Physiological Role of Leghaemoglobin Heterogeneity in Pea Root Nodule Development

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Disk-gel-electrophoresis of the leghaemoglobin isolated from pea root nodules revealed two major (Lb I and Lb IV) and three minor components. The ratio of the two major components (Lb I/Lb IV) decreased with increasing age. This ratio was higher in the distal than in proximal region when nodules were cut into distal and proximal sections. In young nodules, the incorporation of radioactive leucine into Lb I was much higher than into Lb IV. In older nodules, the radioactivities were much higher in Lb IV than in Lb I. These data suggest that the change in this ratio is due mainly to differences in the rates of biosynthesis. Two major components (Lb I and Lb IV) which were isolated separately had different 02-binding affinities. The 02-binding affinity of the component synthesized mainly in older nodules (Lb IV) was higher than that of the component synthesized mainly in young nodules (Lb I). These results indicate that changes in the relative contents of leghaemoglobin during nodule development contribute to more effective nitrogen fixation which is mediated by changes in the capacities of oxygen transport.
日本植物生理学会の論文