JXB Advance Access originally published online on June 18, 2004
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Journal of Experimental Botany, Vol. 55, No. 402, pp. 1455-1462, July 2004
Journal of Experimental Botany, Vol. 55, No. 402, © Society for Experimental Biology 2004; all rights reserved
RESEARCH PAPER |
The import of phosphoenolpyruvate by plastids from developing embryos of oilseed rape, Brassica napus (L.), and its potential as a substrate for fatty acid synthesis


Department of Metabolic Biology, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, UK
To whom correspondence should be addressed. Fax: +44 (0)1603 450014. E-mail: steve.rawsthorne{at}bbsrc.ac.uk
The plastidial phosphoenolpyruvate (PEP)/phosphate translocator (PPT) is expressed in the developing embryos of oilseed rape (Brassica napus L.). PEP can be imported by plastids isolated from embryos and used for fatty acid synthesis at rates that are sufficient to account for one-third of the rate of fatty acid synthesis in vivo. This provides the first experimental evidence for uptake of PEP and incorporation of carbon from it into fatty acids by plastids. PEP metabolism in isolated plastids is able to provide some of the ATP required for fatty acid synthesis. Expression of the PPT and related glucose 6-phosphate (Glc-6-P) translocator (GPT) is high in early embryo and leaf development and then declines. The marked decline in the abundance of PPT and GPT transcripts between the pre- and mid-oil accumulating stages of embryo development in B. napus does not correlate with the corresponding translocator activities, which both increase over the same period. This means that transcript abundance cannot be used to infer the activity of the translocators.
Key words: Brassica napus, embryo, fatty acid synthesis, phosphoenolpyruvate translocator, plastid
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