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Articles

Effect of Supra-Ambient Oxygen on Nitrogenase Activity (C₂H₂) and Root Respiration of Soybeans and Isolated Soybean Bacteroids ¹

Boyce Thompson Institute, Tower Road, Ithaca, New York 14853

Isolated soybean (Glycine max [L.] Merr. cv Wilkin) bacteroids have O₂-dependent nitrogenase activity which is strongly inhibited by supraoptimal O₂ concentrations. Oxygen-inhibited nitrogenase activity is recovered by addition of 10 millimolar sodium succinate or by lowering the O₂ concentration.

Brief treatment of roots of intact soybean plants with 1.0 atmosphere O₂ reduces nitrogenase activity (C₂H₂). There is a rapid partial recovery of activity within 2 to 3 hours, and a slower return to near normal levels by 36 hours. The drop and recovery of nitrogenase activity is accompanied by a parallel drop and increase in root respiration. There is a direct relationship between the change in respiration and the change in acetylene reduction following O₂ treatment. The O₂-mediated changes in nitrogenase activity and root respiration are not affected by the planting medium. The ratio of the change in respiration to the change in nitrogenase activity was the same in 13 soybean cultivars.

¹ Supported by grant 05-0560 from the United Nations Development Program to the International Institute for Tropical Agriculture, and by grant DE-AC02-82ER12066 from the Department of Energy.