Allium Cepa Root Cells Research Articles

Lead induced genotoxicity and cytotoxicity in root cells of Allium cepa and Vicia faba

The cytotoxic and genotoxic effects of lead (Pb) were studied in A. cepa L. and V. faba L. The plants were exposed to lead nitrate [Pb (NO3)2] solutions at three concentrations (50, 100 and 200 μM), and root growth, root viability and antioxidant enzyme activity was assessed. In addition genotoxicity was evaluated by changes in the mitotic index (MI) chromosomal aberrations (CAs), and DNA strand breaks. The exposure to Pb caused serious damage in the roots, which was accompanied by a decrease in divisional frequency of cell, increase in chromosomal aberrations, DNA fragmentation and micronucleus frequency in both the plants. The enzymes guaiacol peroxidase (GPX) and catalase (CAT) activities increased in both the plants. Increased level of malonaldehyde (MDA) an indicator of lipid peroxidation was noted. A positive correlation of the activity of GPX and CAT with malonaldehyde (MDA) content was recorded at all concentrations of Pb. This finding suggest that exposure of high Pb concentration is cytotoxic as well as genotoxic for A. cepa L. and V. faba L., and are correlated to the oxidative stress.

English

  Increased pesticides application in agriculture and public health has contributed to the pollution of the environment. This study evaluates the cytogenotoxic effects of emulsifiable concentrate of cypermethrin, deltamethrin, lambdacyhalothrin and endosulfan on Allium cepa root cells. Five concentrations (1.0, 5.0, 10.0, 20.0 and 40.0 ppm) of each pesticide were used for microscopic (48 h) and macroscopic (72 h) evaluations with distilled water as the control. Data were analyzed by Student's t-test. A dose dependent reduction in A. cepa root length was observed for the pesticides. Significant reduction in treated root length was observed at 10.0 ppm of deltamethrin, cypermethrin and lambdacyhalothrin, and at 20.0 and 40.0 ppm of all the pesticides compared to the control (P<0.05). The EC50 values showed growth inhibition in the order of lambdacyhalothrin > cypermethrin > deltamethrin >endosulfan, while that of total aberrant cells was cypermethrin > lambdacyhalothrin > deltamethrin > endosulfan. Microscopic aberrations observed in the pesticide-treated onions include sticky chromosomes, disturbed spindle and chromosome bridges.Dose dependent reduction was observed in the total mitotic dividing cells and mitotic index of the pesticide-treated A. cepa, except for 5.0 ppm of endosulfan. The pesticides induced growth inhibition and caused cytogenotoxic effects on the meristematic cells of Allium cepa. The data herein provide more information on the pesticides of which exposure to substantial concentration might constitute health risk to non-target organisms.   Key words: Pesticides, mitotic aberration, pyrethroid, organochlorine, growth.

Genotoxic effects of Bismuth (III) oxide nanoparticles by Allium and Comet assay

Genotoxic effects of Bismuth (III) oxide nanoparticles (BONPs) were investigated on the root cells of Allium cepa by Allium and Comet assay. A. cepa roots were treated with the aqueous dispersions of BONPs at five different concentrations (12.5, 25, 50, 75, and 100ppm) for 4h. Exposure of BONPs significantly increased mitotic index (MI) except 12.5ppm, total chromosomal aberrations (CAs) in Allium test. While stickiness chromosome laggards, disturbed anaphase–telophase and anaphase bridges were observed in anaphase–telophase cells, pro-metaphase and c-metaphase in other cells. A significant increase in DNA damage was also observed at all concentrations of BONPs except 12.5ppm by Comet assay. The results were also analyzed statistically by using SPSS for Windows; Duncan’s multiple range test was performed. These results indicate that BONPs exhibit genotoxic activity in A. cepa root meristematic cells.

Chromium (VI)-induced hormesis and genotoxicity are mediated through oxidative stress in root cells of Allium cepa L.

Chromium (VI) genotoxicity was evaluated in Allium bioassay by using different treatment protocols. Treatment of bulbs of Allium cepa L. with Cr(VI) at a range of concentrations for 5 days (120 h) exhibited low dose (12.5 μM) stimulation and high dose (25–200 μM) inhibition of root growth apparently indicating hormesis. Inhibition of root growth was correlated with the dose-dependent increase in generation of reactive oxygen species (ROS), cell death, lipid peroxidation, repression of antioxidative enzymes (catalase, superoxide dismutase, ascorbate peroxidase), induction of DNA damage, chromosome aberrations or micronuclei in root cells. The above effects were, however, reversed when the duration of Cr(VI) treatment was limited to 3–24 h followed by recovery in tap water for 4 days that resulted in the dose-dependent stimulation of root growth, mitosis and increased activity of the antioxidative enzymes that obliterated oxidative stress and genotoxicity. The above Cr(VI)-induced stimulation of root growth was effectively countered by pre- or post-treatments of dimethylthiourea, a ROS-scavenger. These findings underscored that Cr(VI), depending on the magnitude of the dose (concentration × time), could either be stimulatory or inhibitory for root growth that underlined the crucial role of ROS having obvious implications in agriculture, post harvest technology and human health.

DNA integrity of onion root cells under catechol influence

Catechol is a highly toxic organic pollutant, usually abundant in the waste effluents of industrial processes and agricultural activities. The environmental sources of catechol include pesticides, wood preservatives, tanning lotion, cosmetic creams, dyes, and synthetic intermediates. Genotoxicity of catechol at a concentration range 5 × 10(-1)-5 mM was evaluated by applying random amplified polymorphic DNA (RAPD) and time-lapse DNA laddering tests using onion (Allium cepa) root cells as the assay system. RAPD analysis revealed polymorphisms in the nucleotidic sequence of DNA that reflected the genotoxic potential of catechol to provoke point mutations, or deletions, or chromosomal rearrangements. Time-lapse DNA laddering test provided evidence that catechol provoked DNA necrosis and apoptosis. Acridine orange/ethidium bromide staining could distinguish apoptotic from necrotic cells in root cells of A. cepa.

Calcium channel blockers protect against aluminium-induced DNA damage and block adaptive response to genotoxic stress in plant cells

Calcium is an important second messenger in signal transduction pathways. The role of Ca2+ signalling in Al-induced DNA damage, cell death, and adaptive response to genotoxic stress caused by ethyl methanesulfonate (EMS) or methylmercuric chloride (MMCl) in the root cells of Allium cepa was investigated in the current study. Root cells in planta were treated with Al3+ (800μM of AlCl3) for 3h without or with 2h pre-treatment with the Ca2+ chelator (EGTA) or Ca2+ channel blockers (lanthanum chloride, verapamil) or CaM/CDPK antagonist (W7). In addition, root cells in planta were conditioned by treatment with Al3+ (5 or 10μM of AlCl3) for 2h followed by the genotoxic challenge with MMCl (1.25μM) or EMS (2.5 or 5mM) for 3h without or with the pre-treatment of the chosen Ca2+ chelator/channel blockers/antagonist. Following the treatments, cell death and DNA damage were investigated in the root cells by comet assay. Furthermore, genotoxicity in the root meristems was determined after 18–30h of recovery. These results revealed that Al3+ (800μM) significantly induced DNA damage and cell death in the root cells of A. cepa. On the other hand, conditioning of the root cells with Al3+ at low concentrations (5 or 10μM) offered adaptive response leading to the protection against genotoxic stress induced by MMCl and EMS. Pre-treatment of root cells with the Ca2+ chelator/channel blockers/antagonist not only alleviated Al3+-induced DNA damage and cell death induced but also blocked the Al3+-mediated adaptive response to genotoxic stress induced by MMCl and EMS. For the first time, the results of the present study highlighted the role of Ca2+ signalling underlying the biphasic mode of action of Al3+ that induced DNA damage and cell death at high doses and offered adaptation to genotoxic response in plants at low doses.

Biodecolorization of Azo Dye Remazol Orange by Pseudomonas aeruginosa BCH and Toxicity (Oxidative Stress) Reduction in Allium cepa Root Cells

In this report a textile azo dye Remazol orange was degraded and detoxified by bacterium Pseudomonas aeruginosa BCH in plain distilled water. This bacterial decolorization performance was found to be pH and temperature dependent with maximum decolorization observed at pH8 and temperature 30°C. Bacterium tolerated higher dye concentrations up to 400mg l(-1). Effect of initial cell mass showed that higher cell mass concentration can accelerate decolorization process with maximum of 92% decolorization observed at 2.5g l(-1) cell mass within 6.5h. Effect of various metal ions showed Mn has inducing effect whereas Zn strongly inhibited the decolorization process at 5mM concentration. Analysis of biodegradation products carried out with UV-vis spectroscopy, HPTLC and FTIR confirmed the decolorization and degradation of Remazol orange. Possible route for the degradation of dye was proposed based on GC-MS analysis. During toxicological scrutiny in Allium cepa root cells, induction in the activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX) and inhibition of catalase (CAT) along with raised levels of lipid peroxidation and protein oxidation in dye treated samples were detected which conclusively indicated the generation of oxidative stress. Less toxic nature of the dye degraded products was observed after bacterial treatment.

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

Plants under stress incur an oxidative burst that involves a rapid and transient overproduction of reactive oxygen species (ROS: O(2) (•-) , H(2) O(2) , (•) OH). We hypothesized that aluminum (Al), an established soil pollutant that causes plant stress, would induce an oxidative burst through the activation of cell wall-NADH peroxidase (NADH-PX) and/or plasma membrane-associated NADPH oxidase (NADPH-OX), leading to DNA damage in the root cells of Allium cepa L. Growing roots of A. cepa were treated with Al(3+) (800 μM of AlCl(3) ) for 3 or 6 hr without or with the pretreatment of inhibitors specific to NADH-PX and NADPH-OX for 2 hr. At the end of the treatment, the extent of ROS generation, cell death, and DNA damage were determined. The cell wall-bound protein (CWP) fractions extracted from the untreated control and the Al-treated roots under the aforementioned experimental conditions were also subjected to in vitro studies, which measured the extent of activation of peroxidase/oxidase, generation of (•) OH, and DNA damage. Overall, the present study demonstrates that the cell wall-bound NADH-PX contributes to the Al-induced oxidative burst through the generation of ROS that lead to cell death and DNA damage in the root cells of A. cepa. Furthermore, the in vitro studies revealed that the CWP fraction by itself caused DNA damage in the presence of NADH, supporting a role for NADH-PX in the stress response. Altogether, this study underscores the crucial function of the cell wall-bound NADH-PX in the oxidative burst-mediated cell death and DNA damage in plants under Al stress.

Genotoxicity and toxicity evaluations of ECF cellulose bleaching effluents using the Allium cepa L. Test

Toxicity and genotoxicity tests were performed on root cells of Allium cepa in order to evaluate wastewater quality following an ECF cellulose bleaching process. The results revealed a toxic effect of the effluent, with inhibition of meristem growth and generally lower values of metaphase, anaphase and telophase indices at pH 10.5 than pH 7 for all effluent concentrations. The genotoxicity effect was different from the toxic effect given that the micronucleus and the chromosomal aberration tests in anaphase-telophase cells were low over all ranges of the studied effluent concentrations.

Biodegradation of Rubine GFL by Galactomyces geotrichum MTCC 1360 and subsequent toxicological analysis by using cytotoxicity, genotoxicity and oxidative stress studies

Galactomyces geotrichum MTCC 1360 showed 87 % decolorization of the azo dye Rubine GFL (50 mg l(-1)) within 96 h at 30 °C and pH 7.0 under static conditions, with significant reduction of chemical oxygen demand (67 %) and total organic carbon (59 %). Examination of oxidoreductive enzymes, namely laccase, tyrosinase and azo reductase, confirmed their role in decolorization and degradation of Rubine GFL. Biodegradation of Rubine GFL into different metabolites was confirmed using high-performance TLC, HPLC, Fourier transform IR spectroscopy and GC-MS analysis. During toxicological studies, cell death was observed in Rubine GFL-treated Allium cepa root cells. Toxicological studies before and after microbial treatment were done with respect to cytotoxicity, genotoxicity, oxidative stress, antioxidant enzyme status, protein oxidation and lipid peroxidation using root cells of A. cepa. The analysis with A. cepa showed that the dye exerts oxidative stress and subsequently has a toxic effect on the root cells, whereas its metabolites are less toxic. Phytotoxicity studies revealed the less toxic nature of the metabolites as compared with Rubine GFL.

Determination of genotoxic effects of chlorfenvinphos and fenbuconazole in Allium cepa root cells by mitotic activity, chromosome aberration, DNA content, and comet assay

Genotoxic effects of Chlorfenvinphos and fenbuconazole were examined by using mitotic index, mitotic phase, chromosomal abnormalities, 2C DNA content and Comet assay on the root meristem cells of Allium cepa. The roots were treated with 10, 20, 40, 60, 80, and 100ppm concentrations for 24 and 48h. The results indicated that Chlorfenvinphos and fenbuconazole significantly decreased the mitotic index in all treatments when compared with their controls. The percentages of mitotic phases have changed. Chlorfenvinphos and fenbuconazole significantly increased the abnormal cell frequency at all concentrations and treatment periods when compared with their controls. Different abnormal mitotic figures were observed in all mitotic phases. Among these abnormalities were stickiness, anaphase bridges, c-mitosis, laggards, and micronucleus. These pesticides remarkably depressed the 2C DNA content in the root meristems of A. cepa. The genotoxicity of chlorfenvinphos and fenbuconazole in A. cepa root cells was analyzed using comet assay, which allows the detection of single strand breaks. In all concentrations, chlorfenvinphos and fenbuconazole induced a significant increase in DNA damage. Additionally, it was also researched to determine if there is a relation between the amount of DNA and the DNA damage and a regression analyses was conducted. When the data that was accumulated via comet analysis from A. cepa root tip cells that are treated with type chlorfenvinphos and fenbuconazole, was compared to the data that was acquired as the result of the measurement of 2C DNA amount, a relation with negative correlation was found, (respectively, r=−0.80 and r=−0.82). This relation factor is statistically important and strong (p<0.05).

Genoprotective potential of Brassica juncea (L.) Czern. against mercury-induced genotoxicity in Allium cepa L.

Brassica juncea (L.) Czern. is an important species of the family Brassicaceae with immense medicinal value. The main goal of this study was to investigate the antigenotoxic effects of different concentrations (0.1%-1.0%) of chloroform extract of B. juncea seeds on mercury-induced (0.75 ppm) genotoxic effects in root cells of Allium cepa. Three different modes of treatment were performed: pretreatment, posttreatment, and simultaneous treatment. For pretreatment, freshly emerged root tips were first treated with different concentrations of seed extract for 3 h and then treated with Hg for 3 h. For posttreatment, the roots were first treated with Hg and then with extract concentrations. For simultaneous treatment, different concentrations of extract were added along with the Hg. The study revealed that chloroform extract was neither toxic nor in possession of genotoxic activity. Treatment with Hg caused a decrease in mitotic index and induction of chromosomal aberrations as compared to the negative control. This effect was reversed by treatment with different concentrations of chloroform extract of seeds of B. juncea. Maximum percentage inhibition (95.3%) of genotoxic effects was observed with 1% chloroform extract (post- and simultaneous treatment). This study clearly indicates that the chloroform extract of B. juncea seeds has antigenotoxic potential against mercury-induced genotoxicity in a dose-dependent manner by evaluating A. cepa root chromosomal aberration assay.

Oxidative stress-mediated genotoxicity of wastewaters collected from two different stations in northern India

Oxidative stress-mediated genotoxicity of wastewaters taken from two different cities, Saharanpur (SWW) and Aligarh (AWW), were compared with a battery of short-term assays namely the Allium cepa genotoxicity test, the plasmid-nicking assay, and the Ames fluctuation test. Both test-water samples – when used undiluted – increased the frequency of chromosomal abnormalities and/or micronuclei and alterations in the mitotic index of root cells of Allium cepa. Bridges and fragmentation of the chromosome were the predominant effects of the Saharanpur water sample while the Aligarh sample induced mainly chromosome fragmentation. Single- and double-strand breaks were also observed in plasmid DNA treated with these test wastewaters. The plasmid-nicking assay performed on SWW resulted in linearization of plasmid DNA when 18 μl was tested (in a total reaction volume of 20 μl). However, with the same amount of AWW, all three forms of plasmid, viz. supercoiled, open circular and linear were observed. Supplementation with specific scavengers of reactive oxygen species (ROS) caused a significant decline in mutagenicity of test-water samples in all the tests, pointing at oxidative stress as the mediator of the observed genotoxicity. The role of heavy metals in the AWW-induced oxidative stress and that of phenolics in SWW cannot be ruled out.

Biochemical degradation pathway of textile dye Remazol red and subsequent toxicological evaluation by cytotoxicity, genotoxicity and oxidative stress studies

Remazol red (RR), a monochloro sulphonated azo dye was degraded up to 97% within 20 min at 40 °C and pH 7 at dye concentration 50 mg l −1 by Pseudomonas aeruginosa BCH. Examination of enzyme status exposed the involvement of various oxidoreductive enzymes viz. laccase, veratryl alcohol oxidase and NADH-DCIP reductase. Analytical studies viz. HPTLC, HPLC, FTIR and GC-MS carried out with dye and dye metabolites formed after dye decolorization confirmed that the decolorization was due to degradation. Based on enzymatic status and GC-MS analysis the possible metabolic pathway followed by bacterial strain for the degradation of RR was proposed. During toxicological scrutiny, cell death was observed in RR treated Allium cepa ( A. cepa) root cells. The observed inhibition of catalase (CAT) activity and induction in enzyme activities of sulfur oxide dismutase (SOD) and ascorbate peroxidase (APX) along with raised protein oxidation and lipid peroxidation signified that RR generated the oxidative stress in A. cepa roots. These toxicological studies along with genotoxicity studies using A. cepa roots and phytotoxicity studies using Phaseolus mungo ( P. mungo) and Sorghum vulgare ( S. vulgare) conclusively designated the toxicity of RR and comparatively less toxic nature of metabolites formed after dye degradation by P. aeruginosa BCH.

Cytogenetic and genotoxic effects of zinc oxide nanoparticles on root cells of Allium cepa

Increasing use of zinc oxide nanoparticles (ZnO NP) in consumer products may enhance its release into the environment. Phytotoxicity study is important to understand its possible environmental impact. Allium cepa (Onion bulb) is the best model organism to study genetic toxicology of nanoparticles. Here we have reported cytogenetic and genotoxic effects of ZnO NPs on the root cells of A. cepa. The effects of ZnO NPs on the mitotic index (MI), micronuclei index (MN index), chromosomal aberration index, and lipid peroxidation were determined through the hydroponic culturing of A. cepa. A. cepa roots were treated with the dispersions of ZnO NPs at four different concentrations (25, 50, 75, and 100 μg ml −1). With the increasing concentrations of ZnO NPs MI decreased with the increase of pycnotic cells, on the other hand MN and chromosomal aberration index increased. The frequency of micronucleated cells was higher in ZnO NPs treated cells as compared to control (deionized distilled water). The number of cells in each mitotic phase changed upon ZnO NPs treatment. The effect of ZnO NPs on lipid peroxidation as examined by measuring TBARS concentration was evident at all the concentrations compared to bulk ZnO. The TEM image showed internalization of ZnO NPs like particles. SEM image of treated A. cepa demonstrated that the internalized nanoparticles agglomerated depending on the physico-chemical environment inside the cell. Our results demonstrated that ZnO NPs can be a clastogenic/genotoxic and cytotoxic agent. In conclusion, the A. cepa cytogenetic test can be used for the genotoxicity monitoring of novel nanomaterials like ZnO NPs, which is used in many consumer products.

Vegetal test-system investigation on cytotoxicity of water from urban streams located in the northeastern region of Maringá, Paraná State, Brazil

The increase in consumption of water, the destruction of riparian forests and the pollution caused by humans, have severely degraded several water resources. Numerous stream crisscross the city of Maringá, Paraná state, Brazil and most of their sources are scattered through the urban region. Current analysis assesses the cytotoxic potential of water from the Corregozinho, Isalto, Morangueira and Ozório streams, located within the high-populated northeastern region of Maringá, inside the urban perimeter. Root meristematic cells of Allium cepa were used as test-system. The roots of onion were prepared by Feulgen’s reaction and stained with Schiff's reagent. Results showed that there were no statistically significant changes evaluated by the chi-square test on the rates of cell division in cells of Allium cepa roots treated with the water of the streams when compared to data from controls. However, further analyses should be undertaken at different times for a periodic assessment of conditions in the streams, coupled with an awareness of the population on the environment.

Textile dye degradation by bacterial consortium and subsequent toxicological analysis of dye and dye metabolites using cytotoxicity, genotoxicity and oxidative stress studies

The present study aims to evaluate Red HE3B degrading potential of developed microbial consortium SDS using two bacterial cultures viz. Providencia sp. SDS (PS) and Pseudomonas aeuroginosa strain BCH (PA) originally isolated from dye contaminated soil. Consortium was found to be much faster for decolorization and degradation of Red HE3B compared to the individual bacterial strain. The intensive metabolic activity of these strains led to 100% decolorization of Red HE3B (50mgl−1) with in 1h. Significant induction of various dye decolorizing enzymes viz. veratryl alcohol oxidase, laccase, azoreductase and DCIP reductase compared to control, point out towards their involvement in overall decolorization and degradation process. Analytical studies like HPLC, FTIR and GC–MS were used to scrutinize the biodegradation process. Toxicological studies before and after microbial treatment was studied with respect to cytotoxicity, genotoxicity, oxidative stress, antioxidant enzyme status, protein oxidation and lipid peroxidation analysis using root cells of Allium cepa. Toxicity analysis with A. cepa signifies that dye Red HE3B exerts oxidative stress and subsequently toxic effect on the root cells where as biodegradation metabolites of the dye are relatively less toxic in nature. Phytotoxicity studies also indicated that microbial treatment favors detoxification of Red HE3B.

Comparative evaluation of promutagens o-PDA, m-PDA and MH for genotoxic response in root cells of Allium cepa L.

A wide number of chemicals from different sources are released into the environment, some of which upon metabolic activation are converted to mutagenic products. These chemicals might hence possess threat to public health. Genotoxic potential of three promutagens – o-phenylenediamine (o-PDA), m-phenylenediamine (m-PDA) and maleic hydrazide (MH) was evaluated using Allium cepa as the test system. Following treatment the genotoxic endpoints measured in the root tissue were mitotic index, cells with mitotic or chromosome aberration and micronuclei. DNA damage in root cells was evaluated by comet assay. EC50 determined on the basis of root growth for o-PDA, m-PDA, MH were between 7–8 mg/l, 65–70 mg/l and 9–10 mg/l respectively. All the three agents induced genotoxicity significantly, that followed a dose response. While o-PDA and m-PDA did not induce DNA damage significantly, induction of DNA damage by MH was significant and dose dependent. The study identifies the genotoxic potential and re-establishes the fact that Allium cepa could ideally be used for evaluation of chromosome aberration and DNA damage.

Development of a Non-Scanning Vibrational Sum-Frequency Generation Detected Infrared Super-Resolution Microscope and its Application to Biological Cells

We report single-cell infrared (IR) imaging of onion (Allium cepa) root cells using an IR super-resolution microscope based on vibrational sum-frequency generation (VSFG). The resolution of recorded IR images was less than 2 microm and IR super-resolution was achieved by virtue of the VSFG detection. In addition, IR spectra measurements were successfully performed on distinct intra-cellular assemblies. The IR absorption intensity of the cell nuclear edge and the nucleolus in the 3055-3130 cm(-1) region was stronger than that from the cytoplasmic part. This is because the cell nucleus and nucleolus contain larger amounts of nucleic acid. Thus, the obtained IR spectra reflect differences in chemical composition among different cellular structures. In addition, the ability of our novel IR super-resolution microscope to obtain distinct information on both VSFG and two-photon fluorescence is demonstrated.

Aluminium-induced DNA damage and adaptive response to genotoxic stress in plant cells are mediated through reactive oxygen intermediates

Experiments employing growing root cells of Allium cepa were conducted with a view to elucidate the role of reactive oxygen intermediates (ROI) in aluminium (Al)-induced DNA damage, cell death and adaptive response to genotoxic challenge imposed by ethyl methanesulphonate (EMS) or methyl mercuric chloride (MMCl). In a first set of experiments, root cells in planta were treated with Al at high concentrations (200-800 microM) for 3 h without or with pre-treatments of dihydroxybenzene disulphonic acid (Tiron) and dimethylthiourea (DMTU) for 2 h that trap O(2)(.-)and hydrogen peroxide (H(2)O(2)), respectively. At the end of treatments, generation of O(2)(.-) and H(2)O(2), cell death and DNA damage were determined. In a second set of experiments, root cells in planta were conditioned by Al at low concentrations (5 or 10 microM) for 2 h and after a 2 h intertreatment interval challenged by MMCl or EMS for 3 h without or with a pre-treatment of Tiron or DMTU. Conditioning treatments, in addition, included two oxidative agents viz rose bengal and H(2)O(2) for comparison. Following treatments, root cells in planta were allowed to recover in tap water. Genotoxicity and DNA damage were evaluated by micronucleus (MN), chromosome aberration (CA) or spindle aberration (SA) and comet assays at different hours (0-30 h) of recovery. The results demonstrated that whereas Al at high concentrations induced DNA damage and cell death, in low concentrations induced adaptive response conferring genomic protection from genotoxic challenge imposed by MMCl, EMS and Al. Pre-treatments of Tiron and DMTU prevented Al-induced DNA damage, cell death, as well as genotoxic adaptation to MMCl and EMS, significantly. The findings underscored the biphasic (hormetic) mode of action of Al that at high doses induced DNA damage and at low non-toxic doses conferred genomic protection, both of which were mediated through ROI but perhaps involving different networks.