Kinetics of Nodule Development in Glycine soja

Nodule development in the interaction of Glycine soja Sieb. & Zucc. PI468.397 with Bradyrhizobium japonicum USDA110 was studied by hypochlorite clearing and methylene blue staining. Even the earliest stages of nodule development could be observed. The entire length of the primary root was examined up to 15 d postinoculation. Markedly curled root hairs and the first cell divisions in the hypodermal layer (stage I) were observed 2 d postinoculation, and by 3 d cell division activity had spread to the outer layers of the cortex (stage II). Cortical cell division centers not associated with curled root hairs, frequently observed in soybean (Glycine max [L.] Merr.), were very rare in G. soja. The cortical cell division centers that had developed a well-defined nodule meristem (at or beyond stage IV) by 6 d postinoculation continued to develop, but the less-advanced stages became arrested. Almost all nodules developed near the position of the root tip at the time of inoculation. In the parts of the root that developed after inoculation, regions with a high density of markedly curled root hairs per root length were observed. The percentage of the curled root hairs associated with cortical cell division centers, however, declined with each successive peak. Regulation of nodule development in G. soja was similar to that previously reported in soybean, although the rate of nodule development was slower.