Overexpression of ATP Sulfurylase in Indian Mustard: Effects on Tolerance and Accumulation of Twelve Metals

zation by plant roots (Berti and Cunningham, 2000). In the technology called rhizofiltration, accumulation of Indian mustard (Brassica juncea (L.) Czern.) transgenics overex- metals by roots in a hydroponic setup is followed by pressing ATP sulfurylase (APS plants) were shown previously to have higher levels of total thiols, S, and Se. The present study explores the harvesting of the plant biomass (Dushenkov and Kapul- effect of ATP sulfurylase overexpression on tolerance and accumula- nik, 2000). Phytoextraction, another promising technol- tion of other metals, both oxyanions and cations, reasoning that some ogy in metal phytoremediation, involves the accumula- anions may react directly with ATP sulfurylase, while other ions tion of metals in shoot tissue followed by harvesting of may be bound by its thiol end products. The APS transgenics were the shoot biomass (Blaylock and Huang, 2000). The compared with wild-type plants with respect to tolerance and accumu- metal-laden plant material may be used for nonfood lation of As, Cd, Cr, Cu, Hg, Mn, Mo, Ni, Pb, V, W, and Zn, supplied purposes or ashed, followed by recycling of the metals individually in agar medium (seedlings) or in hydroponics (mature or disposal in a landfill (Chaney et al., 2000). These plants). At the seedling stage, APS transgenics were more tolerant metal phytoremediation technologies are already being than wild type to As(III), As(V), Cd, Cu, Hg, and Zn, but less tolerant used effectively (Salt et al., 1998; Blaylock, 2000), and to Mo and V. The APS seedlings had up to 2.5-fold higher shoot concentrations of As(III), As(V), Hg, Mo, Pb, and V, and somewhat are gaining acceptance, since phytoremediation is rela- lower Cr levels. Mature APS plants contained up to 2.5-fold higher tively cost-effective and aesthetically pleasing, and may shoot concentrations of Cd, Cr, Cu, Mo, V, and W than wild type. They be used in conjunction with more conventional remedia- also contained 1.5- to 2-fold higher levels of the essential elements Fe, tion methods. Mo, and S in most of the treatments. Mature APS plants showed no To further increase the effectiveness of metal phytor- differences in metal tolerance compared with the wild type. Overex- emediation, several approaches may be employed, in- pression of ATP sulfurylase may be a promising approach to create cluding identification of new suitable plant species via plants with enhanced phytoextraction capacity for mixtures of metals. screening studies, optimization of agronomic practices for maximal element uptake, and improvement of se- lected plant species by classical breeding or genetic engi-