Genomic damage induced in tobacco plants by chlorobenzoic acids—Metabolic products of polychlorinated biphenyls

Tobacco seedlings (Nicotiana tabacum var. xanthi) were treated for 24 h with mono-(2- and 3-CBA), di-(2,5- and 3,4-CBA), and tri-(2,4,6- and 2,3,5-CBA)-chlorobenzoic acids (CBAs) and with the mixture of polychlorinated biphenyls – Delor 103, or cultivated for 1 or 2 weeks in soil polluted with the CBAs. DNA damage in nuclei of leaves and roots was evaluated by the comet assay. A significant increase in DNA damage was observed only at concentrations of CBAs that caused withering of leaves or had lethal effects within 2–4 weeks after the treatments. As the application of CBAs did not induce somatic mutations, the induced DNA migration is probably caused by necrotic DNA fragmentation and not by DNA damage resulting in genetic alteration. In contrast, the application of the monofunctional alkylating agent ethyl methanesulphonate as a positive control resulted in a dose–response increase of DNA damage and an increase of somatic mutations. Thus, the EMS-produced DNA migration is probably associated with genotoxin-induced DNA fragmentation. The data demonstrate that the comet assay in plants should be conducted together with toxicity studies to distinguish between necrotic and genotoxin-induced DNA fragmentation. The content of 2,5-CBA in tobacco seedlings was measured by reverse-phase high pressure liquid chromatography.     

Monitoring toxicity, DNA damage, and somatic mutations in tobacco plants growing in soil heavily polluted with polychlorinated biphenyls

Heterozygous tobacco (Nicotiana tabacum var. xanthi) plants were cultivated in soil from a dump site highly polluted with polychlorinated biphenyls (PCBs) at Lhenice in South Bohemia, Czech Republic. The total amount of PCBs in the polluted soil, measured by gas chromatography varied from 165 to 265mgkg(-1) of soil. In tobacco plants cultivated for 8 weeks in the polluted soil the amount of PCB in the leaves varied from 11 to 28 and in the roots from 104 to 308mgkg(-1) dry mass. The average leaf area of tobacco plants growing in the PCB-polluted soil was significantly reduced and the DNA damage in leaf nuclei, measured by the comet assay, was slightly but significantly increased compared with controls. The tobacco plants with increased DNA damage showed reduced growth and had distorted leaves. No increase in the frequency of somatic mutations was detected in tobacco plants growing in the PCB-polluted soil.     

Tissue damage after acute intoxication by polychlorinated biphenyls in cockroaches

It is common knowledge that polychlorinated biphenyls (PCBs) represent a serious threat to the health of both vertebrates and invertebrates. As far as the former are concerned, especially as regards human beings, a broad literature describes the direct and indirect effects induced by the PCBs on their systems and organs. Among invertebrates, the information available is mostly related to arthropods and is, however, very scarce. The aim of this work was to evaluate the effects of polychlorinated biphenyls (PCBs) on tissues and organs of individuals belonging to a species of Blattaria (Blattella germanica) treated with various doses of this toxic material. The pathologies found became more serious as the dosage increased and were present throughout the entire digestive system, in the fat body and in the male gonads: in these areas cell and tissue breakdown and severely damaged spermiogenesis were observed. In particular, the testes, Malpighian tubules and fat body accumulated an amorphous basophilic PAS-positive substance. Furthermore, the NOS-dependent NADPH diaphorase activity pattern in the retina and optic lobes was more evident in the treated than in the control insects.     

Evaluation of DNA damage and mutagenicity induced by lead in tobacco plants

Tobacco (Nicotiana tabacum L. var. xanthi) seedlings were treated with aqueous solutions of lead nitrate (Pb2+) at concentrations ranging from 0.4 mM to 2.4 mM for 24 h and from 25 microM to 200 microM for 7 days. The DNA damage measured by the comet assay was high in the root nuclei, but in the leaf nuclei a slight but significant increase in DNA damage could be demonstrated only after a 7-day treatment with 200 microM Pb2+. In tobacco plants growing for 6 weeks in soil polluted with Pb2+ severe toxic effects, expressed by the decrease in leaf area, and a slight but significant increase in DNA damage were observed. The tobacco plants with increased levels of DNA damage were severely injured and showed stunted growth, distorted leaves and brown root tips. The frequency of somatic mutations in tobacco plants growing in the Pb2+-polluted soil did not significantly increase. Analytical studies by inductively coupled plasma optical emission spectrometry demonstrate that after a 24-h treatment of tobacco with 2.4 mM Pb2+, the accumulation of the heavy metal is 40-fold higher in the roots than in the above-ground biomass. Low Pb2+ accumulation in the above-ground parts may explain the lower levels or the absence of Pb2+-induced DNA damage in leaves.     

Evaluation of DNA damage and mutagenicity induced by lead in tobacco plants

Tobacco (Nicotiana tabacum L. var. xanthi) seedlings were treated with aqueous solutions of lead nitrate (Pb²⁺) at concentrations ranging from 0.4 mM to 2.4 mM for 24 h and from 25 μM to 200 μM for 7 days. The DNA damage measured by the comet assay was high in the root nuclei, but in the leaf nuclei a slight but significant increase in DNA damage could be demonstrated only after a 7-day treatment with 200 μM Pb²⁺. In tobacco plants growing for 6 weeks in soil polluted with Pb²⁺ severe toxic effects, expressed by the decrease in leaf area, and a slight but significant increase in DNA damage were observed. The tobacco plants with increased levels of DNA damage were severely injured and showed stunted growth, distorted leaves and brown root tips. The frequency of somatic mutations in tobacco plants growing in the Pb²⁺-polluted soil did not significantly increase. Analytical studies by inductively coupled plasma optical emission spectrometry demonstrate that after a 24-h treatment of tobacco with 2.4 mM Pb²⁺, the accumulation of the heavy metal is 40-fold higher in the roots than in the above-ground biomass. Low Pb²⁺ accumulation in the above-ground parts may explain the lower levels or the absence of Pb²⁺-induced DNA damage in leaves.     

Characterization of pancreatic-type tissue in the liver of rat induced by polychlorinated biphenyls

Pancreatic-type tissue induced in the livers of rats treated with polychlorinated biphenyls was characterized by transmission electron microscopy and high-resolution immunocytochemistry. The cells of pancreatic-type tissue were arranged as acini and in small groups. By electron microscopy the pancreatic-type tissue showed features very similar to normal pancreatic acinar tissue, such as well developed rough endoplasmic reticulum (RER), large numbers of mature zymogen granules, and a basally located nucleus. Protein A-gold imunocytochemical technique showed localization of amylase and trypsinogen over the zymogen granules and RER. These findings confirm that this tissue in the liver is morphologically and functionally identical to pancreatic acinar tissue.     

Dynamics of heat-shock induced DNA damage and repair in senescent tobacco plants

Oxidative stress plays an important role in plant ageing and in response to different stresses. Oxidative DNA damage, unless repaired, may have detrimental consequences and increase genetic instability. Therefore, we determined the role of heat-shock induced oxidative stress on induction and repair of DNA damage in relation to oxidative stress tolerance in senescent tobacco plants. One-month-old (young) and three-month-old (senescent) plants were exposed to 42 °C for 2 and 4 h and left to recover at 26 °C for 24 and 72 h. The progression of senescence was characterized by the lower soluble protein and malondialdehyde content compared to young plants. Immediately after the heat shock, an increase in lipid peroxidation and guaiacol peroxidase activity, as well as DNA damage measured by the Comet assay were induced to higher extent in the young plants than in the senescent ones compared to their respective controls. Moreover, after 24-h recovery, the DNA damage further increased in the young plants whereas tendency of DNA repair was observed in the senescent plants. Upon 72-h recovery, no significant differences were noticed in all parameters studied (regardless of plant age) compared to the controls. The random amplified polymorphic DNA (RAPD) analysis confirmed genetic stability of the tobacco plants during the heat-shock exposures as well as the subsequent recovery periods.     

Biodegradation of polychlorinated biphenyls by plant cells

The PCB biodegradative ability of plant cells cultivated in vitro in media containing a mixture of PCB congeners, Delor 103, is demonstrated. For experiments we used submerged cultures of Armoracia rusticana, Solanum aviculare, Atropa bella-donna, transformed hairy root or embryogenic cultures of Solanum nigrum. Transformation of PCB was followed by gas chromatography after cultivations of the above-mentioned cultures with Delor 103 (10 mg 100 ml⁻¹). The overall PCB metabolizing capability and also degradation of individual congeners greatly differed from strain to strain. The highest capability to metabolize PCB was assayed with differentiated cultures of Solanum nigrum. Beside the capability of PCB degradation, total peroxidase activity in the medium and the cell extract was also followed. Differentiated or hairy root cultures exhibiting higher degradation abilities of PCB also showed increase of peroxidase activities.     

Microorganisms--degraders of polychlorinated biphenyls

Four strains belonging to the genus Bacillus, capable of degrading polychlorinated biphenyls (PCB), were isolated by screening the collection strains of soil bacteria, degrading a organochlorine pesticide, hexachlorocyclohexane (HCCH). A method for production of tritium-labeled PCB was developed. Consumption and degradation of PCB by the soil bacterial strains selected were studied using tritium-labeled PCB and GLC. It was demonstrated that PCB are degradable both in culture media and under in model soil samples.     

Effects of polychlorinated biphenyls and environmental biotransformation products on aquatic nitrification.

The effects of polychlorinated biphenyls (PCBs) on nitrification were examined for pure cultures and natural reservoir samples. PCBs at concentrations greater than 10 microgram liter-1 inhibited nitrification, principally ammonium oxidation, in one of two natural reservoir environments. However, this inhibition could not be reproduced in pure high-cell-density cultures or in previously contaminated reservoir waters. A PCB environmental biotransformation product, p-chlorophenylglyoxylic acid, and p-chloromandelic acid had no effect on nitrification.     

零价金属降解多氯联苯(PCBs)

多氯联苯(polychlorinated biphenyls,简称PCBs)是一类对环境有不利影响的有毒有机物,它在环境中广泛而大量分布。许多科学家都在致力于有效处理PCBs污染介质(包括水、油、沉积物和土壤)的修复技术的研究。本文综述了国内外在零价金属还原脱氯降解PCBs领域的研究状况。在高温等特殊条件下或有钯、铂、镍和铜等催化剂存在的条件下,零价金属能有效促进PCBs还原脱氯。讨论了零价铁还原脱氯的3个可能的途径:金属直接反应,将零价铁表面的电子转移到有机氯化物使之脱氯;铁腐蚀的直接产物Fe2 具有还原能力,它可使得一部分氯代烃脱氯;铁反应产生的氢气可使有机氯化物还原。评述了零价金属还原脱氯PCBs具有有效、廉价和易得的特点。展望了零价金属还原脱氯降解PCBs研究领域的发展前景。     

Alteration of serotonin system by polychlorinated biphenyls exposure

Although commercial production of polychlorinated biphenyls (PCBs) was banned in 1979, PCBs continue to be an environmental and health concern due to their high bioaccumulation and slow degradation rates. In fact, PCBs are still present in our food supply (fish, meat, and dairy products). In laboratory animals, exposure to single PCB congener or to mixtures of different congeners induces a variety of physiological alterations. PCBs cross the placenta and even exposure at low level is harmful for the foetus by leading to neurodevelopment alterations. Serotonin system which regulates many physiological functions from platelet activation to high cerebral processes and neurodevelopment is one of the targets of PCBs toxicity. The effects of PCBs exposure on serotonin system have been investigated although to a lesser extent compared to its effect in other neurotransmitter systems. This review provides a summary of the results concerning the impact of PCBs exposure (in vitro and in vivo) on serotonin system. Further research is needed to correlate specific deficits with PCB-induced changes in the serotonin system.     

多氯联苯的生物修复

多氯联苯(Polychlorinated biphenyls,PCBs)是一种持久性有机污染物,对人类和自然环境具有很大的威胁,降解PCBs一直是研究的热点。在目前的研究方法中生物降解最具潜力,生物降解主要分为微生物降解、植物修复和微生物-植物共同修复3个方面。文章着重介绍了微生物降解PCBs菌株的分离,降解相关基因的克隆和改造;同时对植物修复,植物与微生物共同修复以及植物转基因修复进行了讨论。     

Aerobic degradation of polychlorinated biphenyls

The microbial degradation of polychlorinated biphenyls (PCBs) has been extensively studied in recent years. The genetic organization of biphenyl catabolic genes has been elucidated in various groups of microorganisms, their structures have been analyzed with respect to their evolutionary relationships, and new information on mobile elements has become available. Key enzymes, specifically biphenyl 2,3-dioxygenases, have been intensively characterized, structure/sequence relationships have been determined and enzymes optimized for PCB transformation. However, due to the complex metabolic network responsible for PCB degradation, optimizing degradation by single bacterial species is necessarily limited. As PCBs are usually not mineralized by biphenyl-degrading organisms, and cometabolism can result in the formation of toxic metabolites, the degradation of chlorobenzoates has received special attention. A broad set of bacterial strategies to degrade chlorobenzoates has recently been elucidated, including new pathways for the degradation of chlorocatechols as central intermediates of various chloroaromatic catabolic pathways. To optimize PCB degradation in the environment beyond these metabolic limitations, enhancing degradation in the rhizosphere has been suggested, in addition to the application of surfactants to overcome bioavailability barriers. However, further research is necessary to understand the complex interactions between soil/sediment, pollutant, surfactant and microorganisms in different environments.     

Bacterial metabolism of polychlorinated biphenyls

Microbial metabolism is responsible for the removal of persistent organic pollutants including PCBs from the environment. Anaerobic dehalogenation of highly chlorinated congeners in aquatic sediments is an important process, and recent evidence has indicated that Dehalococcoides and related organisms are predominantly responsible for this process. Such anaerobic dehalogenation generates lower chlorinated congeners which are easily degraded aerobically by enzymes of the biphenyl upper pathway (bph). Initial biphenyl 2,3-dioxygenases are generally considered the key enzymes of this pathway which determine substrate range and extent of PCB degradation. These enzymes have been subject to different protein evolution strategies, and subsequent enzymes have been considered as crucial for metabolism. Significant advances have been made regarding the mechanistic understanding of these enzymes, which has also included elucidation of the function of BphK glutathione transferase. So far, the genomes of two important PCB-metabolizing organisms, namely Burkholderia xenovorans strain LB400 and Rhodococcus sp. strain RHA1, have been sequenced, with the rational to better understand their overall physiology and evolution. Genomic and proteomic analysis also allowed a better evaluation of PCB toxicity. Like all bph gene clusters which have been characterized in detail, particularly in strains LB400 and RHA1, these genes were localized on mobile genetic elements endowing single strains and microbial communities with a high flexibility and adaptability. However, studies show that our knowledge on enzymes and genes involved in PCB metabolism is still rather fragmentary and that the diversity of bacterial strategies is highly underestimated. Overall, metabolism of biphenyl and PCBs should not be regarded as a simple linear pathway, but as a complex interplay between different catabolic gene modules.     

Dehalorespiration with polychlorinated biphenyls by an anaerobic ultramicrobacterium

Anaerobic microbial dechlorination is an important step in the detoxification and elimination of polychlorinated biphenyls (PCBs), but a microorganism capable of coupling its growth to PCB dechlorination has not been isolated. Here we describe the isolation from sediment of an ultramicrobacterium, strain DF-1, which is capable of dechlorinating PCBs containing double-flanked chlorines added as single congeners or as Aroclor 1260 in contaminated soil. The isolate requires Desulfovibrio spp. in coculture or cell extract for growth on hydrogen and PCB in mineral medium. This is the first microorganism in pure culture demonstrated to grow by dehalorespiration with PCBs and the first isolate shown to dechlorinate weathered commercial mixtures of PCBs in historically contaminated sediments. The ability of this isolate to grow on PCBs in contaminated sediments represents a significant breakthrough for the development of in situ treatment strategies for this class of persistent organic pollutants.     

Inhibition of purified rabbit muscle phosphorylase a and phosphorylase b by polychlorinated biphenyls, polychlorinated biphenylols and polybrominated biphenyls

Polychlorinated biphenyls, polychlorinated biphenylols and polybrominated biphenyls inhibited both rabbit muscle phosphorylase a and phosphorylase b (1,4-alpha-D-glucan:orthophosphate alpha-d-glucosyltransferase, EC 2.4.1.1). The degree of inhibition was dependent upon the relative hydrophobicity of the compounds and steric hinderance. 2,4,5,2',4',5'-Hexabromobiphenyl and Firemaster BP-6 were the most effective inhibitors (Ki, 15 . 10(-6) M). Phosphorylase b was inhibited by compounds of all three groups. 2,4,5,2',4',5'-Hexachlorobiphenyl and 2,4,5,2',4',5'-hexabromobiphenyl did not significantly inhibit phosphorylase a. All of the compounds inhibited phosphorylase a less than phosphorylase b, except 2',3',4',5,5'-pentachloro-2-biphenylol, which was equally effective on each enzyme. Kinetic analysis showed the inhibition was non-competitive and mixed. The results indicate that the compounds bind to hydrophobic site(s) on phosphorylase, access to which is limited by phosphorylation of serine 24.