Testing models of fatty acid transfer and lipid synthesis in spinach leaf using in vivo oxygen-18 labeling
Oxygen-18 labeling has been applied to the study of plant lipid biosynthesis for the first time. [{sup 13}C{sub 2}{sup 18}O{sub 2}]Acetate was incubated with spinach (Spinacia oleracea) leaves and the {sup 18}O content in fatty acid methyl esters isolated from different lipid classes measured by gas chromatography-mass spectrometry. Fatty acids isolated from lipids synthesized within the plastid, such as monogalactosyldiacylglycerol, show an {sup 18}O content consistent with the exogenous acetate undergoing a single activation step and with the direct utilization of acyl-acyl carrier protein by the acyl transferases of the chloroplast. In contrast, fatty acids isolated from lipids assembled in the cytosol, such as phosphatidylcholine, show a 50% reduction in the {sup 18}O content. This is indicative of export of the fatty acyl groups from the plastid via a free carboxylate anion, and is consistent with the acyl-acyl carrier protein thioesterase:acyl-coenzyme A (CoA) synthetase mediated export mechanism. If this were not the case and the acyl group was transferred directly from acyl-acyl carrier protein to an acyl acceptor on the cytosolic side, there would be either complete retention of {sup 18}O or, less likely, complete loss of {sup 18}O, but not a 50% loss of {sup 18}O. Thus, existing models for fatty acid transfer from the plastid and for spatially separate synthesis of prokaryotic and eukaryotic lipids have both been confirmed.
- Research Organization:
- Michigan State Univ., East Lansing, MI (US)
- Sponsoring Organization:
- US Department of Energy
- OSTI ID:
- 20006199
- Journal Information:
- Plant Physiology (Bethesda), Journal Name: Plant Physiology (Bethesda) Journal Issue: 4 Vol. 121; ISSN 0032-0889; ISSN PLPHAY
- Country of Publication:
- United States
- Language:
- English
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