D. Bates , Timothy P. Durrett , John B. Ohlrogge , and Mike Pollard *

Departments of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, USA; Plant Biology, Michigan State University, East Lansing, MI, USA

* Corresponding author; email: pollard9{at}msu.edu.

The reactions leading to triacylglycerol (TAG) synthesis in oilseeds have been well characterized. However, quantitative analyses of acyl group and glycerol backbone fluxes that comprise extra-plastidic phospholipid and TAG synthesis, including acyl editing and phosphatidylcholine-diacylglycerol (PC-DAG) interconversion are lacking. To investigate these fluxes we rapidly labeled developing soybean (Glycine max) embryos with [14C]acetate and [14C]glycerol. Cultured intact embryos that mimic in planta growth were used. The initial kinetics of newly synthesized acyl chain and glycerol backbone incorporation into PC, DAG and TAG were analyzed along with their initial labeled molecular species and positional distributions. Almost 60% of the newly synthesized fatty acids first enter glycerolipids through PC acyl editing, largely at the sn-2 position. This flux, mostly of oleate, was over three times the flux of nascent [14C]fatty acids incorporated into the sn-1 and sn-2 positions of DAG through glycerol-3-phosphate acylation. Furthermore, the total flux for PC acyl editing, which includes both nascent and pre-existing fatty acids, was estimated to be 1.5 to 5 times the flux of fatty acid synthesis. Thus recycled acyl groups (16:0, 18:1, 18:2 and 18:3) in the acyl-CoA pool provide most of the acyl chains for de novo glycerol-3-phosphate acylation. Our results also show kinetically distinct DAG pools. DAG utilized for TAG synthesis is mostly derived from PC, whereas de novo synthesized DAG is mostly used for PC synthesis. In addition, two kinetically distinct sn-3 acylations of DAG were observed, providing TAG molecular species enriched in saturated or polyunsaturated fatty acids respectively.




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