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Articles

Proteolytic Activity in Soybean Root Nodules ¹

Activity in Host Cell Cytosol and Bacteroids throughout Physiological Development and Senescence

Department of Agricultural Biochemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68583-0718

Root nodules were harvested from chamber-grown soybean (Glycine max L. Merrill cv Woodworth) plants throughout development. Apparent nitrogenase activity (acetylene reduction) peaked before seeds began to develop, but a significant amount of activity remained as the seeds matured. Nodule senescence was defined as the period in which residual nitrogenase activity was lost. During this time, soluble protein and leghemoglobin levels in the host cell cytosol decreased, and proteolytic activity against azocasein increased. Degradative changes were not detected in bacteroids during nodule senescence. Total soluble bacteroid protein per gram of nodule remained constant, and an increase in proteolytic activity in bacteroid extracts was not observed. These results are consistent with the view that soybean nodule bacteroids are capable of redifferentiation into free-living bacteria upon deterioration of the legume-rhizobia symbiosis.

¹ Supported in part by United States Department of Energy/Science and Education Administration-CRGO Grant No. 509-0410-9-0233 and the Nebraska Soybean Development, Utilization and Marketing Board, Contract No. 380-82-12. Published as Paper No. 6982, Journal Series, Nebraska Agricultural Experiment Station.

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