Iron Uptake by Symbiosomes from Soybean Root Nodules

Abstract

To identify possible iron sources for bacteroids in planta, soybean (Glycine max L. Merr.) symbiosomes (consisting of the bacteroidcontaining peribacteroid space enclosed by the peribacteroid membrane [PBMI) and bacteroids were assayed for the ability to transport iron supplied as various ferric [Fe(lll)l-chelates. lron presented as a number of Fe(lll)-chelates was transported at much higher rates across the PBM than across the bacteroid membranes, suggesting the presence of an iron storage pool in the peribacteroid space. Pulse-chase experiments confirmed the presence of such an iron storage pool. Because the PBM is derived from the plant plasma membrane, we reasoned that it may possess a ferric-chelate reductase activity similar to that present in plant plasma membrane. We detected ferric-chelate reductase activity associated with the PBM and suggest that reduction of Fe(lll) to ferrous [Fe(ll)l plays a role in the movement of iron into soybean symbiosomes.Rhizobia are totally dependent on their plant hosts for nutrients when living within the nodule. Bacteroids are surrounded by a PBM of plant origin (reviewed by Mellor, 1989), which may influence the transfer of a11 substances that pass between the plant and the bacteroids. The PBM possesses some of the properties of the plant PM from which it is derived but also has a set of PBM-specific proteins, some of which are presumed to be involved in the nitrogen fixation process (reviewed by Verma, 1992). Because the PBM is the interface between the plant host and the bacteroid, its role in controlling the flux of metabolites between the two compartments is likely to be important in the regulation of nitrogen fixation.Studies of the PBM have shown that this membrane has selective permeability to metabolites. Symbiosomes (consisting of the bacteroid-containing PBS enclosed by the PBM; Roth et al., 1988) prepared from soybean and French bean have dicarboxylate-transporting ability (Udvardi et al., 1988; Herrada et al., 1989), and dicarboxylates are thought to be the major carbon and energy source available for bacteroids. The form(s) of nitrogen transported to bacteroids is not currently known (Whitehead et al., 1995); however, the rescue of various amino acid auxotrophs in

Medicago truncatula Natural Resistance-Associated Macrophage Protein1 Is Required for Iron Uptake by Rhizobia-Infected Nodule Cells

“…From there, a putative homolog of LjSEN1 may be responsible for iron translocation across the SM (Hakoyama et al, 2012). In this process, an additional citrate transporter might play a role, given that iron-citrate is the preferred source of chelated iron for some rhizobia (LeVier et al, 1996). Future studies will be directed toward testing this model as well as toward determining the identity of transporters responsible for iron release from the vasculature.…”

The FtsZ-Like Protein FtsZm of Magnetospirillum gryphiswaldense Likely Interacts with Its Generic Homolog and Is Required for Biomineralization under Nitrate Deprivation

“…Symbiosis and nitrogen fixation in this environment may be linked to alternative reductant flows as well, and it requires efficient uptake of iron from the peribacteroid space (53). Interestingly, Fe 2ϩ is transported more efficiently into the symbiosome than Fe 3ϩ , but Fe 3ϩ uptake is stimulated by NADH (54,55). It would be interesting to see whether deletion of ftsZ2 in S. meliloti affects iron uptake in bacteroids.…”

Genomic Inventory and Transcriptional Analysis of Medicago truncatula Transporters

“…Iron transport across the SM and bacteroid membranes of soybean nodules has been characterized biochemically (Moreau et al, 1995(Moreau et al, , 1998LeVier et al, 1996), and a nodule-induced divalent metal transporter, GmDMT1, capable of ferrous iron transport has been cloned and characterized (Kaiser et al, 2003). GmDMT1 was localized to the SM and also appears to transport zinc, copper, and manganese, so it may play a role in supplying a variety of metal ions to bacteroids (Kaiser et al, 2003).…”