Hyperaccumulator
[1][2] The metals are concentrated at levels that are toxic to closely related species not adapted to growing on the metalliferous soils.
[1] Hyperaccumulating plants are of interest for their ability to extract metals from the soils of contaminated sites (phytoremediation) to return the ecosystem to a less toxic state.
Evidence has conveyed that the traits of tolerance and accumulation are separate to each other and are moderated by genetic and physiological mechanisms.
[4] Several gene families are involved in the processes of hyperaccumulation including upregulation of absorption and sequestration of heavy-metal metals.
Expression of HA genes provides the plant with capacity to uptake and sequester metals such as As, Co, Fe, Cu, Cd, Pb, Hg, Se, Mn, Zn, Mo and Ni in 100–1000x the concentration found in sister species or populations.
[9] The ability to hyperaccumulate is determined by two major factors: environmental exposure and the expression of ZIP gene family.
As there is a wide variety among hyperaccumulating species that span across different plant families, it is likely that HA genes were eco-typically selected for.
[11] This suggests that overexpression of ZIP family genes that encode cation transporters is a characteristic genetic feature of hyperaccumulation.
Because the presence and expression of zinc transporter gene families are highly prevalent in hyperaccumulators, the ability to accumulate a diverse range of heavy metals is most likely due to the zinc transporters' inability to discriminate against specific metal ions.
[9] In another study, using metallophytic and non-metallophytic Arabidopsis populations, back crosses indicated pleiotropy between Cd and Zn tolerances.
[14] This response suggests that plants are unable to detect specific metals, and that hyperaccumulation is likely a result of an overexpressed Zn transportation system.
[16] An important trait of hyperaccumulating plant species is enhanced translocation of the absorbed metal to the shoot.
[17] Hyperaccumulators are plants that have both the second technique and the ability to absorb more than 100 times higher metal concentrations than typical organisms.
[19] When grown on mildly polluted soils, a closely related species, Thlaspi ochroleucum, is a heavy metal-tolerant plant, but it accumulates much less Zn in the shoots than T. caerulescens.
