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Synthesis of Ethanolamine and Its Regulation in Lemna paucicostata

Plant Physiology 91(2): 587-597

Synthesis of Ethanolamine and Its Regulation in Lemna paucicostata

The metabolism of ethanolamine and its derivatives in Lemna paucicostata has been investigated, with emphasis on the pathway for synthesis of phosphoethanolamine, a precursor of phosphatidylcholine in higher plants. In experiments involving labeling of intact plants with radioactive serine, ambiguities of interpretation due to entry of radioactivity into methyl groups of methylated ethanolamine derivatives were mitigated by pregrowth of plants with methionine. Difficulties due to labeling of diacylglyceryl moieties of phospholipids were avoided by acid hydrolysis of crucial samples and determination of radioactivity in isolated serine or ethanolamine moieties. The results obtained from such experiments are most readily reconciled with the biosynthetic sequence: serine leads to ethanolamine leads to phosphoethanolamine leads to phosphatidylethanolamine. A possible alternative is: serine leads to phosphatidylserine leads to phosphatidylethanolamine leads to ethanolamine leads to phosphoethanolamine. Cell-free extracts of L. paucicostata were shown to produce CO2 from the carbon originating as C-1 of serine at a rate sufficient to satisfy the demand for ethanolamine moieties. A number of experiments produced no support for a hypothetical role for phosphoserine in phosphoethanolamine formation. Uptake of exogenous ethanolamine comensurately down-regulates the synthesis of ethanolamine moieties (considered as a whole, and regardless of their state of derivatization at the time of their formation). In agreement with previous observations, uptake of exogenous choline down-regulates the methylation of phosphoethanolamine, without being accompanied by secondary accumulation of a marked excess of ethanolamine derivates.

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Accession: 001962567

PMID: 16667073

DOI: 10.1104/pp.91.2.587

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