Phytoremediation is an emerging technology that holds great promise for the decontamination of organic-, metal- and salt-impacted sites. It is a versatile technology that provides a cost-effective, non-intrusive, aesthetic way to remediate a broad range of environmental pollutants in situ. Thus, it is an attractive alternative to traditional remediation strategies such as excavation and chemical washing. One criteria that is essential for successful phytoremediation is high biomass production. Unfortunately, plants growing in contaminated soils are often subjected to the combined stress of nutritional deficiency and chemical toxicity. This results in the production of stress ethylene, which leads to plant growth inhibition and decreases in plant biomass. One strategy for increasing the efficacy of phytoremediation is to use contaminant-tolerant plant species in conjunction with plant growth-promoting rhizobacteria (PGPR) with 1-aminocyclo-propane-1-carboxylic acid (ACC) deaminase activity. This enzyme hydrolyzes ACC, the immediate precursor to ethylene in plants, to ammonia and a-ketobutyrate. Thus, the presence of ACC deaminase can lower the rate of ethylene biosynthesis in plants and facilitate plant growth under stress conditions. Alternatively, transgenic plants can be constructed that express the ACC deaminase gene. Although phytoremediation can be used in both aquatic and terrestrial systems, the focus of this review is on the remediation of terrestrial sites.
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