Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Plant Physiology 69:728-733 (1982)
© 1982 American Society of Plant Biologists

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Diffusion Limitation of Oxygen Uptake and Nitrogenase Activity in the Root Nodules of Parasponia rigida Merr. and Perry 1

John D. Tjepkema and Robert J. Cartica

Harvard Forest, Harvard University, Petersham, Massachusetts 01366

Parasponia is the first non-legume genus proven to form nitrogen-fixing root nodules induced by rhizobia. Infiltration with India ink demonstrated that intercellular air spaces are lacking in the inner layers of the nodule cortex. Oxygen must diffuse through these layers to reach the cells containing the rhizobia, and it was calculated that most of the gradient in O2 partial pressure between the atmosphere and rhizobia occurs at the inner cortex. This was confirmed by O2 microelectrode measurements which showed that the O2 partial pressure was much lower in the zone of infected cells than in the cortex. Measurements of nitrogenase activity and O2 uptake as a function of temperature and partial pressure of O2 were consistent with diffusion limitation of O2 uptake by the inner cortex. In spite of the presumed absence of leghemoglobin in nodules of Parasponia rigida Merr. and Perry, energy usage for nitrogen fixation was similar to that in legume nodules. The results demonstrate that O2 regulation in legume and Parasponia nodules is very similar and differs from O2 regulation in actionorhizal nodules.

1 Supported by the Maria Moors Cabot Foundation for Botanical Research of Harvard University and USDA Research Grant 78-59-2252-0-1-055-1.




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C. A. APPLEBY, J. D. TJEPKEMA, and M. J. TRINICK
Hemoglobin in a Nonleguminous Plant, Parasponia: Possible Genetic Origin and Function in Nitrogen Fixation
Science, May 27, 1983; 220(4600): 951 - 953.
[Abstract] [PDF]


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Copyright © 1982 by the American Society of Plant Biologists