Multiple biomarkers response in maize (Zea mays L.) during exposure to copper

Improving plant-based genotoxicity bioassay through AFLP technique for trace metal-contaminated water: insights from Myriophyllum aquaticum (Vell.) Verdc. and Cd

In this work, we evaluated whether the species Myriophyllum aquaticum (Vell.) Verdc. can be a promising material for devising reliable eco-toxicological tests for Cd-contaminated waters. Plants of M. aquaticum were exposed to Cd, using different concentrations (1 mg L-1, 2.5 mg L-1, 5 mg L-1, and 10 mg L-1; experiment 1) and exposure times (2.5 mg L-1 for 3 days, 7 days, 14 days, and 21 days; experiment 2). Plant growth and Cd accumulation were monitored during the treatment period, and Cd genotoxicity was assessed by analyzing Cd-induced changes in the AFLP fingerprinting profiles using famEcoRI(TAC)/MseI(ATG) and hexEcoRI(ACG)/MseI(ATG) pairs of primers. Root and shoot growth was reduced already at the lowest Cd concentration used (about 20% reduction for roots and 60% for shoots at 1 mg L-1; experiment 1) and after 7 days (about 50% reduction for roots and 70% for shoots; experiment 2). The primer combinations produced 154 and 191 polymorphic loci for experiments 1 and 2, respectively. Mean genetic diversity (He) reduction among the treatment groups was observed starting from 2.5 mg L-1 (He 0.211 treated vs 0.236 control; experiment 1) and after 3 days (He 0.169 treated vs 0.261 control; experiment 2), indicating that results obtained from AFLP profiles did not match with plant growth measurements. Therefore, our results showed that M. aquaticum proved to be a suitable model system for the investigation of Cd genotoxicity through AFLP fingerprinting profile, whereas the more classic eco-toxicological tests based only on biometric parameters could not correctly estimate the risk associated with undetected Cd genotoxicity.

Morphological and functional responses of a metal-tolerant sunflower mutant line to a copper-contaminated soil series

The potential use of a metal-tolerant sunflower mutant line for biomonitoring Cu phytoavailability, Cu-induced soil phytotoxicity, and Cu phytoextraction was assessed on a Cu-contaminated soil series (13-1020 mg Cu kg^-1) obtained by fading a sandy topsoil from a wood preservation site with a similar uncontaminated soil. Morphological and functional plant responses as well as shoot, leaf, and root ionomes were measured after a 1-month pot experiment. Hypocotyl length, shoot and root dry weight (DW) yields, and leaf area gradually decreased as soil Cu exposure rose. Their dose-response curves (DRC) plotted against indicators of Cu exposure were generally well fitted by sigmoidal curves. The half-maximal effective concentration (EC₅₀) of morphological parameters ranged between 203 and 333 mg Cu kg^-1 soil, corresponding to 290-430 μg Cu L^-1 in the soil pore water, and 20 ± 5 mg Cu kg^-1 DW in the shoots. The EC₁₀ for shoot Cu concentration (13-15 mg Cu kg^-1 DW) coincided to 166 mg Cu kg^-1 soil. Total chlorophyll content and total antioxidant capacity (TAC) were early biomarkers (EC₁₀: 23 and 51 mg Cu kg^-1 soil). Their DRC displayed a biphasic response. Photosynthetic pigment contents, e.g., carotenoids, correlated with TAC. Ionome was changed in Cu-stressed roots, shoots, and leaves. Shoot Cu removal peaked roughly at 280 μg Cu L^-1 in the soil pore water.

Malathion and dithane induce DNA damage in Vicia faba

The increasing use of pesticides such as malathion and dithane in agriculture causes environmental mutagenicity. However, their genotoxicity in edible crops is seldom assessed. In this study, the genotoxic potential of malathion and dithane was evaluated in the roots of Vicia faba L. All three concentrations (0.05, 0.1, and 0.2%) of malathion and dithane tested resulted in a significant decrease in root length and inhibited seed germination. Cytological observations showed that the mitotic frequency in the root meristematic cells decreased parallel to the increase in concentrations, and the increase in chromosome aberrations and micronuclei frequency was concentration dependent. Alkaline comet assay revealed significant onset of DNA damage at all tested concentrations. For the randomly amplified polymorphic (RAPD)-polymerase chain reaction (PCR) analyses, 10 random RAPD primers were found to produce 116 unique polymorphic RAPD band fragments of 223–3139 bp. Each primer generated 3–15 RAPD bands on an average. The percentage of polymorphic DNA fragments was higher in malathion-exposed plants than dithane ones. The changes in RAPD profiles included disappearance and/or appearance of DNA bands in malathion and dithane treatment. Hence, DNA damage observed by the cytogenetic endpoints and comet assay corroborated with RAPD-PCR analysis. A total of 15 new protein bands of molecular weight ranging 11.894–226.669 kDa were observed in roots of Vicia plants that were exposed to the pesticides. The number of new protein bands was higher in malathion-treated DNA samples than in dithane-treated ones. Based on the results, we conclude that the pesticides can alter genomic template stability and change protein profiles. Malathion was more genotoxic than dithane. Therefore, RAPD assays can be useful in determining genotoxicity of pesticides in V. faba and other crops along with other quantitative parameters.

Determination of genotoxic effects of boron and zinc on Zea mays using protein and random amplification of polymorphic DNA analyses

In this research, we aimed to determine genotoxic effects of boron (B) and zinc (Zn) on Zea mays by using total soluble protein content and random amplification of polymorphic DNA (RAPD) analyses. For the RAPD analysis, 16 RAPD primers were found to produce unique polymorphic band profiles on treated maize seedlings. With increased Zn and B concentrations, increased polymorphism rate was observed, while genomic template stability and total soluble protein content decreased. The treatment with Zn was more effective than that of B groups on the levels of total proteins. The obtained results from this study revealed that the total soluble protein levels and RAPD profiles were performed as endpoints of genotoxicity and these analyses can offer useful biomarker assays for the evaluation of genotoxic effects on Zn and B polluted plants.

Zebrafish genome instability after exposure to model genotoxicants

Sublethal exposure to environmental genotoxicants may impact genome integrity in affected organisms. It is therefore necessary to develop tools to measure the extent and longevity of genotoxicant-induced DNA damage, and choose appropriate model organisms for biomonitoring. To this end, markers of DNA damage were measured in zebrafish larvae and adults following exposure to model genotoxicants (benzo[a]pyrene and ethyl methanesulfonate). Specifically, we assessed primary DNA damage and the existence of potentially persistent genomic alterations through application of the comet assay, quantitative random amplified polymorphic DNA (qRAPD) and amplified fragment length polymorphism (AFLP) assays. Furthermore, expression of genes involved in DNA repair, oxidative stress response and xenobiotic metabolism was evaluated as well. Additionally, the AFLP method was applied to adult specimens 1 year after larval exposure to the genotoxicants to evaluate the longevity of the observed DNA alterations. Large numbers of DNA alterations were detected in larval DNA using the comet assay, qRAPD and AFLP, demonstrating that zebrafish larvae are a sensitive model for revealing genotoxic effects. Furthermore, some of these genomic alterations persisted into adulthood, indicating the formation of stable genomic modifications. qRAPD and AFLP methods proved to be highly sensitive to genotoxic effects, even in cases when the comet assay indicated a lack of significant damage. These results thus support the use of zebrafish larvae as a sensitive model for monitoring the impact of genotoxic insult and give evidence of the longevity of genomic modifications induced by genotoxic agents.

Evaluation of arsenic trioxide genotoxicity in wheat seedlings using oxidative system and RAPD assays

Arsenic is a metalloid that is toxic to living organisms. It is known that high concentration of arsenic causes toxic damage to cells and tissues of plants. While the toxic effect of arsenic is known, limited efforts have been made to study its genotoxic effect on the crops. In the present study, effects of arsenic trioxide (As2O3) on seed germination, root length, reactive oxygen species (ROS), lipid peroxidation (malondialdehyde (MDA)), and activities of antioxidant enzymes, as well as DNA in wheat seedlings were investigated. Seedlings were exposed to different (10 to 40 mg/L) As2O3 concentrations for 7 days. Seed germination and root elongation decreased with increase of As2O3 concentration. The values of hydrogen peroxide (H2O2), superoxide anion (O2 (·-)), and MDA contents significantly increased by As2O3 concentrations. The highest values for H2O2, O2 (·-), and MDA were obtained in 40 mg/L treated wheat seedling. A significant increase of peroxidase (POX) and catalase (CAT) activity in seedlings were observed with increased concentration of As2O3, then decreased when reaching a value of 40 mg/L, whereas the activities of superoxide dismutase (SOD) were gradually enhanced with increasing As2O3 concentration. Alterations of DNA in wheat seedlings were detected using randomly amplified polymorphic DNA (RAPD) technique. The changes occurring in RAPD profiles of seedlings following As2O3 treatment included loss of normal bands and appearance of new bands in comparison to that of control seedlings. The results of our study showed that As2O3 induced DNA damage in a dose-dependent meaner, and the root cells of wheat studied showed a defense against As2O3-induced oxidative stress by enhancing their antioxidant activities.

Physiological and genetic effects of chromium (+VI) on toxitolerant lichen species, Pyxine cocoes

Chromium is a highly toxic non-essential metal, which causes a variety of metabolic activities in plants. Pyxine cocoes a well known toxitolerant lichen species was considered to evaluate the possible physiological, biochemical, and genetic changes that occur due to chromium Cr (+VI) stress. The physiological (chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, protein, and Fv/Fm) and genetic (ISSR-PCR and ITS) parameters were used to estimate the changes in P. cocoes. Different concentrations of Cr (+VI) (0, 10, 25, 50, 75, and 100 μM) for 10, 20, 30, and 45 days were employed on transplanted lichen species. The results revealed that the exposure of Cr (+VI) for 10, 20, 30, and 45 days under controlled conditions caused a significant decline in physiological processes with increasing metal stress. Amino acid profile at different concentrations on the 45th day too indicated prevailing stress condition as proline content significantly increased at 100 μM concentration. Inter-simple sequence repeat (ISSR) and internal transcribed spacer (ITS) techniques were used to evaluate the genotoxicity induced by chromium stress. ISSR profiles showed a consistent increase in appearance and disappearance of bands with increasing concentration of the chromium. ISSR technique, therefore, is more sensitive and reproducible to study polymorphism induced by environmental stress. The present study revealed that the physiological and genetic changes induced by the Cr (+VI) can be used as a tool to study environmental stress and polymorphisms due to genotoxicity. To the best of our knowledge, application of ISSR-PCR and ITS sequences in toxitolerant species (P. cocoes) appears to be the maiden attempt to evaluate the genotoxicity.

Determination of genotoxic effects of fipronil in Vicia faba using random amplified polymorphic DNA analysis

This study was undertaken to appreciate genotoxic potential of fipronil herbicides in the roots of Vicia faba seedlings. Fipronil was clearly dose dependent on root growth inhibitors, total soluble protein, and random amplified polymorphic DNA (RAPD) assays. Increase in concentration of fipronil resulted in decreased amount of root length and increased level of protein. For the RAPD analyses, 15 RAPD primers were found to produce unique polymorphic band patterns and were subsequently used to produce a total of 110 bands of 45–1250 bp. Each primer generated 4–11 RAPD bands across 15 primers. The changes occurring in RAPD profiles following fipronil treatment included variation becoming evident as disappearance and/or appearance of DNA bands compared with the normal seedlings. These results indicated that genomic template stability was significantly affected at the above fipronil concentration. This study further confirmed that the RAPD assays are useful in determining potential genotoxicity of fipronil.

Comparative biochemical and RAPD analysis in two varieties of rice (Oryza sativa) under arsenic stress by using various biomarkers

Multiple biomarker systems have been frequently used to measure the genotoxic effects of environmental pollutants (including heavy metals) on living organisms. In this study, we used leaves of hydroponically grown 14 days old seedlings of rice (Oryza sativa) varieties (PB1 and IR64) treated with 50, 150 and 300 μM arsenite (As(III)) for 24 and 96 h duration. Reduction in seed germination, root-shoot length, chlorophyll and protein were observed with increasing As(III) concentration and duration in both varieties, being more in IR64. Increase/decrease of antioxidant enzymes and stress related parameters showed much changes at higher concentration for 24 and 96 h duration in both varieties. Eleven primers were found in RAPD analysis to produce polymorphic band pattern and produced a total of 51 (control), 79 (treated) and 42 (control) and 29 (treated) bands in PB1 and IR64 varieties, respectively. These results indicated that genomic template stability (GTS, changes in RAPD profile) was significantly affected at all tested As(III) concentration, when compared with other parameters. Differential response was observed in both varieties with PB1 being more tolerant. We concluded that DNA polymorphism detected by RAPD analysis in conjunction with other biochemical parameters could be a powerful eco-toxicological tool in bio-monitoring arsenic pollution.

Assessment of air pollution genotoxicity by RAPD in Evernia prunastri L. Ach. from around iron-steel factory in Karabük, Turkey

Lichens are widely used in biomonitoring studies of air pollution, either as bioindicators of air quality or as bioaccumulators of atmospheric deposition. Over the past decade, several molecular techniques have been developed to provide information on diversity, genotoxicology, genetic relationships, etc. The heavy metal contents of Evernia prunastri samples were determined by atomic absorption spectrometry. The Random Amplified Polymorphic DNA Polymerase Chain Reaction (RAPD-PCR) method was used to describe the pattern of DNA band variation in the samples influenced by the environmental pollution. The study was designed to describe the level of pollution in an area contaminated with smoke and waste from an iron-steel factory, and to reveal the level of potential genotoxic agents around this source of pollution. The study also examined the suitability of the lichen samples for the detection of genotoxicity.

Biomarkers in aquatic plants: selection and utility

This review emphasizes the predictive ability, sensitivity and specificity of aquatic plant biomarkers as biomonitoring agents of exposure and effect. Biomarkers of exposure are those that provide functional measures of exposure that are characterized at a sub-organism level. Biomarkers of effect require causal linkages between the biomarker and effects, measured at higher levels of biological organization. With the exception of pathway specific metabolites, the biomarkers assessed in this review show variable sensitivity and predictive ability that is often confounded by variations in growth conditions, rendering them unsuitable as stand alone indicators of environmental stress. The use of gene expression for detecting pollution has been, and remains immature; this immaturity derives from inadequate knowledge on predictive ability, sensitivity and specificity. Moreover, the ability to the detect mode of action of unknown toxicants using gene expression is not as clear-cut as initially hypothesized. The principal patterns in gene expression is not as clear-cut as initially hypothesized. The principal patterns in gene expression are generally derived from stress induced genes, rather than on ones that respond to substances with known modes of action (Baerson et al. 2005). Future developments in multivariate statistics and chemometric methods that enhance pattern analyses in ways that could produce a "fingerprint", may improve methods for discovering modes of action of unknown toxicants. Pathway specific metabolites are unambiguous, sensitive, correlate well to growth effects, and are relatively unaffected by growth conditions. These traits make them excellent biomarkers under both field and laboratory conditions. Changes in metabolites precede visible growth effects; therefore, measuring changes in metabolite concentrations (Harring et al. 1998; Shaner et al. 2005). The metabolic phase I enzymes (primarily associated with P-450 activity) are non-specific biomarkers, and few studies relate them to growth parameters. P-450 activity both increases and decreases in response to chemical stress, often confounding interpretation of experimental results. Alternatively, phase II metabolic enzymes (e.g., glutathione S-transferases; GST's) appear to be sensitive biomarkers of exposure, and potentially effect. Some GST's are affected by growth factors, but others may only be induced by xenobiotics. Measuring xenobiotic-induced GST's, or their gene expression patterns, are good candidates for future biomarkers of the cumulative load of chemical stress, both in the laboratory and under field conditions. Phytochelatins respond to some but not all metal ions, and may therefore be used as biomarkers of exposure to identify the presence and bioavailability of ions to which they respond. However, more data on their specificity to, and interactions with growth factors, in more species are needed. The flavenoids are only represented by one heavy metal exposure study; therefore their use as biomarkers is currently difficult to judge. Stress proteins tend to be specific for toxicants that affect protein function. Growth factors are known to affect the level of stress proteins; hence, the use of stress proteins as biomarkers will be confined to experiments performed under controlled growth conditions, where they can be excellent indicators of proteotoxicity. Reactive oxygen species (ROS), ROS scavenging enzymes, changes in pigment content, photosynthesis and chlorophyll fluorescence are all affected by growth factors, particularly light and nutrient availability. Therefore, these biomarkers are best suited to investigate the mode of action of toxicants under controlled growth conditions. These biomarkers are sensitive to xenobiotic stressors that affect various processes in the photosynthetic apparatus, and can be used to diagnose which photosynthetic process or processes are primarily affected. Chlorophyll fluorescence is a non-destructive measure, and is thereby well suited for repeated measures of effect and recovery (Abbaspoor and Streibig 2005; Abbaspoor et al. 2006; Cedergreen et al. 2004). Bi-phasic responses (over time and with dose) are probably major sources of variation in sensitivity for many biomarkers. Metabolic enzymes, stress proteins, ROS and their corresponding scavenging enzymes increase in a time-frame and at doses in which plant cell damage is still repairable. However, when toxicity progresses to the point of cell damage, the concentration/activity of the biomarker either stabilizes or decreases. Examples of this response pattern are given in Lei et al. (2006); Pflugmacher et al. (2000b); Teisseire et al. (1998); and Teisseire and Guy (2000). Gene expression is also a time-dependent phenomenon varying several fold within a few hour. Therefore, bi-phasic response patterns make timing and dose-range, within which the biomarkers can be used as measures of both exposure and effect, extremely important. As a result, most biomarkers are best suited for situations in which the time and dose dependence of the biomarker, in the investigated species, are established. Notwithstanding the previously mentioned limitations, all assessed biomarkers provide valuable information on the physiological effects of specific stressors, and are valuable tools in the search for understanding xenobiotic modes of action. However, the future use of aquatic plant biomarkers will probably be confined to laboratory studies designed to assess toxicant modes of action, until further knowledge is gained regarding the time, dose and growth-factor dependence of biomarkers, in different species. No single biomarker is viable in gaining a comprehensive understanding of xenobiotic stress. Only through the concomitant measurement of a suite of appropriate biomarkers will our diagnostic capacity be enhanced and the field of ecotoxicology, as it relates to aquatic plants, advanced.