The location of the enzymes of mmonia assimilation in root nodules of Phaseolus vulgaris L.

Abstract

The location of the enzymes potentially involved in ammonia assimilation in nitrogen fixing root nodules of Phaseolus vulgaris has been examined by sucrose density gradient separation of the bacteroids from plant organelles. Glutamine synthetase is almost entirely present in the plant cytoplasm, glutamate dehydrogenase (GDH) is in the mitochondria. The results also show that there is little evidence for the presence of significant proportions of the total glutamine synthetase and glutamate synthase activity being present in the bacteriod. In contrast however, by far the greater proportion of the total nodule GDH activity was found in the bacteroid. The problems encountered by previous workers in assaying and localising glutamate synthase and GDH in legume root nodules are discussed.