Phytoextraction process
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Phytoextraction is a subprocess of phytoremediation in which plants remove metal ions from soil or water. Phytoextraction could in principle be used to remove contaminants from the soil,[1] or, in the case of phytomining, be used to accumulate valuable metals from water and soils.
Pathway
Metals ions in solution are susceptible to extraction.[2] For example, ligands secreted by plant - phytosiderophores, organic acids, or carboxylates -can selectively binds certain ions.[3][4] The benefit for a plant to hyperaccumulate remains a puzzle.[5] One theory is that root-to-shoot transport system drives hyper-accumulation by creating a metal deficiency response in roots.[6]
Examples: As and Cd
Water hyacinth have been demonstrated to remove arsenic from water.[7] Cadmium accumulation has been reviewed.[8][9][10]
One of the most well-documented HMAs is HMA4, which belongs to the Zn/Co/Cd/Pb HMA subclass and is localized at xylem parenchyma plasma membranes.[5] HMA4 is upregulated when plants are exposed to high levels of Cd and Zn, but it is downregulated in its non-hyperaccumulating relatives.[11] Also, when the expression of HMA4 is increased there is a correlated increase in the expression of genes belonging to the ZIP (Zinc regulated transporter Iron regulated transporter Proteins) family.