Aluminum induces oxidative burst, cell wall NADH peroxidase activity, and DNA damage in root cells of Allium cepa L

Sensitivity of genotypically diverse rice varieties to radiation and the related changes to antioxidant enzyme activities

PURPOSE

Radiation mutagenesis, which typically involves gamma rays, is important for generating new rice germplasm resources. Determining the appropriate radiation dose range is critical for the success of radiation mutagenesis. Clarifying the sensitivity and tolerance of genotypically diverse rice varieties to gamma irradiation as well as the radiation-induced changes to reactive oxygen species (ROS) generation and antioxidant enzyme activities is crucial for increasing the utility of radiation mutagenesis in rice breeding programs.

MATERIALS AND METHODS

The seeds of the following four rice varieties with different genotypes were used as test materials: indica Zhe 1613, glutinous indica Zhe 1708, japonica Zhejing 100, and glutinous japonica Zhenuo 65. Additionally,60Co was used as the source of gamma rays. The rice seeds were irradiated with 14 doses (0, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, and 750 Gy). Non-irradiated seeds were used as the control. The seedling survival rate for each variety was recorded at 3, 7, 14, and 28 days after sowing. Moreover, the median lethal dose (LD50) and critical dose (LD40) were calculated according to the seedling survival rates at 28 days after sowing. The seedling superoxide anion (O2•-), hydrogen peroxide (H2O2), and malondialdehyde (MDA) contents and the superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) activities were analyzed at 7 days after sowing.

RESULTS

As the radiation dose increased, the seedling survival rate decreased. The seedling survival rate also decreased significantly as the number of days after sowing increased. Among the rice genotypes, the rank-order of the radiation tolerance was as follows: indica Zhe 1613 > glutinous indica Zhe 1708 > japonica Zhejing 100 > glutinous japonica Zhenuo 65. The LD50 values were 426.7 Gy for Zhe 1613, 329.2 Gy for Zhe 1708, 318.3 Gy for Zhejing 100, and 316.6 Gy for Zhenuo 65. Increases in the radiation dose resulted in significant increases in the seedling O2•- and H2O2 contents, but only up to a certain point. Further increases in the radiation dose caused the seedling O2•- and H2O2 contents to decrease. The H2O2 content for each variety peaked when the radiation dose was very close to the LD50. We propose that the radiation dose associated with the highest H2O2 content (±50 Gy) should be used as the recommended dose for the gamma irradiation of rice. The radiation dose that resulted in peak seedling O2•- contents in the analyzed rice varieties was very close to the LD40. In all rice varieties, the MDA content increased as the radiation dose increased. The SOD, CAT, POD, and APX activities increased as the radiation dose increased within a certain range (less than 600 Gy for Zhe 1613 and 400 Gy for the other varieties), but there were slight differences among the rice varieties.

CONCLUSIONS

Genotypically diverse rice varieties vary regarding their sensitivity to gamma irradiation. Our findings suggest that ROS generation and antioxidant enzyme activities are important factors associated with the radiation mutagenesis of rice. The close relationship between the activities of key antioxidant enzymes, such as SOD, POD, APX, and CAT, and the LD50 and LD40 may be exploited to enhance radiation mutagenesis through the use of plant growth regulators.

Environmental implications of combustion of rice husk at high temperatures and for an extended period for energy generation

The most common alternative for the management and valorization of rice processing waste is the combustion of rice husk (RH) for energy generation. The environmental risk assessment of the ash generated during the combustion of the RH to obtain energy has remained understudied. Disposal of rice husk ash (RHA) on agricultural land is the most common outcome, which could pose a risk to both natural ecosystems and human health. The objective of this study was to characterize the physicochemical composition and the phytotoxicity, cytotoxicity, and genotoxicity of RHA obtained from three distinct combustion processes. The evaluation processes were 800-900 °C in up to 5 min (I), 800-900 °C in 15-20 min (II), and 600-700 °C in 15-20 min (III). Furthermore, the content, pH, and concentrations of Al, Cd, Cu, Fe, Mg, Mn, Mo, Na, Ni, and Ti present in the ashes were determined. The germination index for two vegetable seeds was subsequently evaluated. By measuring the mitotic index and frequency of chromosomal aberrations, the cytotoxicity and genotoxicity were determined. It was observed that RHA produced by combustion of RH at higher combustion temperatures for an extended period exhibited different physicochemical properties, in addition to higher levels of phytotoxicity, cytotoxicity, and genotoxicity.

Evaluating the genotoxicity of salinity stress and secondary products gene manipulation in lime, Citrus aurantifolia, plants

Salinity is a significant abiotic stress that has a profound effect on growth, the content of secondary products, and the genotoxicity of cells. Lime, Citrus aurantifolia, is a popular plant belonging to the family Rutaceae. The interest in cultivating this plant is due to the importance of its volatile oil, which is included in many pharmaceutical industries, but C. aurantifolia plants are affected by the NaCl salinity levels. In the present study, a comet assay test has been applied to evaluate the genotoxic impact of salinity at 0, 50, 100, and 200 mM of NaCl on C. aurantifolia tissue-cultured plants. Furthermore, terpene gene expression was investigated using a semi-quantitative real-time polymerase chain reaction. Results from the two analyses revealed that 200 mM of NaCl stress resulted in high levels of severe damage to the C. aurantifolia plants' DNA tail 21.8%, tail length 6.56 µm, and tail moment 3.19 Unit. The relative highest expression of RtHK and TAT genes was 2.08, and 1.693, respectively, when plants were exposed to 200 mM of NaCl, whereas pv4CL2RT expressed 1.50 in plants subjected to 100 mM of NaCl. The accumulation of transcripts for the RTMYB was 0.951 when plants were treated with NaCl at 50 mM, and RtGPPS gene was significantly decreased to 0.446 during saline exposure at 100 mM. We conclude that the comet assay test offers an appropriate tool to detect DNA damage as well as RtHK, TAT, and pv4CL2RT genes having post-transcriptional regulation in C. aurantifolia plant cells under salinity stress. Future studies are needed to assess the application of gene expression and comet assay technologies using another set of genes that show vulnerability to different stresses on lime and other plants.

Melatonin-mediated endogenous nitric oxide coordinately boosts stability through proline and nitrogen metabolism, antioxidant capacity, and Na+/K+ transporters in tomato under NaCl stress

The interactions between nitric oxide (NO) and melatonin in alleviating sodium chloride (NaCl) toxicity in plants are poorly comprehended. Here, the associations between the exogenous application of melatonin and endogenous NO levels in inducing tomato seedlings' defense response during NaCl toxicity were investigated. The results indicated that the application of melatonin (150 μM) increased height (23.7%) and biomass (32.2%), improved chlorophyll (a (137%) and b (92.8%)), and proline metabolisms, and reduced the contents of superoxide anion radicals (49.6%), hydrogen peroxide (31.4%), malondialdehyde (38%), and electrolyte leakage (32.6%) in 40-day-old tomato seedlings grown under NaCl (150 mM) treatment. Melatonin increased the antioxidant defense system in NaCl-stressed seedlings by increasing the activity of the antioxidant enzymes. Melatonin also improved N metabolism and endogenous NO content in NaCl-stressed seedlings by upregulating the activity of enzymes implicated in N assimilation. Furthermore, melatonin improved ionic balance and reduced Na content in NaCl-exposed seedlings by upregulating the expression of genes involved in K/Na ratio homeostasis (NHX1-4) and increasing the accumulation of mineral nutrients (P, N, Ca, and Mg). However, the addition of cPTIO (100 μM; an NO scavenger) reversed the beneficial impacts of melatonin, indicating the effective function of NO in melatonin-induced defense mechanisms in NaCl-stressed tomato seedlings. Therefore, our results revealed that melatonin improves the tolerance of tomato plants during NaCl toxicity by mediating internal NO.

Low-dose priming of gamma radiation enhanced cadmium tolerance in Chlamydomonas reinhardtii by modulating physio-biochemical pathways

Microalgae are natural biotic models for exploring the genotoxic effect of heavy metals, irradiation, other external stimuli and the toxicant elimination. The effective removal of heavy metals from the aquatic environment using microalgae has gained considerable attention. However, limited research was carried out on cadmum toxicity in microalgae and their use as bio-accumulants. Previous research suggested that low-dose priming with non-ionizing radiations, such as gamma radiation, increased heavy metal tolerance in plants and aquatic photosynthetic microalgae. In the present study, we have hypothesized the growth inhibitory physiochemical properties of cadmium (Cd) in Chlamydomonas reinhardtii, and analyzed the protective role of low-dose gamma radiations priming against Cd-induced growth inhibition by emphasizing mechanism of cell survival by antioxidant defence system. Experimentally, the gamma-primed C. reinhardtii exhibited higher cell survival and Cd tolerance with effective modulation of biochemical responses such as antioxidant enzymes. The current investigation revealed that low-dose priming of gamma radiation masks Cd-mediated oxidative stress and enhances cellular detoxification via intracellular antioxidant enzymes in C. reinhardtii.

Transcriptome Analysis Revealed the Mechanisms Involved in Ultrasonic Seed Treatment-Induced Aluminum Tolerance in Peanut

Ultrasonic (US) treatment is an efficient method to induce crop tolerance against heavy metal toxicity; however, US-induced aluminum (Al) tolerance in peanuts was rarely studied. This study was comprised of two treatments, namely, CK, without ultrasonic treatment, and US, an ultrasonic seed treatment, for 15 min. Both treated and non-treated treatments were applied with Al in the form of AlCl3.18H2O at 5 mmol L-1 in Hoagland solution at one leaf stage. Results depicted that plant height, main root length, and number of lateral roots increased significantly under US treatment. Transcriptome analysis revealed that plant hormone signal transduction and transcription factors (TFs) were significantly enriched in the differentially expressed genes (DEGs) in US treatment, and the plant hormones were measured, including salicylic acid (SA) and abscisic acid (ABA) contents, were substantially increased, while indole acetic acid (IAA) and jasmonic acid (JA) contents were decreased significantly in US treatment. The TFs were verified using quantitative real-time (qRT)-PCR, and it was found that multiple TFs genes were significantly upregulated in US treatment, and ALMT9 and FRDL1 genes were also significantly upregulated in US treatment. Overall, the US treatment induced the regulation of hormone content and regulated gene expression by regulating TFs to improve Al tolerance in peanuts. This study provided a theoretical rationale for US treatment to improve Al tolerance in peanuts.

Aluminum can activate grapevine defense through actin remodeling

In the current study, we used a grapevine cell line in which actin filaments are labeled by GFP to show that aluminum causes actin remodeling through activation of NADPH oxidase in the plasma membrane, followed by activation of phytoalexin synthesis genes. Elimination of actin filaments by latrunculin B disrupts gene activation and inhibition of MAPK signaling by the inhibitor PD98059. Interestingly, aluminum also induces the transcription of ISOCHORISMATE SYNTHASE, a key enzyme for the synthesis of salicylic acid, as well as PR1, a gene that is known to be responsive to salicylic acid. However, while salicylic acid responses are usually a hallmark of the hypersensitive response, aluminum-triggered defense is not accompanied by cell death. Both actin remodeling and gene activation in response to aluminum can be suppressed by the natural auxin indole acetic acid, suggesting that the actin response is not caused by nonspecific signaling. Further evidence for the specificity of the aluminum-triggered activation of phytoalexin synthesis genes comes from experiments in which plant peptide elicitors induce significant cellular mortality but do not evoke induction of these transcription. The response in grapevine cells can be recapitulated in grapevine leaf discs from two genotypes contrasting in stilbene inducibility. Here, aluminum can induce accumulation of the central grapevine phytoalexin, the stilbene aglycone trans-resveratrol; this is preceded by a rapid induction of transcription for RESVERATROL SYNTHASE and the regulating transcription factor MYB14. The amplitude of this induction reflects the general stilbene inducibility of these genotypes, indicating that the aluminum effect is not caused by nonspecific toxicity but by activation of specific signaling pathways. The findings are discussed in relation to a model in which actin filaments activate a specific branch of defense signaling, acting in concert with calcium-dependent PAMP-triggered immunity. This pathway links the apoplastic oxidative burst through MAPK signaling with the activation of defense-related transcription.

Iron oxide nanoparticles alleviate arsenic phytotoxicity in rice by improving iron uptake, oxidative stress tolerance and diminishing arsenic accumulation

The food chain contaminated with arsenic (As) has developed a hazardous threat to the growth and development of plants, animals and humans. The present study was conducted to examine the application of iron oxide nanoparticles (FeNPs) on biochemical and molecular traits of roots and leaves of rice plants under As phytotoxicity. The results showed that As reduced the accumulation of Fe in roots and leaves and thus reduced photosynthetic pigments and growth of rice plants. As stress enhanced the accumulation of hydrogen peroxide, superoxide anion and methylglyoxal by increasing the accumulation of As in roots and leaves, resulting in damage to membrane lipids and raised electrolyte leakage (EL). However, FeNPs strengthen the glyoxalase system and antioxidant enzymes, thereby alleviating oxidative stress and reducing EL. FeNPs protected plant cells from As phytotoxicity by enhancing the accumulation of chelating agents (proline, glutathione and phytochelatins) and the sequestration and immobilization of As in the vacuoles and the cell walls. FeNPs downregulated the expression of genes involved in As uptake and translocation (Lsi1 and Lsi2) and, consequently, reduced As accumulation in the roots and leaves of As-stressed plants. FeNPs also improved the accumulation of Fe in the roots and leaves by modulating the expression of genes that regulate Fe uptake and its transport to leaves (IRT1, IRT2, YSL2, YSL13, FRDL1, DMAS1, NAS2 and NAS3), resulting in the restoration of photosynthetic pigments and the growth of As-stressed plants. Our findings authenticate the role of FeNPs in diminishing As phytotoxicity on rice.

Effects of saline elicitors on saponin production in Agave salmiana plants grown in vitro

Agave plants are natives of Mexico and have an important role in the functional food industry. Agave salmiana grows in dry and desert soils, which are high in salt content; however, little is known about its response to saline conditions. In this study, A. salmiana plants grown in vitro were exposed to 0.1, 0.5, and 1.0 mM of salt elicitors, including AlCl₃, NaCl, and CoCl₂, and saponin synthesis and morphological characteristics were examined. Saponins were identified and quantified in ethanolic extracts using HPLC-ELSD. Root length and number, leaf length and number, and plant fresh weight were evaluated to determine the phenological condition of the plant. The presence of salts at various concentrations did not affect the physiological characteristics of the plant. Moreover, 0.5 mM NaCl induced a higher production of total saponin. Chlorogenin glycoside 1 (CG1) and hecogenin glycoside 1 (HG1) content remained unchanged across treatments. By contrast, CG2 and HG2 concentrations tended to decrease in response to increased concentrations of AlCl₃, NaCl, or CoCl₂. In vitro salt elicitors could be a feasible tool in the synthesis of specific saponins, without compromising on plant biomass. Our findings can be used in further generation of low saponin agave plants in field for the improvement of fermentation yield.

Demarcating antioxidant response against aluminum induced oxidative stress in Westiellopsis prolifica Janet 1941

Aluminum metal pollution is considered as a primary limiting factor that reduced crop yield in South Asian subtropical country like India. In national context, Odisha contributes around more than 40% of total ore availability. Moreover, industrial mining and smelting aid are major concern for aluminum metal toxicity in territorial vicinity affecting the soil fertility, ecosystem and human health through food chain. The aluminum metal accumulation limits the soil fertility by antagonistic regulation of photosynthetic and nitrogen fixing microbiota. The increasing concern regarding aluminum pollution enterprise critical investigations for their bioremediation in contamination sites. In this notion, the current study was hypothesized to decrypt the rate limiting factors, their explicit mode of action and intracellular detoxification in a cyanobacterium, i.e., Westiellopsis prolifica isolated from ash pond of NALCO (National Aluminum Company Limited), Angul, Odisha. In the experimental setup, treatment with different concentrations of AlCl₃ (0-0.1 mM) was marked a decline in the growth of the strain due to the adverse regulation of photosynthetic pigments. However, the enforcement of catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), guaiacol peroxidase (GPX) and glutathione reductase (GR) was critical for sustaining strain viability under oxidative imbalance. The observation of an increase in the antioxidant enzyme and MDA content was evident to sustain strain viability under such oxidative imbalance. The outcome of the anticipated study was apparent to demonstrate a colossal interlink between Al mediated induction of oxidative stress and their cellular detoxification via intracellular antioxidant enzymes and removal of H₂O₂ accumulation in cyanobacterium, W. prolifica. Statement of novelty Aluminum metal toxicity renders growth of Westiellopsis prolifica via affecting photosynthesis associated pigments. Westiellopsis prolifica deploys antioxidant defense enzymes to combat against aluminum mediated oxidative upset. Intracellular antioxidant enzymes provoke cellular survival of Westiellopsis prolifica under excessive uptake of aluminum in contaminated habitats.

Sulfate nutrition improves short-term Al3+-stress tolerance in roots of Lolium perenne L

Trivalent aluminum ions (Al³⁺) in acidic soils are a major constraint for crop productivity inhibiting root elongation and promoting cell death. Al³⁺-toxicity has adverse biochemical and physiological effects on plant root growth. Sulfur is an essential macronutrient assimilated from the soil in the form of sulfate. However, the implication of sulfate nutritional status in the modulation of short-term Al³⁺-tolerance mechanisms in plant roots has not been previously reported. Here, we evaluated the effects of increased sulfate supply on short-term Al³⁺-toxicity in roots of Lolium perenne, measuring Al, Ca, Mg and S uptake, lipid peroxidation, total SOD activity, and transcriptional levels of Cu/Zn and Fe-SOD genes. First, the nitrogen sulfur ratio (N/S) in the TF nutrient solutions used in this study were computed to confirm that L. perenne plants were grown in sulfate deficiency (120 μM), optimal supply (240 μM), or overdoses conditions (360 μM), without affecting dry root biomass. Sulfate supplementation (>240 μM, and N/S ratio < 16) played a significant protection to Al³⁺-stress that prevents morphological changes in root tips, inhibits lipid peroxidation and differentially up-regulates total SOD activity, due changes in SOD gene expression. The results support the importance of sulfate nutritional status, on plant tissue homeostasis, enhancing the physiological tolerance mechanisms modulating lipid peroxidation damage induced by short-term Al³⁺-toxicity.

Selenomethionine induces oxidative stress and modifies growth in rice (Oryza sativa L.) seedlings through effects on hormone biosynthesis and primary metabolism

Although the chemical characteristics of selenomethionine (SeMet) are similar to those of methionine (Met), the physiological activity of SeMet apparently differs in its ability to stimulate ethylene production in plant tissues. Since selenium alters root architecture of rice seedlings by modifying ethylene production, the investigation of the effect of SeMet and Met on rice growth would be a step forward towards unraveling factors that underlie selenium toxicity. Here, we report that SeMet increased concentrations of reactive oxygen species (ROS), inhibiting auxin and increasing ethylene production in rice seedlings. The effect of SeMet on seedlings was mediated by the inhibition of the abundance of transcripts encoding auxin transport and cell expansion proteins. Moreover, SeMet led to increased seedling respiration, which was positively correlated with organic acids consumption, but negatively with sugars consumption, thereby decreasing seedling growth. In contrast with SeMet treatment, Met did not affect ROS production, hormone biosynthesis and seedling growth, indicating an exclusive selenium effect. The singlet oxygen scavenger, 1,4-diazabicyclooctane, overrode the repressive effect of SeMet in seedling growth. Our results demonstrate a phytotoxic effect of SeMet for rice seedlings and reveal a relationship between reactive oxygen species, hormone homeostasis and carbon availability, which regulates growth responses.

DNA Damage Inducible Protein 1 is Involved in Cold Adaption of Harvested Cucumber Fruit

Chilling stress can cause cellular DNA damage, affecting the faithful transmission of genetic information. Cold acclimation enhances chilling tolerance, but it is not clear that the process of cold adaption involves DNA damage responses, as cold acclimation does not form real chilling stress. Here we showed with cucumber fruit that pre-storage cold acclimation (PsCA) reduces chilling injury and upregulates DNA damage inducible protein1 (CsDDI1), suggesting that the chilling tolerance induced by cold acclimation involves CsDDI1 transcription. Application of nitric oxide (NO), abscisic acid (ABA) or H₂O₂ biosynthesis inhibitor before PsCA treatment downregulates CsDDI1 and aggravates chilling injury, while H₂O₂ generation inhibition plus exogenous NO or ABA application before PsCA treatment restores chilling tolerance, but does not restore CsDDI1 expression, suggesting H₂O₂ plays a crucial role in triggering cold adaption. CsDDI1 overexpression Arabidopsis lines show faster growth, stronger chilling tolerance, lower reactive oxygen species levels, enhanced catalase and superoxide dismutase activities and higher expression of nine other Arabidopsis defense genes under chilling stress, suggesting CsDDI1 strengthens defenses against chilling stress by enhancing antioxidant defense system. Taken together, CsDDI1 positively regulates chilling tolerance induced by cold acclimation in cucumber. In addition, H₂O₂ is involved in initiation of cold acclimation. While CsDDI1 upregulation requires H₂O₂ as a key signaling molecule, the upregulation of CsDDI1 activates an antioxidant system to reduce biotoxic accumulation of H₂O₂ and helps in DNA repair.

The defense system for Bidens pilosa root exudate treatments in Pteris multifida gametophyte

According to the novel weapons hypothesis, root exudates are the inhibition factors for native species growth and development through invasive plants. It is hypothesized that antioxidant system (AOS) presents an effective role in plant defense system. The allelopathy indexes of P. multifida gametophyte biomass and sporogonium conversions rates turn negative with the dose and time effects, and the synthetical allelopathic effect index was -55.07% at 100% treatments under root exudates treatments. Under transmission electron microscopy, the cell structures turn burry. Next, AOS and programmed cell death (PCD) were tested in this study. In AOS, strong activities of superoxide dismutase, catalase, glutathione reductase and glutathione S-transferase (GST) were identified in gametophyte cells under the treatments, as well as the contents of glutathione, ascorbic acid and reduced ascorbate, while GPX activity decreased. Based on the input (SOD activity) and the output (GST activity) of antioxidant system, and the decreasing system control would be a reason leading gametophyte death under root exudates. At day 10, PCD would get its peak of 46.93% at 100% root exudates. We found a dynamic balance of PCD and AOS under the exudates treatments. We detected hexadecanoic acid, ethylene glycol and undecane are three major chemicals in root exudates. Our results provide a reference of AOS and PCD working under root exudates treatments in plants and offer novel strategy for the native species protection and invasion plants control in environment science.

Effects of occupational exposure to aluminium on some oxidative stress and DNA damage parameters

Aim:

The aim of this work was to investigate the relationships between aluminium levels, oxidative status and DNA damage in workers occupationally exposed to aluminium.

Subjects and methods:

This study was conducted in a secondary aluminium smelter. It included 96 male workers occupationally exposed to aluminium fume and dust compared to 96 male nonexposed individuals. Full history and clinical examination were done for all participants. Laboratory investigations in the form of serum aluminium, total antioxidant capacity (TAC), urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG) and comet assay test were performed.

Results:

Serum aluminium level ranged from 4 to 30 µg/L of median: 10 µg/L; urinary 8-OHdG ranged from 2.7 to 17.2 ng/mg creatinine of median: 7.6 ng/mg creatinine; comet tail length (CTL) ranged from 19.7 to 50.5 µm of median: 45 µm, were statistically significantly increased in the exposed group compared to nonexposed group. In exposed workers, a statistically significant positive correlations were found between serum aluminium level and urinary 8-OHdG ( r = 0.75, p < 0.001); aluminium level and CTL ( r = 0.71, p < 0.001); and urinary 8-OHdG and CTL ( r = 0.71, p < 0.001). There was a statistically significant negative correlation between serum aluminium and TAC ( r = −0.76, p < 0.001).

Conclusion:

Occupational exposure to aluminium in secondary aluminium smelters was related to the induction of oxidative stress and DNA damage. This may promote the development of adverse health hazards in the exposed workers

Reliability of plant root comet assay in comparison with human leukocyte comet assay for assessment environmental genotoxic agents

Comet assay is an efficient test to detect genotoxic compounds based on observation of DNA damage. The aim of this work was to compare the results obtained from the comet assay in two different type of cells extracted from the root tips from Lactuca sativa L. and human blood. For this, Spent Pot Liner (SPL), and its components (aluminum and fluoride) were applied as toxic agents. SPL is a solid waste generated in industry from the aluminum mining and processing with known toxicity. Three concentrations of all tested solutions were applied and the damages observed were compared to negative and positive controls. It was observed an increase in the frequency of DNA damage for human leukocytes and plant cells, in all treatments. On human leukocytes, SPL induced the highest percentage of damage, with an average of 87.68%. For root tips cells of L. sativa the highest percentage of damage was detected for aluminum (93.89%). Considering the arbitrary units (AU), the average of nuclei with high levels of DNA fragmentation was significant for both cells type evaluated. The tested cells demonstrated equal effectiveness for detection of the genotoxicity induced by the SPL and its chemical components, aluminum and fluoride. Further, using a unique method, the comet assay, we proved that cells from root tips of Lactuca sativa represent a reliable model to detect DNA damage induced by genotoxic pollutants is in agreement of those observed in human leukocytes as model. So far, plant cells may be suggested as important system to assess the toxicological risk of environmental agents.

Cytotoxicity and genotoxicity induced by coal and coal fly ash particles samples in V79 cells

Exposure to coal and coal ashes can cause harmful effects in in vitro and in vivo systems, mainly by the induction of oxidative damage. The aim of this work was to assess cytotoxic and genotoxic effects using the V79 cell line treated with coal and coal fly ash particles derived from a coal power plant located in Santa Catarina, Brazil. Two coal samples (COAL11 and COAL16) and two coal fly ash samples (CFA11 and CFA16) were included in this study. COAL16 was co-firing with a mixture of fuel oil and diesel oil. The comet assay data showed that exposure of V79 cells to coal and coal fly ash particles induced primary DNA lesions. Application of lesion-specific endonucleases (FPG and ENDO III) demonstrated increased DNA effects indicating the presence of high amounts of oxidative DNA lesions. The cytokinesis-block micronucleus cytome assay analysis showed that exposure of V79 cells to high concentrations of coal and coal fly ash particles induced cytotoxic effects (apoptosis and necrosis) and chromosomal instability (nucleoplasmic bridges, nuclear buds, and micronucleus (MN) formation). These results may be associated with compounds contained in the surface of the particles as hazardous elements, ultrafine/nanoparticles, and polycyclic aromatic hydrocarbons (PAHs) which were detected in the samples. Graphical abstract ᅟ.

Elevation of arginine decarboxylase-dependent putrescine production enhances aluminum tolerance by decreasing aluminum retention in root cell walls of wheat

Aluminum (Al) stress induces putrescine (Put) accumulation in several plants and this response is proposed to alleviate Al toxicity. However, the mechanisms underlying this alleviation remain largely unknown. Here, we show that exposure to Al clearly increases Put accumulation in the roots of wheat plants (Triticum aestivum L. 'Xi Aimai-1') and that this was accompanied by significant increase in the activity of arginine decarboxylase (ADC), a Put producing enzyme. Application of an ADC inhibitor (d-arginine) terminated the Al-induced Put accumulation, indicating that increased ADC activity may be responsible for the increase in Put accumulation in response to Al. The d-arginine treatment also increased the Al-induced accumulation of cell wall polysaccharides and the degree of pectin demethylation in wheat roots. Thus, it elevated Al retention in cell walls and exacerbated Al accumulation in roots, both of which aggravate Al toxicity in wheat plants. The opposite effects were true for exogenous Put application. These results suggest that ADC-dependent Put accumulation plays important roles in providing protection against Al toxicity in wheat plants through decreasing cell wall polysaccharides and increasing the degree of pectin methylation, thus decreasing Al retention in the cell walls.

Reactive oxygen species: Reactions and detection from photosynthetic tissues

Reactive oxygen species (ROS) have long been recognized as compounds with dual roles. They cause cellular damage by reacting with biomolecules but they also function as agents of cellular signaling. Several different oxygen-containing compounds are classified as ROS because they react, at least with certain partners, more rapidly than ground-state molecular oxygen or because they are known to have biological effects. The present review describes the typical reactions of the most important ROS. The reactions are the basis for both the detection methods and for prediction of reactions between ROS and biomolecules. Chemical and physical methods used for detection, visualization and quantification of ROS from plants, algae and cyanobacteria will be reviewed. The main focus will be on photosynthetic tissues, and limitations of the methods will be discussed.

The use of comet assay in plant toxicology: recent advances

The systematic study of genotoxicity in plants induced by contaminants and other stress agents has been hindered to date by the lack of reliable and robust biomarkers. The comet assay is a versatile and sensitive method for the evaluation of DNA damages and DNA repair capacity at single-cell level. Due to its simplicity and sensitivity, and the small number of cells required to obtain robust results, the use of plant comet assay has drastically increased in the last decade. For years its use was restricted to a few model species, e.g., Allium cepa, Nicotiana tabacum, Vicia faba, or Arabidopsis thaliana but this number largely increased in the last years. Plant comet assay has been used to study the genotoxic impact of radiation, chemicals including pesticides, phytocompounds, heavy metals, nanoparticles or contaminated complex matrices. Here we will review the most recent data on the use of this technique as a standard approach for studying the genotoxic effects of different stress conditions on plants. Also, we will discuss the integration of information provided by the comet assay with other DNA-damage indicators, and with cellular responses including oxidative stress, cell division or cell death. Finally, we will focus on putative relations between transcripts related with DNA damage pathways, DNA replication and repair, oxidative stress and cell cycle progression that have been identified in plant cells with comet assays demonstrating DNA damage.

The hydroxyl radical in plants: from seed to seed

The hydroxyl radical (OH(•)) is the most potent yet short-lived of the reactive oxygen species (ROS) radicals. Just as hydrogen peroxide was once considered to be simply a deleterious by-product of oxidative metabolism but is now acknowledged to have signalling roles in plant cells, so evidence is mounting for the hydroxyl radical as being more than merely an agent of destruction. Its oxidative power is harnessed to facilitate germination, growth, stomatal closure, reproduction, the immune response, and adaptation to stress. It features in plant cell death and is a key tool in microbial degradation of plant matter for recycling. Production of the hydroxyl radical in the wall, at the plasma membrane, and intracellularly is facilitated by a range of peroxidases, superoxide dismutases, NADPH oxidases, and transition metal catalysts. The spatio-temporal activity of these must be tightly regulated to target substrates precisely to the site of radical production, both to prevent damage and to accommodate the short half life and diffusive capacity of the hydroxyl radical. Whilst research has focussed mainly on the hydroxyl radical's mode of action in wall loosening, studies now extend to elucidating which proteins are targets in signalling systems. Despite the difficulties in detecting and manipulating this ROS, there is sufficient evidence now to acknowledge the hydroxyl radical as a potent regulator in plant cell biology.

Mitogen-activated protein kinase signal transduction and DNA repair network are involved in aluminum-induced DNA damage and adaptive response in root cells of Allium cepa L

In the current study, we studied the role of signal transduction in aluminum (Al(3+))-induced DNA damage and adaptive response in root cells of Allium cepa L. The root cells in planta were treated with Al(3+) (800 μM) for 3 h without or with 2 h pre-treatment of inhibitors of mitogen-activated protein kinase (MAPK), and protein phosphatase. Also, root cells in planta were conditioned with Al(3+) (10 μM) for 2 h and then subjected to genotoxic challenge of ethyl methane sulfonate (EMS; 5 mM) for 3 h without or with the pre-treatment of the aforementioned inhibitors as well as the inhibitors of translation, transcription, DNA replication and repair. At the end of treatments, roots cells were assayed for cell death and/or DNA damage. The results revealed that Al(3+) (800 μM)-induced significant DNA damage and cell death. On the other hand, conditioning with low dose of Al(3+) induced adaptive response conferring protection of root cells from genotoxic stress caused by EMS-challenge. Pre-treatment of roots cells with the chosen inhibitors prior to Al(3+)-conditioning prevented or reduced the adaptive response to EMS genotoxicity. The results of this study suggested the involvement of MAPK and DNA repair network underlying Al-induced DNA damage and adaptive response to genotoxic stress in root cells of A. cepa.