UPTAKE OF IRON BY SYMBIOSOMES AND BACTEROIDS FROM SOYBEAN NODULES

Symbiosomes and bacteroids isolated from soybean nodules are able to t ake up the iron-citrate complex, The kinetics are characterized by ini tial high rates of iron internalization, and ATPase inhibitors signifi cantly lower the uptake, This is consistent,vith an energy-dependent p rocess on both membranes, although the involvement of a simultaneous f acilitated diffusion can not be completely ruled out, Citrate alone is poorly absorbed by symbiosomes; this uptake is greatly enhanced by ad dition of iron, Iron-citrate was found both in the nodule cytosol and in the bacteroids, These results provide the first experimental eviden ce for the existence, at least in young nodules, of an important iron trafficking system from the plant host cell to the microsymbiont, thro ugh the peribacteroid membrane.