"Zinc (Zn) is an essential micronutrient for humans and plants. The agricultural soils of large parts of the world are deficient in Zn, which causes Zn malnutrition to millions of people. This is of particular concern to economies depending on rice as major crop such as the developing countries in Asia. The development of Zn-efficient rice, able to tolerate low Zn levels and achieve a sufficient Zn concentration in grains, would have a very positive influence on the economy and health of the affected communities. However, our poor understanding about the mechanisms of Zn uptake, transport, and efficiency in plants poses a barrier to the breeders.The roots of grasses like rice exudate metal chelating agents in response to Fe deficiency, called phytosiderophores (PS). PS solubilise Fe and form PS-Fe complexes, which are efficiently taken up by roots. Recent results of the Weiss group at Imperial College London on Zn isotope fractionation in rice provided the first evidence that Zn uptake also depends on PS (Plant Cell Environ, 2010). This has been a major break through.We propose here to further investigate Zn uptake by rice in Zn-deficient soils. Our objectives are: a) to confirm the involvement of PS in Zn uptake, b) to determine the relative contribution of PS to total Zn uptake, and c) to examine the relationship between PS production and Zn-efficiency in rice, by comparing various rice strains differing in these two traits.The conclusions of the proposed research will help to focus the future work of the breeders on the most relevant mechanisms for Zn-efficiency in rice, and will be extensible to other metals and species of agricultural interest. The isotopic effects observed will have strong implications to understand plant contribution to Zn cycles. New isotope fractionation methodologies and experimental approaches for studying metal solubilisation and uptake processes in plants will be brought together in a multidisciplinary approach."