The proteomics of heavy metal hyperaccumulation by plants.

Hyperaccumulators are distinguished from non-hyperaccumulators on the basis of their capacity to extract heavy metal ions from the soil, their more efficient root-to-shoot translocation of these ions and their greater ability to detoxify and sequester heavy metals in the shoot. The understanding of the mechanisms underlying metal ion accumulation has progressed beyond the relevant biochemistry and physiology to encompass the genetic and molecular regulatory systems which differentiate hyperaccumulators from non-hyperaccumulators. This paper reviews the literature surrounding the application of proteomics technology to plant metal hyperaccumulation, in particular involving the elements As, Cd, Cu, Ni, Pb and Zn. The hyperaccumulation process across a number of unrelated plant species appears to be associated with proteins involved in energy metabolism, the oxidative stress response and abiotic and biotic stress. The relevance of transducers of the metal stress response to the phenomenon of hyperaccumulation is summarized. Proteomic data complement the more voluminous genomic and transcriptomic data sets in providing a more nuanced picture of the process, and should therefore help in the identification of the major genetic determinants of the hyperaccumulation phenomenon.

Visioli G ，Marmiroli N 《-》

Heavy metal hyperaccumulating plants: how and why do they do it? And what makes them so interesting?

The term "hyperaccumulator" describes a number of plants that belong to distantly related families, but share the ability to grow on metalliferous soils and to accumulate extraordinarily high amounts of heavy metals in the aerial organs, far in excess of the levels found in the majority of species, without suffering phytotoxic effects. Three basic hallmarks distinguish hyperaccumulators from related non-hyperaccumulating taxa: a strongly enhanced rate of heavy metal uptake, a faster root-to-shoot translocation and a greater ability to detoxify and sequester heavy metals in leaves. An interesting breakthrough that has emerged from comparative physiological and molecular analyses of hyperaccumulators and related non-hyperaccumulators is that most key steps of hyperaccumulation rely on different regulation and expression of genes found in both kinds of plants. In particular, a determinant role in driving the uptake, translocation to leaves and, finally, sequestration in vacuoles or cell walls of great amounts of heavy metals, is played in hyperaccumulators by constitutive overexpression of genes encoding transmembrane transporters, such as members of ZIP, HMA, MATE, YSL and MTP families. Among the hypotheses proposed to explain the function of hyperaccumulation, most evidence has supported the "elemental defence" hypothesis, which states that plants hyperaccumulate heavy metals as a defence mechanism against natural enemies, such as herbivores. According to the more recent hypothesis of "joint effects", heavy metals can operate in concert with organic defensive compounds leading to enhanced plant defence overall. Heavy metal contaminated soils pose an increasing problem to human and animal health. Using plants that hyperaccumulate specific metals in cleanup efforts appeared over the last 20 years. Metal accumulating species can be used for phytoremediation (removal of contaminant from soils) or phytomining (growing plants to harvest the metals). In addition, as many of the metals that can be hyperaccumulated are also essential nutrients, food fortification and phytoremediation might be considered two sides of the same coin. An overview of literature discussing the phytoremediation capacity of hyperaccumulators to clean up soils contaminated with heavy metals and the possibility of using these plants in phytomining is presented.

Rascio N ，Navari-Izzo F 《-》

Molecular mechanisms of metal hyperaccumulation in plants.

Verbruggen N ，Hermans C ，Schat H 《-》

Behavior of native species Arrhenatherum elatius (Poaceae) and Sonchus transcaspicus (Asteraceae) exposed to a heavy metal-polluted field: plant metal concentration, phytotoxicity, and detoxification responses.

Lu Y ，Li X ，He M ，Zeng F ... -  《INTERNATIONAL JOURNAL OF PHYTOREMEDIATION》

A nonpathogenic Fusarium oxysporum strain enhances phytoextraction of heavy metals by the hyperaccumulator Sedum alfredii Hance.

Low biomass and shallow root systems limit the application of heavy metal phytoextraction by hyperaccumulators. Plant growth-promoting microbes may enhance hyperaccumulators'phytoextraction. A heavy metal-resistant fungus belonged to the Fusarium oxysporum complex was isolated from the Zn/Cd co-hyperaccumulator Sedum alfredii Hance grown in a Pb/Zn mined area. This Fusarium fungus was not pathogenic to plants but promoted host growth. Hydroponic experiments showed that 500 μM Zn(2+) or 50 μM Cd(2+) combined with the fungus increased root length, branches, and surface areas, enhanced nutrient uptake and chlorophyll synthesis, leading to more vigorous hyperaccumulators with greater root systems. Soil experiments showed that the fungus increased root and shoot biomass and S. alfredii-mediated heavy metal availabilities, uptake, translocation or concentrations, and thus increased phytoextraction of Zn (144% and 44%), Cd (139% and 55%), Pb (84% and 85%) and Cu (63% and 77%) from the original Pb/Zn mined soil and a multi-metal contaminated paddy soil. Together, the nonpathogenic Fusarium fungus was able to increase S. alfredii root systems and function, metal availability and accumulation, plant biomass, and thus phytoextraction efficiency. This study showed a great application potential for culturable indigenous fungi other than symbiotic mycorrhizas to enhance the phytoextraction by hyperaccumulators.

Zhang X ，Lin L ，Chen M ，Zhu Z ，Yang W ，Chen B ，Yang X ，An Q ... -  《-》