Supply of O2 regulates O2 demand during utilization of reserves of poly-beta-hydroxybutyrate in N2-fixing soybean bacteroids
| Autor: | F.J. Bergersen, G. L. Turner |
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| Rok vydání: | 1992 |
| Předmět: |
Time Factors
General Immunology and Microbiology Plant nodule Chemistry Polyesters Analytical chemistry Hydroxybutyrates General Medicine General Biochemistry Genetics and Molecular Biology Oxygen Kinetics Oxygen Consumption Biochemistry Rhizobiaceae Nitrogen Fixation Soybeans Reaction chamber General Agricultural and Biological Sciences Volume concentration General Environmental Science |
| Zdroj: | Proceedings. Biological sciences. 249(1325) |
| ISSN: | 0962-8452 |
| Popis: | A liquid reaction medium containing dissolved air and oxyleghaemoglobin, but no energy-yielding substrate, was supplied to bacteroids confined in a stirred flow reaction chamber. The relative oxygenation of the leghaemoglobin in the chamber was determined automatically by spectrophotometry of the effluent solution, and the concentrations of free, dissolved (O$_{2}$ ([O$_{2}$]) and rates of O$_{2}$ consumption were calculated. Dissolved CO$_{2}$ and NH$_{3}$ from N$_{2}$ fixation were determined in fractions of the effluent solution. Bacteroids utilized endogenous reserves of poly-$\beta $-hydroxybutyrate (PHB), which were depleted by 9.2% during a typical 5 h-long experiment. Stepwise increases in flow rate (increasing supply of O$_{2}$ initially produced a drop in O$_{2}$ demand and resulted in a rise in [O$_{2}$] and a decline in N$_{2}$ fixation. Subsequently, O$_{2}$ demand rose (presumably because of increased mobilization of substrate from PHB) and [O$_{2}$] declined to a low level. N$_{2}$ fixation was fully restored, or even enhanced, within 15-20 min of establishment of a new, steady [O$_{2}$]. This pattern of regulation by O$_{2}$ supply was completely eliminated by adding low concentrations (20-50 $\mu $M) of oxidizable substrate (succinate, malate, ethanol) to the reaction medium. During endogenous activity, rates of CO$_{2}$ evolution were proportional to, but less than, rates of O$_{2}$ consumption up to 5.4 nmol O$_{2}$ min$^{-1}$ mg$^{-1}$, above which CO$_{2}$ evolution exceeded O$_{2}$ consumption. These and other features of endogenous activity are discussed in relation to sustaining N$_{2}$ fixation by nodules in vivo. |
| Databáze: | OpenAIRE |
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