Photosensitizing effects and physicochemical properties of chlorophyll a derivatives with hydrophilic oligoethylene glycol fragments at the macrocycle periphery

In this work, screening studies of the cytotoxic effect of chlorins with fragments of di-, tri-, and pentaethylene glycol at the macrocycle periphery in relation to HeLa, A549, and HT29 cells were performed. It is shown that, despite different hydrophobicity, all the compounds studied have a comparable photodynamic effect. The conjugate of chlorin e6 with pentaethylene glycol, which has the lowest tendency to association among the studied compounds with tropism for low density lipoproteins and the best characteristics of the formation of molecular complexes with Tween 80, has a significant difference in dark and photoinduced toxicity (ratio IC50(dark)/IC50(photo) approximately 2 orders of magnitude for all cell lines), which allows to hope for a sufficiently large "therapeutic window". A study of the interaction of this compound with HeLa cells shows that the substance penetrates the cell and, after red light irradiation induces ROS appearance inside the cell, associated, apparently, with the photogeneration of singlet oxygen. These data indicate that photoinduced toxic effects are caused by damage to intracellular structures as a result of oxidative stress. Programmed type of cell death characterized with caspase-3 induction is prevailing. So, the conjugate of chlorin e6 with pentaethylene glycol is a promising antitumor PS that can be successfully solubilized with Tween 80, which makes it suitable for further in vivo studies.

Soil Microbiome in Conditions of Oil Pollution of Subarctic Ecosystems

The present study aimed to investigate the recovery of soil quality and the bacterial and fungal communities following various recultivation methods in areas contaminated with oil. Oil spills are known to have severe impacts on ecosystems; thus, the restoration of contaminated soils has become a significant challenge nowadays. The study was conducted in the forest-tundra zone of the European North-East, where 39 soil samples from five oil-contaminated sites and reference sites were subjected to metagenomic analyses. The contaminated sites were treated with different biopreparations, and the recovery of soil quality and microbial communities were analyzed. The analysis of bacteria and fungi communities was carried out using 16S rDNA and ITS metabarcoding. It was found that 68% of bacterial OTUs and 64% of fungal OTUs were unique to the reference plot and not registered in any of the recultivated plots. However, the species diversity of recultivated sites was similar, with 50-80% of bacterial OTUs and 44-60% of fungal OTUs being common to all sites. New data obtained through soil metabarcoding confirm our earlier conclusions about the effectiveness of using biopreparations with indigenous oil-oxidizing micro-organisms also with mineral fertilizers, and herbaceous plant seeds for soil remediation. It is possible that the characteristics of microbial communities will be informative in the bioindication of soils reclaimed after oil pollution.

Dose-Dependent Effect of Mitochondrial Superoxide Dismutase Gene Overexpression on Radioresistance of HEK293T Cells

Over the last two decades, a multitude of gain-of-function studies have been conducted on genes that encode antioxidative enzymes, including one of the key enzymes, manganese superoxide dismutase (SOD2). The results of such studies are often contradictory, as they strongly depend on many factors, such as the gene overexpression level. In this study, the effect of altering the ectopic expression level of major transcript variants of the SOD2 gene on the radioresistance of HEK293T cells was investigated using CRISPRa technology. A significant increase in cell viability in comparison with the transfection control was detected in cells with moderate SOD2 overexpression after irradiation at 2 Gy, but not at 3 or 5 Gy. A further increase in the level of SOD2 ectopic expression up to 22.5-fold resulted in increased cell viability detectable only after irradiation at 5 Gy. Furthermore, a 15-20-fold increase in SOD2 expression raised the clonogenic survival of cells after irradiation at 5 Gy. Simultaneous overexpression of genes encoding SOD2 and Catalase (CAT) enhanced clonogenic cell survival after irradiation more effectively than separate overexpression of both. In conjunction with the literature data on the suppression of the procarcinogenic effects of superoxide dismutase overexpression by ectopic expression of CAT, the data presented here suggest the potential efficacy of simultaneous overexpression of SOD2 and CAT to reduce oxidative stress occurring in various pathological processes. Moreover, these results illustrate the importance of selecting the degree of SOD2 overexpression to obtain a protective effect.

Systematic review of comparative transcriptomic studies of cellular resistance to genotoxic stress

The development of resistance by tumor cells to various types of therapy is a significant problem that decreases the effectiveness of oncology treatments. For more than two decades, comparative transcriptomic studies of tumor cells with different sensitivities to ionizing radiation and chemotherapeutic agents have been conducted in order to identify the causes and mechanisms underlying this phenomenon. However, the results of such studies have little in common and often contradict each other. We have assumed that a systematic analysis of a large number of such studies will provide new knowledge about the mechanisms of development of therapeutic resistance in tumor cells. Our comparison of 123 differentially expressed gene (DEG) lists published in 98 papers suggests a very low degree of consistency between the study results. Grouping the data by type of genotoxic agent and tumor type did not increase the similarity. The most frequently overexpressed genes were found to be those encoding the transport protein ABCB1 and the antiviral defense protein IFITM1. We put forward a hypothesis that the role played by the overexpression of the latter in the development of resistance may be associated not only with the stimulation of proliferation, but also with the limitation of exosomal communication and, as a result, with a decrease in the bystander effect. Among down regulated DEGs, BNIP3 was observed most frequently. The expression of BNIP3, together with BNIP3L, is often suppressed in cells resistant to non-platinum genotoxic chemotherapeutic agents, whereas it is increased in cells resistant to ionizing radiation. These observations are likely to be mediated by the binary effects of these gene products on survival, and regulation of apoptosis and autophagy. The combined data also show that even such obvious mechanisms as inhibition of apoptosis and increase of proliferation are not universal but show multidirectional changes.

AOX1a Expression in Arabidopsis thaliana Affects the State of Chloroplast Photoprotective Systems under Moderately High Light Conditions

Alternative oxidase (AOX) in the mitochondrial electron transport chain is considered important for sustaining photosynthesis under high light conditions. Here, we examined the effects of the AOX pathway on the state of chloroplast photoprotective systems. Arabidopsis thaliana plants (4 weeks old), comprising three genotypes (wild type [WT], overexpressing [XX-2] and antisense [AS-12] lines for AOX1a), were exposed to moderately high light conditions (MHL, 400 μmol m^-2 s^-1) in a short-term experiment (8 h). After 8 h of MHL, the WT and XX-2 plants showed stable non-photochemical quenching (qN) and violaxanthin cycle activity. Antisense plants displayed the lowest level of qN and a lower de-epoxidation state (DEPS) relative to plants of the same line after 4-6 h MHL, as well as compared to WT and XX-2 plants after 8 h MHL. The decline in DEPS in AS-12 plants was attributed to an insufficient violaxanthin de-epoxidase activity, which in turn was associated with a decrease in reduced ascorbate levels in the chloroplasts and leaves. Simultaneously, gene expression and the activity of ascorbate peroxidase in the antisense line increased after 8 h of MHL, supporting the compensatory effect of the antioxidant system when AOX1a expression is suppressed. This study emphasizes the role played by AOX in modulating the photoprotection processes and in the maintenance of relationships between mitochondria and chloroplasts by influencing ascorbate content.

Responses of genes of DNA repair, alternative oxidase, and pro-/antioxidant state in Arabidopsis thaliana with altered expression of AOX1a to gamma irradiation

PURPOSE

High doses of gamma (γ) irradiation cause oxidative stress and DNA damage. Alternative oxidase (AOX) catalyzes the energy-dissipating cyanide-resistant alternative pathway in plant mitochondria and is an important part of the cellular defense network under stress conditions. In this study, Arabidopsis thaliana plants with an altered expression of the AOX1a gene were exposed by high dose-rate ionizing radiation to assess the expression of genes of DNA repair and pro-/antioxidant states to elucidate the functional significance of AOX in plant stress response.

MATERIALS AND METHODS

Five-week-old A. thaliana plants, either with basal AOX1a gene expression (wild-type Colombia-0 (Col-0)), antisense silencing of AOX1a (AS-12), and overexpression of the gene (XX-2), were γ-irradiated at a dose of 200 Gy. Gene expression and biochemical analyses were performed 12 h after irradiation.

RESULTS

Acute γ-irradiation caused different responses between the genotypes. XX-2 plants, either control or irradiated, showed the highest expression of AOX1a gene and AOX protein, and the lowest expression of DNA repair genes. Wild type and AS-12 plants exposed to γ-irradiation upregulated another stress-induced gene, AOX1d, and DNA repair genes. Furthermore, a higher activity of Mn-dependent superoxide dismutase (Mn-SOD) was observed in the irradiated AS-12 plants than in the untreated plants of this line. However, AS-12 plants were less effective than Col-0 plants in controlling the accumulation of the superoxide anion. XX-2 plants had the lowest reactive oxygen species (ROS) levels among the genotypes.

CONCLUSIONS

AS-12 plants display a compensatory mechanism by increasing the expression of AOX1d and the synthesis of the AOX protein, as well as by Mn-SOD activation. However, these were insufficient to maintain the background level of embryonic lethal mutations, and thereby the reproductive capacity. These results highlight the importance of AOX in the successful adaptation of plants to acute γ-irradiation, and indicate that AOX1a plays a key role in the regulation of the stress response.

Dimeric derivatives of chlorophyll a with fragments of oligoethylene glycols as spacers between macrocycles: Synthesis, dark and photoinduced cytotoxic activity

In the present work, new dimeric derivatives of chlorophyll [Formula: see text] with oligoethylene glycol fragments as spacers between macrocycles were synthesized and their dark and photoinduced cytotoxic activities were studied in experiments in vitro. Dimeric derivatives were found to have a relatively low dark cytotoxic activity. It should be noted that most of the studied dimeric derivatives exhibited photoinduced cytotoxic activity at concentrations that were several times lower than those for dark cytotoxic activity. The photoinduced action of one of the most active compounds, a phorbin-chlorin dimer with the triethylene glycol fragment as a spacer between the macrocycles (13), was analysed in more detail in experiments in vitro. Compound (13) was shown to rapidly enter HeLa cells, however, its cytotoxic effect on these cells develops rather slowly. The results of the analysis of the activity of caspase-3 showed that Compound (13) does not cause apoptosis of HeLa cells. Analysis of the degree of hemolysis of mammalian erythrocytes as a result of exposure to Compound (13) showed that plasma membranes are a probable target of this substance.

The gene expression profiles of mitochondrial respiratory components in Arabidopsis plants with differing amounts of ALTERNATIVE OXIDASE1a under high intensity light

We compared the expression of mitochondrial alternative oxidase (AOX) and other non-phosphorylating respiratory components (NPhPs) in wild type and AOX1a transgenic Arabidopsis thaliana following short-term transfer of plants to higher irradiance conditions to gain more insight into the mechanisms of AOX functioning under light. The AOX1a overexpressing line (XX-2) showed the highest amount of AOX1a transcripts and AOX1A synthesis during the entire experiment, and many NPhPs genes were down-regulated after 6-8 h under the higher light conditions. Antisense AS-12 plants displayed a compensatory effect, typically after 8 h of exposure to higher irradiance, by up-regulating their expression of the majority of genes encoding AOX and other respiratory components. In addition, AS-12 plants displayed 'overcompensation effects' prior to their transfer to high light conditions, i.e., they showed a higher expression level of certain genes. As a result, the ROS content in AS-12, as in XX-2, was consistently lower than in the wild type. All NPhPs genes share, in common with AOX1a, light- and stress-related cis-acting regulatory elements (CAREs) in their promoters. However, the expression of respiratory genes does not always depend on the level of AOX1a expression. This suggests the presence of multiple combinations of signaling pathways in gene induction. Based on our results, we outline possible directions for future research.

Radioresistance, DNA Damage and DNA Repair in Cells With Moderate Overexpression of RPA1

Molecular responses to genotoxic stress, such as ionizing radiation, are intricately complex and involve hundreds of genes. Whether targeted overexpression of an endogenous gene can enhance resistance to ionizing radiation remains to be explored. In the present study we take an advantage of the CRISPR/dCas9 technology to moderately overexpress the RPA1 gene that encodes a key functional subunit of the replication protein A (RPA). RPA is a highly conserved heterotrimeric single-stranded DNA-binding protein complex involved in DNA replication, recombination, and repair. Dysfunction of RPA1 is detrimental for cells and organisms and can lead to diminished resistance to many stress factors. We demonstrate that HEK293T cells overexpressing RPA1 exhibit enhanced resistance to cell killing by gamma-radiation. Using the alkali comet assay, we show a remarkable acceleration of DNA breaks rejoining after gamma-irradiation in RPA1 overexpressing cells. However, the spontaneous rate of DNA damage was also higher in the presence of RPA1 overexpression, suggesting alterations in the processing of replication errors due to elevated activity of the RPA protein. Additionally, the analysis of the distributions of cells with different levels of DNA damage showed a link between the RPA1 overexpression and the kinetics of DNA repair within differentially damaged cell subpopulations. Our results provide knew knowledge on DNA damage stress responses and indicate that the concept of enhancing radioresistance by targeted alteration of the expression of a single gene is feasible, however undesired consequences should be considered and evaluated.

Genetic analysis in earthworm population from area contaminated with radionuclides and heavy metals

This study assessed the effects of environmental contamination by naturally occurring radionuclides and heavy metals on the genetic structure of a population of the earthworm Aporrectodea caliginosa. A. caliginosa were collected from four sites and characterized by amplified fragment length polymorphism (AFLP) analyses. No differences in genetic structure and diversity were found between sites that differed greatly in soil contamination levels of radionuclides and metals. However, when the genetic structure of the A. caliginosa population was analyzed without considering information about the sampling site, a complex intraspecific genetic structure was identified. At least three highly divergent lineages were found, in unequal proportions, of each genetically isolated group from each study site. No associations were found between the distribution of the detected genetic clusters and the geographical origin of the samples. Thus, no noticeable adaptive changes or signs of directional selection were detected, despite the long history of genotoxic waste disposal at the sampling site. These results suggest a combined effect of three factors on the genetic structure and diversity of A. caliginosa in soils: the complexity of the contaminant composition, the heterogeneous spatial distribution of the pollutants, and the complexity of the intraspecific genetic structures of A. caliginosa.

Microsatellite polymorphism of Trifolium pratense population at the conditions of radioactive and chemical contamination of soil (Komi republic, Russia)

There is no clear understanding of microevolutionary changes in natural populations of plants and animals due to anthropogenic contamination of the environment with toxicants and mutagens. But such data are necessary to forecast long-term effects of human activity. In this research, we studied genetic polymorphism in T. pratense sampled from seven sites varying in radioactive and chemical soil contamination in the vicinity of Vodny settlement (Komi, Russia). Analysis of five SSR loci was shown to be similar in a whole (N), mean (N_a) and effective (N_e) numbers of alleles, heterozygosity indexes (H_o and H_e), and the Shannon index (I). Difference in the private allele numbers was registered: the most contaminated site has 5 and others from 0 up 2 private alleles. No difference was found in the genetic structure of T. pratense population growing at the conditions of radioactive and chemical contamination. The Bayesian analysis provided evidence of a single cluster (K = 1) due to a similar genetic structure of samples, while AMOVA results demonstrated a high variability within individuals (75%) and a low variability (1%) among groups of T. pratense from sites that differ in the contamination level. Thus, the long-term radioactive and heavy metal contamination of soil did not result in significant microevolutionary changes in T. pratense population.

Differential Molecular Stress Responses to Low Compared to High Doses of Ionizing Radiation in Normal Human Fibroblasts

Understanding the mechanisms producing low dose ionizing radiation specific biological effects represents one of the major challenges of radiation biology. Although experimental evidence does suggest that various molecular stress response pathways may be involved in the production of low dose effects, much of the detail of those mechanisms remains elusive. We hypothesized that the regulation of various stress response pathways upon irradiation may differ from one another in complex dose-response manners, causing the specific and subtle low dose radiation effects. In the present study, the transcription level of 22 genes involved in stress responses were analyzed using RT-qPCR in normal human fibroblasts exposed to a range of gamma-doses from 1 to 200 cGy. Using the alkali comet assay, we also measured the level of DNA damages in dose-response and time-course experiments. We found non-linear dose responses for the repair of DNA damage after exposure to gamma-radiation. Alterations in gene expression were also not linear with dose for several of the genes examined and did not follow a single pattern. Rather, several patterns could be seen. Our results suggest a complex interplay of various stress response pathways triggered by low radiation doses, with various low dose thresholds for different genes.

[The level of DNA damage and DNA reparation rate in cells of earthworms sampled from natural populations for numerous generations inhabited territories with anthropogenically enhanced levels of radionuclides in soil]

Low doses of ionizing radiation and chemical toxic agent effects on biological systems on different organization levels have been studied by numerous researchers. But there is a clear lack of experimental data that allow one to reveal molecular and cellular adaptations of plants and animals from natural populations to adverse effects of environmental factors. The present study was aimed to assess genotoxic effects in earthworms Aporrectodea caliginosa Savigny and Lumbricus rubellus Hoffmeister sampled from the populations that during numerous generations inhabited the territories with a technogeneously enhanced content of natural origin radionuclides and heavy metals in soil. The levels ofthe DNA damage detected with alkaline and neutral versions of Comet-assay in invertebrates from contaminated territories were established not to differ from the spontaneous level found in the animals from the reference population. At the same time the rate of the DNA damage reparation induced in A. caliginosa sampled from the contaminated sites with additional acute γ-irradiation (4 Gy) was found to be considerably higher as compared with earthworms from the reference population.

[Cytogenetic effects in Allium schoenoprasum growing on the anthropogenically contaminated soil]

Cytogenetic effects in Allium schoenoprasum meristematic root tip cells grown for a year on the territory contaminated with 235U, 238U and 232Th decay series radionuclides, heavy metals and As were studied. The area is characterized with different concentrations of chemical compounds in soil affecting a toxic element migration in biocoenosis. Analysis of the chromosome aberration spectrum showed an ambiguous cell response to soil contamination. Within the weighted absorbed dose range up to 1.2 Gy the higher the dose the aberrant cell frequency increase was shown. But further increase in the dose resulted in a genotoxic effect decrease due to high toxic effects of heavy metals and radionuclides in soil. This was registered as a mitotic index decrease that can provoke a chromosome aberration frequency underestimation and result in erroneous conclusions about genotoxic effects in A. schoenoprasum used as a bioindicator.

[Radiation risk assessment for plant reference species (Pinus sylvestris and Vicia cracca) from the area of radium production waste storage]

The risk of an enhanced level of radionuclides of the uranium and thorium decay series in the environment for reference plant species (Pinus sylvestris and Vicia cracca) was assessed. 238U, 230Th, 226Ra, 210Po, 232Th and 228Th concentration factors for plants were found to be lower than one. The aboveground parts of Vicia cracca sampled from the area of the radium production waste storage mainly accumulated 22Ra, Pinus sylvestris branches--210Pb, 226Ra and 210Po. LOEDR calculated for the chromosome aberration frequency in both plant studies was 17-71 microGy/h. LOERD values for the reproductive capacity decrease in P. sylvestris and V. cracca were 17-71 microGy/h and 116-258 microGy/h, correspondingly. EDR10 for the chromosome aberration frequency in P. sylvestris and V. cracca were 148 and 347 microGy/h, that is, correspondingly, 255 and 708 times higher that background values. EDR10 for the plant reproductive capacity was 11-34 microGy/h, which 19-69 times increases the background values.

[Regularities of lateral distribution of uranium and thorium decay series radionuclides in the anthropogenically changed soils from the area of radium production waste storage]

Cartographical investigations of the territory of radium production waste storage has shown some changes in lateral differentiation of radionuclides of uranium and thorium decay series to occur during 27 years (1981-2008). Those changes are caused mostly by flat denudation typical for fluvial terrace. At present radionuclides of uranium and thorium decay series are concentrated mostly in flood lands and relief depressions. At the same time, decrease in the radionuclide activity concentration in 0-20 cm soil layer is observed with changes in lateral distribution. Total stocks of 226Ra, 210Pb and 210Po within catena soils studied in the northern and southern parts of the waste storage decreased 3-6 times, 238U - 2 times, and did not significantly change in case of 232Th during 27 years. Nonetheless, most of the samples studied are referred to radioactive waste both according to Russian standards (SPORO-2002) and IAEA safety norms (IAEA, 2004).

[Assessment of soil degradation in regions of nuclear power explosions at Semipalatinsk Nuclear Test Site]

Degree of the soil cover degradation at the "Balapan" and "Experimental field" test sites was assessed based on Allium-test of soil toxicity results and international guidelines on radioactive restriction of solid materials (IAEA, 2004) and environment (Smith, 2005). Soil cover degradation maps of large-scale (1 : 25000) were made. The main part of the area mapped belongs to high-contaminated toxic degraded soil. A relationship between the soil toxicity and the total radionuclide activity concentrations was found to be described by power functions. When the calculated value (equal to 413-415 Bq/kg of air dry soil) increases, the soil becomes toxic for plants. This value is 7.8 times higher than the maximal value for background territories (53 Bq/kg) surrounding SNTS. Russian sanitary and hygienic guidelines (Radiation safety norms, 2009; Sanitary regulations of radioactive waste management, 2003) underestimate the degree of soil radioactive contamination for plants.

[The assessment of no adverse effect doses for plant populations chronically exposed to radionuclides of uranium and thorium decay series]

Dose rates cause no adverse effects on natural populations of Pinus sylvestris L. and Vicia cracca L. inhabiting territories contaminated by uranium mill tailings and radium production wastes (Vodny settlement, Komi Republic) were determined. A significant increase in embryonic lethal mutation frequency in V. cracca legumes and decrease in seedlings survival rate as compared with control values were registered at dose rate equal to 1.67 mGy/day, that is 280 times higher than the one calculated for the reference site. The adverse effects in P. sylvestris expressed in increased frequency of chromosome aberrations in meristematic root tips and decreased reproductive capacity of seeds were determined at absorbed dose rate equal to 0.083 mGy/day. Data obtained show that the decrease in plant reproductive capacity in case of chronic exposure of radionuclides of uranium and thorium decay series can observe at lower weighted absorbed dose rates than in case of environmental contamination by artificial radionuclides.

[The assessment of radionuclide contamination and toxicity of soils sampled from "experimental field" site of Semipalatinsk nuclear test site]

Large-scale maps (1:25000) of soil contamination with radionuclides, lateral distribution of 137Cs, 90Sr, Fe and Mn water-soluble compounds and soil toxicity in "Experimental field" site of Semipalatinsk nuclear test site were charted. At present soils from studied site (4 km2) according to basic sanitary standards of radiation safety adopted in Russian Federation (OSPORB) do not attributed to radioactive wastes with respect to data on artificial radionuclide concentration, but they do in compliance with IAEA safety guide. The soils studied can not be released from regulatory control due to radioactive decay of 137Cs and 90Sr and accumulation-decay of 241Am up to 2106 year according to IAEA concept of exclusion, exemption and clearance. Data on bioassay "increase of Chlorella vulgaris Beijer biomass production in aqueous extract from soils" show that the largest part of soils from the studied site (74%) belongs to stimulating or insignificantly influencing on the algae reproduction due to water-soluble compounds effect. Toxic soils occupy 26% of the territory. The main factors effecting the algae reproduction in the aqueous extracts from soil are Fe concentration and 90Sr specific activity: 90Sr inhibits but Fe stimulates algae biomass production.

[Assessment of modern radioecological situation at nuclear explosion "Chagan" (Balapan Site, Semipalatinsk Nuclear Test Site, Kazakhstan)]

Results on estimation of modern radioecological situation at nuclear explosion "Chagan" based on large-scale cartographic studies (1:25000) of a test area (4 km2) are presented. Maximum gamma-irradiation doses were observed at bulk of ground surrounded a crater and at radioactive fall-outs extended to the North-East and to the SouthWest from the crater. Based on data on artificial radionuclide specific activity most part of soil samples were attributed to radioactive wastes according to IAEA (1996) and OSPORB (1999). Natural decrease of soil radioactivity up to safety level due to 60Co, 137Cs, 90Sr, 152Eu, 154Eu radioactive decay and 241Am accumulation-decay will not take place within the next 60 years at the studied area.

[The estimation of ionizing irradiation impact on Vicia cracca cenopopulations growing on the territory contaminated with the wastes of radium production]

The radiation exposure on cenopopulations Vicea cracca L. growing on the territory contaminated with the wastes of radium production was estimated. The relationship between the chromosome aberration in seedlings root tip cells and irradiation dose was found to be linear. The significant cytogenetic effects in chronically irradiated Vicia cracca cenopopulation are observed at doses (equal to 0.006-0.7 Gy) 10 times upward the natural radiation background level. The reduced reproductive success (significantly increased embryonic lethal mutation level) is observed at weighted absorbed doses (equal to 0.2-0.7 Gy) up to 200-700 times higher than the natural radiation background level. It is showh, that the radiation hygienic standards of permissible exposure are noticeably stricter that the radioecological limits.

[The mechanisms of 232Th and of Ce (III) toxic action on Chlorella vulgaris Beijer. Estimation of 232Th radiation impact contribution into toxic effect induced]

232Th and Ce (III) toxic effects and its modifications with caffeine and D,L-buthionine-(S,R)-sulphoximine on Chlorella vulgaris Beijer were studied using an optical density measure after 24 hours growth. Concentrations of 232Th or of Ce--toxic effect relationship were shown to be nonlinear. In the first (nontoxic) concentration range (for Ce 0.036-1.642 micromol/L and for 232Th 0.001-1.551 micromol/L) algae biomass production registered by optical density do not significantly differ from the control one. In the second (toxic) concentration range dose-effect relationship for 232Th is characterized with quadratic dependence and in the case of Ce--with exponential dependence. 232Th radiation component contribution into effect observed is appeared as induction of DNA damages additional to spontaneous at the radionuclide concentration (equal to 0.345 micromol/L) that is three times lower than in case of the non-radioactive chemical analog Ce (1.071 micromol/L).

[Quantitative estimation combined chemical and radioactive exposure on biological objects]

We summarized the researches to estimate the methods of combined (chemical and/or radioactive nature) factor action on biological objects. The data examined indicate that methods commonly used need a revision and adaptation in case of analyzing data on biological effects in natural plant and animal populations. Basic principles of evaluation of man-caused factor contribution into variation level observed in natural population are discussed.

[Genetic variance in Vicia cracca cenopopulation inhabiting site with enhanced level of natural radioactivity]

The contribution of low dose rate ionizing radiation into genetic variance in Vicia cracca L. cenopopulation inhabiting high natural background territories more then 40 years quantity estimation was made. Incorporated in the aboveground parts of Vicia cracca 230Th determine both the level of intrapopulation genetic variance and the adaptive possibility. Significantly increased frequency of double fragments was revealed in root tips of plants inhabiting all experimental plots. This type of damages depends on 226Ra concentrations accumulated in the aboveground parts of Vicia cracca. External irradiation influences the embryonic lethals. It was found that the relative contribution on mutagenesis induced by ionizing radiation was significant and was about 3-5% of the total variance.

Effects on non-human species inhabiting areas with enhanced level of natural radioactivity in the north of Russia: a review

Results of long-term radioecological investigations in areas with an enhanced level of natural radioactivity in the north of Russia are summarized. Deleterious changes within animal and plant populations inhabiting areas with an enhanced level of natural radioactivity in the Komi Republic were revealed. These changes are expressed in enhanced levels of mutagenesis, destructive processes in the tissues of animals, disturbances of reproductive functions and reduced offspring viability. Compensatory processes, resulting in animal and plant survival under extremely adverse conditions of radium and uranium-radium contamination, were observed as well. However, obvious signs of adaptation failed to be detected. The findings suggest that adverse somatic and genetic effects are possible in plants and animals in the dose range observed at sites with an enhanced level of natural radioactivity. In contrast, different plant species inhabiting an area with an enhanced level of natural radioactivity in the taiga zone of the Sakha Republic (Yakutia) reveal a stimulation of growth processes, photosynthesis, endogenous low molecular weight antioxidant synthesis as well as adaptive response. It is apparent from the data presented that naturally occurring differences in terrestrial radiation level could be of genetic and ecological consequence.

[Mechanisms of 232Th effects on Chlorella vulgaris Beljer and modifications of it's toxic effect with caffeine and buthionine sulfoximine]

232Th effects and its modifications with caffeine and D, L-buthionine-(S, R)-sulphoximine in Chlorella vulgaris Beijer cells was studied with use an optical density measure after 24 hours growth. Was shown relationship between concentration and toxic effect that is nonlinear and characterized with three parts different in induced damages level. In the first concentration range (0.001-1.551 micromol/l) chlorella growth parameters don't significantly differ from control ones. In the second one (1.724-3.017 micromol/1) statistically significant increase of optical density is but the effect does not dependent on 232Th concentration. The 232Th concentration (>3.448 micromol/l) increase the monotonous decrease in optical density was observed. The main role in 232Th toxic effect decrease make processes of DNA reparation, but not free radical scavenging with glutathione.

[The influence of cadmium and potassium on the level of cytogenetic effects induced by thorium-232 in Allium cepa root meristem]

The influence of different concentrations of cadmium and potassium on the levels of mutagenic and cytotoxic effects induced by thallium-232 in Allium cepa root meristem has been studied. The combined action of 232Th (0.8 microM) with cadmium in non-toxic (0.009 microM) and toxic (5 microM) concentrations resulted in sinergetic increase of the frequency of aberrant cells in Allium cepa root meristem. Decrease of the mutagenic effect to the additive level and antagonism with respect to the cytotoxic one was observed only at the certain concentrations of 232Th (0.8 microM) and Cd (0.09 microM) and the time of impact 30 h. In contrast to the heavy metal cadmium the essential for plants potassium at all studied concentrations (0.008, 6, 13 mM) decreased the number of cytogenetic aberrations in control experiments and under the effect of 232Th. The maximum protective effect of potassium was detected at the concentration 13 mM.

[Toxic and cytogenetic effects induced in Allium cepa with low concenrations of Cd and 232th]

232Th (7.76 x 10(-7) M) and Cd (0.89 x 10(-8) M) in concentrations which do not exceed officially prescribed standards when entering with water do not increase the frequency of chromosome aberrations in comparison with the control. Such concentrations do not cause toxic effects in plants on the levels of tissues and of the whole organism but they do display their activity on the cell level damaging division spindle. Dependence "cadmium concentration-effect" is not linear for any type of cytogenetical damages. At the concentration of cadmium 0.89 x 10(-7) M its influence on formation of division spindle is weakened and the frequency of chromosome aberrations is reducing in comparison with the control and with the effects induced at lower concentrations of cadmium in solution (0.89 x 10(-8) M). Cadmium in high concentration (5.34 x 10(-5) M) causes significant toxic and mutagenic effects.