Siderophore-bound iron in the peribacteroid space of soybean root nodules

Water-soluble, non-leghemoglobin iron (125 mu mol kg(-1) wet weight nodule) is found in extracts of soybean root nodules. This iron is probably confined to the peribacteroid space of the symbiosome, where its estimated concentration is 0.5 - 2.5 mM. This iron is bound by siderophores (compounds binding ferric iron strongly) which are different for each of the three strains of Bradyrhizobium japonicum with which the plants were inoculated. One of these, that from nodules inoculated with strain CC 705, is tentatively identified as a member of the pseudobactin family of siderophores. Leghemoglobin is present in only very small amounts in the peribacteroid space of symbiosomes isolated from soybean root nodules, and may be absent from the peribacteroid space of the intact nodule.