Hordeum Vulgare Seedlings Research Articles

Antioxidative parameters in the seedlings of Hordeum vulgare in response priming seeds with diatomite solution under salt stress

Antioxidative parameters in the seedlings of Hordeum vulgare in response priming seeds with diatomite solution under salt stress

Studying The Responses of Hordeum vulgare Seedlings to Salinity and Osmotic Stresses: Oxidative Stress/Antioxidants Play Crucial Roles دراسة إستجابات بادرات الشعير للإجهاد الملحي والأسموزي: الإجهاد بالأکسدة ومضاداتها يلعبان دورا هاما

Salinity and osmotic stresses are prime reasons of plant growth and productivity reduction in semi-arid regions and cause complex series of physiological, cellular, and molecular changes. Since osmotic and ionic effects are correlated and initiated by salinity, separating both is an important step in understanding the basis of salt tolerance. Barely seedlings(cultivar Giza 134)were treated with either NaCl(150 mM)or iso-osmotic polyethylene glycol 6000 (19.5% PEG). Treatments were applied two times before sampling and collected after two weeks from emergence. Results showed decreasing of fresh matter in treated seedlings, especially those treated with PEG. Furthermore, significant increase of non-enzymatic antioxidants, oxidative markers in addition to enzymatic antioxidants examined (peroxidase (POX), and polyphenol oxidase (PPO)) was detected with PEG treatment. The osmoregulators including proline (Pro) and glycine betaine(GB) increased in the root tissue, in conjunction with enhancement in the antioxidant status of leaves by applying PEG. Based on molecular analysis using real-time RT-PCR, HvNHX gene (coding for Na+/H+ antiporter) was highly expressed after 48 h from treatment in the roots under salinity, but it was expressed in PEG-treated leaves rather than salt-treated ones, and the opposite was true for HvGORK gene (regulate voltage-gated K+-permeable channels).On the other hand, HvDREB gene(coding for dehydration responsive element binding protein)has recorded higher expression in the roots under PEG treatment compared to control. Taken together, the current study suggests that the studied barley cultivar possesses higher tolerance to salt stress than osmotic stress imposed by PEG, so it could be more suitable for cultivation under salinity conditions.

Barley (Hordeum vulgare) seedling growth declines with increasing exposure to silver nanoparticles in biosolid-amended soils

Silver nanoparticles (AgNPs), a component of many consumer products, are considered an environmental risk due to the broad-spectrum toxicity of Ag+ to non-target organisms. Most AgNPs released from consumer products will end up as biosolids in wastewater treatment plants, which are often applied as a fertilizer to agriculture. Land application of biosolids may add AgNPs to the soil–plant system, with unknown consequences. This study investigated the growth of Hordeum vulgare seedlings, Ag bioconcentration and distribution in shoot and root tissues of barley exposed to biosolid-amended Delacour and Organization for Economic Co-operation and Development (OECD) soils spiked with AgNPs (up to 366 mg Ag kg−1 dry soil). In both soils, root and shoot growth declined linearly as the concentration of AgNPs increased. Barley had higher Ag bioconcentration values when grown in the OECD soil than in the Delacour soil. Silver bioavailability was greater in the OECD soil due to its physicochemical properties, such as low calcium concentration and acidic pH, relative to the Delacour soil. Barley seedlings exhibited morphological changes, including smaller shoots and shorter, thick roots after 14 d exposure to AgNPs. We conclude that plant structural responses, particularly changes in root biomass, could be an early diagnostic of seedling exposure to AgNPs in biosolid-amended soils.

Di-n-butyl phthalate-induced phytotoxicity in Hordeum vulgare seedlings and subsequent antioxidant defense response

Di-n-butyl phthalate (DBP) is one of the frequently detected phthalates in environmental samples. The effects of phthalates are extensively studied in the animals but the effects on plants are scarce. Therefore, the present study is aimed to envisage the effects of DBP on the antioxidative defense system in Hordeum vulgare L. seedlings grown under laboratory conditions for 7 d. The activities of different antioxidative enzymes were enhanced in the shoots. In the roots, the activity of guaiacol peroxidase increased and the catalase activity decreased initially but increased at higher DBP concentrations, whereas the activities of superoxide dismutase, ascorbate peroxidase, and glutathione reductase declined. Furthermore, the content of polyphenols elevated after exposure of seedlings to DBP. The possible reason for these responses of barley seedlings is the oxidative burst, i.e., enhanced production of reactive oxygen species, which were confirmed using confocal microscopy in terms of loss in plasma membrane integrity. DBP also disturbed the normal stomatal morphology of barley seedlings. The study may help to provide insights into the defense of crop plants against phthalate stress.

Stress Ameliorative Effects of Indole Acetic Acid on Hordeum vulgare L. Seedlings Subjected to Zinc Toxicity

The heavy metals present in the environment accumulate in the plants and affect their productivity and yield. By entering the food chain, metals cause several serious health problems in human beings as well as in other organisms. Indole acetic acid (IAA) is known to act as a signaling molecule between symbiotic association of metal accumulating plants and plant growth promoting rhizobacteria (PGPR). Present study demonstrated a protective role of IAA against surplus Zinc (Zn)-induced toxicity to Hordeum vulgare seedlings. Elevated Zn concentrations suppressed the plant growth, caused a reduction in leaf relative water contents (RWC) and elevated free proline and non-protein thiols (NPT) accumulation. Zinc treatment also led to enhanced lipid peroxidation (MDA contents) as well as the activity of ascorbate peroxidase (APX), showing the involvement of antioxidative defense mechanism to reduce Zn induced toxicity. IAA oxidase activity was also observed to increase due to Zn treatment. IAA pretreatment of H. vulgare caryopsis could partly revert the Zn-induced toxicity in seedlings.

Maleic acid and EDTA mediated extenuation of Co(II) stress in Hordeum vulgare seedlings

The present study was performed to assess the effects of maleic acid (MA), ethylenediaminetetraacetic acid (EDTA) amendments on biochemical parameters of 7 days old seedlings of Hordeum vulgare L. under Co(II) stress. Application of MA, EDTA, Co(II) alone significantly reduced the root length and shoot length, whereas combination of MA and Co(II), and EDTA and Co(II) enhances the root and shoot length. The antioxidative enzymes such as superoxide dismutase, catalase, guaiacol peroxidase, ascorbate peroxidase and glutathione reductase were significantly enhanced under application of MA, EDTA, Co(II) alone, while their combinations reduced the activities of all the antioxidative enzymes. Multivariate regression analysis and β-regression coefficients showed that β1(Co) and β2(MA) have positive regression on the antioxdative enzymes, while β3(Co×MA) have negative regression with the antioxidative enzymes. Similarly, β1(Co) and β2(EDTA), and β3(Co×EDTA) showed the similar trend as that of Co and MA. Malondialdehyde (MDA) content is increased under Co stress, whereas MA and EDTA alone or in combination with Co reduce the MDA content. Multiple linear regression analysis also showed that MDA content is significantly enhanced under β1(Co) stress, whereas in combination with MA or EDTA decreases the MDA content.

Tartaric Acid Mediated Cr Hyperaccumulation and Biochemical alterations in seedlings of Hordeum vulgare L.

The present study was done to evaluate the effects of tartaric acid (TA) amendment on physiology of Hordeum vulgare L. seedlings under Cr(VI) stress. Cr(VI) at higher concentrations decreased the shoot and root dry weights of seedlings. However, amendment of Cr(VI) media with TA enhanced the root and shoot dry weights, activities of antioxidative enzymes (ascorbate peroxidase, guaiacol peroxidase, superoxide dismutase, catalase, and glutathione reductase), and contents of pigments (total chlorophyll and carotenoids). Cr(VI) also increased the malondialdehyde content, an indicator of lipid peroxidation and stress. However, application of TA in combination with higher concentrations of Cr(VI) reduced the malondialdehyde content. Amendment of 0.5 mM Cr(VI) with 1.5 mM TA increased the Cr uptake content in the roots of the seedlings by 208.7% with respect to treatment with 0.5 mM Cr(VI) only. The shoot and root bio-concentration factors (BCF) were enhanced with the application of TA to culture media. Further, the results were statistically analyzed by employing various multivariate techniques such as analysis of variance, multiple regression analysis, beta regression analysis, correlation analysis, principal component analysis, factor analysis, non-metric multidimensional scaling, canonical correspondence analysis, and two-block partial least squares. The present study confirmed that TA acts as an antagonist to Cr(VI) in the seedlings of H. vulgare by increasing their antioxidative potential and enhancing their capability of chromium accumulation. The present study also suggests that multivariate techniques, which are mainly applied for data analysis in the field of ecology, can also be applied for experimental biology studies.

Effect of Different Anabaena variabilis (Kütz) Treatments on Some Growth Parameters and Physiological Aspects of Hordeum vulgare L. and Trigonella foenum-graecum L.

CYANOBACTERIA are a diverse group of prokaryotes which occupies many environments. In terrestrial habitats, they were famed to benefit both soil and plants through releasing bioactive substances of various biological functions. In the present study four treatments of Anabaena variabilis (seeds primed in 1% fresh cyanobacterial extract, seeds sown in soils inoculated with 3g fresh or dry cyanobacterial cells per 1 kg soil and wet seeds primed with 3g dry cyanobacterial powder per 1 kg seeds) were examined for their effect on Hordeum vulgare and Trigonella foenum-graecum L. plants. All treatments increased the germination percentage, shoot length, fresh and dry weights. The photosynthetic pigments, proteins, glutamic-oxaloacetic and glutamic-pyruvic transaminases (GOT and GPT) activities were also markedly increased specially in seeds primed with cyanobacterium dried cells. The protein profile of Hordeum vulgare seedlings revealed the appearance of newly formed protein band with molecular weight of 220 KDa in response to soaking the seeds in fresh cells extract. On the other hand, the protein profile of Trigonella foenum-graecum L. shows the induction of low molecular weight protein bands 10-14 KDa with all treatments. The plant growth promotive effect was attributed to the bioactive materials like phytohormones, exopolysaccharides, nitrogen, phosphorus and potassium estimated in the cyanobacterial biomass. The results recommended bio-priming the seeds of the two examined plants in dried cyanobacterial biomass as an economical and safe route fertilizer.

Developing Microbial Inocula to Support Biofuel Crop Cultivation on Tributyltin Contaminated Marine Sediments

Tributyltin (TBT) is a synthetic organotin compound and is recognised as the most toxic chemical ever knowingly introduced into the marine environment. Organotins have a wide range of application with an estimated global production of 50,000 tons per year therefore impacts from TBT can be seen or anticipated in many environments including protected areas like aqua farms and world heritage sites effecting aquaculture and undisturbed ecosystems. Due to the impact of TBT a necessity exists for the treatment of contaminated sediment and soil using nature-based solutions as it is both non-invasive and sustainable. However these remediation techniques must also be economically interesting to increase its acceptance. Thus using the biomass from plant species with the ability to cultivate in dredged sediment for biofuel and biomaterials production should be considered to ensure that renewable energy consumption of 10% is meet by 2020. The objectives of this study is to investigate the potential of Hordeum vulgare and Brassica napus to cultivate in marine sediments despite the salinity and TBT pollution for a 30 day pot trial. Further to inoculate seedling roots with known TBT degrading bacteria to enhance the phytoremediation capacity. Also to establish if bacterial isolates C7 and C22 are plant growth promoting bacteria. Statistical analysis on seedlings biomass was carried out followed by analytical analyses by atomic absorption spectroscopy (AAS) and sediment analysis by gas chromatography mass spectrometry (GC-MS). Results showed a maximum decrease of ≥ 82% and ≥ 80% of TBT in sediment samples respectively with bacteria inoculum C7 (KX881905) and C22 (KX881904), further Hordeum vulgare seedlings were the ideal candidate plant species with a significant production of biomass.

Horizontal natural product transfer: A potential source of alkaloidal contaminants in phytopharmaceuticals

BackgroundIt was recently shown that nicotine and pyrrolizidine alkaloids that leach out from decomposing plant material (donor plants) are subsequently taken up by the roots of acceptor plants and translocated into their leaves. Furthermore, it is well established that plant roots take up xenobiotics, generally by simple diffusion, and that this passive import depends on the physico-chemical properties of the substances. HypothesisBased on the well-known uptake of xenobiotics, we assumed that in analogy, the uptake of alkaloids, which are leached out from plant material (donor plants) represents a quite general feature of plant biology. MethodsUsing barley as a model plant, we analyzed the uptake of alkaloids by applying them to Hordeum vulgare seedlings. Based on HPLC analyses, the presence of the particular alkaloids in the acceptor plants was determined. ResultsWe demonstrated that numerous alkaloids of different structural types are able to diffuse through biomembranes and are taken up by acceptor plants. In contrast, an uptake of quaternary alkaloids, with a permanent positive charge, could not be detected. ConclusionAs most alkaloidal plants generally die back afield, and the corresponding natural products are leached out into the soil. Our findings have substantial relevance for all plant-derived commodities, especially for the production of phytopharmaceuticals and the related safety issues. Moreover, the evidence that plants are inherently able to take up alkaloids from the soil, which are derived from other plants, will alter our appraisal of plant–plant interactions. In this context, the classical definition of xenobiotics, which are considered as “non-natural” substances, might be also extended by including natural products leached out into the soil.

Evidence of Phytotoxicity and Genotoxicity in Hordeum vulgare L. Exposed to CeO2 and TiO2 Nanoparticles.

Engineered nanoscale materials (ENMs) are considered emerging contaminants since they are perceived as a potential threat to the environment and the human health. The reactions of living organisms when exposed to metal nanoparticles (NPs) or NPs of different size are not well known. Very few studies on NPs–plant interactions have been published, so far. For this reason there is also great concern regarding the potential NPs impact to food safety. Early genotoxic and phytotoxic effects of cerium oxide NPs (nCeO2) and titanium dioxide NPs (nTiO2) were investigated in seedlings of Hordeum vulgare L. Caryopses were exposed to an aqueous dispersion of nCeO2 and nTiO2 at, respectively 0, 500, 1000, and 2000 mg l-1 for 7 days. Genotoxicity was studied by Randomly Amplified Polymorphism DNA (RAPDs) and mitotic index on root tip cells. Differences between treated and control plants were observed in RAPD banding patterns as well as at the chromosomal level with a reduction of cell divisions. At cellular level we monitored the oxidative stress of treated plants in terms of reactive oxygen species (ROS) generation and ATP content. Again nCeO2 influenced clearly these two physiological parameters, while nTiO2 were ineffective. In particular, the dose 500 mg l-1 showed the highest increase regarding both ROS generation and ATP content; the phenomenon were detectable, at different extent, both at root and shoot level. Total Ce and Ti concentration in seedlings was detected by ICP-OES. TEM EDSX microanalysis demonstrated the presence of aggregates of nCeO2 and nTiO2 within root cells of barley. nCeO2 induced modifications in the chromatin aggregation mode in the nuclei of both root and shoot cells.

Physiological and biochemical reactions of Hordeum vulgare seedlings to the action of silver nanoparticles

Morphometrical indexes, and spectrophotometrically measured protein and glutathione (GSH, GSSG) contents and activity of peroxidase (POD, EC 1.11.1.7), glutathione-reductase (GR, EC 1.6.4.2) and glutathione S-transferase (GST, EС 2.5.1.18) were examined in Hordeum vulgare L. seedlings after 0.01 and 0.1 mg/l AgNPs treatment during 24 h. We tested the hypothesis that the action of nanoparticles has a stressful effect on the physiological and biochemical processes of seedlings. Growth of roots was inhibited and fresh weight decreased by 29% and 21% under low and high concentrations respectively. Conversely, leaf growth was intensified, and leaf length (16% and 18%) and fresh weight (35% and 44%) increased at low and high concentrations respectively. POD activity in roots increased by 26% and 7%, and decreased in leaves to 57% and 81% of control at low and high concentrations respectively. GSH content changed insignificantly, but GSSG content increased in roots (2 and 2.5-fold) and in leaves (13% and 30%) at both AgNPs concentrations. GSH/GSSG-ratio decreased in roots (1.9 and 2.6-fold) and in leaves (1.1 and 1.3-fold) at low and high concentrations respectively. GR activity decreased at a concentration of 0.01 mg/l (7% in roots and 17% in leaves respectively) and increased at 0.1 mg/l (52% in roots and 6% in leaves). GST activity increased in leaves (52% and 78% at low and high concentrations) but decreased by 17% in roots under high concentration of nanosilver. Thus, the action of AgNPs on barley seedlings had a dose-dependent and organ-specific character. The various directions of changes in growth, metabolic processes and activity of antioxidant defense systems appear to be a stress response of barley seedlings to the impact of AgNPs, which underlines the necessity of detailed study of plant intracellular processes exposed to the action of nanomaterial.

Variation in Nitrification Inhibition Activity of Neem Leaves Collected from Different Locations of Lucknow (India)

This study was carried out to assess the variation in nitrification inhibition (NI) activity of neem leaves obtained from trees growing in same agroclimate. The study was accomplished in the year 2012, in Lucknow city of Uttar Pradesh State of India. Dried leaves of four neem trees growing at different locations within Lucknow were screened for their NI potential. Treatments comprised of 6 combinations of urea-N and inhibitors as urea with dried leaf powder of New Hyderabad (NH) location tree, urea with dried leaf powder of Gomti Nagar (GN) location tree, urea with dried leaf powder of Hazratganj (HG) location tree, urea with dried leaf powder of Indira Nagar (IN) location tree, urea alone (without any inhibitor) and control (without urea-N and without any inhibitor). Concentrations of NH4-N and NO3-N present in soil were quantified on 1,3,7,14,21 and 28 day/s after treatment (DAT) by standard methods. Significant difference was observed in NI potential, as high concentration of NH4-N was maintained during experimental period when dried leaf powder of NH location tree was used whereas low concentration of NH4-N was obtained with the leaves of HG location tree. In the first week leaves of NH location tree, showed 90% NI which remained 56.98% till the third week, whereas it was least for HG by the third week, i.e., about 23%. Leaves obtained from NH location tree Original Research Article Arora and Srivastava; IJPSS, Article no. IJPSS.2014.003 458 proved to be the best inhibitor for nitrification amongst all treatments. Further, growth response of seedlings of Hordeum vulgare (barley) was used as a biological check of soil nutritive value with the supplementation of dried leaf powder of four trees individually. NH location tree leaves treated soils were found to be the best with respect to growth parameters of barley. Study gives an indication for pre-screening of trees growing in different locations for better results at commercial levels.

Assessment of the Suitability of Phytotoxkit Plastic Vertical Containers Compared with Petri Dishes for Standard Seedling Growth Tests

This study compares two cultivation methods (Petri dishes vs. Phytotoxkit containers; tap water vs. Knop's solution) for standard seedling growth tests. Seeds and young seedlings of Sinapis alba and Hordeum vulgare were used as study subjects and the adverse effect of Cd was assessed. Under testing conditions, only H. vulgare showed a significant decrease in seed germination in Petri dishes when tap water was used as the growth medium (70.8 % ± 46.4 %). No significant differences in IC50 values were found in either plant type for root growth between plants cultivated in Phytotoxkit containers and those cultivated in Petri dishes. The same findings were confirmed for shoot growth in H. vulgare, but not in S. alba. Suitability of Phytotoxkit containers over traditionally used Petri dishes for phytotoxicity determination was confirmed by higher correlation coefficients for all tests.

PREPARATIVE ISOLATION AND PURIFICATION OF LUTONARIN AND SAPONARIN FROM BARLEY SEEDLINGS BY HSCCC

In order to isolate large amounts of pure lutonarin and saponarin, a high performance method for isolation and purification of these two flavonoids from barley (Hordeum vulgare) seedlings was successfully established by utilizing high-speed counter-current chromatography (HSCCC). Separation was performed with a two-phase solvent system: ethyl acetate/n-butanol/water (3:2:5, v/v/v). A total of 24 mg lutonarin and 14 mg saponarin was obtained in one-step separation from 100 mg sample. High performance liquid chromatography (HPLC) analysis showed that the purity of each of the two compounds was over 98%. Their chemical structures were confirmed by UV, 1H NMR, and 13C NMR data.

Light promotes an increase of cytokinin oxidase/dehydrogenase activity during senescence of barley leaf segments

Following a study of the relationship between cytokinin oxidase/dehydrogenase (CKX) and senescence in darkened barley leaf segments, we have now investigated the influence of light on the in vitro activity of CKX. Seedlings of Hordeum vulgare L. were grown for 8 d under a light/dark regime of 18 h white light and 6 h darkness. Then apical parts of 7 cm length were cut from the first foliage leaves and their bases were placed in water. In segments kept in the dark, the CKX activity measured by cleavage of N 6-(Δ 2-isopentenyl)adenine rose from 0.1 pkat (g FW) −1 to 0.8 pkat (g initial FW) −1 within the first 4 d of incubation. In contrast, in segments kept under the light/dark regime it reached a value of 8.6 pkat (g initial FW) −1 over the same time period. The chlorophyll a content declined slightly slower during light/dark cycling than in darkness . In contrast to segments and isolated laminae, corresponding attached laminae exhibited less CKX activity after 2 d under light/dark conditions than after 2 d in the dark. The activity in attached laminae of first foliage leaves of plants growing in light/dark cycling increased strongly only when the plants were older than 4 weeks . In line with this, the CKX activity in attached laminae of flag leaves of barley growing in fields increased in a late developmental state. The senescence of darkened isolated laminae of Zea mays L. and Phragmites australis (Cav.) Trin. ex Steudel was associated with an enhancement of CKX activity too. Because in most cases a positive correlation between CKX activity and senescence was found, it is likely that the enzyme promotes senescence by destroying cytokinins, which help to keep Poaceae leaves green. Light may promote not only cytokinin degradation but also the formation of bioactive cytokinins in leaf segments.

Trifluralin-induced disorganization of microtubular cytoskeleton alters the development of roots inHordeum vulgareL.

The extensive use of herbicides in agriculture becomes an important factor in environmental pollution, especially in case of slowly degradable compounds. Some agents act on plants during a long period of time, even if a very low concentration of the herbicide remains in the soil. Here, we investigated the toxicological effect of a low concentration of dinitroaniline herbicide, trifluralin, on growing seedlings of Hordeum vulgare L. Trifluralin in concentration of 1 microg/ml inhibited root growth. The mitotic activity of meristematic cells was suppressed due to the retardation of metaphase progression--alteration that can be caused by cytoskeleton disorder. Using antibodies to alpha-tubulin, we investigated the distribution of microtubules in root meristem cells. During all stages of mitosis, the highly regular system of microtubular cytoskeleton observed in control cells was slightly disorganized. An examination of root structure using light and electron microscopy demonstrated that the cell walls did not form normally during cell division that led to the appearance of large multinucleated cells. Also, the premature (pathological) cell differentiation was induced by trifluralin. A part of differentiating cells showed intracellular structural changes that are consistent with programmed cell death. It seems that the development of alterations in trifluralin-treated roots was due to the microtubular cytoskeleton disorganization.

Effect of salt on physiological responses of barley to iron deficiency

Iron chlorosis is very common on alkaline soils such as calcareous ones, since iron availability is limited by high pH. Under these conditions of iron deficiency, graminaceous plant species induce special mechanisms for iron acquisition, involving enhanced release of iron chelators called phytosiderophores. On the other hand, it is known that most of salt soils have alkaline pH. So, plants growing on this kind of soils are often subjected simultaneously to salinity and iron deficiency. This work aimed at (i) studying the physiological responses of barley ( Hordeum vulgare L.) to iron deficiency, and (ii) evaluating the effect of salt on the iron nutrition and the phytosiderophore release. For this purpose, seedlings of Hordeum vulgare L. were cultivated under controlled conditions, either in a complete nutrient solution with or without NaCl, or in an iron free nutrient solution containing or not NaCl. The plant morphological aspect, chlorophyll content of young leaves, iron status, biomass production, and phytosiderophore release by roots were assessed. Plants subjected to Fe deficiency exhibited a severe chlorosis, accompanied by a significant biomass reduction. These plants developed more lateral roots than the control with a highly stimulated phytosiderophore release. However, the latter was greatly diminished when iron deficiency was associated to salinity. A depressive effect of salt on iron acquisition in plants subjected only to salt stress which was also observed and further confirmed by the important decrease of efficiency in iron acquisition. These results suggest that salinity may reduce capacity of plants to acquire iron from alkaline soils by inhibiting phytosiderophore release.

Cytogenetic effect of low dose γ-radiation in Hordeum vulgare seedlings: non-linear dose–effect relationship

Cytogenetic effect of low dose γ-radiation in Hordeum vulgare seedlings: non-linear dose–effect relationship

Cytogenetic effect of low dose γ-radiation in Hordeum vulgare seedlings: non-linear dose–effect relationship

The induction of chromosome aberrations in Hordeum vulgare germinated seeds was studied after ionizing irradiation with doses in the range of 10-1,000 mGy. The relationship between the frequency of aberrant cells and the absorbed dose was found to be nonlinear. A dose-independent plateau in the dose range from about 50 to 500 mGy was observed, where the level of cytogenetic damage was significantly different from the spontaneous level. The comparison of the goodness of the experimental data fitting with mathematical models of different complexity, using the most common quantitative criteria, demonstrated the advantage of a piecewise linear model over linear and polynomial models in approximating the frequency of cytogenetical disturbances. The results of the study support the hypothesis of indirect mechanisms of mutagenesis induced by low doses. Fundamental and applied implications of these findings are discussed.