Iron is an important micronutrient for all living organisms. Although iron is abundant in the Earth's crust, iron deficiency is a common problem throughout the food chain. Legume seeds have relatively high but also highly variable iron content. Little is known about the mechanisms controlling seed iron loading and only a few genes involved in seed iron metabolism have been described. Understanding the mechanisms that control seed iron loading and iron bioavailability can assist in breeding legumes with more bioavailable iron. The aim of our study is to find Lotus genes responsible for the regulation of seed iron loading and plant iron metabolism, and use this knowledge to find the corresponding genes in Phaseolus species. For our studies we use the model legume L. japonicus for which large number of EST and genomic sequences are available, and the closely related Lotus filicaulis whose seed iron content differs from L. japonicus. Furthermore, we have recombinant inbred lines (RILs) from a cross between L. japonicus and L. filicaulis with good marker coverage. In our study we have characterized mature seeds of L. japonicus and L. filicaulis. We have studied the distribution of iron in untreated mature seeds by simultaneously using Micro-PIXE and proton backscattering. In addition, biochemical staining of iron in mature and germinated seeds was performed, and this material was studied by light microscopy before and after tissue fixation and sectioning. Our studies show that the iron distribution in L. filicaulis seeds is similar to that in common beans, while the seeds of L. japonicus show a different pattern of iron accumulation. RILs from a cross between these two species are being studied in order to find genes that are important for seed iron distribution. Furthermore, we are characterizing these two Lotus species in order to elucidate the physiological mechanisms behind the differential accumulation of iron in the aerial parts of the plants. We are studying the plants' ability to reduce the pH of the growth media, the iron reducing activity of their roots, and the effects of different concentrations of iron in the growth media on the plants' iron concentration. Our studies indicate that Lotus plants are good model organisms for studying seed iron loading in legumes. The work was supported by HarvestPlus, 2033 K Street, NW, Washington DC 20006-1002, USA and The Ministry of Science, Technology and Innovation, Denmark and the Research Fundation of the University of Aarhus, Denmark.