SYMBIOTIC PROPERTIES OF ANTIBIOTIC-RESISTANT MUTANTS OF RHIZOBIUM-GALEGAE

Mutagenesis provoked by exposure to increased concentration of antibio tics of five indigenous Rhizobium galegae strains resulted in the gene ration of several antibiotic-resistant mutants. The mutants differed f rom the wild type and one from another in respect to the nodulation ca pacity, the nitrogenase activity, the nodule ultrastructure, and the p lant growth response, Galega plants inoculated with mutants resistant to streptomycin and rifampicin formed nodules with higher nitrogenase activity and accumulated more shoot dry biomass than plants inoculated with the parent strains. Resistance to kanamycin and nalidixic acid w as associated with significant decrease of nitrogenase activity. A cor relation between nitrogen-fixing efficiency and nodule infected cell u ltrastructure was found. When the bacteroids occupied about 10 times h igher area in infected cells of nodule than peribacteroid spaces and h ost cytosol had electron dense and homogenous structure, the nitrogena se activity was the highest.