Plants metal transport proteins

Some metals may need to be mobilized from the environment to make them bioavailable. Iron in particular must be rendered more soluble to be accessible for uptake. Microorganisms and some plants have evolved with secreted ligands known as siderophores (or phytosiderophores). These ligands bind Fe + with extraordinary affinity. For example, a complex of the siderophore enterobactin with ferric iron has a formal stability constant of 10 (19). Once siderophores compete with other environmental ligands for iron, the ferric iron-siderophore complex then binds to specific transport proteins at the microbial... 

Once metals have been transported to their target tissue, they need to be distributed within the subcellular compartments where they are required, and need to be safely stored when they are in excess. Nearly 90% of Fe in plants is located in the chloroplasts, where it is required in the electron transfer chain, and in the synthesis of chlorophylls, haem, and Fe—S clusters. Fe, Cu, and Zn are also required in chloroplasts as cofactors for superoxide dismutases to protect against damage by reactive oxygen species during chloroplast development, and Cu is also required in other enzymes including the essential Cu protein plastocyanin. Pathways of intracellular metal transport in plant cells are illustrated in Fig. 8.10. Transport into the chloroplast is best characterised for Cu,... 

A number of genes involved in metal transport in plants have been identified. Many of these belong to previously described transporter families such as the P-type APTases (Axelsen et al. 1998) and the Nramp proteins (natural resistance-associated macrophage protein) (Cellier et al. 

Keywords excluder plants hyperaccumulator plants indicator plants natural overexpression of transport proteins phytoremediation phytomining vacuolar metal sequestration... 

As we saw in Chapter 7, zinc uptake in plants involves proteins of the ZIP family, some of which are root specific while others are found in both roots and shoots. The transport of zinc from the cytosol in many organisms is often associated with members of the cation diffusion facility (CDF) family. Although there are 12 predicted family members in Arabidopsis, only one, MTP1, has been characterized, which seems to function in the transport of Zn into the vacuole. Two members of the heavy metal ATPase (HMA) family, HMA2 and HMA4, have been shown to function in the transport of zinc out of the cells across the plasma membrane. 

Y He, Z., and Stoffells, P.J., Molecular mechanisms of heavy metal hyperaccumulation and phytoremediation, J. Trace Elem. Med. Biol. 18, 339-353, 2005 Mackenzie, S.A., Plant organellar protein targeting a traffic plan still under construction. Trends Cell Biol. 15, 548-554, 2005 Thompson, M.V., Phloem the long and the short of it. Trends Plant Sci. 11, 26-32, 2006 Takahashi, H., Yoshimoto, N., and Saito, K., Anionic nutrient transport in plants the molecular basis of the sulfate transporter gene family. Genet. Eng. 27, 67-80, 2006. 

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