Comparative Studies of Nitrogen Fixation by Soybean Root Nodules, Bacteroid Suspensions and Cell-free Extracts

Abstract

SUMMARY: Rhizobium japonicum (CC711) was used to infect soybean seeds from which plants were grown. From the root nodules, bacteroid suspensions with initial rates of nitrogen fixation as high as those calculated for bacteroids in intact nodules were prepared. Oxygen, which was required for fixation by intact nodules and bacteroid suspensions, caused the eventual loss of bacteroid nitrogen-fixing ability, accompanied by an increase in O2-uptake. In intact nodules and in bacteroid suspensions, increasing O2 pressures resulted in higher values for Km of nitrogen fixation. Vmax also increased with increasing pO2 and this was shown to be consistent with the characteristics of nitrogen fixation by anaerobic cell-free extracts of bacteroids which required an energy source (ATP), and a reductant (sodium dithionite).