Natural Hyperaccumulators

Several plant genera, as well as some microbes and fungi, are natural hyperaccumulators of heavy metals. It is suspected that their enhanced abilities to accumulate, translocate, and detoxify and sequester heavy metal ions evolved in some taxa to protect against disease and insect herbivores, similar to the function of glucosinolates (Salt 2006). The Brassicaceae family contains the largest number of hyperaccumulators with 11 genera (Prasad and Freitas 2003). Thlaspi species can accumulate cadmium, nickel, lead, and zinc. Cysteine and other low molecular weight thiols have been implicated in the ability of Thlaspi caerulescens to hyperaccumulate cadmium (Hernandez-Allica et al. 2006). B. juncea (Indian mustard) is known for its ability to accumulate cadmium, chromium, copper, nickel, lead, and zinc. Several aquatic species, such as duckweed (Lemma minor) and water hyacinth (Eichhornia crassipes) take up metal ions from contaminated water. Sunflower has been shown to remove lead, uranium, cesium, and strontium from hydroponic solution (Prasad and Freitas 2003). Physiological and biochemical comparisons of hyperaccumulators and their nonhyperaccumulating counterparts have discovered genes at key steps in accumulation, translocation, and vacuolar sequestration (Salt 2006). By comparison with A. thaliana, A. halleri appears to derive its ability to hyperaccumulate zinc from overexpression of zinc transporters from the ZIP family (Becher et al. 2004). Constitutive overexpression of the CDF-family member MTP1 contributes to the abilities of several species to compartmentalize cadmium, nickel, and zinc into vacuoles (Küpper et al. 1999, 2001; Krämer et al. 2000; Ma et al. 2005). A group of genes involved in iron balance, including NAS2, NAS3, IRT1, and FRO2 are also overexpressed in hyperaccumulators (Lombi et al. 2001). Many of the important genes have become useful in genetic engineering, in order to exploit these traits for the application of phytoremediation. The problem with using most natural hyperaccumulators for phytoremediation of polluted soils is that they are slow growing and tend to have low biomass. For these reasons there is ongoing research in the incorporation of certain genes into trans-genic high-biomass crop plants.

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  • bertha maggot
    What are natural hyper accumulators?
    4 years ago