Plant Physiology 87:296-299 (1988)
© 1988 American Society of Plant Biologists
Molecular Biology and Gene Regulation
Regulation of O2 Concentration in Soybean Nodules Observed by in Situ Spectroscopic Measurement of Leghemoglobin Oxygenation 1
Bryan J. King,
Stephen Hunt,
Glenn E. Weagle,
Kerry B. Walsh,
Roy H. Pottier,
David T. Canvin and
David B. Layzell
Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6,
Department of Chemistry and Chemical Engineering, Royal Military College of Canada, Kingston, Ontario, Canada K7K 5L0
A fiber optic spectrophotometric system was used to monitor the in vivo oxygenation of leghemoglobin in intact, attached soybean root nodules (Glycine max L. Merr. x USDA 16 Bradyrhizobium japonicum) which were flattened during development by growth in narrow, glass-walled cuvettes. When equilibrated at an external pO2 of 20 kilopascals, leghemoglobin was 36.6 ± 5.4% oxygenated, a value estimated to represent an infected cell O2 concentration of 21.5 nanomolar. Increasing the external pO2 from 20 to 25 kilopascals caused a rapid increase in leghemoglobin oxygenation, followed by a recovery to the initial level, all within 7.5 minutes. At 25 kilopascals O2, the rates of H2 and CO2 evolution were similar to those at 20 kilopascals. Since respiration had not increased, the results support the proposal that nodules adapt to increased external pO2 by regulating their resistance to O2 diffusion.
1 Supported by grants from the Natural Sciences and Engineering Research Council of Canada (D. B. L., D. T. C.), the Department of National Defence (R. H. P.), and the Queen's University Advisory Research Council (B. J. K.). B. J. K. and K. B. W. acknowledge support from a Natural Sciences and Engineering Research Council of Canada Post-Graduate Scholarship and a Commonwealth Scholarship, respectively.
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