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Nitrogen fixation by Rhizobium cultured on a defined medium

Naturevolume 256pages406407 (1975) | Download Citation



IT has been widely believed that the legume root-nodule bacteria (Rhizobium spp.; rhizobia) fix N2 only within the tissues of the host plant1. There have however been recent reports that a strain of cowpea rhizobia, 32H1, developed nitrogenase activity when grown in association with legume or non-legume plant cells2,3. The induction of nitrogenase was apparently due to a diffusible factor(s) secreted by the plant cells, since nitrogenase activity was detected when strain 32H1 was grown adjacent to, but not in contact with, tobacco cells3. Several plant metabolites, including sugars known to favour rhizobial growth4,5 and citric acid cycle intermediates6,7, were examined for their effect on this latter system and as possible direct inducers of nitrogenase activity in cultured rhizobia. This led to the formulation of a defined medium on which strain 32H1 fixed N2 in the absence of plant cells.

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  1. Division of Plant Industry, CSIRO, PO Box 1600, Canberra City, ACT, 2601, Australia

    • J. D. PAGAN
    • , J. J. CHILD
    • , W. R. SCOWCROFT
    •  & A. H. GIBSON


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