Acetylene reduction and respiration of bacteroids isolated from French‐beans receiving nitrate

Abstract

The competition between combined nitrogen and nitrogen fixation in legumes was studied after a 24 h exposure of nodulated French‐beans to nitrate. Acetylene reduction by bacteroids was significantly inhibited and even nitrogenase extracted from nitrate‐treated plant nodules showed reduced activity. Sensitivity to nitrate was directly related to nodule age and also increased with increasing oxygen tensions in the bacteroid incubations with or without a gas phase; it was particularly marked when glucose was used in place of succinate as energy‐yielding substrate. Bacteroid respiration was also depressed by nitrate‐treatment of the plants, leading to diminished acetylene reduction and this effect increased with increasing oxygen concentrations. Added oxyleghemoglobin partly restored oxygen consumption and acetylene reduction by bacteroid suspensions.