Distribution and Remobilization of Iron and Copper in Wheat

Growing grains and moving metals

In considering the nutritional quality of cereal grains we sometimes forget the importance of grain mineral content. Thus, the investigation by Garnett and Graham (University of Adelaide, pp. 817�826) on the distribution to the grain of Fe and Cu in wheat plants is very timely. The soil in which the plants were grown contained Fe at a low concentration and Cu at a very low concentration. Higher concentrations were achieved by watering the soil with a micronutrient solution. Initial studies showed that Fe concentration did not affect plant growth. However, without added Cu, growth was extremely poor and, in order to ensure seed set, the low Cu treatment included adding some Cu. Plants subjected to the low Cu treatment showed a delay in all phases of growth, including anthesis and senescence, and a reduction in plant biomass and grain yield. In relation to the nutrient quality of the grain, it is the re-mobilization of Fe and Cu to the grain that is important. The authors clearly showed that both elements are readily mobilized post-anthesis. For Fe, adequate concentrations were maintained in the plant during growth and then about 77 % of shoot Fe was transfe rred to the grain. For the high Cu treatment, about 62 % of plant Cu was transferred to the grain but in the low Cu treatment it was a different story. Low Cu plants were able to maintain only a barely adequate Cu content during growth and only about 40 % of this low Cu content was transferred to the grain. Interestingly, in field-grown plants, Fe is much less mobile than in these experiments and the authors suggest that adding Fe in the field is not the way to increase grain Fe content. Instead they propose that the focus should be on improving the phloem pathway for Fe movement, a challenging target for the plant breeder.