Characterization and symbiotic nitrogen fixation ofrhizobiumthat modulates Chinese milk vetch (Astragalus sinicus, L.)

Abstract

Abstract Strains of Rhizobia were isolated from nodules of Chinese milk vetch (Astragalus sinicus, L.) collected from paddy fileds in Japan. Taxonomical investigation revealed that they belonged to the genus Rhizobium, a fast-growing bacterium on yeast extract-mannitol agar plate. As the nodules formed on the plants inoculated with these strains gave values of specific C2H2-reducing activity (10-20 nmol C2H4 production/(h·mg nodule fr. wt.)) similar to those of soybean nodules, the effectiveness of Chinese milk vetch as green manure was suggested. Since the addition of nitrate to the nutrient solution reduced the total C2H2-reducing activity of the plant, but not the specific activity of the nodules, it was considered that the addition of nitrate inhibited the formation and development of the nodules. The leg-haemoglobin content was not affected by the nitrate addition. The leghaemoglobin of the milk vetch nodules was separated into five components by PAGE (polyacrylamide gel electrophoresis) and their relative amounts varied with the growth stages of the plant. Among them, the relative amount of one component was correlated with the specific C2H2-reducing activity of the nodules.