Exposure to toxic volatile organic compounds (VOCs) continues to pose a significant risk to human health. VOCs such as chloroform, carbon tetrachloride (CT) and trichloroethylene (TCE), along with benzene and other single-ring aromatics are among the most common contaminants in water and air. These compounds share a susceptibility to oxidation by the mammalian hepatic cytochrome P450 2E1. In past NIEHS-funded work at UW, we have demonstrated that TCE and CT are oxidized by axenic poplar cell cultures using a pathway similar to that in mammals, and that wild-type poplar are able to take up and degrade TCE and CT. Our work has led to the realization that TCE and CT uptake by wild-type plants is too weak to significantly reduce their concentration in root zone water, providing motivation for the development of plants with increased degradative activity toward VOCs. Toward this end we have expressed mammalian cytochrome P450 2E1 (CYP2E1) in plants, achieving orders of magnitude greater oxidation of TCE in transgenic poplar. We are presently engaged in testing TCE degradation by wild-type and CYP2E1 transgenic poplar at field scale in a test bed facility capable of mass balance measurements. In this application we propose the following specific aims: compare the abilities of wild-type and existing CYP2E1 transgenic poplar lines to degrade TCE, CT, and PCE in field tests;identify genes that are up-regulated by the presence of pollutants;clone and analyze the plant genes involved in the degradation of TCE and its metabolites;determine the metabolites of TCE and benzene in CYP2E1 transgenic poplar;increase the uptake of VOCs from the air by increasing the number of open stomata on leaf surfaces;express the organophosphorus hydroxylase, paraoxonase PON1, in plants for the degradation of organophosphate neurotoxins;and determine the ecotoxicity to earthworms of root materials, leaf litter and rhizosphere soil of CYP2E1 transgenic plants exposed to VOCs.
Toxic organic compounds such as chloroform, trichloroethylene, and benzene are among the most common contaminants in water and air, and organophosphorus compounds are important neurotoxins. Phytoremediation, the degradation of toxic compounds by plants, promises to provide an inexpensive and unintrusive method for reducing human exposure, if plant degradation activity can be increased significantly, as can be accomplished by genetically modifying selected plants with detoxifying genes.
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