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. 1989 Apr;89(4):1150–1157. doi: 10.1104/pp.89.4.1150

Significance of Phosphoenolpyruvate Carboxylase during Ammonium Assimilation

Carbon Isotope Discrimination in Photosynthesis and Respiration by the N-Limited Green Alga Selenastrum minutum1

Robert D Guy 1, Greg C Vanlerberghe 1, David H Turpin 1
PMCID: PMC1055989  PMID: 16666678

Abstract

The effect of N-assimilation on the partitioning of carbon fixation between phosphoenolpyruvate carboxylase (PEPcase) and ribulose bisphosphate carboxylase/oxygenase (Rubisco) was determined by measuring stable carbon isotope discrimination during photosynthesis by an N-limited green alga, Selenastrum minutum (Naeg.) Collins. This was facilitated by a two process model accounting for simultaneous CO2 fixation and respiratory CO2 release. Discrimination by control cells was consistent with the majority of carbon being fixed by Rubisco. During nitrogen assimilation however, discrimination was greatly reduced indicating an enhanced flux through PEPcase which accounted for upward of 70% of total carbon fixation. This shift toward anaplerotic metabolism supports a large increase in tricarboxylic acid cycle activity primarily between oxaloacetate and α-ketoglutarate thereby facilitating the provision of carbon skeletons for amino acid synthesis. This provides an example of a unique set of conditions under which anaplerotic carbon fixation by PEPcase exceeds photosynthetic carbon fixation by Rubisco in a C3 organism.

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Selected References

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

  1. Birch D. G., Elrifi I. R., Turpin D. H. Nitrate and Ammonium Induced Photosynthetic Suppression in N-Limited Selenastrum minutum: II. Effects of NO(3) and NH(4) Addition to CO(2) Efflux in the Light. Plant Physiol. 1986 Nov;82(3):708–712. doi: 10.1104/pp.82.3.708. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Elrifi I. R., Holmes J. J., Weger H. G., Mayo W. P., Turpin D. H. RuBP Limitation of Photosynthetic Carbon Fixation during NH(3) Assimilation : Interactions between Photosynthesis, Respiration, and Ammonium Assimilation in N-Limited Green Algae. Plant Physiol. 1988 Jun;87(2):395–401. doi: 10.1104/pp.87.2.395. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Elrifi I. R., Turpin D. H. Nitrate and Ammonium Induced Photosynthetic Suppression in N-Limited Selenastrum minutum. Plant Physiol. 1986 May;81(1):273–279. doi: 10.1104/pp.81.1.273. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Elrifi I. R., Turpin D. H. The Path of Carbon Flow during NO(3)-Induced Photosynthetic Suppression in N-Limited Selenastrum minutum. Plant Physiol. 1987 Jan;83(1):97–104. doi: 10.1104/pp.83.1.97. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Kanazawa T., Kirk M. R., Bassham J. A. Regulatory effects of ammonia on carbon metabolism in photosynthesizing Chlorella pyrenoidosa. Biochim Biophys Acta. 1970 Jun 30;205(3):401–408. doi: 10.1016/0005-2728(70)90106-4. [DOI] [PubMed] [Google Scholar]
  6. Melzer E., O'leary M. H. Anapleurotic CO(2) Fixation by Phosphoenolpyruvate Carboxylase in C(3) Plants. Plant Physiol. 1987 May;84(1):58–60. doi: 10.1104/pp.84.1.58. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Miller A. G., Turpin D. H., Canvin D. T. Growth and Photosynthesis of the Cyanobacterium Synechococcus leopoliensis in HCO(3)-Limited Chemostats. Plant Physiol. 1984 Aug;75(4):1064–1070. doi: 10.1104/pp.75.4.1064. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. O'Leary M. H., Rife J. E., Slater J. D. Kinetic and isotope effect studies of maize phosphoenolpyruvate carboxylase. Biochemistry. 1981 Dec 8;20(25):7308–7314. doi: 10.1021/bi00528a040. [DOI] [PubMed] [Google Scholar]
  9. O'leary M. H., Treichel I., Rooney M. Short-term measurement of carbon isotope fractionation in plants. Plant Physiol. 1986 Feb;80(2):578–582. doi: 10.1104/pp.80.2.578. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Weger H. G., Birch D. G., Elrifi I. R., Turpin D. H. Ammonium Assimilation Requires Mitochondrial Respiration in the Light : A Study with the Green Alga Selenastrum minutum. Plant Physiol. 1988 Mar;86(3):688–692. doi: 10.1104/pp.86.3.688. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Weger H. G., Turpin D. H. Mitochondrial Respiration Can Support NO(3) and NO(2) Reduction during Photosynthesis : Interactions between Photosynthesis, Respiration, and N Assimilation in the N-Limited Green Alga Selenastrum minutum. Plant Physiol. 1989 Feb;89(2):409–415. doi: 10.1104/pp.89.2.409. [DOI] [PMC free article] [PubMed] [Google Scholar]

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