Abstract
It has been previously proposed that acetylene reduction data at subsaturating acetylene concentrations could be interpreted by use of the Michaelis-Menten equation, based on the acetylene concentration external to the nodules. One difficulty of this view is that the assumption that the system is not diffusion limited is violated when studying intact nodules. The presence of a gas diffusion barrier in the nodule cortex leads to an alternate expression for the gas exchange rates at subsaturating gas concentrations. A theoretical comparison of the `apparent' Michaelis-Menten model and diffusion model illustrated the difficulties observed in the former model of overestimating the Michaelis-Menten coefficient and yielding a correlation between the Michaelis-Menten coefficient and the maximum rate. On the other hand, use of a diffusion model resulted in (a) estimates of the Michaelis-Menten coefficient consistent with enzyme studies, (b) stability of the estimates of the Michaelis-Menten coefficient independent of treatment, and (c) a sensitivity of the diffusion barrier conductance to plant drought stress. It was concluded that all studies of nodule gas exchange need to consider possible effects caused by the presence of a diffusion barrier.
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Selected References
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- Davis L. C., Wang Y. L. In vivo and in vitro kinetics of nitrogenase. J Bacteriol. 1980 Mar;141(3):1230–1238. doi: 10.1128/jb.141.3.1230-1238.1980. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hardy R. W., Holsten R. D., Jackson E. K., Burns R. C. The acetylene-ethylene assay for n(2) fixation: laboratory and field evaluation. Plant Physiol. 1968 Aug;43(8):1185–1207. doi: 10.1104/pp.43.8.1185. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Koch B., Evans H. J. Reduction of acetylene to ethylene by soybean root nodules. Plant Physiol. 1966 Dec;41(10):1748–1750. doi: 10.1104/pp.41.10.1748. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mederski H. J., Streeter J. G. Continuous, automated acetylene reduction assays using intact plants. Plant Physiol. 1977 Jun;59(6):1076–1081. doi: 10.1104/pp.59.6.1076. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sinclair T. R., Goudriaan J. Physical and morphological constraints on transport in nodules. Plant Physiol. 1981 Jan;67(1):143–145. doi: 10.1104/pp.67.1.143. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Tjepkema J. D., Cartica R. J. Diffusion Limitation of Oxygen Uptake and Nitrogenase Activity in the Root Nodules of Parasponia rigida Merr. and Perry. Plant Physiol. 1982 Mar;69(3):728–733. doi: 10.1104/pp.69.3.728. [DOI] [PMC free article] [PubMed] [Google Scholar]