Contaminat tolerant plants that can grow in the presence of high levels of toxic compounds and accumulate them in their tissues
The removal from the environment of many potentially toxic compounds is complicated by the numerous classes and types of these chemicals. For example, many soils are contaminated with one or more metals, radioactive or inorganic compounds. Of these, the metals may include lead, zinc, cadmium, selenium, chromium, cobalt, copper, nickel and mercury; the radioactive compounds may be uranium, cesium or strontium; and the other inorganic compounds might include arsenic, sodium, nitrate, ammonia or phosphate. Soil may become polluted with high concentrations of metals by either a natural phenomenon such as proximity to an ore body, or as a consequence of industrial activities. The remediation of heavily metal-contaminated soils often involves excavation and removal of soil to "secured" landfills, a technology that is expensive and requires site restoration (Glick, B.R. 2003). As an alternative, in the past few years, several groups of scientists have begun to develop technological approaches to using certain plants to remove metal contaminants from the soil.
Phytoremediation is a relatively new approach to removing contaminants from the environment. It may be defined as the use of plants to remove, destroy or sequester hazardous substances from the environment. Unfortunately, even plants that are relatively tolerant of various environmental contaminants often remain small in the presence of the contaminant (Glick, B.R. 2003).
Genetic modification of plants has been useful in bio-remediation. Some plants have been specially bio-engineered to enable them remove toxic waste from the environment. Several researchers have reported encouraging results using plants like mustard greens, alfalfa, river reeds, poplar trees, and special weeds to clean up the ravages of industries, agriculture, and petroleum production (Contreras et al., 1991; Howe, 1997; Paoletti and Pimental, 1996). In some cases, plants can digest the poisons, and convert them to inert compounds (Gray, 1998).
Tomato plant genes used to increase metal stress tolerance of Canola plants for phytoremediation (Nie, L. et al. 2002).
It was previously observed that transgenic tomato plants that express the Enterobacter cloacae UW4 1-aminocyclopropane-1-carboxylate (ACC) deaminase (EC 4.1.99.4) gene, and thereby produce lower levels of ethylene, were partially protected from the deleterious effects of six different metals. However, since tomato plants are unlikely to be utilized in the phytoremediation of contaminated terrestrial sites, transgenic canola (Brassica napus) plants that constitutively express the same gene were generated and tested for their ability to proliferate in the presence of high levels of arsenate in the soil and to accumulate it in plant tissues. The ability of the plant growth-promoting bacterium E. cloacae CAL2 to facilitate the growth of both non-transformed and ACC deaminase-expressing canola plants was also tested. In the presence of arsenate, in both the presence and absence of the added plant growth-promoting bacterium, transgenic canola plants grew to a significantly greater extent than non-transformed canola plants.
