Effect of the Hydrogenase System in Rhizobium japonicum on the Nitrogen Fixation and Growth of Soybeans at Different Stages of Development1
- R. M. Zablotowicz,
- S. A. Russell and
- H. J. Evans2
The process of N fixation is energy consuming and inefficient. In most cases 20 to 40% of the energy that is supplied to nitrogenase for the reduction of N2 is utilized for the reduction of protons to H2. Some strains of R. japonicum contain a membrane-bound hydrogenase that is capable of oxidizing all of the H2 that is produced during N2 fixation. This study was conducted to evaluate the effects of inoculation of soybeans [Glycine max (L.) Merr.] with Rhizobium japonicum containing H2 recycling capability on N fixation efficiency and soybean yield at various physiological stages of growth.
In these experiments, a H2-oxidizing strain SR (Hup+) and SR3 (Hup−), a mutant derived from SR which is unable to oxidize H2, were utilized. Soybeans cv. ‘Wilkin’ were grown under bacteriological conditions utilizing a drip-irrigated nutriculture system. Nodules from plants inoculated with SR evolved no measurable amount of H2, while nodules from plants innoculated with SR3 evolved between 2.7 and 10 µmoles of H2/g nodules/ hour depending upon physiological age. Acetylene reduction rates by strain SR were significantly higher than those of nodules formed from SR3 during the vegetative, late pod-fill, and leaf senescence stage of growth, respectively. Dry matter accumulation was significantly higher in plants inoculated with SR than in plants inoculated with SR3 (31% increase during vegetative stage, 25% during flowering, and 27% during pod-fill stage). Nitrogen contents of shoots and seeds were significantly higher in plants inoculated with strain SR, demonstrating increased N fixation by nodules formed by Hup+Rhizobium. Our results support the conclusion that strains of R. japonicum selected for inoculation purposes should contain H2-oxidizing capability as one of their desired characteristics.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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