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. 1983 Mar;71(3):692–700. doi: 10.1104/pp.71.3.692

14C Tracer Evidence for Synthesis of Choline and Betaine via Phosphoryl Base Intermediates in Salinized Sugarbeet Leaves 1

Andrew D Hanson 1,2,2, David Rhodes 1,2
PMCID: PMC1066101  PMID: 16662890

Abstract

Like other chenopods, sugarbeets (Beta vulgaris L. cv Great Western D-2) accumulate glycine betaine when salinized; this may be an adaptive response to stress. The pathway of betaine synthesis in leaves of salinized (150-200 millimolar NaCl) sugarbeet plants was investigated by supplying [14C]formate, phosphoryl[14C]monomethylethanolamine ([14C][unk] MME) or phosphoryl[14C]choline ([14C][unk] choline) to leaf discs and following 14C incorporation into prospective intermediates. The 14C kinetic data were used to develop a computer model of the betaine pathway.

When [14C]formate was fed, [unk] MME, phosphoryldimethylethanolamine ([unk] DME) and [unk] choline were the most prominent methylated products at short labeling times, after which 14C appeared in free choline and in betaine. Phosphatidylcholine labeled more slowly than [unk] choline, choline, and betaine, and behaved as a minor end product. Very little 14C entered the free methylethanolamines. When [14C][unk] MME was supplied, a small amount was hydrolyzed to the free base but the major fate was conversion to [unk] DME, [unk] choline, free choline, and betaine; label also accumulated slowly in phosphatidylcholine. Label from supplied [14C][unk] choline entered choline and betaine rapidly, while phosphatidylcholine labeled only slowly and to a small extent.

These results are consistent with the pathway [unk] MME →[unk] DME → [unk] choline → choline → → betaine, with a minor side branch leading from [unk] choline into phosphatidylcholine. This contrasts markedly (a) with the pathway of stress-induced choline and betaine synthesis in barley, in which phosphatidylcholine apparently acts as an intermediate (Hitz, Rhodes, Hanson 1981, Plant Physiol 68: 814-822); (b) with choline biogenesis in mammalian liver and microorganisms. Computer modeling of the experimental data pointed strongly to regulation at the [unk] choline → choline step, and also indicated that the rate of [unk] choline synthesis is subject to feedback inhibition by [unk] choline.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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