Root nodules of Glycine max infected with Rhizobium japonicum were investigated by means of scanning electron microscope and transmission electron microscope.
The surface of the nodule was not flat, and root hair like structure was not observed. In the plotoplasts of bacteroidal tissues obtained by critical point drying treatment, numerous bacteria were observed. Most nodule bacteria were rod-shaped, however, varied in size. The cells of protective tissue in the nodule contained developed amyloplasts and lipid droplets. Bacteroidal bodies were not recognized in the nuclei of the bacteroidal cells. The plastids and mitochondria in the bacteroidal cells were mainly located abutting on the cell wall. Host cell wall infected by Rhizobium japonicum were thicker than those of healthy cell walls. The bacteria released from the infection thread were surrounded by an unit membrane which might be derived from the host cell membrane. It is likely that the bacteria are not contacted directly with cytoplasm of host cell, because they are enclosed by those membranes.