SIDEROPHORE-BOUND IRON IN THE PERIBACTEROID SPACE OF SOYBEAN ROOT-NODULES

Water-soluble, non-leghemoglobin iron (125 mu mol kg(-1) wet weight no dule) is found in extracts of soybean root nodules. This iron is proba bly confined to the peribacteroid space of the symbiosome, where its e stimated concentration is 0.5 - 2.5 mM. This iron is bound by sideroph ores (compounds binding ferric iron strongly) which are different for each of the three strains of Bradyrhizobium japonicum with which the p lants were inoculated. One of these, that from nodules inoculated with strain CC 705, is tentatively identified as a member of the pseudobac tin family of siderophores. Leghemoglobin is present in only very smal l amounts in the peribacteroid space of symbiosomes isolated from soyb ean root nodules, and may be absent from the peribacteroid space of th e intact nodule.