Carbon Metabolism Related to Nitrogen Fixation in Soybean Root Nodules

Specific activities of several enzymes involved in the carbon metabolism were compared between roots and nodules of soybean, or between the free-living bacteria, Rhizobium japonicum, and the bacteroids isolated from soybean nodules. Alcohol dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, and phosphoenolpyruvate carboxylase showed higher activities in the nodules than in the roots. Alcohol dehydrogenase and phosphoenolpyruvate carboxylase were localized mostly in the host plant cells of the nodules. Activities of aldehyde dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, and malate dehydrogenase in the bacteroids were higher than those in the free-living bacteria. The sucrose stimulated-acetylene reduction of detached soybean nodules was inhibited by inhibitors of glycolysis, but not by those of the tricarboxylic acid cycle. The respective specific inhibitor of alcohol dehydrogenase, phosphoenolpyruvate carboxylase, and aldehyde dehydrogenase also depressed the acetylene reducing activity of the nodules.