Intercellular Nodule Localization and Nodule Specificity of Xanthine Dehydrogenase in Soybean

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Abstract
The distribution of xanthine dehydrogenase throughout the soybean plant [inoculated with Rhizobium japonicum] as well as the intercellular localization of xanthine dehydrogenase within soybean nodules was determined. Polyclonal antibodies against purified xanthine dehydrogenase were prepared and used in an enzyme-linked immunosorbent assay to determine whether xanthine dehydrogenase is a nodule-specific protein. Xanthine dehydrogenase is present in far greater concentration in the nodule than in any other plant organ. Immunodiffusion tests showed that anti-soybean nodule xanthine dehydrogenase would cross-react with nodule crude extracts from the ureide producers, soybean, cowpea and lima bean [G. max, Vigna unguiculata and Phaseolus lunatus, respectively] but would not cross-react with those of the amide producers, alfalfa and lupine [Medicago sativa and Lupinus albus, respectively]. A crude extract from pea nodules cross-reacted slightly with anti-soybean xanthine dehydrogenase. Anti-soybean xanthine dehydrogenase did not cross-react with buttermilk xanthine oxidase either by enzyme-linked immunosorbent assay or by immunodiffusion test. Fresh nodule sections from the ureide-producers, soybean, cowpea and lima bean, all stained positively for xanthine dehydrogenase. The substrate-dependent stain was inhibited by allopurinol and was observed only in the infected nodule cells of these species. Nodules from the amide producers, alfalfa and white lupine, did not stain for xanthine dehydrogenase.