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. 1991 Mar;95(3):753–759. doi: 10.1104/pp.95.3.753

N2-Fixation by Freshly Isolated Nostoc from Coralloid Roots of the Cycad Macrozamia riedlei (Fisch. ex Gaud.) Gardn. 1

Peter Lindblad 1,2, Craig A Atkins 1,2, John S Pate 1,2
PMCID: PMC1077602  PMID: 16668050

Abstract

Nitrogenase (EC 1.7.99.2) activity (acetylene reduction) and nitrogen fixation (15N2 fixation) were measured in cyanobacteria freshly isolated from the coralloid roots of Macrozamia riedlei (Fisch. ex Gaud.) Gardn. Light and gas phase oxygen concentration had marked interactive effects on activity, with higher (up to 100-fold) rates of acetylene reduction and 15N2 fixation in light. The relationship between ethylene formation and N2-fixation varied in the freshly isolated cyanobacteria from 4 to 7 nanomoles of C2H4 per nanomole 15N2. Intact coralloid roots, incubated in darkness and ambient air, showed a value of 4.3. Maximum rates of nitrogenase activity occurred at about 0.6% O2 in light, while in darkness there was a broad optimum around 5 to 8% O2. Inhibition of nitrogenase, in light, by pO2 above 0.6% was irreversible. Measurements of light-dependent O2 evolution and 14CO2 fixation indicated negligible photosynthetic electron transport involving photosystem II and, on the basis of inhibitor studies, the stimulatory effect of light was attributed to cyclic photophos-phorylation. Nitrogenase activity of free-living culture of an isolate from Macrozamia (Nostoc PCC 73102) was only slightly inhibited by O2 levels above 6% O2 and the inhibition was reversible. These cells showed rates of light-dependent O2 evolution and 14CO2 fixation which were 100- to 200-fold higher than those by the freshly isolated symbiont. Furthermore, nitrogenase activity was dependent on both photosynthetic electron transport and photophosphorylation. These data indicate that cyanobacteria within cycad coralloid roots are differentiated specifically for symbiotic functioning in a microaerobic environment. Specializations include a high heterocyst frequency, enhanced permeability to O2, and a direct dependence on the cycad for substrates to support nitrogenase activity.

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Selected References

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

  1. Atkins C. A., Sanford P. J., Storer P. J., Pate J. S. Inhibition of nodule functioning in cowpea by a xanthine oxidoreductase inhibitor, allopurinol. Plant Physiol. 1988 Dec;88(4):1229–1234. doi: 10.1104/pp.88.4.1229. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Haury J. F., Wolk C. P. Classes of Anabaena variabilis mutants with oxygen-sensitive nitrogenase activity. J Bacteriol. 1978 Nov;136(2):688–692. doi: 10.1128/jb.136.2.688-692.1978. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Peters G. A., Toia R. E., Lough S. M. Azolla-Anabaena azollae Relationship: V. N(2) Fixation, Acetylene Reduction, and H(2) Production. Plant Physiol. 1977 Jun;59(6):1021–1025. doi: 10.1104/pp.59.6.1021. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Stanier R. Y., Kunisawa R., Mandel M., Cohen-Bazire G. Purification and properties of unicellular blue-green algae (order Chroococcales). Bacteriol Rev. 1971 Jun;35(2):171–205. doi: 10.1128/br.35.2.171-205.1971. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Stewart W. D., Fitzgerald G. P., Burris R. H. In situ studies on N2 fixation using the acetylene reduction technique. Proc Natl Acad Sci U S A. 1967 Nov;58(5):2071–2078. doi: 10.1073/pnas.58.5.2071. [DOI] [PMC free article] [PubMed] [Google Scholar]

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