CARBON METABOLISM RELATED TO NITROGEN FIXATION IN SOYBEAN ROOT NODULES

概要

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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, phosphenolpyruvate carboxylase, and aldehyde dehydrogenase also depressed the acetylene-reducing activity of the nodules. These results suggest that ethanol formation and CO_2 dark fixation are active in the host plant cell side of the soybean nodule and the respective metabolic products, acetaldehyde, and malate, are supplied to the bacteroids as carbon sources for nitrogen fixation.
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