Abstract
The ammonia diffusion hypothesis states that ammonia generated within the bacteroid by nitrogenase reaches the plant cytosol by diffusion Ammonia is found in the external medium of resuspended nitrogen-fixing bacteroid preparations. The purification of soybean nodule bacteroids by the sucrose density procedure has been shown to remove contaminating plant nodule cytosol proteins (Waters et al., 1985; Karr and Emerich, 1988; Karr et a1.,1990). When sucrose density gradient purified bacteroids were isolated anaerobically and incubated under nitrogen-fixing conditions, alanine was released, but not ammonia. If plant nodule cytosol was added to sucrose density gradient purified bacteroids, alanine was no longer excreted but ammonia was found instead. This indicates that alanine, and not ammonia, is the primary nitrogen carrier out of the soybean bacteroid.
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Waters, J.K., Hughes, B.L., Purcell, L.C., Gerhardt, K., Mawhinney, T.P., Emerich, D.W. (1999). Alanine and Ammonia Release by N2-Fixing Bradyrhizobium Japonicum Bacteroids. In: Martĺnez, E., Hernández, G. (eds) Highlights of Nitrogen Fixation Research. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-4795-2_6
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DOI: https://doi.org/10.1007/978-1-4615-4795-2_6
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