Iron distribution through the developmental stages of Medicago truncatula nodules

Abstract

Paramount to symbiotic nitrogen fixation (SNF) is the synthesis of a number of metalloenzymes that use iron as a critical component of their catalytical core. Since this process is carried out by endosymbiotic rhizobia living in legume root nodules, the mechanisms involved in iron delivery to the rhizobia-containing cells are critical for SNF. In order to gain insight into iron transport to the nodule, we have used synchrotron-based X-ray fluorescence to determine the spatio-temporal distribution of this metal in nodules of the legume Medicago truncatula with hitherto unattained sensitivity and resolution. The data support a model in which iron is released from the vasculature into the apoplast of the infection/differentiation zone of the nodule (zone II). The infected cell subsequently takes up this apoplastic iron and delivers it to the symbiosome and the secretory system to synthesize ferroproteins.Upon senescence, iron is relocated to the vasculature to be reused by the shoot. These observations highlight the important role of yet to be discovered metal transporters in iron compartmentalization in the nodule and in the recovery of an essential and scarce nutrient for flowering and seed production.

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

“…Because iron is released into the apoplast of zone II cells, and because little or no iron remains in the zone III apoplast (Rodríguez-Haas et al, 2013), the conclusion is that Nramp or ZIP transporter(s) must mediate iron uptake from the apoplast into the cytosol of cells in this region of the nodule. Promoter::gus fusion data and the gene expression information from the Symbimics database for MtNramp1 indicated that the gene is expressed in zone II of the nodule.…”

“…Synchrotron-based x-ray fluorescence results indicate that, at least in indeterminate nodules, iron is primarily delivered by the vasculature and released into the apoplast of zone II (Rodríguez-Haas et al, 2013). In this zone and probably in the interzone with the nitrogen-fixing zone III, iron has to be delivered from apoplast into cells before it is transported to the bacteria in symbiosomes.…”

“…Taking advantage of state-of-the-art metal visualization methods, the pathway for iron delivery to the nodule has been elucidated (Rodríguez-Haas et al, 2013). Synchrotronbased x-ray fluorescence studies on Medicago truncatula indeterminate nodules indicate that most of the iron is delivered by the vasculature to the apoplast of zone II.…”

Functional diversity of five homologous Cu+-ATPases present in Sinorhizobium meliloti

“…Intact nodules were imaged using a stereoscopic microscope Nikon SMZ-U (Nikon) and SPOT 5.1 software (Diagnostic Instrument). Nodules were fixed in buffer containing 4 % paraformaldehyde, 0.25 % glutaraldehyde and 2.5 % sucrose in 50 mM potassium phosphate buffer, pH 7.4, and incubated overnight at 4 uC with gentle agitation (Rodríguez-Haas et al, 2013). Dehydration was carried out using a graded ethanol series (0, 30, 50, 70, 85, 90, 95, 100 %) at 4 uC.…”

Papel de COPT1, COPT2, MTP2 y ZIP6 en el transporte y la homeostasis de metales en Medicago truncatula

“…De hecho, la deficiencia de cobre en suelos reduce la actividad fijadora de nitrógeno de los nódulos (Hallsworth, 1960;Seliga, 1993;Snowbal et al, 1980). Al igual que ocurre con el hierro, se hipotetiza que el cobre viaja por los haces vasculares desde la raíz al nódulo y se libera en el apoplasto de la zona de infección/ diferenciación de los nódulos de tipo indeterminado (Rodríguez-Haas et al, 2013).…”