KINETICS OF NODULE DEVELOPMENT IN GLYCINE-SOJA

Nodule development in the interaction of Glycine soja Sieb. & Zucc. P1 468.397 with Bradyrhizobium japonicum USDA110 was studied by hypochlor ite 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 ha irs and the first cell divisions in the hypodermal layer (stage I) wer e observed 2 d postinoculation, and by 3 d cell division activity had spread to the outer layers of the cortex (stage II). Cortical cell div ision centers not associated with curled root hairs, frequently observ ed in soybean (Glycine max [L.] Merr.), were very rare in G. soja. The cortical cell division centers that had developed a well-defined nodu le meristem (at or beyond stage IV) by 6 d postinoculation continued t o develop, but the less-advanced stages became arrested. Almost all no dules developed near the position of the root tip at the time of inocu lation. In the parts of the root that developed after inoculation, reg ions with a high density of markedly curled root hairs per root length were observed. The percentage of the curled root hairs associated wit h cortical cell division centers, however, declined with each successi ve peak. Regulation of nodule development in G. soja was similar to th at previously reported in soybean, although the rate of nodule develop ment was slower.