Differential induction of glutathione transferases and glucosyltransferases in wheat, maize and Arabidopsis thaliana by herbicide safeners

By learning lessons from weed science we have adopted three approaches to make plants more effective in phytoremediation: (1) The application of functional genomics to identify key components involved in the detoxification of, or tolerance to, xenobiotics for use in subsequent genetic engineering/breeding programmes. (2) The rational metabolic engineering of plants through the use of forced evolution of protective enzymes, or alternatively transgenesis of detoxification pathways. (3) The use of chemical treatments which protect plants from herbicide injury. In this paper we examine the regulation of the xenome by herbicide safeners, which are chemicals widely used in crop protection due to their ability to enhance herbicide selectivity in cereals. We demonstrate that these chemicals act to enhance two major groups of phase 2 detoxification enzymes, notably the glutathione transferases and glucosyltransferases, in both cereals and the model plant Arabidopsis thaliana, with the safeners acting in a chemical- and species-specific manner. Our results demonstrate that by choosing the right combination of safener and plant it should be possible to enhance the tolerance of diverse plants to a wide range of xenobiotics including pollutants.     

Contamination of human ovarian follicular fluid and serum by chlorinated organic compounds in three Canadian cities.

OBJECTIVES: To determine the extent of contamination of ovarian follicular fluid and serum samples in women undergoing in-vitro fertilization and to study the effect of the contaminants on reproductive outcome. DESIGN: Inception cohort study. PATIENTS: Seventy-four women undergoing in-vitro fertilization at three regional clinics in Halifax, Hamilton, Ont., and Vancouver. MAIN OUTCOME MEASURES: Follicular fluid and serum levels of contaminants, cleavage rates and time to cleavage of first egg. RESULTS: Five chlorinated organic chemicals were frequently found in the two types of samples: alpha-chlordane (ALCH), dichlorochlorophenylethylene (DDE), heptachloroepoxide-oxychlordane (OXCH), hexachlorobenzene (HCB) and polychlorinated biphenyl (PCB). The levels were generally low. Regional differences between the three clinics were present. Samples from the Halifax clinic had the lowest frequency and level of contamination. The source of drinking water (well, bottled or municipal) was an important confounder. The concentrations of the five contaminants did not affect the cleavage rate or the time to cleavage of the first egg. CONCLUSION: Trace amounts of toxic and persistent chlorinated organic chemicals found in the follicular fluid of Canadian women undergoing in-vitro fertilization did not seem to have any adverse biologic effect on the rate of fertilization and the time to cleavage. Reasons for regional differences in the concentrations of contaminants require further study.     

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.     

Herbicide safeners and glutathione metabolism

Herbicide safeners are chemicals which protect crop plants from injury by certain herbicides, without affecting weed control efficacy of the herbicides. The protective mechanism of herbicide safeners has not yet been fully elucidated, but there is increasing evidence that safeners act by selectively enhancing herbicide detoxification in crop plants. To date, two main detoxification pathways have been related to the mode of action of herbicide safeners. The first includes oxidation and subsequent glucose conjugation, mediated by cytochrome P450 -dependent monooxygenases and UDP-glucosyltransferases, respectively. This pathway appears to be important predominantly in safener protection to aryloxyphenoxypropionate and sulfonylurea herbicides. The second pathway represents the conjugation of thiocarbamate sulfoxides and chloroacetanilide herbicides with glutathione. This mechanism is accomplished by either elevating the levels of reduced glutathione or the activity of glutathione S-transferase, or both. Since glutathione has been reported to be involved in several stress situations of plants its function associated with safener-induced herbicide tolerance will be discussed in more detail in this review.     

Molecular targets that link dioxin exposure to toxicity phenotypes

Many toxicology studies have elucidated health effects associated with exposure to various chemicals, but few have identified the molecular targets that cause specific endpoints of toxicity. Our understanding of the toxicity of dioxins, a group of chemicals capable of causing toxicity at environmentally relevant levels of exposure, is no exception. Dioxins are unique compared to most chemicals that we are exposed to in the environment because they activate a high affinity receptor, aryl hydrocarbon receptor (AhR), that was identified more than three decades ago. In recent years, several lines of experimental evidence have provided clues for opening the "black box" that contains the molecular mechanisms of dioxin action. These clues have emerged by toxicologists beginning to identify the molecular targets that link AhR signaling to tissue-specific toxicity phenotypes. Endpoints of dioxin toxicity for which downstream molecular targets have begun to be elucidated are observed in developmental or tissue regeneration processes, and include impaired prostate development and hydronephrosis in mouse fetuses and pups, reduced midbrain blood flow and jaw malformation in zebrafish embryos, and impaired fin regeneration in larval and adult zebrafish. Significant progress in identifying molecular targets for dioxin-induced hepatotoxicity in adult mice also has occurred. Misregulation of AhR downstream pathways, such as conversion of arachidonic acid to prostanoids via cyclooxygenase-2, and altered Wnt/β-catenin signaling downregulating Sox9, and signaling by receptors for inflammatory cytokines have been implicated in tissue-specific endpoints of dioxin toxicity. These findings may not only begin to clarify the molecular targets of dioxin action but shed light on new molecular events associated with development and disease.     

Herbicide resistant rice (Oryza sativa L.): Global implications for weedy rice and weed management*

Rice cultivars resistant to broad‐spectrum herbicides have been developed and their commercial release is imminent, especially for imidazolinone and glufosinate resistant varieties in the USA and Latin America. Glyphosate‐resistant rice should follow within a few years. Rice growers throughout the world could benefit from the introduction of herbicide‐resistant rice cultivars that would allow in‐crop, selective control of weedy Oryza species. Other perceived benefits are the possibility to control ‘hard‐to‐kill’ weed species and weed populations that have already evolved resistance to herbicides currently used in rice production, especially those of the Echinochloa species complex. Weed management could also be improved by more efficient post‐emergence control. Introduction of herbicide resistant rice could also bring areas heavily infested with weedy rice that have been abandoned back to rice production, allow longer term crop rotations, reduce consumption of fossil fuels, promote the replacement of traditional chemicals by more environmentally benign products, and provide more rice grain without adding new land to production. There are also concerns, however, about the impact of releasing herbicide‐resistant rice on weed problems. Of most concern is the possibility of rapid transfer of the resistance trait to compatible weedy Oryza species. Development of such herbicide resistant weedy rice populations would substantially limit the chemical weed management options for farmers. Herbicide‐resistant rice volunteers also could become problematic, and added selection pressure to weed populations could aggravate already serious weed resistance problems. Because of the risk of weedy Oryza species becoming resistant to broad‐spectrum herbicides, mitigating measures to prevent gene flow, eventually attainable by both conventional breeding and molecular genetics, have been proposed. With commercialisation of the first herbicide resistant varieties planned for 2001, these mitigating measures will not be available for use with this first generation of herbicide resistant rice products. Release of herbicide resistant rice should depend on a thorough risk assessment especially in areas infested with con‐specific weedy rice or intercrossing weedy Oryza species. Regulators will have to balance risks and benefits based on local needs and conditions before allowing commercialisation of herbicide‐resistant rice varieties. If accepted, these varieties should be considered as components of integrated weed management, and a rational herbicide use and weedy rice control should be promoted to prevent losing this novel tool.     

Validation of housekeeping genes for quantitative real-time PCR in in-vivo and in-vitro models of cerebral ischaemia

Background  

Studies of gene expression in experimental cerebral ischaemia models can contribute to understanding the pathophysiology of brain ischaemia and to identifying prognostic markers and potential therapeutic targets. The normalization of relative qRT-PCR data using a suitable reference gene is a crucial prerequisite for obtaining reliable conclusions. No validated housekeeping genes have been reported for the relative quantification of the mRNA expression profile activated in in-vitro ischaemic conditions, whereas for the in-vivo model different reference genes have been used.     

细胞色素P450酶系与除草剂代谢

细胞色素P450是广泛存在于动物、植物和微生物体内的一类具有混合功能的血红素氧化酶系。它不但能够催化苯丙烷类、萜类化合物和脂肪酸等内源性物质的生物合成 ,而且参与许多外源性物质包括除草剂等的生物氧化。综述了代谢除草剂的细菌、哺乳动物和植物细胞色素P450酶系 ,概述了细胞色素P450酶系参与除草剂代谢的作用方式 :脱烷基化作用、环甲基化羟基化作用和芳环的羟基化作用等。这些细胞色素P450酶系在培育除草剂抗性作物、生物安全和生物修复方面表现出了巨大的潜能     

Terbuthylazine interferes with iron nutrition in maize (<Emphasis Type="Italic">Zea mays</Emphasis>) plants

Many chemicals, including herbicides, are routinely applied to crops for weed management and food production improvement. However, the intensive use of herbicides could lead eventually to a great environmental threat due to their persistence and accumulation in the ecosystems and contamination of soils. Furthermore, the possible effect of these chemicals on nutrient uptake and assimilation in crops has only recently been discussed. The present study aimed at understanding the effect of the herbicide terbuthylazine (TBA), a herbicide commonly applied to control weeds in leguminous species and triazine tolerant crops, on the capability of maize plants to cope with iron (Fe) shortage. The application of 2 and 5 mg L^?1 TBA caused a significant reduction of root Fe concentration. This reduction might be attributed to a decreased release of phytosiderophores, which in turn could be ascribed to a reduced sulfur assimilation. Results provide evidence that TBA impairs Fe uptake and accumulation in non-target plants most likely interacting with sulfur-assimilating enzymes [ATP sulfurylase and O-acetylserine(thiol)lyase].     

Metabolism-dependent activation and toxicity of chemicals in nasal glands

The mucosae of the nasal passages contain a large amount of glands which express secretory proteins as well as phase I and phase II biotransformation enzymes. In this review the metabolic activation, covalent binding and toxicity of chemicals in the Bowman's glands in the olfactory mucosa, in the sero-mucous glands in the nasal septum and in the lateral nasal glands and maxillary glands around the maxillary sinuses are discussed. Light microscopic autoradiographic studies have demonstrated a selective covalent binding of nasal toxicants and carcinogens such as halogenated hydrocarbons and N-nitrosamines, especially in the Bowman's glands following a single systemic exposure, suggesting a high rate of metabolic activation of chemicals in these glands. Special attention is put on the herbicide dichlobenil which induces necrosis in the olfactory mucosa following a cytochrome-P450-mediated metabolic activation and covalent binding in the Bowman's glands.     

Herbicide Selection Promotes Antibiotic Resistance in Soil Microbiomes

Herbicides are one of the most widely used chemicals in agriculture. While they are known to be harmful to nontarget organisms, the effects of herbicides on the composition and functioning of soil microbial communities remain unclear. Here we show that application of three widely used herbicides—glyphosate, glufosinate, and dicamba—increase the prevalence of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in soil microbiomes without clear changes in the abundance, diversity and composition of bacterial communities. Mechanistically, these results could be explained by a positive selection for more tolerant genotypes that acquired several mutations in previously well-characterized herbicide and ARGs. Moreover, herbicide exposure increased cell membrane permeability and conjugation frequency of multidrug resistance plasmids, promoting ARG movement between bacteria. A similar pattern was found in agricultural soils across 11 provinces in China, where herbicide application, and the levels of glyphosate residues in soils, were associated with increased ARG and MGE abundances relative to herbicide-free control sites. Together, our results show that herbicide application can enrich ARGs and MGEs by changing the genetic composition of soil microbiomes, potentially contributing to the global antimicrobial resistance problem in agricultural environments.     

The molecular bases for resistance to acetyl co-enzyme A carboxylase (ACCase) inhibiting herbicides in two target-based resistant biotypes of annual ryegrass (Lolium rigidum)

Acetyl-CoA carboxylase (ACCase) (EC.6.4.1.2) is an essential enzyme in fatty acid biosynthesis and, in world agriculture, commercial herbicides target this enzyme in plant species. In nearly all grass species the plastidic ACCase is strongly inhibited by commercial ACCase inhibiting herbicides [aryloxyphenoxypropionate (APP) and cyclohexanedione (CHD) herbicide chemicals]. Many ACCase herbicide resistant biotypes (populations) of L. rigidum have evolved, especially in Australia. In many cases, resistance to ACCase inhibiting herbicides is due to a resistant ACCase enzyme. Two ACCase herbicide resistant L. rigidum biotypes were studied to identify the molecular basis of ACCase inhibiting herbicide resistance. The carboxyl-transferase (CT) domain of the plastidic ACCase gene was amplified by PCR and sequenced. Amino acid substitutions in the CT domain were identified by comparison of sequences from resistant and susceptible plants. The amino acid residues Gln-102 (CAG codon) and Ile-127 (ATA codon) were substituted with a Glu residue (GAG codon) and Leu residue (TTA codon), respectively, in both resistant biotypes. Amino acid positions 102 and 127 within the fragment sequenced from L. rigidum corresponded to amino acid residues 1756 and 1781, respectively, in the A. myosuroides full ACCase sequence. Allele-specific PCR results further confirmed the mutations linked with resistance in these populations. The Ile-to-Leu substitution at position 1781 has been identified in other resistant grass species as endowing resistance to APP and CHD herbicides. The Gln-to-Glu substitution at position 1756 has not previously been reported and its role in herbicide resistance remains to be established.     

Chromosome Contraction by o-Isopropyl-N-Phenylcarbamate (IPC)

A selective herbicide IPC (o-isopropyl-N-phenlycarbamate) causes contraction of chromosomes in the prophase, metaphase, and anaphase stages of mitosis in cells of treated root tips. Effective concentrations in aqueous solution lie between 2.5 and 50 ppm, and effective times between 1 and 4 hr, depending upon the species of plant. A suggested starting combination is 10 ppm for 2 hr. This compound is effective in causing contraction of chromosomes in a wide range of plant species, as well as enhancing separation in acetocarmine and aceto-orcein squashes in many cases. Possibly, it may produce similar results in species which have been found to be unaffected by colchicine, 8-hydroxyquinoline, p-dichlorobenzene, and other commonly used chemicals.     

Bioassays with a floating aquatic plant (Lemna minor) for effects of sprayed and dissolved glyphosate

Macrophytes in forested areas and in prairie wetlands furnish critical habitat for aquatic communities and for several species of birds and mammals. North American agriculture relies heavily on herbicides and these compounds are detected routinely in surface waters of Western Canada. The question is whether these residues have biological meaning. There is surprisingly little literature on the responses of macrophytes to herbicides, or indeed to other chemicals. Previously we have used common duckweed in efforts to detect effects of herbicides and other chemicals. Duckweed clones were developed from local collections and grown axenically. In this study the plants were exposed to glyphosate herbicide either by dissolving formulated Roundup^® (Monsanto Canada Inc.) in the culture media or by spraying of the cultures in a laboratory spray chamber. Plant growth was monitored by counting the fronds present on several occasions over a 2-week period following treatment and by taking wet and dry weights of plants after the final counting period. Plant growth, as measured by increased numbers of fronds or increased wet or dry weights was relatively insensitive to glyphosate dissolved in the culture medium. However, the plants were killed by application of glyphosate as a spray.     

Prediction of molecular targets of cancer preventing flavonoid compounds using computational methods

Plant-based polyphenols (i.e., phytochemicals) have been used as treatments for human ailments for centuries. The mechanisms of action of these plant-derived compounds are now a major area of investigation. Thousands of phytochemicals have been isolated, and a large number of them have shown protective activities or effects in different disease models. Using conventional approaches to select the best single or group of best chemicals for studying the effectiveness in treating or preventing disease is extremely challenging. We have developed and used computational-based methodologies that provide efficient and inexpensive tools to gain further understanding of the anticancer and therapeutic effects exerted by phytochemicals. Computational methods involving virtual screening, shape and pharmacophore analysis and molecular docking have been used to select chemicals that target a particular protein or enzyme and to determine potential protein targets for well-characterized as well as for novel phytochemicals.     

IDMap: facilitating the detection of potential leads with therapeutic targets

Pharmaceutical industry has been striving to reduce the costs of drug development and increase productivity. Among the many different attempts, drug repositioning (retargeting existing drugs) comes into the spotlight because of its financial efficiency. We introduce IDMap which predicts novel relationships between targets and chemicals and thus is capable of repositioning the marketed drugs by using text mining and chemical structure information. Also capable of mapping commercial chemicals to possible drug targets and vice versa, IDMap creates convenient environments for identifying the potential lead and its targets, especially in the field of drug repositioning. AVAILABILITY: IDMap executable and its user manual including color images are freely available to non-commercial users at http://www.equispharm.com/idmap     

Gene flow from transgenic rice to red rice (Oryza sativa L.) in the field

In this study, we simulate a transgenic rice crop highly infested with red rice to examine transgene transfer from a transgenic line (A2504) resistant to glufosinate ammonium to cohabitant red rice. The red rice was sown along with the transgenic line at the highest density found in naturally infested crops in the region. Agricultural practices similar to those used to control red rice infestation in northern Italy rice fields were used to reproduce the local rice production system. During the first 2 years, the field was treated with herbicide at the appropriate time; in the first year the dosage of herbicide was three times the recommended amount. In this first year, detectable red rice plants that escaped herbicide treatment were manually removed. Nevertheless, two herbicide‐resistant hybrid plants (named 101 and 104) were identified in the experimental field during the second year of cultivation. Phenotypic and molecular characterisation suggests the hybrid nature of these two plants, deriving from crossing events involving A2504, respectively, with red rice (plant 101) and the buffer cultivar Gladio (plant 104). The progeny of two subsequent generations of the two plants were examined and the presence of the transgene detected, indicating stable transfer of the transgene across generations. In conclusion, despite control methods, red rice progeny tolerant to the herbicide can be expected following use of transgenic rice and, consequently, difficulties in controlling this weed with chemicals will emerge in a relatively short time.     

Physiology and toxicology of hormone-disrupting chemicals in higher plants

Higher plants are exposed to natural environmental organic chemicals, associated with plant–environment interactions, and xenobiotic environmental organic chemicals, associated with anthropogenic activities. The effects of these chemicals result not only from interaction with metabolic targets, but also from interaction with the complex regulatory networks of hormone signaling. Purpose-designed plant hormone analogues thus show extensive signaling effects on gene regulation and are as such important for understanding plant hormone mechanisms and for manipulating plant growth and development. Some natural environmental chemicals also act on plants through interference with the perception and transduction of endogenous hormone signals. In a number of cases, bioactive xenobiotics, including herbicides that have been designed to affect specific metabolic targets, show extensive gene regulation effects, which are more in accordance with signaling effects than with consequences of metabolic effects. Some of these effects could be due to structural analogies with plant hormones or to interference with hormone metabolism, thus resulting in situations of hormone disruption similar to animal cell endocrine disruption by xenobiotics. These hormone-disrupting effects can be superimposed on parallel metabolic effects, thus indicating that toxicological characterisation of xenobiotics must take into consideration the whole range of signaling and metabolic effects. Hormone-disruptive signaling effects probably predominate when xenobiotic concentrations are low, as occurs in situations of residual low-level pollutions. These hormone-disruptive effects in plants may thus be of importance for understanding cryptic effects of low-dosage xenobiotics, as well as the interactive effects of mixtures of xenobiotic pollutants.