Marine Oscillatoria (Trichodesmium): Explanation for Aerobic Nitrogen Fixation Without Heterocysts

Nitrogen fixation in marine Oscillatoria appears to be associated with differentiated cells located in the center of the colony. These central cells exhibit reduced pigmentation relative to peripherally located cells and do not incorporate $^{14}$CO$_{2}$ in photosynthesis. Central cells apparently...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 1976-03, Vol.191 (4233), p.1278-1280
Main Authors: Carpenter, Edward J., Price, Charles C.
Format: Article
Language:English
Subjects:
Alkynes
Circles
College students
Continents
Eukaryota - cytology
Eukaryota - metabolism
Nitrogen fixation
Nitrogen Fixation - drug effects
Oxygen - pharmacology
Plate tectonics
Population density
Seas
Serenity
Trichomes
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Summary:Nitrogen fixation in marine Oscillatoria appears to be associated with differentiated cells located in the center of the colony. These central cells exhibit reduced pigmentation relative to peripherally located cells and do not incorporate $^{14}$CO$_{2}$ in photosynthesis. Central cells apparently do not produce O$_{2}$ which would deactivate nitrogenase. When central cells are exposed to O$_{2}$ via disruption of the colonies, N$_{2}$ fixation (acetylene reduction) decreases sharply even though individual trichomes remain intact. Disruption of colonies in the absence of O$_{2}$ does not cause reduced nitrogenase activity. In the sea, turbulence from wave action apparently separates trichomes allowing O$_{2}$ to enter thus decreasing nitrogenase activity. These observations explain how Oscillatoria is able to fix N$_{2}$ without heterocysts in an aerobic environment and why its blooms virtually always occur in calm seas.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.1257749