Question

Which of the following are correct with respect to nodule formation by rhizobium species

Answer 1

Answer:

. Plasmids play an important role in determining symbiotic phenotypes, including host range, nodulation ability, and the capacity to fix nitrogen in the nodules. Indeed, some of the genes that code for nitrogenase appear to be plasmid-linked. The involvement of plasmids should not be too surprising as it is well known that in another member of the Rhizobiaceae, Agrobacterium tumefaciens, plasmids are responsible for the tumorigenicity of this species. Rhizobium and Agrobacterium have in common the ability to induce cellular proliferation on plants. In the case of R. phaseoli, the transconjugants differed from the wild type R. phaseoli in another character, namely, the ability to produce a black pigment. It was found that many field isolates of R. phaseoli produce a black pigment after prolonged incubation, 2–3 weeks, on complete medium. A number of strains of Rhizobium have been shown to be capable of nitrogen fixation in vitro.