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. 1974 Jul;119(1):258–265. doi: 10.1128/jb.119.1.258-265.1974

Nitrogenase Activity and Photosynthesis in Plectonema boryanum

N M Weare 1, John R Benemann 1
PMCID: PMC245597  PMID: 4209777

Abstract

Nitrogen-starved Plectonema boryanum 594 cultures flushed with N2/CO2 or A/CO2 (99.7%/0.3%, vol/vol) exhibited nitrogenase activity when assayed either by acetylene reduction or hydrogen evolution. Oxygen evolution activities and phycocyanin pigments decreased sharply before and during the development of nitrogenase activity, but recovered in the N2/CO2 cultures after a period of active nitrogen fixation. Under high illumination, the onset of nitrogenase activity was delayed; however, the presence of 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea (DCMU) eliminated this lag. Oxygen was a strong and irreversible inhibitor of nitrogenase activity at low (>0.5%) concentrations. In the dark, low oxygen tensions (0.5%) stimulated nitrogenase activity (up to 60% of that in the light), suggesting a limited but significant respiratory protection of nitrogenase at low oxygen tensions. DCMU was not a strong inhibitor of nitrogenase activity. A decrease in nitrogenase activity after a period of active nitrogen fixation was observed in the N2/CO2−, but not in the A/CO2−, flushed cultures. We suggest that this decrease in nitrogenase activity is due to exhaustion of stored substrate reserves as well as inhibition by the renewed oxygen evolution of the cultures. Repeated peaks of alternating nitrogenase activity and oxygen evolution were observed in some experiments. Our results indicate a temporal separation of these basically incompatible reactions in P. boryanum.

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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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