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To investigate rate-limiting factors for glutathione and phytochelatin (PC) production and the importance of these compounds for heavy metal tolerance, Indian mustard (Brassica juncea) was genetically engineered to overexpress the Escherichia coli gshI gene encoding ␥-glutamylcysteine synthetase (␥-ECS), targeted to the plastids. The ␥-ECS transgenic seedlings showed increased tolerance to Cd and had higher concentrations of PCs, ␥-GluCys, glutathione, and total non-protein thiols compared with wild-type (WT) seedlings. When tested in a hydroponic system, ␥-ECS mature plants accumulated more Cd than WT plants: shoot Cd concentrations were 40% to 90% higher. In spite of their higher tissue Cd concentration, the ␥-ECS plants grew better in the presence of Cd than WT. We conclude that overexpression of ␥-ECS increases biosynthesis of glutathione and PCs, which in turn enhances Cd tolerance and accumulation. Thus, overexpression of ␥-ECS appears to be a promising strategy for the production of plants with superior heavy metal phytoremediation capacity.Heavy metals and metalloids such as Cd, Pb, Hg, As, and Se are an increasing environmental problem worldwide. Plants can be used to remove heavy metals by accumulating, stabilizing, or biochemically transforming them. This cost-effective and environment-friendly technology has been called "phytoremediation" (Salt et al., 1995). Hyperaccumulators-plant species that accumulate extremely high concentrations of heavy metals in shoots-offer one option for the phytoremediation of metal-contaminated sites. However, hyperaccumulators tend to grow slower and produce little biomass (Brooks, 1994). An alternative approach is to genetically engineer fast-growing species to improve their metal tolerance and metal-accumulating capacity. A suitable target species for this strategy is Indian mustard (Brassica juncea), which has a large biomass production, a relatively high trace element accumulation capacity (Dushenkov et al., 1995), and can be genetically engineered .Non-protein thiols (NPTs), which contain a high percentage of Cys sulfhydryl residues in plants, play a pivotal role in heavy metal detoxification. The reduced form of glutathione (␥-Glu-Cys-Gly, GSH) is one of the most important components of NPT metabolism. GSH may play several roles in heavy metal tolerance and sequestration. It protects cells from oxidative stress damage, such as that caused by heavy metals in plants (Gallego et al

Wetland plants are being used successfully for the phytoremediation of trace elements in natural and constructed wetlands. This study demonstrates the potential of water hyacinth (Eichhornia crassipes), an aquatic floating plant, for the phytoremediation of six trace elements. The ability of water hyacinth to take up and translocate six trace elements—As(V), Cd(II), Cr(VI), Cu(II), Ni(II), and Se(VI)—was studied under controlled conditions. Water hyacinth accumulated Cd and Cr best, Se and Cu at moderate levels, and was a poor accumulator of As and Ni. The highest levels of Cd found in shoots and roots were 371 and 6103 mg kg−1 dry wt., respectively, and those of Cr were 119 and 3951 mg kg−1 dry wt., respectively. Cadmium, Cr, Cu, Ni, and As were more highly accumulated in roots than in shoots. In contrast, Se was accumulated more in shoots than in roots at most external concentrations. Water hyacinth had high trace element bioconcentration factors when supplied with low external concentrations of all six elements, particularly Cd (highest BCF = 2150), Cr (1823), and Cu (595). Therefore, water hyacinth will be very efficient at phytoextracting trace elements from wastewater containing low concentrations of these elements. We conclude that water hyacinth is a promising candidate for phytoremediation of wastewater polluted with Cd, Cr, Cu, and Se.

Relaxor ferroelectrics are promising candidates for pulsed power dielectric capacitor applications because of their excellent energy-storage properties.

Recent developments in various technologies, such as hybrid electric vehicles and pulsed power systems, have challenged researchers to discover affordable, compact, and super-functioning electric energy storage devices. Among the existing energy storage devices, polymer nanocomposite film capacitors are a preferred choice due to their high power density, fast charge and discharge speed, high operation voltage, and long service lifetime. In the past several years, they have been extensively researched worldwide, with 0D, 1D, and 2D nanofillers being incorporated into various polymer matrixes. However, 1D nanofillers appeared to be the most effective in producing large dipole moments, which leads to a considerably enhanced dielectric permittivity and energy density of the nanocomposite. As such, this Review focuses on recent advances in polymer matrix nanocomposites using various types of 1D nanofillers, i.e., linear, ferroelectric, paraelectric, and relaxor−ferroelectric for energy storage applications. Correspondingly, the latest developments in the nanocomposite dielectrics with highly oriented, surface-coated, and surface-decorated 1D nanofillers are presented. Special attention has been paid to identifying the underlying mechanisms of maximizing dielectric displacement, increasing dielectric breakdown strength, and enhancing the energy density. This Review also presents some suggestions for future research in low-loss, high energy storage devices.

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