The Occurrence of Phytoferritin and Its Relationship to Effectiveness of Soybean Nodules

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Abstract
Polyacrylamide gel electrophoresis and electron microscopy revealed that accumulation of iron-protein in soybean nodules is influenced by nodule age, mutation in bradyrhizobia, and rhizobial/bradyrhizobial strain-soybean cultivar interactions. Iron-protein concentrations (micrograms per milligram protein) were inversely related to heme concentrations (nanomoles per milligram protein), with correlation coefficients (r values) ranging from −0.98 in young nodules to −0.83 in mature ones. Bradyrhizobium japonicum symbiotic mutants HS 129 and HS 145 (Nod+ Fix−) produced nodules high in iron-protein. Electrophoresis of homogenate prepared from nodules on Lee 68 produced by B. japonicum HS 129 yielded two different forms of the iron-proteins, 570 and 600 kilodaltons. The 570 kilodalton iron-protein isolated by preparative polyacrylamide gel electrophoresis behaved like horse-spleen-ferritin in responses to iron-stains, heat stability, ultraviolet absorption spectrum, iron unloading and reloading, and characteristic appearance in electron micrographs. These properties led to the conclusion that the 570 kilodalton iron-protein is phytoferritin. The nodule phytoferritin differed from horse-spleen-ferritin in electrophoretic mobility, serological properties, and molecular size and was distinct from most other known phytoferritins in that it was composed of different subunit types.