Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2000
Publication Date: N/A
Citation: Interpretive Summary: Heavy metal contamination of soils poses serious problems to both human health and agriculture in the U.S. Current engineering-based technologies used to remediate soils are quite costly, and often dramatically disturb the landscape. Recently, there has been considerable interest focused on the use of terrestrial plants to absorb heavy metals from the soil and concentrate them in the easily harvestable shoot tissues as an alternative remediation technology. A small number of very interesting plant species have been identified that can grow in soils containing high levels of heavy metals, and will also accumulate these metals to high concentrations in the shoot. Despite the intense interest in these hyperaccumulator plants, very little is known about mechanisms of heavy metal transport, translocation and sequestration involved in heavy metal hyperaccumulation in plants. Therefore, in this study we conducted an integrated molecular and physiological characterization of Zn accumulation in the heavy metal hyperaccumulating plant, Thlaspi caerulescens. A Zn transport gene was cloned from T. caerulescens and found to be expressed to very high levels in the root and shoot. In a related non-accumulator plant (T. arvense), the same gene was expressed to very low levels in Zn sufficient plants , and then expression of the gene increased with Zn deficiency. Thus, the mechanisms by which Zn transporters are regulated by Zn status are altered in the hyperaccumulator, such that Zn transporters are produced at very high levels throughout the plant. This information will help us gain a better understanding of metal hyperaccumulation, and this information will be used to develop more effective remediating plant species and agronomic practices that enhance phytoremediation.
Technical Abstract: An integrated molecular and physiological investigation of the fundamental mechanisms of heavy metal accumulation was conducted in Thlaspi caerulescens, a Zn/Cd hyperaccumulating plant species. A heavy metal transporter cDNA, ZNT1, was cloned from Thlaspi caerulescens via functional complementation in yeast and was shown to mediate high affinity Zn2+ uptake eas well as low affinity Cd2+ uptake. It was found that this transporter is expressed at very high levels in roots and shoots of the hyperaccumulator. A study of ZNT1 expression and high affinity Zn2+ uptake in roots of T. caerulescens and a related non-accumulator, Thlaspi arvense, showed that alteration in the regulation of ZNT1 gene expression by plant Zn status results in the over expression of this transporter and increased Zn influx in roots of the hyperaccumulating Thlaspi species. By gaining insights into the molecular basis for heavy metal transport in this model Zn/Cd hyperaccumulator, we will contribute to the advancement of phytoremediatio by the future engineering of plants with improved heavy metal uptake and tolerance.