THE ROLE OF MUGINEIC ACID IN UPTAKE OF TRACE METALS IN PLANTS

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Zinc (Zn) deficiency in agricultural soils is leading worldwide to the production of stunted rice and to human malnutrition. Some rice varieties take up Zn even if it is present in soil in low bioavailable amount, but the underlying process is unknown. One mechanism proposed includes the secretion of organic ligands (i.e. deoxymugineic acid-DMA), its complexation with Zn in soil and the uptake of the complex into the plant. Indirect evidence comes from isotopes studies but the direct proof (i.e. measure DMA secretion in soil and DMA complexation with Zn in competition with other cations) is missing. To this end, we will determine the fluxes of DMA secreted by roots. The challenges are to develop an experimental system that reproduces Zn deficiency in laboratory and to develop analytical methods that enable the identification and determination of the mass fluxes of DMA. We propose to use pot and hydroponic experiments with different Zn supply. The Zn deficiency in the soil/solution, will allow us to predict the stimulation of DMA production. The latest generation of LC-MS/MS with hugely improved sensitivity will be used to quantify the concentrations of DMA and Zn-DMA complexes. Moreover, we will establish an accurate stability series for Zn and other cations complexing with DMA and we will determine the reaction mechanisms and structure of Zn with DMA. The stability series will address the question of whether competition by other cations prevents the formation of the Zn-DMA complex in soil. Understanding the reaction mechanisms of Zn with DMA and establishing its structure will give invaluable insights into the stability of the complexes. We will achieve this conducting carefully designed laboratory and theoretical chemistry experiments. A prompt application of this research will enable plant breeders to select genes to enhance crop production in low Zn conditions.