Atrazine Tolerance Research Articles

Screening of Atrazine Tolerant Aquatic Plant and Roles of Plant Growth Regulators on Plant Growth and Atrazine Tolerance

The extensive use of atrazine to control weeds in agricultural areas has contaminated atrazine in surface water and groundwater. Atrazine contamination in water resources causes human health concerns. Thus, this study investigated the possible use of aquatic plants for removing atrazine from contaminated water. The experiment was performed under plant nursery conditions and divided into two parts: (1) the atrazine-tolerant plants were screened, and (2) the most atrazine-tolerant plant was used for atrazine phytoremediation stimulated by plant growth regulators. The results showed that atrazine was toxic to all aquatic plants, as the dry weight of the plants was significantly decreased when exposed to 20 mg/L of atrazine (P<0.05). Based on five aquatic plants grown under 2.5–20 mg/L atrazine-contaminated water, <i>Azolla microphylla</i> Kaulf. was the most tolerant aquatic plant and was more suitable for use in atrazine phytoremediation than the other aquatic plants (<i>Ceratophyllum demersum</i> L., <i>Eichhornia crassipes</i> (Mart.) Solms, <i>Hydrilla verticillata</i> (L. f.) Royle, and <i>Salvinia cucullata</i> Roxb. ex Bory). The total chlorophyll, carotenoid, and proline contents in the biomass of <i>A. microphylla</i> cultured in 2.5–20 mg/L of atrazine did not significantly differ between the atrazine concentrations (P>0.05). Meanwhile, the proline contents in the other four aquatic plants increased with increasing atrazine concentrations, and the chlorophyll content significantly decreased with an increase in the atrazine concentration. However, <i>A. microphylla</i> could not remove atrazine from contaminated water, and the application of plant growth regulators (6-benzyladenine, gibberellic acid, indole-3-butyric acid, and salicylic acid) did not improve the atrazine removal from water. Atrazine in the water was around 21–26 mg/L on day five of <i>A. microphylla</i> cultivation compared to the initial concentration (25 mg/L). Using a plant growth regulator was ineffective for stimulating growth and atrazine removal by <i>A. microphylla</i>. Future research should explore other potential mechanisms for enhancing atrazine removal by <i>A. microphylla</i>.

Herbicide atrazine impairs metabolic plasticity of mixotrophic organisms: Evidence in photochemistry, morphology, and gene expression

Herbicide pollution is a main form of water pollution. As a result of additional harms to other non-target organisms, it threatens the function and structure of ecosystems. Previous researches mainly focused on the assessment of the toxicity and ecological effect of herbicides on monotrophic organisms. Responses of mixotrophs as an important component of functional groups are rarely understood in contaminated waters, although their metabolic plasticity and unique ecological functions in ecosystem stability are a major concern. This work aimed to investigate the trophic plasticity of mixotrophic organisms in atrazine-contaminated waters, and a primarily heterotrophic Ochromonas was used as the tested organism. Results showed that the herbicide atrazine significantly inhibited the photochemical activity and impaired the photosynthetic machine of Ochromonas, and photosynthesis activated by light was sensitive to atrazine. However, phagotrophy was unaffected by atrazine and closely correlated with growth rate, indicating that heterotrophy helped population maintenance during herbicide exposure. Mixotrophic Ochromonas upregulated the gene expression level involved in photosynthesis, energy synthesis, and antioxidation to adapt to increasing atrazine after long-term exposure. Compared with bacterivory, herbivory increased atrazine tolerance of photosynthesis under mixotrophic status. This study systematically illustrated the mechanism by which mixotrophic Ochromonas respond to the herbicide atrazine at population, photochemical activity, morphology, and gene expression levels and demonstrated the potential effect of atrazine on the metabolic flexibility and ecological niches of mixotrophs. These findings will provide important theoretical reference for governance and management decision-making in contaminated environments.

Integration of Metabolomics and Transcriptomics for Investigating the Tolerance of Foxtail Millet (Setaria italica) to Atrazine Stress

Foxtail millet (Setaria italica) is a monotypic species widely planted in China. However, residual atrazine, a commonly used maize herbicide, in soil, is a major abiotic stress to millet. Here, we investigated atrazine tolerance in millet based on the field experiments, then obtained an atrazine-resistant variety (Gongai2, GA2) and an atrazine-sensitive variety (Longgu31, LG31). To examine the effects of atrazine on genes and metabolites in millet plants, we compared the transcriptomic and metabolomic profiles between GA2 and LG31 seedling leaves. The results showed that 2,208 differentially expressed genes (DEGs; 501 upregulated, 1,707 downregulated) and 192 differentially expressed metabolites (DEMs; 82 upregulated, 110 downregulate) were identified in atrazine-treated GA2, while in atrazine-treated LG31, 1,773 DEGs (761 upregulated, 1,012 downregulated) and 215 DEMs (95 upregulated, 120 downregulated) were identified. The bioinformatics analysis of DEGs and DEMs showed that many biosynthetic metabolism pathways were significantly enriched in GA2 and LG31, such as glutathione metabolism (oxiglutatione, γ-glutamylcysteine; GSTU6, GSTU1, GSTF1), amino acid biosynthesis (L-cysteine, N-acetyl-L-glutamic acid; ArgB, GS, hisC, POX1), and phenylpropanoid biosynthesis [trans-5-o-(4-coumaroyl)shikimate; HST, C3′H]. Meanwhile, the co-expression analysis indicated that GA2 plants had enhanced atrazine tolerance owing to improved glutathione metabolism and proline biosynthesis, and the enrichment of scopoletin may help LG31 plants resist atrazine stress. Herein, we screened an atrazine-resistant millet variety and generated valuable information that may deepen our understanding of the complex molecular mechanism underlying the response to atrazine stress in millet.

Growth and degradation characteristics of an efficient and broad-spectrum atrazine-degrading strain SB5

In this study, triazine-degrading strain SB5 was isolated and screened from the activated sludge contaminated with atrazine by enrichment culture technology. Based on its morphology and 16S rRNA gene analysis, strain SB5 was initially identified as Paenarthrobacter sp. It contained the atrazine-degrading genes trzN, atzB, and atzC. The addition of glucose, sucrose, sodium citrate, yeast extract and peptone to the culture medium significantly increased the biomass and atrazine degradation efficiency of strain SB5. The addition of (NH4)2SO4 and NH4Cl inhibited the biomass of strain SB5, but did not affect its degradation efficiency for atrazine. The addition of starch did not affect the biomass of strain SB5, but significantly inhibited its degradation for atrazine. Strain SB5 showed good atrazine tolerance and atrazine degradation ability in the temperature range of 4-42 ℃, initial pH of 4-10 and initial concentration of 50-1000 mg·L-1. Using 100 mg·L-1 atrazine as the sole carbon source, the strain SB5 degraded 100% of atrazine within 36 h under the optimal conditions of 37 ℃ and initial pH 8.0. The results of degradation spectrum analysis showed that strain SB5 had a good degradation effect on the six triazine herbicides (simazine, terbuthylazine, propazine, cyanazine, ametryn and prometryn) at an initial concentration of 100 mg·L-1, and the degradation rates were 86.4%, 92%, 98.6%, 95.6%, 100% and 99.2% after 48 h of incubation, respectively. The results demonstrated that SB5 was an efficient and broad-spectrum degradation strain. The strain SB5 further enriched the strain resources for atrazine biodegradation, and its high-efficient and broad-spectrum degradation characteristics for triazine herbicides showed a potential application value in the development of bioremediation technology for the pollution of triazine herbicides.

Toxicological sensitivity of Pennisetum americanum (L.) K. Schum to atrazine exposure

ABSTRACTThe tolerance of Pennisetum americanum (L.) K Schum (P. americanum) to the herbicide atrazine, as well as the atrazine accumulation in exposed plants, was investigated in this study. The germination of P. americanum seeds was not significantly inhibited by exposure to atrazine at concentrations below 100 mg·L−1. The roots of the seedlings were much more sensitive to atrazine than the shoots were, as shown by observations that shoot and root elongation were significantly inhibited by treatment with 100 and 50 mg·kg−1 of atrazine, respectively. In addition, significant differences were found in the dry weights of the seedling shoots and roots after exposure to 50 and 20 mg·kg−1 of atrazine, respectively. Atrazine accumulated readily in the roots of exposed seedlings, and the root ultrastructure was visibly damaged by exposure to lower levels of atrazine compared to the ultrastructure of the shoot. The contents of chlorophyll a and chlorophyll b and the transcription of psbA were inhibited by exposure to atrazine at concentrations above 20 mg·kg−1. Finally, the tolerance threshold of P. americanum to atrazine was about 20 mg·kg−1, indicating that the test plant exhibited some atrazine tolerance.

The APL4 Subunit of ADP-glucose Pyrophosphorylase (Starch Synthesis) as Potential Target for Improvement of Photosynthesis and Source-sink Relationships

There is currently a major challenge to improve photosynthetic yield for increased sustainable crop production and meeting mankind's nutritional requirements. Among other factors, suboptimal carbon partitioning and suboptimal photoprotection may contribute to limitations of photosynthetic efficiency (1). Herbicide and oxidative stress tolerance can involve mechanisms that are related to photosynthesis efficiency and carbon dynamics (2-4). In this context, an Arabidopsis thaliana T-DNA insertional mutant was identified and characterized for enhanced tolerance to the singlet-oxygen-generating herbicide atrazine in comparison to wild-type (5). This enhanced atrazine tolerance mutant was affected in the promoter structure and gene expression regulation of the APL4 subunit of ADP-glucose pyrophosphorylase, a key enzyme of starch biosynthesis (6), thus resulting in decrease of APL4 mRNA levels. The impact of this regulatory mutation was confirmed by analysis of an independent T-DNA insertional mutant also affected in the APL4 gene promoter. The resulting tissue-specific modifications of carbon partitioning and the effects on plant growth and stress tolerance revealed specific and non-redundant roles of APL4, primarily in root tissues, with important consequences for carbon dynamics, shoot-root relationships and sink regulations of photosynthesis. The apl4 phenotype of increased carbohydrate accumulation, not only in roots, but also in shoots, associated with enhanced root and shoot biomass, pointed out to enhanced photosynthesis and carbon fixation. On the other hand, given the effects of exogenous sugar treatments and of endogenous sugar levels on atrazine tolerance in wild-type Arabidopsis plantlets (2,7), atrazine tolerance of this apl4 mutant could be ascribed to perception of carbon status and to investment of sugar allocation in xenobiotic and oxidative stress responses (8,9). Such relationships between carbon partitioning, carbon/nitrogen balance, shoot-root development and stress responses are likely to be important for plant breeding in the context of global change and of rising demands for food and bioenergy. The characteristics of these apl4 mutants indicate that novel regulations of root:shoot ratios remain to be characterized and that the regulatory subunits of ADP-glucose pyrophosphorylase and the mutations and polymorphisms affecting their regulation could be important targets of plant breeding for improving jointly yield potential and abiotic stress tolerance.

Identification of an Indigenous Atrazine Herbicide Tolerant Microbial Consortium in Beans (Phaseolus vulgaris L.) as a Potential Soil Bioremediator

The present article reports the isolation and identification of atrazine-tolerant strains of indigenous microorganisms recovered from three representative agricultural sites representing agronomic characteristics of the Tulancingo Valley, Central part of Mexico (disturbed and undisturbed). Biochemical and morphological tests were performed for microorganism’s identification and the minimum inhibitory concentration assay was followed to assess atrazine tolerance. Results showed the microorganism populations varied from 10-5 to 10-6 UFC g-1 of soil for bacteria and 104 - 105 conidia g-1 of soil for fungi. The bacterial genera isolated and identified were: Agrobacterium sp., Bacillus sp., Erwinia sp., Micrococcus sp., Pediococcus sp., Rhizobium sp., Serrantia sp. and Sphingomonas sp. Identified fungal genera were: Alternaria sp., Aspergillus sp., Mucor sp., Cladosporium sp., Penicillium sp., Fusarium sp. and Trichoderma sp. Tests for herbicide tolerance indicate the isolated microorganisms do not show inhibitory growth at 500 to 2,500 ppm of atrazine concentrations under laboratory conditions. The strains of the fungal genera and Rhizobium sp. showed greater tolerance rates to atrazine, based on their growth without inhibition in the presence of 5,000 to 10,000 ppm of the agrochemical. Results suggest the isolated microorganisms may be useful as a viable inoculum for bioremediation purposes in agricultural atrazine-contaminated soils.

Oxidative stress response in atrazine-degrading bacteria exposed to atrazine

Rhodobacter sphaeroides W16 and Acinetobacter lwoffii DNS32 which were isolated from soil in cold area subjected to a long-term atrazine application in Heilongjiang Province (China) can degrade atrazine efficiently. The investigation of their antioxidant properties will be useful for bioremediation and engineering applications of atrazine-degrading bacteria. Superoxide dismutase (SOD) and catalase (CAT) from two atrazine-degrading bacteria and one non-atrazine-degrading bacterium were tested for response to the oxidative stress caused by atrazine. Atrazine produced a greater inhibition of growth in Bacillus subtilis B19. The three bacteria apparently produced two activity peaks of SOD and CAT. The results demonstrated all three bacteria possessed a mechanism for atrazine tolerance that may include controlling the cellular redox balance by producing reactive oxygen species (ROS) and the subsequent scavenging of the ROS, but such response was more rapid and at lower levels in the two atrazine-degrading bacteria, suggesting less oxidative damage in these cells upon atrazine exposure. Compared to B. subtilis B19, atrazine-degrading bacteria had relatively high tolerance to atrazine stress, especially R. sphaeroides W16. Therefore, R. sphaeroides W16 and A. lwoffii DNS32 have a good application prospect of bioremediation project for soil contaminated by atrazine in cold area in Heilongjiang Province.

Carbon Dynamics, Development and Stress Responses in Arabidopsis: Involvement of the APL4 Subunit of ADP-Glucose Pyrophosphorylase (Starch Synthesis)

An Arabidopsis thaliana T-DNA insertional mutant was identified and characterized for enhanced tolerance to the singlet-oxygen-generating herbicide atrazine in comparison to wild-type. This enhanced atrazine tolerance mutant was shown to be affected in the promoter structure and in the regulation of expression of the APL4 isoform of ADP-glucose pyrophosphorylase, a key enzyme of the starch biosynthesis pathway, thus resulting in decrease of APL4 mRNA levels. The impact of this regulatory mutation was confirmed by the analysis of an independent T-DNA insertional mutant also affected in the promoter of the APL4 gene. The resulting tissue-specific modifications of carbon partitioning in plantlets and the effects on plantlet growth and stress tolerance point out to specific and non-redundant roles of APL4 in root carbon dynamics, shoot-root relationships and sink regulations of photosynthesis. Given the effects of exogenous sugar treatments and of endogenous sugar levels on atrazine tolerance in wild-type Arabidopsis plantlets, atrazine tolerance of this apl4 mutant is discussed in terms of perception of carbon status and of investment of sugar allocation in xenobiotic and oxidative stress responses.

Natural variation reveals relationships between pre-stress carbohydrate nutritional status and subsequent responses to xenobiotic and oxidative stress in Arabidopsis thaliana

Soluble sugars are involved in responses to stress, and act as signalling molecules that activate specific or hormone cross-talk transduction pathways. Thus, exogenous sucrose treatment efficiently induces tolerance to the herbicide atrazine in Arabidopsis thaliana plantlets, at least partially through large-scale modifications of expression of stress-related genes. Availability of sugars in planta for stress responses is likely to depend on complex dynamics of soluble sugar accumulation, sucrose-starch partition and organ allocation. The question of potential relationships between endogenous sugar levels and stress responses to atrazine treatment was investigated through analysis of natural genetic accessions of A. thaliana. Parallel quantitative and statistical analysis of biochemical parameters and of stress-sensitive physiological traits was carried out on a set of 11 accessions. Important natural variation was found between accessions of A. thaliana in pre-stress shoot endogenous sugar levels and responses of plantlets to subsequent atrazine stress. Moreover, consistent trends and statistically significant correlations were detected between specific endogenous sugar parameters, such as the pre-stress end of day sucrose level in shoots, and physiological markers of atrazine tolerance. These significant relationships between endogenous carbohydrate metabolism and stress response therefore point to an important integration of carbon nutritional status and induction of stress tolerance in plants. The specific correlation between pre-stress sucrose level and greater atrazine tolerance may reflect adaptive mechanisms that link sucrose accumulation, photosynthesis-related stress and sucrose induction of stress defences.

Phytoremediation potential of the novel atrazine tolerant Lolium multiflorum and studies on the mechanisms involved

Atrazine impact on human health and the environment have been extensively studied. Phytoremediation emerged as a low cost, environmental friendly biotechnological solution for atrazine pollution in soil and water. In vitro atrazine tolerance assays were performed and Lolium multiflorum was found as a novel tolerant species, able to germinate and grow in the presence of 1 mg kg −1 of the herbicide. L. multiflorum presented 20% higher atrazine removal capacity than the natural attenuation, with high initial degradation rate in microcosms. The mechanisms involved in atrazine tolerance such as mutation in psbA gene, enzymatic detoxification via P 450 or chemical hydrolysis through benzoxazinones were evaluated. It was demonstrated that atrazine tolerance is conferred by enhanced enzymatic detoxification via P 450. Due to its atrazine degradation capacity in soil and its agronomical properties, L. multiflorum is a candidate for designing phytoremediation strategies for atrazine contaminated agricultural soils, especially those involving run-off avoiding.

Involvement of the ethylene-signalling pathway in sugar-induced tolerance to the herbicide atrazine in Arabidopsis thaliana seedlings

Soluble sugars can induce tolerance to otherwise lethal concentrations of the herbicide atrazine in Arabidopsis thaliana seedlings. This sugar-induced tolerance involves modifications of gene expression which are likely to be related to sugar and xenobiotic signal transduction. Since it has been suggested that ethylene- and sugar-signalling pathways may interact, the effects of glucose (Glc) and sucrose (Suc) on seedling growth and tolerance to atrazine were analysed in etr1-1, ein2-1, ein4, and sis1/ctr1-12 ethylene-signalling mutant backgrounds, where key steps of ethylene signal transduction are affected. Both ethylene-insensitive and ethylene-constitutive types of mutants were found to be affected in sugar-induced chlorophyll accumulation and root growth and in sugar-induced tolerance to atrazine. Interactions between ethylene and sugars were thus shown to take place during enhancement of seedling growth by low-to-moderate (up to 80 mM) sugar concentrations. The strong impairment of sugar-induced atrazine tolerance in etr1-1, ein2-1, and ein4 mutants demonstrated that this tolerance required active signalling pathways and could not be ascribed to mere metabolic effects nor to mere growth enhancement. Sugar-induced atrazine tolerance thus seemed to involve activation by sugar and atrazine of hexokinase-independent sugar signalling pathways and of ethylene signalling pathways, resulting in derepression of hexokinase-mediated Glc repression and in induction of protection mechanisms against atrazine injury.

Influence of Phosphate on the Response of Periphyton to Atrazine Exposure

After indications from the literature that nutrient concentrations may modify the toxicity of herbicides to natural periphyton communities, this study aims to provide experimental proof for atrazine. In this microcosm experiment, phosphate (P) addition did not ameliorate atrazine toxicity to periphyton. Three weeks of P addition did not increase atrazine tolerance (measured as EC50 in acute toxicity tests), whereas exposure to atrazine under conditions that were either P-limited or non-P-limited clearly reduced the development of algal biomass. Long-term exposure to atrazine induced tolerance of the community to the herbicide, and this was not influenced by P addition. Tolerance induction in this microcosm experiment has been compared with previously published field data from the same area of study and indicates that tolerance induction by atrazine may take place under atrazine exposure in streams as well as in microcosms.

Atrazine Tolerance of Grass Species with Potential for Use in Vegetated Filters in Australia

The response of introduced (Pennisetum clandestinum Hochst.) and native (Stipa aristiglumis F. Muell., Themeda australis (R. Br.) Stapf, Danthonia spp. (L.) grasses to the herbicide atrazine was studied in plants with the potential for use in vegetated filters (biofilters) designed to reduce chemical loads in agricultural runoff. The response was detected by photosynthetic inhibition using leaf chlorophyll fluorescence. With continuous short-term (14 days) dosing with atrazine in sand culture, P. clandestinum showed the greatest tolerance, regardless of the dose (20–500 μg/L). In a clay vertosol soil in the glasshouse, the four species were tolerant to longer-term (84 days) application of three successive doses of simulated run-on, each dose containing 100 μg/L atrazine, a concentration which is comparable to the highest reported in runoff from agricultural land in Australia. Even with a subsequent single atrazine dose at ∼ ∼5000 μg/L, established plants of the four species showed signs of quick recovery (7–21 days) to normal photosynthetic activity. In a field experiment with simulated run-on, applied to P. clandestinum pasture in sandy loam soil, repeated doses at concentrations up to 1000 μg/L gave no significant response; only a subsequent single dose of 5000 μg/L had significant effects, from which plants soon recovered. Although damage from atrazine can be demonstrated with continuous dosing in non-adsorbing media, in soil culture the tolerance of the four selected species to repeat doses of atrazine shows they may be used confidently for biofiltering purposes. P. clandestinum was especially tolerant.

Sugar-induced tolerance to the herbicide atrazine in Arabidopsis seedlings involves activation of oxidative and xenobiotic stress responses

Exogenous sucrose confers to Arabidopsis seedlings a very high level of tolerance to the herbicide atrazine that cannot be ascribed to photoheterotrophic growth. Important differences of atrazine tolerance between sucrose and glucose treatments showed that activation of chloroplast biogenesis per se could not account for induced tolerance. Sucrose-induced acquisition of defence mechanisms was shown by the gene expression pattern of a chloroplastic iron superoxide dismutase and by enhancement of whole-cell glucose-6-phosphate dehydrogenase activity. Activation of these defence mechanisms depended on both soluble sugar and atrazine. Moreover, acquisition of sucrose protection was shown to unmask atrazine-induced gene expression, such as that of a cytosolic glutathione-S-transferase, which remained otherwise cryptic because of the lethal effects of atrazine in the absence of soluble sugars.

Induction of atrazine tolerance in a natural soil assemblage of microalgae reared in the laboratory

We investigated the occurrence of tolerance to atrazine (2-chloro-4-ethylamino-6-isopropylamino- s-triazine) in soil microalgae by means of the pollution-induced community tolerance methodology. To this end, a natural soil assemblage of microalgae, reared under laboratory conditions, was used as experimental model. Experimental cultures were exposed to 0.46, 0.93, 1.85, 2.70, and 5.40 mg atrazine/L medium for 40 days. After this chronic exposure, both untreated and atrazine-pretreated cultures were subjected to a short-term dose–effect study with atrazine using average growth rate as endpoint. Results showed that chronic exposure to atrazine induced significant changes at the community level, increasing its atrazine tolerance. In addition, atrazine-pretreated assemblages seemed to display, on average, a reduced growth rate compared with untreated assemblages in the absence of atrazine. Response to the presence of atrazine could thus be achieved with some fitness cost. This suggests that the soil microalgal productivity could be diminished after exposure to atrazine.

Sugar-induced tolerance to atrazine in Arabidopsis seedlings: interacting effects of atrazine and soluble sugars on psbA mRNA and D1 protein levels

In order to assess the potential environmental impact of atrazine on wild terrestrial plants, the physiological determinants for atrazine sensitivity were investigated in the model plant Arabidopsis thaliana. Atrazine treatment arrested development of Arabidopsis at the stage of heterotrophy–phototrophy transition, with cotyledon bleaching and seedling death. However, sucrose and, to a markedly lesser extent, glucose were found to confer to Arabidopsis seedlings a high level of tolerance to atrazine, with maintenance of chlorophylls, carotenoids, and D1 protein, and protection of photosystem II. Moreover, atrazine in the presence of sucrose was found to have a paradoxically positive effect on seedling development. The effects of different carbon substrates and the analysis of Arabidopsis sugar-response mutants showed that sucrose-induced atrazine tolerance was not due to carbon compensation of photosynthesis and probably relied on hexokinase-independent signalling pathways. Enhancement of seedling growth, and of chlorophyll and carotenoid accumulation, by sucrose occurred both in the absence and presence of atrazine. In contrast, whereas sucrose treatment in the absence of atrazine decreased psbA mRNA and D1 protein levels, the combined effects of sucrose and atrazine resulted in increased levels of psbA mRNA and of D1 protein levels, which may thus significantly contribute to the induction of atrazine tolerance.

Isolation and molecular characterization of atrazine tolerant barley mutants.

Two atrazine-tolerant barley mutants were isolated from atrazine-selection experiments performed on barley chloroplast-mutator plants. Genetic analysis demonstrated that atrazine tolerance was maternally inherited. Molecular characterization of the mutants was performed by PCR amplification of an internal fragment of the chloroplast gene psbA. The BstXI restriction patterns of the amplified fragments showed two bands in both tolerant barley mutants and only one in the atrazine-sensitive control. The 277-bp amplified fragments from the parental line and both atrazine-tolerant mutants were cloned and sequenced. Sequence analysis showed a single nucleotide substitution in both barley atrazine-tolerant mutants, i.e. A to G at the +790 position of the psbA gene-coding sequence. This point mutation corresponds to an amino-acid change of serine- to -glycine and creates a BstXI restriction site. Our results confirmed the conservative variability involved in atrazine tolerance which was previously reported for several other species. To our knowledge this is the first report on the obtention of atrazine-tolerant barley. This finding provides support to the hypothesis that, in addition to a wide variety of chlorophyll deficiencies, the barley chloroplast mutator genotype induces variability in other traits, which could include agronomically valuable mutants.

A risk assessment of pollution: induction of atrazine tolerance in phytoplankton communities in freshwater outdoor mesocosms, using chlorophyll fluorescence as an endpoint

We investigated the validity and sensitivity of assessments of the induction of atrazine tolerance in freshwater outdoor mesocosmic phytoplankton communities, using the in vivo fluorescence of chlorophyll a as an endpoint, for monitoring ecotoxicology and for risk assessment programs applied to phytoplankton contaminated by photosystem II herbicides. Atrazine inhibits the photosynthetic process, and so the rise in in-vivo fluorescence could be used as a physiological manifestation of acute toxicity. Short-term tests (1 h) were used, in which increasing concentrations of the herbicide were applied to phytoplankton samples taken every two days from the mesocosms, and used to plot dose–response curves. The concentration at which atrazine increased the fluorescence by 25% relative to control samples was used to demonstrate the sensitivity of the phytoplankton, and the values found were compared for samples from different mesocosms (contaminated and non-contaminated). The taxonomic composition of the phytoplankton was also determined. The data showed that chronic exposure (25 days) to 30 μg/L of atrazine significantly increased the apparent tolerance of the phytoplankton to further contamination by the same compound. The use of in vivo fluorescence of chlorophyll a appears to be a reliable and effective parameter for monitoring the effects of atrazine pollution, and detecting the changes in community tolerance driven by pollution selection pressure.

Evaluation of the capacity for development of atrazine tolerance in periphyton from a swedish freshwater site as determined by inhibition of photosynthesis and sulfolipid synthesis

AbstractPeriphyton communities were established onglassdisksks undëcontinuous exposure tatrazine (0.056–3.2 μM, or 12–700 μg/L) in a microcosm flowthrough system with water from the Göta Älv river in Southern Sweden. The effects of atrazine on chlorophyll a content, ash‐free dry weight, algal species composition, and adenine and thymidine incorporation activity were determined after 4 weeks of continuous exposure. Tolerance of the algal community to atrazine was also determined by short‐term inhibition of photosynthesis and sulfolipid synthesis. The no‐effect concentrations for the long‐term exposure as determined with the different methods were between 0.040 and 0.28 μM of atrazine. The algal community seemed to have a low potential for development of tolerance to atrazine. Tolerant algae, however, seemed to have some capacity to replace the more sensitive species at low long‐term exposure (0.056–0.56 μM), which was reflected in a small but consistent increase of community tolerance. At higher concentrations, no algal species remained unaffected by atrazine, and consequently, no further increase in community tolerance was possible. On the contrary, the algal community appeared to become more sensitive.