The development of bacteroids in alfalfa (Medicago sativa) nodules



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DNA-dependent DNA polymerase was purified to near homogeneity from extracts of cultured Rhizobium meliloti F28. The enzyme required the presence of a full complement of deoxyribonucleoside triphosphates, Mg++ or Mn++, and DNA primer-template for maximum activity. The enzyme was also sensitive to p-chloromercuribenzoate and N-ethylmaleimide. The process of development and transformation of R. meliloti F28 in nodules of alfalfa (Medicago sativa Buffalo) into symbiotic bacteroids and the associated development of symbiotic dinitrogen fixation and leghemoglobin in alfalfa nodules were studied with the use of light and electron microscopy, gas-chromatography, and flowmicrofluorometry. Inside the nodules, the rhizobia developed into matured bacteroids which were enlarged and had higher nucleic acid content than the cultured rhizobia. These bacteroids were active in nitrogenase activity and had altered nucleoid structures. Bacteroid senescence was accompanied by a loss in the bacteroid nucleic acid content and nitrogenase activity of the nodules. A model was constructed to describe the process of bacteroid development and transformation in alfalfa nodules. The applicability of the flow-microfluorometry to the studies of bacterial and algal cell and isolated chloroplasts was also examined.