Uninfected cells of soybean root nodules: ultrastructure suggests key role in ureide production.

In soybean root nodules, which export recently fixed nitrogen mainly as the ureides allantoin and allantoic acid, cells uninfected by rhizobia undergo a pronounced ultrastructural differentiation not shown by the infected cells, including enlargement of the microbodies and proliferation of smooth endoplasmic reticulum. Since some of the enzymes contributing to ureide synthesis occur in these subcellular components in root nodule preparations, the uninfected cells may participate in ureide synthesis and thus play an essential role in the symbiosis between host and bacterium.