Specialization of the inner cortex for ureide production in soybean root nodules

Summary The possibility that cells in the inner cortex of determinate root nodules participate in ureide production from recently fixed N₂, as do the uninfected (interstitial) cells of the infected central region, has been investigated in soybean (Glycine max) inoculated as seeds withBradyrhizobium japonicum. Like the interstitial cells, cells of the three innermost cortical layers produce enlarged peroxisomes and a meshwork of tubular ER during differentiation. These changes are most pronounced in the innermost cortical layer, are successively less so in the 2nd and 3rd layers, and are usually undetectable in more distant layers. Peroxisomes in the inner three layers are stained in the DAB (3,3-diaminobenzidine) test for uricase (EC 1.7.3.3) activity, indicative of the potential for ureide formation, but peroxisomes in more distant cortical cells are not stained. A nodulespecific uricase also is demonstrable in the inner three cortical layers by immunogold labeling enhanced with silver for visualization in the light microscope. The observations suggest that with respect to ureide production the cells of the inner layers of the cortex are functionally similar to the interstitial cells of the infected region despite the apparent distinctiveness of the two regions anatomically.Abbreviations DAB 3,3-diaminobenzidine - ER endoplasmic reticulum