Plant cell biodegradation of a xenobiotic nitrate ester, nitroglycerin

Phytotoxicity and uptake of nitroglycerin in a natural sandy loam soil

Nitroglycerin (NG) is widely used for the production of explosives and solid propellants, and is a soil contaminant of concern at some military training ranges. NG phytotoxicity data reported in the literature cannot be applied directly to development of ecotoxicological benchmarks for plant exposures in soil because they were determined in studies using hydroponic media, cell cultures, and transgenic plants. Toxicities of NG in the present studies were evaluated for alfalfa (Medicago sativa), barnyard grass (Echinochloa crusgalli), and ryegrass (Lolium perenne) exposed to NG in Sassafras sandy loam soil. Uptake and degradation of NG were also evaluated in ryegrass. The median effective concentration values for shoot growth ranged from 40 to 231 mg kg(-1) in studies with NG freshly amended in soil, and from 23 to 185 mg kg(-1) in studies with NG weathered-and-aged in soil. Weathering-and-aging NG in soil did not significantly affect the toxicity based on 95% confidence intervals for either seedling emergence or plant growth endpoints. Uptake studies revealed that NG was not accumulated in ryegrass but was transformed into dinitroglycerin in the soil and roots, and was subsequently translocated into the ryegrass shoots. The highest bioconcentration factors for dinitroglycerin of 685 and 40 were determined for roots and shoots, respectively. Results of these studies will improve our understanding of toxicity and bioconcentration of NG in terrestrial plants and will contribute to ecological risk assessment of NG-contaminated sites.

Transgenic alfalfa plants co-expressing glutathione S-transferase (GST) and human CYP2E1 show enhanced resistance to mixed contaminates of heavy metals and organic pollutants

Transgenic alfalfa plants simultaneously expressing human CYP2E1 and glutathione S-transferase (GST) were generated from hypocotyl segments by the use of an Agrobacterium transformation system for the phytoremediation of the mixed contaminated soil with heavy metals and organic pollutants. The transgenic alfalfa plants were screened by a combination of kanamycin resistance, PCR, GST and CYP2E1 activity and Western blot analysis. The capabilities of mixed contaminants (heavy metals-organic compounds) resistance of pKHCG transgenic alfalfa plants became markedly increased compared with the transgenic alfalfa plants expressing single gene (GST or CYP2E1) and the non-transgenic control plants. The pKHCG alfalfa plants exhibited strong resistance towards the mixtures of cadmium (Cd) and trichloroethylene (TCE) that were metabolized by the introduced GST and CYP2E1 in combination. Our results show that the pKHCG transgenic alfalfa plants have good potential for phytoremediation because they have cross-tolerance towards the complex contaminants of heavy metals and organic pollutants. Therefore, these transgenic alfalfa plants co-expressing GST and human P450 CDNAs may have a great potential for phytoremediation of mixed environmental contaminants.

Degradation of nitroesters by plant tissue cultures

Nitrate esters are widely used as effective explosives, important components of explosive ranges, and energetic plasticizers. The environmental problem arising from the production and use of these compounds can be solved using biotechnology. Phytoremediation appears as an efficient technology for this purpose. The uptake and transformation of nitroglycerine (NG) and ethylene glycol dinitrate (EGDN) from wastewater by plants using in vitro regenerants of Juncus inflexus and Phragmites australis were investigated. The plants were exposed to the NG, (600 mg l(-1)), the parent compound disappeared during 20 days and degradation products as dinitroglycerine (DNG) and mononitroglycerine (MNG) were identified in the medium. During 20 days the starting concentration of 100 mg l(-1) EGDN disappeared in the case of J. inflexus or decreased to 5% in the case of P. australis. Ethylene glycol mononitrate as the degradation product was identified. Using this approach directly to the wastewater from production of explosives, the starting concentration of nitroesters mixture (total concentration 270 mg l(-1)) was decreased by in vitro regenerants of reed (P. australis) during 6 weeks to the water contained only MNG (48 mg l(-1)).

Degradation analysis of Reactive Red 198 by hairy roots of Tagetes patula L. (Marigold)

Tagetes patula L. (Marigold) hairy roots were selected among few hairy root cultures from other plants tested for the decolorization of Reactive Red 198. Hairy roots of Tagetes were able to remove dye concentrations up to 110 mg L(-l) and could be successively used at least for five consecutive decolorization cycles. The hairy roots of Tagetes decolorized six different dyes, viz. Golden Yellow HER, Methyl Orange, Orange M2RL, Navy Blue HE2R, Reactive Red M5B and Reactive Red 198. Significant induction of the activity of biotransformation enzymes indicated their crucial role in the dye metabolism. UV-vis spectroscopy, HPLC and FTIR spectroscopy analyses confirmed the degradation of Reactive Red 198. A possible pathway for the biodegradation of Reactive Red 198 has been proposed with the help of GC-MS and metabolites identified as 2-aminonaphthol, p-aminovinylsulfone ethyl disulfate and 1-aminotriazine, 3-pyridine sulfonic acid. The phytotoxicity study demonstrated the non-toxic nature of the extracted metabolites. The use of such hairy root cultures with a high ability for bioremediation of dyes is discussed.

Transgenic plants for phytoremediation of herbicides

Herbicides are economically important, but the non-point pollution that they cause may disrupt the surrounding environment. Phytoremediation of herbicides has been well studied using conventional plants. Transgenic plants produced for metabolizing herbicides and long-persisting pollutants can be used for phytoremediation of foreign chemicals in contaminated soil and water. The genes involved in the metabolism of chemical compounds can be isolated from various organisms, including bacteria, fungi, plants, and animals, and these genes are then introduced into candidate plants. Transgenic plants expressing mammalian P450s and the other enzymes showed tolerance and phytoremediation activity toward target herbicides. Transgenic plants can also enhance the absorption and detoxification of pollutants, thereby aiding the phytoremediation of contaminated environments.

Phytoremediation—A Novel and Promising Approach for Environmental Clean-up

Phytoremediation is an eco friendly approach for remediation of contaminated soil and water using plants. Phytoremediation is comprised of two components, one by the root colonizing microbes and the other by plants themselves, which degrade the toxic compounds to further non-toxic metabolites. Various compounds, viz. organic compounds, xenobiotics, pesticides and heavy metals, are among the contaminants that can be effectively remediated by plants. Plant cell cultures, hairy roots and algae have been studied for their ability to degrade a number of contaminants. They exhibit various enzymatic activities for degradation of xenobiotics, viz. dehalogenation, denitrification leading to breakdown of complex compounds to simple and non-toxic products. Plants and algae also have the ability to hyper accumulate various heavy metals by the action of phytochelatins and metallothioneins forming complexes with heavy metals and translocate them into vacuoles. Molecular cloning and expression of heavy metal accumulator genes and xenobiotic degrading enzyme coding genes resulted in enhanced remediation rates, which will be helpful in making the process for large-scale application to remediate vast areas of contaminated soils. A few companies worldwide are also working on this aspect of bioremediation, mainly by transgenic plants to replace expensive physical or chemical remediation techniques. Selection and testing multiple hyperaccumulator plants, protein engineering ofphytochelatin and membrane transporter genes and their expression would enhance the rate of phytoremediation, making this process a successful one for bioremediation of environmental contamination. Recent years have seen major investments in the R&D, which have also resulted in competition of filing patents by several companies for economic gains. The details of science & technology related to phytoremediation have been discussed with a focus on future trends and prospects of global relevance.

Advances in development of transgenic plants for remediation of xenobiotic pollutants

Phytoremediation-the use of plants for cleaning up of xenobiotic compounds-has received much attention in the last few years and development of transgenic plants tailored for remediation will further enhance their potential. Although plants have the inherent ability to detoxify some xenobiotic pollutants, they generally lack the catabolic pathway for complete degradation/mineralization of these compounds compared to microorganisms. Hence, transfer of genes involved in xenobiotic degradation from microbes/other eukaryotes to plants will further enhance their potential for remediation of these dangerous groups of compounds. Transgenic plants with enhanced potential for detoxification of xenobiotics such as trichloro ethylene, pentachlorophenol, trinitro toluene, glycerol trinitrate, atrazine, ethylene dibromide, metolachlor and hexahydro-1,3,5-trinitro-1,3,5-triazine are a few successful examples of utilization of transgenic technology. As more genes involved in xenobiotic metabolism in microorganisms/eukaryotes are discovered, it will lead to development of novel transgenic plants with improved potential for degradation of recalcitrant contaminants. Selection of suitable candidate plants, field testing and risk assessment are important considerations to be taken into account while developing transgenic plants for phytoremediation of this group of pollutants. Taking advantage of the advances in biotechnology and 'omic' technologies, development of novel transgenic plants for efficient phytoremediation of xenobiotic pollutants, field testing and commercialization will soon become a reality.

Herbicide resistance of transgenic rice plants expressing human CYP1A1

Cytochrome P450 monooxygenases (P450s) metabolize herbicides to produce mainly non-phytotoxic metabolites. Although rice plants endogenously express multiple P450 enzymes, transgenic plants expressing other P450 isoforms might show improved herbicide resistance or reduce herbicide residues. Mammalian P450s metabolizing xenobiotics are reported to show a broad and overlapping substrate specificity towards lipophilic foreign chemicals, including herbicides. These P450s are ideal for enhancing xenobiotic metabolism in plants. A human P450, CYP1A1, metabolizes various herbicides with different structures and modes of herbicide action. We introduced human CYP1A1 into rice plants, and the transgenic rice plants showed broad cross-resistance towards various herbicides and metabolized them. The introduced CYP1A1 enhanced the metabolism of chlorotoluron and norflurazon. The herbicides were metabolized more rapidly in the transgenic rice plants than in non-transgenic controls. Transgenic rice plants expressing P450 might be useful for reducing concentrations of various chemicals in the environment.

Phytotreatment of propellant contamination

Nitroglycerine (NG) and 2,4-dinitrotoluene (2,4-DNT) are propellants often found in soil and groundwater at military firing ranges. Because of the need for training with live ammunition, control or cleanup of these contaminants may be necessary for the continued use of these firing ranges. One inexpensive approach for managing sites exposed to these contaminants is the use phytoremedation, particularly using common or native grasses. In this study, the uptake of NG and 2,4-DNT from water by three common grasses, yellow nutsedge (Cyperus escalantus), yellow foxtail (Setaria glauca), and common rush (Juncus effusus), was investigated using hydroponic reactors. Rapid removal from solution by all grasses was observed, with yellow nutsedge removal rates being the highest. NG or 2,4-DNT accumulated in the tissues in all of the plants, except yellow foxtail did not accumulate NG. Higher concentrations were observed in killed roots, demonstrating the presence of plant-based enzymes actively transforming the contaminants. Yellow nutsedge was also grown in 2,4-DNT spiked soil. Significant uptake into the plants roots and leaves was observed and concentrations in the soil decreased rapidly, although 2,4-DNT concentration also decreased in the unplanted controls. In summary, the three grasses tested appear to be good candidates for phytoremediation of propellant contamination.

Uptake and degradation of DDT by hairy root cultures of Cichorium intybus and Brassica juncea

Hairy root cultures of Cichorium intybus and Brassica juncea were used for their ability to uptake and degrade DDT (1,1,1-trichloro-2,2-bis-(4'-chlorophenyl)ethane). After 24 h of 14C DDT treatment, only 12-13% of the total applied radioactivity was detected in the culture media, indicating the efficient uptake of DDT by the hairy roots. The majority of the applied radioactivity was associated with the roots. DDT was degraded to various other products such as DDD, DDE and DDMU, along with some unknown compounds by hairy root cultures, which were detected by thin layer chromatography (TLC) and autoradiography. The rate of in situ degradation was found to be higher during the initial stages of culture and the residual 14C DDT in the roots was found to decrease from 77% to 61% over a period of 10-days. There was no spontaneous degradation of 14C DDT in media lacking hairy root cultures or in media with autoclaved hairy roots. This suggests that endogenous root enzymes play a role in the breakdown of 14C DDT. These results suggest the potential applicability and advantage of using these plant species for phytoremediation of persistent xenobiotics such as DDT in an eco-friendly and efficient manner for environmental clean up.

Decolorization of RBBR by plant cells and correlation with the transformation of PCBs

An extracellular H2O2-requiring Remazol Brilliant Blue R (RBBR) decolorizing enzyme activity was detected after cultivation of cells of various plant species both in liquid medium and when growing on agar plates containing RBBR. Level of the enzyme activity was compared with the ability to metabolize polychlorinated biphenyls (PCBs). The ability to decolorize RBBR was tested in the presence and absence of PCBs. The cultures with high PCB-transforming activity proved to exhibit RBBR oxidase much more resistant towards the influence of PCBs. In addition low activities of lignin peroxidase (LiP) and manganese dependent peroxidase (MnP) were detected in medium and in plant cells. No correlation of MnP and LiP activities with PCB degradation could be found. The RBBR decolorization could be used as a rough screening method for plant cultures able to metabolize PCBs.

Arabidopsis and the Genetic Potential for the Phytoremediation of Toxic Elemental and Organic Pollutants

In a process called phytoremediation, plants can be used to extract, detoxify, and/or sequester toxic pollutants from soil, water, and air. Phytoremediation may become an essential tool in cleaning the environment and reducing human and animal exposure to potential carcinogens and other toxins. Arabidopsis has provided useful information about the genetic, physiological, and biochemical mechanisms behind phytoremediation, and it is an excellent model genetic organism to test foreign gene expression. This review focuses on Arabidopsis studies concerning: 1) the remediation of elemental pollutants; 2) the remediation of organic pollutants; and 3) the phytoremediation genome. Elemental pollutants include heavy metals and metalloids (e.g., mercury, lead, cadmium, arsenic) that are immutable. The general goal of phytoremediation is to extract, detoxify, and hyperaccumulate elemental pollutants in above-ground plant tissues for later harvest. A few dozen Arabidopsis genes and proteins that play direct roles in the remediation of elemental pollutants are discussed. Organic pollutants include toxic chemicals such as benzene, benzo(a)pyrene, polychlorinated biphenyls, trichloroethylene, trinitrotoluene, and dichlorodiphenyltrichloroethane. Phytoremediation of organic pollutants is focused on their complete mineralization to harmless products, however, less is known about the potential of plants to act on complex organic chemicals. A preliminary survey of the Arabidopsis genome suggests that as many as 700 genes encode proteins that have the capacity to act directly on environmental pollutants or could be modified to do so. The potential of the phytoremediation proteome to be used to reduce human exposure to toxic pollutants appears to be enormous and untapped.

Phytoremediation of organic contaminants in soils

Soil pollution, a very important environmental problem, has been attracting considerable public attention over the last decades. Unfortunately, the enormous costs associated with the removal of pollutants from soils by means of traditional physicochemical methods have been encouraging companies to ignore the problem. Phytoremediation is an emerging technology that uses plants to clean up pollutants in the environment. As overwhelmingly positive results have become available regarding the ability of plants to degrade certain organic compounds, more and more people are getting involved in the phytoremediation of organic contaminants. Phytoremediation of organics appears a very promising technology for the removal of these contaminants from polluted sites.

Cation substitution in cationic phosphonolipids: a new concept to improve transfection activity and decrease cellular toxicity

Cationic lipids have been shown to be an interesting alternative to viral vector-mediated gene delivery into in vitro and in vivo model applications. Prior studies have demonstrated that even minor structural modifications of the lipid hydrophobic domain or of the lipid polar domain result in significant changes in gene delivery efficiency. Previously, we developed a novel class of cationic lipids called cationic phosphonolipids and described the ability of these vectors to transfer DNA into different cell lines and in vivo. Up until now, in all new cationic lipids, nitrogen atoms have always carried the cationic or polycationic charge. Recently we have developed a new series of cationic phosphonolipids characterized by a cationic charge carried by a phosphorus or arsenic atom. In a second step, we have also examined the effects of the linker length between the cation and the hydrophobic domain as regards transfection activity. Transfection activities of this library of new cationic phosphonolipids were studied in vitro in different cell lines (HeLa, CFT1, K562) and in vivo using a luciferase reporter gene. A luminescent assay was carried out to assess luciferase expression. We demonstrated that cation substitution on the polar domain of cationic phosphonolipids (N --> P or As) results in significant increase in transfection activity for both in vitro and in vivo assays and decrease of cellular toxicity.

Phytoremediation of toxic elemental and organic pollutants

Phytoremediation is the use of plants to extract, sequester, and/or detoxify pollutants. Phytoremediation is widely viewed as the ecologically responsible alternative to the environmentally destructive physical remediation methods currently practiced. Plants have many endogenous genetic, biochemical, and physiological properties that make them ideal agents for soil and water remediation. Significant progress has been made in recent years in developing native or genetically modified plants for the remediation of environmental contaminants. Because elements are immutable, phytoremediation strategies for radionuclide and heavy metal pollutants focus on hyperaccumulation above-ground. In contrast, organic pollutants can potentially be completely mineralized by plants.

Biodegradation of explosives by transgenic plants expressing pentaerythritol tetranitrate reductase

Plants offer many advantages over bacteria as agents for bioremediation; however, they typically lack the degradative capabilities of specially selected bacterial strains. Transgenic plants expressing microbial degradative enzymes could combine the advantages of both systems. To investigate this possibility in the context of bioremediation of explosive residues, we generated transgenic tobacco plants expressing pentaerythritol tetranitrate reductase, an enzyme derived from an explosive-degrading bacterium that enables degradation of nitrate ester and nitroaromatic explosives. Seeds from transgenic plants were able to germinate and grow in the presence of 1 mM glycerol trinitrate (GTN) or 0.05 mM trinitrotoluene, at concentrations that inhibited germination and growth of wild-type seeds. Transgenic seedlings grown in liquid medium with 1 mM GTN showed more rapid and complete denitration of GTN than wild-type seedlings. This example suggests that transgenic plants expressing microbial degradative genes may provide a generally applicable strategy for bioremediation of organic pollutants in soil.

Use of plant cell cultures in biotechnology

Plant cell cultures are being widely used in scientific studies on the physiology, biochemistry and molecular biology of primary and secondary metabolism, developmental regulation and cellular responses to pathogens and stress. In this chapter the significance of plant cell cultures in biotechnology is discussed with special emphasis on commercial production of secondary metabolites and pharmaceuticals, the potential of genetically transformed cell cultures, photosynthetically active cell cultures, production of somatic embryos, and novel assay systems based on the use of plant cells. Future aspects of biotechnical applications with respect to the potentials and limitations of these approaches are assessed, particularly in comparison with the productivity of lower eucaryotes.

PHYTOREMEDIATION

Contaminated soils and waters pose a major environmental and human health problem, which may be partially solved by the emerging phytoremediation technology. This cost-effective plant-based approach to remediation takes advantage of the remarkable ability of plants to concentrate elements and compounds from the environment and to metabolize various molecules in their tissues. Toxic heavy metals and organic pollutants are the major targets for phytoremediation. In recent years, knowledge of the physiological and molecular mechanisms of phytoremediation began to emerge together with biological and engineering strategies designed to optimize and improve phytoremediation. In addition, several field trials confirmed the feasibility of using plants for environmental cleanup. This review concentrates on the most developed subsets of phytoremediation technology and on the biological mechanisms that make phytoremediation work.