Abstract
Large amounts of alanine are produced in the first few seconds of photosynthesis in Portulaca oleracea L. The normal precursor-product relationship (phosphoglyceric acid → pyruvate → alanine) does not appear to operate in this species since labeling in pyruvate precedes that in phosphoglyceric acid. Pulse-chase experiments show that the alanine is rapidly metabolized. After a 6-second pulse of 14CO2, the percentage of 11C in alanine drops more than 30% in the first 10 seconds of a 12CO2 chase period. The percentage of 14C in the other early-labeled photosynthetic products, aspartate and malate, also decreases during the 12CO2 chase. The decrease of label in these compounds is concomitant with an increase in the labeling of sucrose and alanine, which in this case is formed via phosphoglyceric acid. Randomization of label within alanine increases gradually throughout the 2-minute chase.
Alpha-keto acids accounts for up to 20% of the total 14CO2 incorporated by young leaf tissue. Pyruvate alone accounts for at least 65% of the radioactivity in the keto acid fraction in both young and mature leaves. Other early-labeled keto acids are oxaloacetate and, in young tissue only, hydroxyphenylpyruvate. We propose that, in Portulaca, pyruvate is one of the earliest-labeled photosynthetic products and serves as the immediate precursor of alanine.
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Selected References
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- Chen T. M., Brown R. H., Black C. C. Photosynthetic CO(2) Fixation Products and Activities of Enzymes Related to Photosynthesis in Bermudagrass and Other Plants. Plant Physiol. 1971 Feb;47(2):199–203. doi: 10.1104/pp.47.2.199. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hatch M. D., Slack C. R. Photosynthesis by sugar-cane leaves. A new carboxylation reaction and the pathway of sugar formation. Biochem J. 1966 Oct;101(1):103–111. doi: 10.1042/bj1010103. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Osmond C. B. Beta-carboxylation during photosynthesis in Atriplex. Biochim Biophys Acta. 1967 Jun 13;141(1):197–199. doi: 10.1016/0304-4165(67)90264-4. [DOI] [PubMed] [Google Scholar]
- TOWERS G. H., MORTIMER D. C. The role of keto acids in photosynthetic carbon dioxide assimilation. Can J Biochem Physiol. 1956 May;34(3):511–519. [PubMed] [Google Scholar]