Genotoxicity of 2,4-D and dicamba revealed by transgenic Arabidopsis thaliana plants harboring recombination and point mutation markers

Teratogenic effects of the dicamba herbicide in Zebrafish (Danio rerio) embryos

Dicamba has been used worldwide for 60 years, but few studies have been conducted on its environmental safety and health effects. Therefore, this study aims to evaluate the acute toxicity, teratogenic effects, oxidative stress, and neurotoxicity of Dicamba in zebrafish embryos. Embryos were exposed to concentrations of 4.5, 18, 72, and 288 mg/L of Dicamba for 96 h. Among the teratogenic effects, yolk sac edema predominated, besides malabsorption of nutrients (grayish yolk sac). The presence of edema may indicate problems with circulation and water efflux from the embryos, which may be related to kidney and cardiovascular problems. Other effects such as hemorrhage, spinal and eye malformations, and dwarfism were also observed. The hatching rate was reduced in the highest concentration, and in the other concentrations, a decrease was noticeable indicating a delay in development. Neurotoxic effects were also observed. Oxidative stress analysis showed a significant decrease in SOD at all concentrations and an increase in GPx, GSH, and LPO at 288 mg/L of Dicamba. It was observed that the herbicide is capable of causing teratogenic effects, developmental delay, and oxidative stress. These results show that exposure to Dicamba, in a commercial formulation, can bring risks during embryonic development. In addition, it highlights the need for further studies on the effects of the herbicide and a reassessment of toxicity categorization.

Determination of genotoxic damages of picloram and dicamba with comet assay in Allium cepa rooted in tissue culture and distilled water

BACKGROUND

Many genotoxicity tests allow us to understand the mechanism of damages on genetic material occurring in living organisms against various physical and chemical agents. One of them is the Comet test. The current study aimed to evaluate genotoxic caused by picloram and dicamba to root meristems of Allium cepa utilizing comet assay.

METHODS

Two different protocols were used for rooting and auxin/pesticide application. (i) A. cepa bulbs were rooted in MS medium and then treated with Murashige and Skoog (MS) medium (control) and 0.67, 1.34, 2.01, 2.68, 3.35, 4.02, and 8.04 mg/L of picloram and dicamba using aseptic tissue culture techniques. (ii) A. cepa bulbs were then rooted in bidistilled water and treated with 0 (control), 0.67, 1.34, 2.01, 2.68, 3.35, 4.02, and 8.04 mg/L of picloram and dicamba in distilled water. The A. cepa root tip cells in both treatment groups were examined using comet test to find the possible DNA damaging effects of picloram and dicamba.

RESULTS

The results obtained at all the concentrations were statistically compared with their control groups. Almost at all the concentrations of Picloram and dicamba increased comet tail intensity (%) and tail moment in roots treated in MS medium. Two highest concentrations revealed toxic effect. On the other hand, DNA damaging effect of both auxins was only noted on the highest (> 4.02 mg/L) in roots treated in distilled water.

CONCLUSIONS

This study approve and confirm genotoxic effects of how growth regulators on plants. These findings give an evidence of DNA damage in A. cepa. Therefore, both picloram and dicamba should only be used in appropriate and recommended concentrations in agriculture to conserve ecosystem and to pose minimum threat to life.

The Influence of Herbicides to Marine Organisms Aliivibrio fischeri and Artemia salina

The aim of this work was to determine the toxic effect of the most used herbicides on marine organisms, the bacterium Aliivibrio fischeri, and the crustacean Artemia salina. The effect of these substances was evaluated using a luminescent bacterial test and an ecotoxicity test. The results showed that half maximal inhibitory concentration for A. fischeri is as follows: 15minIC50 (Roundup® Classic Pro) = 236 μg·L-1, 15minIC50 (Kaput® Premium) = 2475 μg·L-1, 15minIC50 (Banvel® 480 S) = 2637 μg·L-1, 15minIC50 (Lontrel 300) = 7596 μg·L-1, 15minIC50 (Finalsan®) = 64 μg·L-1, 15minIC50 (glyphosate) = 7934 μg·L-1, 15minIC50 (dicamba) = 15,937 μg·L-1, 15minIC50 (clopyralid) = 10,417 μg·L-1, 15minIC50 (nonanoic acid) = 16,040 μg·L-1. Median lethal concentrations for A. salina were determined as follows: LC50 (Roundup® Classic Pro) = 18 μg·L-1, LC50 (Kaput® Premium) = 19 μg·L-1, LC50 (Banvel® 480 S) = 2519 μg·L-1, LC50 (Lontrel 300) = 1796 μg·L-1, LC50 (Finalsan®) = 100 μg·L-1, LC50 (glyphosate) = 811 μg·L-1, LC50 (dicamba) = 3705 μg·L-1, LC50 (clopyralid) = 2800 μg·L-1, LC50 (nonanoic acid) = 7493 μg·L-1. These findings indicate the need to monitor the herbicides used for all environmental compartments.

Cytotoxic and genotoxic effects of clopyralid herbicide on Allium cepa roots

Clopyralid is one of the synthetic pyridine-carboxylate auxin herbicides and used to control perennial and annual broadleaf weeds in wheat, sugar beets, canola, etc. In this study, dose-dependent cytotoxicity and genotoxicity of clopyralid at different concentrations (25, 50, and 100 μg/mL) have been evaluated on the Allium cepa roots. The evaluation has been performed at macroscopic (root growth) and microscopic levels [mitotic index (MI), chromosome aberrations (CAs) in ana-telophase cells, and DNA damage] using root growth inhibition, Allium ana-telophase, and comet tests. The percentage of root growth inhibition and concentration of reducing root growth by 50% (EC₅₀) of clopyralid were determined compared with the negative control by using various concentrations of clopyralid (6.25-1000 μg/L). The 96 h EC₅₀ of clopyralid was recorded as 50 μg/L. The gradual decrease in root growth and the MI reveals the cytotoxic effects of clopyralid. All the tested concentrations of clopyralid induced total CAs (polyploidy, stickiness, anaphase bridges, chromosome laggards, and disturbed ana-telophase) and DNA damage dose and time dependently. These results confirm the cytotoxic and genotoxic effects of clopyralid on non-target organism.

Evaluation of the genotoxic and cytotoxic effects of exposure to the herbicide 2,4-dichlorophenoxyacetic acid in Astyanax lacustris (Pisces, Characidae) and the potential for its removal from contaminated water using a biosorbent

The genotoxic and cytotoxic effects of 2,4-dichlorophenoxyacetic acid (2,4-D) on specimens of Astyanax lacustris were evaluated using different biomarkers. Additionally, this study evaluated the efficiency of an activated carbon filter made from the husks green coconut, which was used as a biosorbent to remove 2,4-D dissolved in the water, and the potential effectiveness of this procedure for the reduction of the toxic effects of this compound on A. lacustris. Three sublethal concentrations of 2,4-D (10, 20, and 40 mg L^-1) were tested over 24, 48, and 72 h, and their effects on Astyanax lacustris were evaluated using chromosomal aberration test, the mitotic index, the frequency of micronuclei and nuclear alterations, and the comet assay. Exposure to 2,4-D increased the frequency of chromosomal aberrations, reduced the mitotic index, and caused significant levels of nuclear modification in some of the treatments, in comparison with the negative control. The comet assay revealed DNA damage (classes 1-3) at all 2,4-D concentrations, reaching significant levels in the 20 mg L^-1 (48 h) and 40 mg L^-1 (72 h) treatments. The coconut husk biosorbent was highly effective for the removal of 2,4-D and the fish exposed to the water decontaminated by this filter had low levels of cellular alteration. The findings of the present study demonstrated, for the first time, the genotoxic and cytotoxic effects of 2,4-D in Astyanax lacustris, as well as suggests the potential application of a biosorbent for the effective decontamination of water contaminated with pesticides.

Potential impact of the herbicide 2,4-dichlorophenoxyacetic acid on human and ecosystems

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is applied directly to aquatic and conventional farming systems to control weeds, and is among the most widely distributed pollutants in the environment. Non-target organisms are exposed to 2,4-D via several ways, which could produce toxic effects depending on the dose, frequency of exposure, and the host factors that influence susceptibility and sensitivity. An increasing number of experimental evidences have shown concerns about its presence/detection in the environment, because several investigations have pointed out its potential lethal effects on non-target organisms. In this review, we critically evaluated the environmental fate and behavior of 2,4-D along with its eco-toxicological effects on aquatic, plants and human life to provide concise assessment in the light of recently published reports. The findings demonstrate that 2,4-D is present in a low concentration in surface water of regions where its usage is high. The highest concentrations of 2,4-D were detected in soil, air and surface water surrounded by crop fields, which suggest that mitigation strategies must be implanted locally to prevent the entry of 2,4-D into the environment. A general public may have frequent exposure to 2,4-D due to its wide applications at home lawns and public parks, etc. Various in vivo and in vitro investigations suggest that several species (or their organs) at different trophic levels are extremely sensitive to the 2,4-D exposure, which may explain variation in outcomes of reported investigations. However, implications for the prenatal exposure to 2,4-D remain unknown because 2,4-D-induced toxicity thresholds in organism have only been derived from juveniles or adults. In near future, introduction of 2,4-D resistant crops will increase its use in agriculture, which may cause relatively high and potentially unsafe residue levels in the environment. The recent findings indicate the urgent need to further explore fate, accumulation and its continuous low level exposure impacts on the environment to generate reliable database which is key in drafting new regulation and policies to protect the population from further exposure.

Evaluation of herbicides action on plant bioindicators by genetic biomarkers: a review

The use of pesticides has increased worldwide, owing to the demand for products of good quality and to satisfy a growing population. Herbicides represent almost half of the total amount of pesticides used. Although important to the reduction of costs and an increase of productivity, their indiscriminate use, as well as that of the other pesticides, is a global environmental problem, since they affect the living organisms. To evaluate the damage caused by herbicides to the environment, different organisms have been used as bioindicators, especially higher plants, due to several advantages. This is a literature review on herbicidal actions in plant bioindicators, as assessed by genetic biomarkers. Also, the present manuscript aimed to characterize the main organisms (Allium cepa, Vicia faba and Tradescantia spp.) and the most used biomarkers (mitotic index, chromosome aberrations, micronuclei, sister chromatid exchange and mutations). We concluded that herbicides induce cytotoxicity and genotoxicity in the assessed bioindicators. The data corroborate the existing warnings of the risks that the indiscriminate and increasing use of pesticides poses to the environment and its biodiversity.

Does 2,4-dichlorophenoxyacetic acid (2,4-D) induce genotoxic effects in tissue cultured Allium roots?

2,4-Dichlorophenoxyacetic acid (2,4-D) is a synthetic plant growth regulator that is highly toxic to most broad leaved plants and relatively nontoxic to monocotyledonous plants; is frequently used as weed killer. The study aimed to investigate cytogenetic effects of different concentrations of 2,4-D (0.67, 1.34, 2.01, 2.68, 3.35 and 4.02 mg/L) on Allium cepa bulblets' root tips treated for 24 and 48 h. The results showed six types of structural aberrations: C-mitosis, stickiness, laggards, bridges, fragments and multipolarity that varied numerically compared to control. It significantly affected mitotic index (MI) at 24 and 48 h treatment. In the Allium test, MI increased significantly at three lower concentrations (0.67, 1.34, 2.01 mg/L) after treatment with 2,4-D for 24 h and decreased significantly at higher concentration. Whereas, 2,4-D treatment for 48 h increased MI at all concentrations with significantly decreased MI at the highest concentration. The experiment was extended using comet test that did not reveal significant difference among treatments except for application of 4.02 mg/L 2,4-D for 48 h; where cell damages were verified by comet test. Rest of the concentrations for any duration of time were not damaging and toxic to cells. The results showed, visible mitodepressive action of 4.02 mg/L 2,4-D when treated for 48 h that had tendency to become toxic if the roots had been in touch with 2,4-D for a longer time.

In vitro genotoxicity assessment of the synthetic plant growth regulator, 1-naphthaleneacetamide

1-Naphthaleneacetamide (NAAm) is a synthetic plant growth regulator in the auxin family that is widely used in agriculture to promote the growth of numerous fruits, for root cuttings and as a fruit thinning agent. The potential genotoxic effects of NAAm were investigated in vitro by the chromosome aberrations (CAs), and cytokinesis-block micronucleus assays in human peripheral blood lymphocytes (PBLs) for the first time. The human PBLs were treated with 20, 40, 80, and 160 µg/mL of NAAm for 24 and 48 h. The results of this study showed that NAAm significantly induced the formation of structural CA and MN for all concentrations (20, 40, 80 and 160 µg/mL) and treatment periods (24 and 48 h) when compared with the negative and the solvent control. In addition, the higher concentrations of NAAm (80 and 160 µg/mL) caused a statistically significant increase in nuclear bud (NBUD) formation for both 24 and 48 h treatment times. With regard to the cell cycle kinetics, at all the tested concentrations, NAAm caused a statistically significant reduction in the mitotic index (MI) only for 48 h treatment period and also in the nuclear division index (NDI) for both 24 and 48 h treatment periods as compared to the control groups. The reductions in the MI and NDI occured in a concentration-dependent manner for both treatment times. In conclusion, the present results indicate that in the tested experimental conditions, NAAm was genotoxic and cytotoxic on human PBLs in vitro.

Comparative proteomics and metallomics studies in Arabidopsis thaliana leaf tissues: evaluation of the selenium addition in transgenic and nontransgenic plants using two-dimensional difference gel electrophoresis and laser ablation imaging

The main goal of this work is to evaluate some differential protein species in transgenic (T) and nontransgenic (NT) Arabidopsis thaliana plants after their cultivation in the presence or absence of sodium selenite. The transgenic line was obtained through insertion of CaMV 35S controlling nptII gene. Comparative proteomics through 2D-DIGE is carried out in four different groups (NT × T; NT × Se-NT (where Se is selenium); Se-NT × Se-T, and T × Se-T). Although no differential proteins are achieved in the T × Se-T group, for the others, 68 differential proteins (by applying a regulation factor ≥1.5) are achieved, and 27 of them accurately characterized by ESI-MS/MS. These proteins are classified into metabolism, energy, signal transduction, disease/defense categories, and some of them are involved in the glycolysis pathway-Photosystems I and II and ROS combat. Additionally, laser ablation imaging is used for evaluating the Se and sulfur distribution in leaves of different groups, corroborating some results obtained and related to proteins involved in the glycolysis pathway. From these results, it is possible to conclude that the genetic modification also confers to the plant resistance to oxidative stress.

Homologous recombination in Arabidopsis seeds along the track of energetic carbon ions

Heavy ion irradiation has been used as radiotherapy of deep-seated tumors, and is also an inevitable health concern for astronauts in space mission. Unlike photons such as X-rays and γ-rays, a high linear energy transfer (LET) heavy ion has a varying energy distribution along its track. Therefore, it is important to determine the correlation of biological effects with the Bragg curve energy distribution of heavy ions. In this study, a continuous biological tissue equivalent was constructed using a layered cylinder of Arabidopsis seeds, which was irradiated with carbon ions of 87.5MeV/nucleon. The position of energy loss peak in the seed pool was determined with CR-39 track detectors. The mutagenic effect in vivo along the path of carbon ions was investigated with the seeds in each layer as an assay unit, which corresponded to a given position in physical Bragg curve. Homologous recombination frequency (HRF), expression level of AtRAD54 gene, germination rate of seeds, and survival rate of young seedlings were used as checking endpoints, respectively. Our results showed that Arabidopsis S0 and S1 plants exhibited significant increases in HRF compared to their controls, and the expression level of AtRAD54 gene in S0 plants was significantly up-regulated. The depth-biological effect curves for HRF and the expression of AtRAD54 gene were not consistent with the physical Bragg curve. Differently, the depth-biological effect curves for the developmental endpoints matched generally with the physical Bragg curve. The results suggested a different response pattern of various types of biological events to heavy ion irradiation. It is also interesting that except for HRF in S0 plants, the depth-biological effect curves for each biological endpoint were similar for 5Gy and 30Gy of carbon irradiation.

Local infection with oilseed rape mosaic virus promotes genetic rearrangements in systemic Arabidopsis tissue

We have previously shown that local infection of tobacco plants with tobacco mosaic virus (TMV) or oilseed rape mosaic virus (ORMV) results in a systemic increase in the homologous recombination frequency (HRF). Here, we analyzed what other changes in the genome are triggered by pathogen infection. For the analysis of HRF, mutation frequency (MF) and microsatellite instability (MI), we used three different transgenic Arabidopsis lines carrying β-glucuronidase (GUS)-based substrates in their genome. We found that local infection of Arabidopsis with ORMV resulted in an increase of all three frequencies, albeit to differing degrees. The most prominent increase was observed in microsatellite instability. The increase in HRF was the lowest, although still statistically significant. The analysis of methylation of the 35S promoter and transgene expression showed that the greater instability of the transgene was not attributed to these changes. Strand breaks brought about a significant increase in non-treated tissues of infected plants. The expression of genes associated with various repair processes, such as KU70, RAD51, MSH2, DNA POL α and DNA POL δ, was also increased. To summarize, our data demonstrate that local ORMV infection destabilizes the genome in systemic tissues of Arabidopsis plants in various ways resulting in large rearrangements, point mutations and microsatellite instability.

Evaluation of 2,4-D and Dicamba genotoxicity in bean seedlings using comet and RAPD assays

The present study was undertaken to evaluate genotoxic potential of two auxinic herbicides [2,4-dicholorophenoxy acetic acid (2,4-D) and 3,6-dichloro-2-methoxybenzoic acid (Dicamba)] in the roots of common bean (Phaseolus vulgaris L.) seedlings. Two-day-old etiolated seedlings were treated with 10 ppm methyl methanesulfonate (MMS, positive control) or 0.1, 0.2, or 0.3 ppm of either 2,4-D or Dicamba. At the end of a 96 h growth period, root growth, total soluble protein content, DNA damage in individual cells (comet assay scores) and randomly amplified polymorphic DNA (RAPD) profiles were used as endpoints of genotoxicity. 2,4-D and Dicamba were clearly dose-dependent root growth inhibitors. Total soluble protein content was significantly decreased in the positive control and at high concentrations (0.2 and 0.3 ppm) of Dicamba. Soluble protein content increased significantly only at 0.3 ppm 2,4-D (P<0.05). In the comet assay, DNA fragmentation increased in a dose-dependent manner. The diagnostic and phenetic analyzes of appeared and/or disappeared RAPD bands indicated that dose-dependent DNA polymorphism was induced by both herbicides. Genomic template stability was significantly affected at all 2,4-D and Dicamba doses tested. Overall 2,4-D and Dicamba have similar effects on DNA damage detected by comet and RAPD assays.

Genotoxicity/mutagenicity of formaldehyde revealed by the Arabidopsis thaliana plants transgenic for homologous recombination substrates

Formaldehyde (FA) is a major industrial chemical and has been extensively used in the manufacture of synthetic resins and chemicals. The use of FA-containing industrial materials in daily life exposes human to FA extensively. Numerous studies indicate that FA is genotoxic, and can induce various genotoxic effects in vitro and in vivo. The primary DNA lesions induced by FA are DNA-protein crosslinks (DPCs). Recently, it has been reported that the homologous recombination (HR) mechanism is involved in the repair of DPCs, suggesting the homologous recombination could be a potential indicator for the genotoxicity/mutagenicity of FA. However, it has not yet been reported that organisms harboring recombination substrates are used for the detection of genotoxic/mutagenic effects of FA. In this present study, an Arabidopsis thaliana-line transgenic for GUS recombination substrates was used to study the genotoxicity/mutagenicity of FA, and the results showed that FA-exposure significantly increased the induction of HR in growing plants, but not in dormant seeds. We also observed an early up-regulation of expression of HR-related gene, AtRAD54, after FA-exposure. Moreover, the pretreatment with glutathione (GSH) suppressed drastically the induction of HR by FA-exposure.

Dicamba-induced genotoxicity in Chinese hamster ovary (CHO) cells is prevented by vitamin E

In the present study the cytogenetic and genotoxic effect of benzoic herbicide dicamba and its Argentinean commercial formulation banvel (57.71% dicamba) was evaluated and whether this effect is mediated through oxidative damage or not. The protective role of vitamin E was also studied. Sister chromatid exchange (SCE) frequency, cell-cycle progression, and cell viability analyses in CHO cells were used as in vitro end-points. Treatments with the test compounds were performed either during 24h (Protocol A) or 12h (Protocol B) before harvesting. Protocol A showed that vitamin E decreased pesticide SCE induction, corrected the cell-cycle delay and partially protected cell-death only in 500 microg/ml dicamba-treated cultures. A similar trend was found in banvel-treated cultures. Protocol B revealed similar protective role of vitamin E only for dicamba-induced geno- and cytotoxicity. Based on these observations it could be suggested that dicamba injures DNA by delivering reactive oxygen species rather than by another type of mechanism/s. Although banvel mimics the effect observed by dicamba, its formulation contains other xenobiotic/s agents able to induce cellular and DNA damage by a different mechanism/s. Further investigations are needed to acquire a comprehensive knowledge of the possible mechanism/s through dicamba and banvel exert their toxic effects.

Transgenic Plants as Sensors of Environmental Pollution Genotoxicity

Rapid technological development is inevitably associated with manyenvironmental problems which primarily include pollution of soil, water and air. In manycases, the presence of contamination is difficult to assess. It is even more difficult toevaluate its potential danger to the environment and humans. Despite the existence ofseveral whole organism-based and cell-based models of sensing pollution and evaluationof toxicity and mutagenicity, there is no ideal system that allows one to make a quick andcheap assessment. In this respect, transgenic organisms that can be intentionally altered tobe more sensitive to particular pollutants are especially promising. Transgenic plantsrepresent an ideal system, since they can be grown at the site of pollution or potentiallydangerous sites. Plants are ethically more acceptable and esthetically more appealing thananimals as sensors of environmental pollution. In this review, we will discuss varioustransgenic plant-based models that have been successfully used for biomonitoringgenotoxic pollutants. We will also discuss the benefits and potential drawbacks of thesesystems and describe some novel ideas for the future generation of efficient transgenicphytosensors.

Herbicide-induced anthocyanin accumulation in transgenic rice by expression of rice OSB2 under the control of rice CYP72A21 promoter

CYP72A21, a rice cytochrome P450 gene, is induced by chloroacetamide herbicides. OSB2, a rice myc-type transcription factor, induces anthocyanin accumulation in rice leaves. To produce plants for biomonitoring by color change, we combined the CYP72A21 promoter and the OSB2 gene and introduced them into the rice isogenic line Taichung-65 CB A (T65), which contains loci CB and A from the rice cultivar Murasakiine. Leaves of the transgenic plants turned red upon treatment with the chloroacetamide herbicides acetochlor, alachlor, and metolachlor. Seedling shoots reddened upon treatment with alachlor or metolachlor at 10 microM, a concentration slightly higher than that used in the field. Anthocyanin content was increased approximately 200% by the treatment. The color changes were consistent with increased shoot expression of OSB2 and the anthocyanidin synthase gene (ANS). This system promises easy detection of rice plant gene expression. Transgenic plants could be used in the future to biomonitor accumulated herbicides.

The chlorophenoxy herbicide dicamba and its commercial formulation banvel® induce genotoxicity and cytotoxicity in Chinese hamster ovary (CHO) cells

The sister chromatid exchange (SCE) frequency, the cell-cycle progression analysis, and the single cell gel electrophoresis technique (SCGE, comet assay) were employed as genetic end-points to investigate the geno- and citotoxicity exerted by dicamba and one of its commercial formulation banvel (dicamba 57.71%) on Chinese hamster ovary (CHO) cells. Log-phase cells were treated with 1.0-500.0 microg/ml of the herbicides and harvested 24 h later for SCE and cell-cycle progression analyses. All concentrations assessed of both test compounds induced higher SCE frequencies over control values. SCEs increased in a non-dose-dependent manner neither for the pure compound (r=0.48; P>0.05) nor for the commercial formulation (r=0.58, P>0.05). For the 200.0 microg/ml and 500.0 microg/ml dicamba doses and the 500.0 microg/ml banvel dose, a significant delay in the cell-cycle progression was found. A regression test showed that the proliferation rate index decreased as a function of either the concentration of dicamba (r=-0.98, P<0.05) or banvel (r=-0.88, P<0.01) titrated into cultures in the 1.0-500.0 microg/ml dose-range. SCGE performed on CHO cells after a 90 min pulse-treatment of dicamba and banvel within a 50.0-500.0 microg/ml dose-range revealed a clear increase in dicamba-induced DNA damage as an enhancement of the proportion of slightly damaged and damaged cells for all concentrations used (P<0.01); concomitantly, a decrease of undamaged cells was found over control values (P<0.01). In banvel-treated cells, a similar overall result was registered. Dicamba induced a significant increase both in comet length and width over control values (P<0.01) regardless of its concentration whereas banvel induced the same effect only within 100.0-500.0 microg/ml dose range (P<0.01). As detected by three highly sensitive bioassays, the present results clearly showed the capability of dicamba and banvel to induce DNA and cellular damage on CHO cells.

Genetic variations in rice in vitro cultures at the EPSPs-RPS20 region

In vitro cultures of plant cells have often been utilized to generate genetic variations, which are designated somaclonal variations. Little is known about the major genetic alterations in the cultured cells and the nature of these genetic changes. Here, we examined different lines of rice Oc cells that have been cultured for more than 20 years on agar media or in liquid media. We surveyed 35 clones obtained from PCR amplification of the 3-kb EPSPs-RPS20 region. The sequence divergence among the Oc cells was even greater than that between Japonica and Indica rice cultivars. The divergent sequences appeared to be maintained as multiple copies in a single cell. Surprisingly, the nucleotide substitutions in the Oc cells were characterized by an extremely high frequency of transition mutations of A/T-to-G/C, a feature which is similar to that of the mutations caused by chemical mutagens such as 5-bromouracil and 2-aminopurine. Although no replacements in the exons of this region were observed among the AA-genome Oryza species, our results revealed that the nucleotide substitutions of the cultured cell lines occurred more frequently at replacement sites in the exons than at synonymous sites. These distinct mutation biases found in rice in vitro cultures might contribute importantly to somaclonal variations.

Genotoxicity analysis of the phenoxy herbicide dicamba in mammalian cells in vitro

The cytogenetic effects exerted by the phenoxy herbicide dicamba and one of its commercial formulations banvel (57.71% dicamba) were studied in in vitro whole blood human lymphocyte cultures. The genotoxicity of herbicides was measured by analysis of the frequency of sister chromatid exchanges (SCEs) and cell-cycle progression assays. Both dicamba and banvel activities were tested within 10.0-500.0 microg/ml doses range. Only concentrations of 200.0 microg/ml of dicamba and 500.0 microg/ml of banvel induced a significant increase in SCE frequency over control values. The highest dose of dicamba tested (500.0 microg/ml) resulted in cell culture cytotoxicity. The cell-cycle kinetics was affected by both test compounds since a significant delay in cell-cycle progression and a significant reduction of the proliferative rate index were observed after the treatment with 100.0 and 200.0 microg/ml of dicamba and 200.0 and 500.0 microg/ml of banvel. For both chemicals, a progressive dose-related inhibition of the mitotic activity of cultures was observed. Moreover, only the mitotic activity statistically differed from control values when doses of both chemicals higher than 100.0 microg/ml were employed. On the basis of our results, the herbicide dicamba is a DNA damage agent and should be considered as a potentially hazardous compound to humans.

Early infection of scutellum tissue with Agrobacterium allows high-speed transformation of rice

Several approaches have recently been adopted to improve Agrobacterium-mediated transformation of rice, both to generate the large number of T-DNA insertion plants needed for functional analysis of the rice genome, and for production of rice with additional agronomical value. However, about 3 months of in vitro culture is still required for isolation of transgenic rice plants. Here, we report the competency of scutellum tissue from 1-day pre-cultured seeds for Agrobacterium-mediated transformation. Furthermore, early infection of rice seeds with Agrobacterium enhanced efficient selection of transformed calli. Using our system, we successfully regenerated transgenic rice plantlets within a month of the start of the aseptic culture of mature seeds. Our new system should reduce the somaclonal variation accompanying prolonged culture of rice cells in the dedifferentiated state and facilitate the molecular breeding of rice.

Evaluation of the alkaline Comet assay conducted with the wetlands plant Bacopa monnieri L. as a model for ecogenotoxicity assessment

Wetlands play a key role in maintaining environmental quality, and wetlands plants could serve as model organisms for determining the genotoxic effects of pollutants contaminating these areas. In the present study, DNA damage was evaluated in a wetlands plant, Bacopa monnieri L., as a potential tool for the assessment of ecogenotoxicity. The Comet assay was used for detecting DNA damage in B. monnieri exposed to two model mutagens, ethyl methanesulfonate (EMS) and methyl methanesulfonate (MMS). Significant (P < 0.05) dose-dependent increases in DNA damage were observed following treatments conducted by exposing both isolated nuclei (acellular or in vitro exposure) and whole plants (in vivo exposure) to 0.01-5 mM EMS and 0.05-100 microM MMS for 2 hr at (26 +/- 2) degrees C. The assay was then used to evaluate the genotoxic potential of cadmium (Cd), a wetlands contaminant. In vitro exposure of nuclei from untreated leaves to 0.001-200 microM Cd for 2 hr resulted in significant (P < 0.05) levels of DNA damage. Cd concentrations >or=0.01 microM induced DNA damage as evidenced by increases in the Olive tail moment. In vivo exposure of plants to 0.01-500 microM Cd for 2, 4, and 18 hr resulted in dose- and time-dependent increases in DNA damage in the nuclei isolated from roots and leaves. Cd-induced DNA damage was greater in roots than leaves. To our knowledge, this is the first report describing the use of a wetlands plant for genotoxicity assessment, using the Comet assay.

Separation and determination of 2,4-D, dicamba and 2,4,5-T in tobacco by nonaqueous capillary electrophoresis

A practical method for residue analysis of 2,4-D, dicamba and 2,4,5-T in baked tobacco leaves has been developed using nonaqueous CE (NACE). The herbicide residues of 2,4-D, dicamba and 2,4,5-T in tobaccos were extracted by ultrasonication with ethyl acetate, followed by a cleanup procedure with gel permeation chromatography. The separation of 2,4-D, dicamba and 2,4,5-T by NACE was optimized based on orthogonal experiment design with four factors at three levels. The optimal NACE condition was established with the running buffer of 40.0 mmol/L ammonium acetate in 90% CH3CN (apparent pH 10.2), and the applied voltage of -25 kV over a capillary of 50 microm id x 46 cm (37.5 cm to the detector window), which gave a baseline separation of 2,4-D, dicamba and 2,4,5-T within 15 min. The LOD were ca. 0.4-0.6 microg/mL for the three herbicides, whereas the overall recovery ranged from 80.8 to 84.1%. The proposed method has been successfully applied to measure 300 real tobacco samples, and the residue profiles of the three herbicides in tobacco samples were obtained and evaluated.

Cytogenetic effects of combined radioactive (137Cs) and chemical (Cd, Pb, and 2,4-D herbicide) contamination on spring barley intercalar meristem cells

The frequency of cytogenetic effects in spring barley intercalar meristem cells was studied in the presence of a range of different stressors. There was a non-linear dependence on the concentrations of 137Cs, Cd, Pb, and dichlorophenoxyacetic acid (2,4-D) herbicide contamination in the exposure ranges used. The frequency of cytogenetic effects increased at the lower concentrations of the pollutants more rapidly than at the higher concentrations. Contamination of the soil by lead at a concentration that meets the current standards for permissible content in soil, and by 2,4-D herbicide at the application levels recommended for agricultural use resulted in a significant increase in aberrant cell frequency. In these cases, the extent of the observed cytogenetic effects was comparable with the effect induced by a 137Cs soil contamination of 49.2 kBq/kg, a level that exceeds by 10-fold the maximum level permitted in radionuclide-contaminated areas where people are resident. In most cases, the experimentally observed combined effects of the pollutants studied differed from those expected from an additive hypothesis. When combined with 137Cs contamination, antagonistic effects became increasingly stronger when the second stressor was changed from cadmium to lead, and then to the herbicide, as measured both by tests of the 'frequency of aberrant cells' and the 'aberrations per cell'. Data from this study and previous reported literature suggest that synergistic increases in cytogenetic effects can be induced by the simultaneous influence of several stressors even at low intensities. This indicates that there is a capability for mutual intensification of the effects of environmental factors that actually occur in situations of low-level exposure.

Luciferase-based transgenic recombination assay is more sensitive than beta-glucoronidase-based

Study of the DNA repair and genome stability in plants is directly dependent on the availability of an easy, inexpensive, and reliable assay. Marker gene-based homologous recombination (HR) assays were introduced more than a decade ago and have been intensively used ever since. Here, we compared several transgenic Arabidopsis and tobacco lines that carried in their genome the luciferase (LUC) or the beta-glucoronidase (uidA or GUS) substrates for HR. The average recombination frequency detected with the luciferase transgene was nearly 9.0-fold higher in Arabidopsis and 12.4-fold higher in tobacco plants. Importantly, both transgenes were under the control of 35S promoter and had similar expression levels throughout the plants. Irradiation with UVC increased the HR frequency similarly in both transgenes. The actual difference in the frequency of HR in Arabidopsis and tobacco possibly results from differing sensitivity to detection of transgene activity. Thus, we could suggest that luciferase recombination assay, due to its higher sensitivity, should be the assay of choice when plant genome stability is studied.