AGROBACTERIUM-RADIOBACTER MUTANTS WITH ALTERED CAPACITY FOR NITROGEN-FIXATION AND INTERACTION WITH PLANTS

Mutants with altered capacity for interaction with plants or nitrogen fixation were obtained through ethyl methanesulfonate and transposon T n5 induction in Agrobacterium radiobacter 5D-1, a saprophytic nitrogen -fixing bacterium capable of associative interaction with plants. The former mutants were selected on a medium containing calcofluor, and th e latter mutants were isolated on a medium with tetrazolium bromide. M utants whose interaction with the plant roots was impaired (Cal(-) and Cal(++)) differed from the wild strain in the activity of nitrogenase when grown in association with rape. When grown in a monoculture, the activity of nitrogenase was unchanged. In mutants with disturbances o f nitrogen metabolism (Nm and Nr), clones were found with alterations in acetylene reduction efficiency. These alterations are manifested ei ther in a similar or in a reverse way in a monoculture and in associat ion with rape. The properties of the obtained mutants suggest that mut ations occur in the genes which exert control over nitrogen fixation r ealized in association with a plant.