[Nitrogen fixing activity of pea nodule bacteria during different phases of host plant development]

The activity of nitrogenase in nodules of pea plants and the rate of diurnal nitrogen fixation were studied at different phases of the plant growth using the acetylene and isotope techniques. At the same time, the morphology of nodule bacteria was studied by electron and phase-contrast microscopy. About 90% of the bacteria in nodules were found in the form of bacteroids from the early phase of the plant growth (budding) to ripening when gemmated arthrospores could be observed on some bacteroids. The highest activity of nitrogenase and nitrogen fixation was detected at the reproductive stage of growth. Therefore, in order to obtain more active strains of pea nodule bacteria, they should be isolated from nodules at this stage of plant growth.