Soybeans grown in the Chernobyl area produce fertile seeds that have increased heavy metal resistance and modified carbon metabolism

Biological impact of Chornobyl radiation: a review of recent progress

The incident of Chernobyl Nuclear Power Plant (CNPP) explosion has pioneered a plethora of studies unfolding various biological effects of radiation stress on several living systems. Determining radiation dose rates at which both acute and chronic biological effects occur in different biological systems will aid in the ex-situ generation of radiation-tolerant organisms. So far, the accumulation of data on different radiation doses from Chernobyl area demonstrating various biological impacts has not been documented altogether vastly. Therefore, this review aims to document the recorded doses in CNPP over the years at which different biological changes have been observed in plants, soil, aquatic organisms, birds, and animals. A total of 72 peer-reviewed papers obtained from PubMed, Google Scholar, Scopus, and Research4life were included in this review. A few factors have come under attention in this review. Firstly, plant and soil systems combinedly showed the most published studies after the catastrophe where plants showed a higher frequency of DNA methylation in their genome to resist radiation stress. Secondly, reduced species abundance, chromosomal aberrations, increased sterility, and mortality were mostly observed in the aftermath of Chernobyl catastrophe among plants, soil, aquatic organisms, birds, and small mammals. Furthermore, major scares of data after 2018 were prominently observed. Very few studies on radiation dose levels after 2018 are available. Hence, a major research area has emerged for radiation biologists to study present radiation levels and any genetic changes in the recent generation of the original victim species. This will help provide a standard dataset that can act as a reference resource for radiation biologists and future research on the impact of both acute and chronic radiation on the different biological systems.

Complexity of responses to ionizing radiation in plants, and the impact on interacting biotic factors

In nature, plants are simultaneously exposed to different abiotic (e.g., heat, drought, and salinity) and biotic (e.g., bacteria, fungi, and insects) stresses. Climate change and anthropogenic pressure are expected to intensify the frequency of stress factors. Although plants are well equipped with unique and common defense systems protecting against stressors, they may compromise their growth and development for survival in such challenging environments. Ionizing radiation is a peculiar stress factor capable of causing clustered damage. Radionuclides are both naturally present on the planet and produced by human activities. Natural and artificial radioactivity affects plants on molecular, biochemical, cellular, physiological, populational, and transgenerational levels. Moreover, the fitness of pests, pathogens, and symbionts is concomitantly challenged in radiologically contaminated areas. Plant responses to artificial acute ionizing radiation exposure and laboratory-simulated or field chronic exposure are often discordant. Acute or chronic ionizing radiation exposure may occasionally prime the defense system of plants to better tolerate the biotic stress or could often exhaust their metabolic reserves, making plants more susceptible to pests and pathogens. Currently, these alternatives are only marginally explored. Our review summarizes the available literature on the responses of host plants, biotic factors, and their interaction to ionizing radiation exposure. Such systematic analysis contributes to improved risk assessment in radiologically contaminated areas.

Implications of ionizing radiation on pollen performance in comparison with diverse models of polar cell growth

Research concerning the effects of ionizing radiation (IR) on plant systems is essential for numerous aspects of human society, as for instance, in terms of agriculture and plant breeding, but additionally for elucidating consequences of radioactive contamination of the ecosphere. This comprehensive survey analyses effects of x- and γ-irradiation on male gametophytes comprising primarily in vitro but also in vivo data of diverse plant species. The IR-dose range for pollen performance was compiled and 50% inhibition doses (ID₅₀ ) for germination and tube growth were comparatively related to physiological characteristics of the microgametophyte. Factors influencing IR-susceptibility of mature pollen and polarized tube growth were evaluated, such as dose-rate, environmental conditions, or species-related variations. In addition, all available reports suggesting bio-positive IR-effects particularly on pollen performance were examined. Most importantly, for the first time influences of IR specifically on diverse phylogenetic models of polar cell growth were comparatively analysed, and thus demonstrated that the gametophytic system of pollen is extremely resistant to IR, more than plant sporophytes and especially much more than comparable animal cells. Beyond that, this study develops hypotheses regarding a molecular basis for the extreme IR-resistance of the plant microgametophyte and highlights its unique rank among organismal systems.

Changes in DNA Methylation in Arabidopsis thaliana Plants Exposed Over Multiple Generations to Gamma Radiation

Previous studies have found indications that exposure to ionising radiation (IR) results in DNA methylation changes in plants. However, this phenomenon is yet to be studied across multiple generations. Furthermore, the exact role of these changes in the IR-induced plant response is still far from understood. Here, we study the effect of gamma radiation on DNA methylation and its effect across generations in young Arabidopsis plants. A multigenerational set-up was used in which three generations (Parent, generation 1, and generation 2) of 7-day old Arabidopsis thaliana plants were exposed to either of the different radiation treatments (30, 60, 110, or 430 mGy/h) or to natural background radiation (control condition) for 14 days. The parental generation consisted of previously non-exposed plants, whereas generation 1 and generation 2 plants had already received a similar irradiation in the previous one or two generations, respectively. Directly after exposure the entire methylomes were analysed with UPLC-MS/MS to measure whole genome methylation levels. Whole genome bisulfite sequencing was used to identify differentially methylated regions (DMRs), including their methylation context in the three generations and this for three different radiation conditions (control, 30 mGy/h, and 110 mGy/h). Both intra- and intergenerational comparisons of the genes and transposable elements associated with the DMRs were made. Taking the methylation context into account, the highest number of changes were found for cytosines followed directly by guanine (CG methylation), whereas only limited changes in CHG methylation occurred and no changes in CHH methylation were observed. A clear increase in IR-induced DMRs was seen over the three generations that were exposed to the lowest dose rate, where generation 2 had a markedly higher number of DMRs than the previous two generations (Parent and generation 1). Counterintuitively, we did not see significant differences in the plants exposed to the highest dose rate. A large number of DMRs associated with transposable elements were found, the majority of them being hypermethylated, likely leading to more genetic stability. Next to that, a significant number of DMRs were associated with genes (either in their promoter-associated region or gene body). A functional analysis of these genes showed an enrichment for genes related to development as well as various stress responses, including DNA repair, RNA splicing, and (a)biotic stress responses. These observations indicate a role of DNA methylation in the regulation of these genes in response to IR exposure and shows a possible role for epigenetics in plant adaptation to IR over multiple generations.

Soybean recovery from stress imposed by multigenerational growth in contaminated Chernobyl environment

Ionizing radiation is a genotoxic anthropogenic stressor. It can cause heritable changes in the plant genome, which can be either adaptive or detrimental. There is still considerable uncertainty about the effects of chronic low-intensity doses since earlier studies reported somewhat contradictory conclusions. Our project focused on the recovery from the multiyear chronic ionizing radiation stress. Soybean (Glycine max) was grown in field plots located at the Chernobyl exclusion zone and transferred to the clean ground in the subsequent generation. We profiled proteome of mature seeds by two-dimensional gel electrophoresis. Overall, 15 differentially abundant protein spots were identified in the field comparison and 11 in the recovery generation, primarily belonging to storage proteins, disease/defense, and metabolism categories. Data suggested that during multigenerational growth in a contaminated environment, detrimental heritable changes were accumulated. Chlorophyll fluorescence parameters were measured on the late vegetative state, pointing to partial recovery of photosynthesis from stress imposed by contaminating radionuclides. A plausible explanation for the observed phenomena is insufficient provisioning of seeds by lower quality resources, causing a persistent effect in the offspring generation. Additionally, we hypothesized that immunity against phytopathogens was compromised in the contaminated field, but perhaps even primed in the clean ground, yet this idea requires direct functional validation in future experiments. Despite showing clear signs of physiological recovery, one season was not enough to normalize biochemical processes. Overall, our data contribute to the more informed agricultural radioprotection.

A review of the impact on the ecosystem after ionizing irradiation: wildlife population

PURPOSE

On 26 April 1986, reactor 4 at the Chernobyl power plant underwent a catastrophic failure leading to core explosions and open-air fires. On 11 March 2011, a combination of earthquake and tsunami led to a similar disaster at the Fukushima Daiichi power plant. In both cases, radioactive isotopes were released and contaminated the air, soil and water in a substantial area around the power plants. Humans were evacuated from the immediate regions but the wildlife stayed and continued to be affected by the ongoing high radiation exposure initially and later decayed amounts of fallout dusts with time. In this review, we will examine the significant effects of the increased radiation on vegetation, insects, fish, birds and mammals.

CONCLUSIONS

The initial intense radiation in these areas has gradually begun to decrease but still remains high. Adaptation to radiation is evident and the ecosystems have dynamically changed from the periods immediately after the accidents to the present day. Understanding the molecular mechanisms that allow the adaptation and recovery of wildlife to chronic radiation challenges would aid in future attempts at ecosystem remediation in the wake of such incidents.

Inter-retrotransposon amplified polymorphism markers revealed long terminal repeat retrotransposon insertion polymorphism in flax cultivated on the experimental fields around Chernobyl

Ionizing radiation in environment comes from various natural and anthropogenic sources. The effect of radioactivity released after the CNPP (Chernobyl Nuclear Power Plant) on plant systems remains of great interest. Even now, more than three decades after the nuclear accident, the long-lived radionuclides represent a strong stress factor. Herein, the emphasis has been placed on analysis of genetic variability represented by activation of LTR (Long Terminal Repeat)-retrotransposons. Polymorphism in LTR-retrotransposon insertions has been investigated throughout the genome of two flax varieties, Kyivskyi and Bethune. For this purpose, two retrotransposon-based marker techniques, IRAP (Inter-Retrotransposon Amplified Polymorphism) and iPBS (inter-Primer Binding Site), have been employed. The hypothesis that chronic radioactive stress may induce mechanism of retransposition has been supported by the activation of FL9, FL11 and FL12 LTR-retrotransposons in flax seeds harvested from radioactive environment. Out of two retrotransposon-based approaches, IRAP appears to be more suitable for identification of LTR-retrotransposon polymorphism. Even though the LTR-retrotransposon polymorphism was identified, the results suggest the high level of plant adaptation in the radioactive Chernobyl area. However, it is not really surprising that plants developed an effective strategy to survive in radio-contaminated environment over the past 30 years.

Natural ecotype of Arabidopsis thaliana (L.) Heynh (Chernobyl-07) respond to cadmium stress more intensively than the sensitive ecotypes Oasis and Columbia

Large areas polluted with toxic heavy metals or radionuclides were formed as a side product of rapid industrial development of human society. Plants, due to their sessile nature, should adapt to these challenging genotoxic environmental conditions and develop resistance. Herein, we evaluated the response of three natural ecotypes of Arabidopsis thaliana (L.) Heynh (Oasis, Columbia-0, and Chernobyl-07) to cadmium, using discovery gel-based proteomics. These accessions are differing by level of tolerance to heavy metal probably achieved by various exposure to chronic ionizing radiation. Based on the pairwise comparison (control versus cadmium-treated) we recognized 5.8-13.4% of identified proteins as significantly altered at the presence of cadmium. Although the majority of photosynthesis-related proteins were found to be less abundant in all ecotypes it was noted that in contrast to the sensitive variants (Col and Oas), the tolerant Che accession may activate the mechanism preserving photosynthesis and energy production. Also, proteins modulating energy budget through alternative route and mediating higher resistance to heavy metals were upregulated in this ecotype. Although we suggest that regulation of enzymes acting in peptide and protein synthesis, protection of the plants against various abiotic stresses, or those neutralizing the effects of reactive oxygen species are rather associated with general response to cadmium, they were found to be altered more intensively in the Che accession. Thus, the identified affected proteins may represent good candidate molecules for molecular breeding to improve tolerance of crops to heavy metal stress.

Fibroblasts from bank voles inhabiting Chernobyl have increased resistance against oxidative and DNA stresses

Background

Elevated levels of environmental ionizing radiation can be a selective pressure for wildlife by producing reactive oxygen species and DNA damage. However, the underlying molecular mechanisms that are affected are not known.

Results

We isolated skin fibroblasts from bank voles (Myodes glareolus) inhabiting the Chernobyl nuclear power plant accident site where background radiation levels are about 100 times greater than in uncontaminated areas. After a 10 Gy dose of gamma radiation fibroblasts from Chernobyl animals recovered faster than fibroblasts isolated from bank voles living in uncontaminated control area. The Chernobyl fibroblasts were able to sustain significantly higher doses of an oxidant and they had, on average, a higher total antioxidant capacity than the control fibroblasts. Furthermore, the Chernobyl fibroblasts were also significantly more resistant than the control fibroblasts to continuous exposure to three DNA damaging drugs. After drug treatment transcription of p53-target gene pro-apoptotic Bax was higher in the control than in the Chernobyl fibroblasts.

Conclusion

Fibroblasts isolated from bank voles inhabiting Chernobyl nuclear power plant accident site show elevated antioxidant levels, lower sensitivity to apoptosis, and increased resistance against oxidative and DNA stresses. These cellular qualities may help bank voles inhabiting Chernobyl to cope with environmental radioactivity.

Electronic supplementary material

The online version of this article (10.1186/s12860-018-0169-9) contains supplementary material, which is available to authorized users.

DNA damage, repair monitoring and epigenetic DNA methylation changes in seedlings of Chernobyl soybeans

This pilot study was carried out to assess the effect of radio-contaminated Chernobyl environment on plant genome integrity 27 years after the accident. For this purpose, nuclei were isolated from root tips of the soybean seedlings harvested from plants grown in the Chernobyl area for seven generations. Neutral, neutral-alkaline, and methylation-sensitive comet assays were performed to evaluate the induction and repair of primary DNA damage and the epigenetic contribution to stress adaptation mechanisms. An increased level of single and double strand breaks in the radio-contaminated Chernobyl seedlings at the stage of primary root development was detected in comparison to the controls. However, the kinetics of the recovery of DNA breaks of radio-contaminated Chernobyl samples revealed that lesions were efficiently repaired at the stage of cotyledon. Methylation-sensitive comet assay revealed comparable levels in the CCGG methylation pattern between control and radio-contaminated samples with a slight increase of approximately 10% in the latter ones. The obtained preliminary data allow us to speculate about the onset of mechanisms providing an adaptation potential to the accumulated internal irradiation after the Chernobyl accident. Despite the limitations of this study, we showed that comet assay is a sensitive and flexible technique which can be efficiently used for genotoxic screening of plant specimens in natural and human-made radio-contaminated areas, as well as for safety monitoring of agricultural products.

Lower prevalence but similar fitness in a parasitic fungus at higher radiation levels near Chernobyl

Nuclear disasters at Chernobyl and Fukushima provide examples of effects of acute ionizing radiation on mutations that can affect the fitness and distribution of species. Here, we investigated the prevalence of Microbotryum lychnidis-dioicae, a pollinator-transmitted fungal pathogen of plants causing anther-smut disease in Chernobyl, its viability, fertility and karyotype variation, and the accumulation of nonsynonymous mutations in its genome. We collected diseased flowers of Silene latifolia from locations ranging by more than two orders of magnitude in background radiation, from 0.05 to 21.03 μGy/h. Disease prevalence decreased significantly with increasing radiation level, possibly due to lower pollinator abundance and altered pollinator behaviour. Viability and fertility, measured as the budding rate of haploid sporidia following meiosis from the diploid teliospores, did not vary with increasing radiation levels and neither did karyotype overall structure and level of chromosomal size heterozygosity. We sequenced the genomes of twelve samples from Chernobyl and of four samples collected from uncontaminated areas and analysed alignments of 6068 predicted genes, corresponding to 1.04 × 10(7)  base pairs. We found no dose-dependent differences in substitution rates (neither dN, dS, nor dN/dS). Thus, we found no significant evidence of increased deleterious mutation rates at higher levels of background radiation in this plant pathogen. We even found lower levels of nonsynonymous substitution rates in contaminated areas compared to control regions, suggesting that purifying selection was stronger in contaminated than uncontaminated areas. We briefly discuss the possibilities for a mechanistic basis of radio resistance in this nonmelanized fungus.

Are Organisms Adapting to Ionizing Radiation at Chernobyl?

Numerous organisms have shown an ability to survive and reproduce under low-dose ionizing radiation arising from natural background radiation or from nuclear accidents. In a literature review, we found a total of 17 supposed cases of adaptation, mostly based on common garden experiments with organisms only deriving from typically two or three sampling locations. We only found one experimental study showing evidence of improved resistance to radiation. Finally, we examined studies for the presence of hormesis (i.e., superior fitness at low levels of radiation compared with controls and high levels of radiation), but found no evidence to support its existence. We conclude that rigorous experiments based on extensive sampling from multiple sites are required.

Do Cupins Have a Function Beyond Being Seed Storage Proteins?

Plants continue to flourish around the site of the Chernobyl Nuclear Power Plant disaster. The ability of plants to transcend the radio-contaminated environment was not anticipated and is not well understood. The aim of this study was to evaluate the proteome of flax (Linum usitatissimum L.) during seed filling by plants grown for a third generation near Chernobyl. For this purpose, seeds were harvested at 2, 4, and 6 weeks after flowering and at maturity, from plants grown in either non-radioactive or radio-contaminated experimental fields. Total proteins were extracted and the two-dimensional gel electrophoresis (2-DE) patterns analyzed. This approach established paired abundance profiles for 130 2-DE spots, e.g., profiles for the same spot across seed filling in non-radioactive and radio-contaminated experimental fields. Based on Analysis of Variance (ANOVA) followed by sequential Bonferroni correction, eight of the paired abundance profiles were discordant. Results from tandem mass spectrometry show that four 2-DE spots are discordant because they contain fragments of the cupin superfamily-proteins. Most of the fragments were derived from the N-terminal half of native cupins. Revisiting previously published data, it was found that cupin-fragments were also involved with discordance in paired abundance profiles of second generation flax seeds. Based on these observations we present an updated working model for the growth and reproductive success of flax in a radio-contaminated Chernobyl environment. This model suggests that the increased abundance of cupin fragments or isoforms and monomers contributes to the successful growth and reproduction of flax in a radio-contaminated environment.

Using 7 cm immobilized pH gradient strips to determine levels of clinically relevant proteins in wheat grain extracts

The aim of the work was to test a relatively simple proteomics approach based on phenol extraction and two-dimensional gel electrophoresis (2-DE) with 7 cm immobilized pH gradient strips for the determination of clinically relevant proteins in wheat grain. Using this approach, 157 2-DE spots were quantified in biological triplicate, out of which 55 were identified by matrix-assisted laser desorption/ionization - time of flight tandem mass spectrometry. Clinically relevant proteins associated with celiac disease, wheat dependent exercise induced anaphylaxis, baker's asthma, and food allergy, were detected in 24 2-DE spots. However, alcohol-soluble gliadins were not detected with this approach. The comparison with a recent quantitative study suggested that gel-based and gel-free proteomics approaches are complementary for the detection and quantification of clinically relevant proteins in wheat grain.

Chernobyl seed project. Advances in the identification of differentially abundant proteins in a radio-contaminated environment

Plants have the ability to grow and successfully reproduce in radio-contaminated environments, which has been highlighted by nuclear accidents at Chernobyl (1986) and Fukushima (2011). The main aim of this article is to summarize the advances of the Chernobyl seed project which has the purpose to provide proteomic characterization of plants grown in the Chernobyl area. We present a summary of comparative proteomic studies on soybean and flax seeds harvested from radio-contaminated Chernobyl areas during two successive generations. Using experimental design developed for radio-contaminated areas, altered abundances of glycine betaine, seed storage proteins, and proteins associated with carbon assimilation into fatty acids were detected. Similar studies in Fukushima radio-contaminated areas might complement these data. The results from these Chernobyl experiments can be viewed in a user-friendly format at a dedicated web-based database freely available at http://www.chernobylproteomics.sav.sk.

Proteomics of field samples in radioactive Chernobyl area

Two serious nuclear accidents during the past quarter of a century contaminated large agricultural areas with radioactivity. The remediation and possible recovery of radio-contaminated areas for agricultural purposes require comprehensive characterization of plants grown in such places. Here we describe the quantitative proteomics method that we use to analyze proteins isolated from seeds of plants grown in radioactive Chernobyl zone.

Transgenic soybeans and soybean protein analysis: an overview

To meet the increasing global demand for soybeans for food and feed consumption, new high-yield varieties with improved quality traits are needed. To ensure the safety of the crop, it is important to determine the variation in seed proteins along with unintended changes that may occur in the crop as a result various stress stimuli, breeding, and genetic modification. Understanding the variation of seed proteins in the wild and cultivated soybean cultivars is useful for determining unintended protein expression in new varieties of soybeans. Proteomic technology is useful to analyze protein variation due to various stimuli. This short review discusses transgenic soybeans, different soybean proteins, and the approaches used for protein analysis. The characterization of soybean protein will be useful for researchers, nutrition professionals, and regulatory agencies dealing with soy-derived food products.

Radioactive Chernobyl environment has produced high-oil flax seeds that show proteome alterations related to carbon metabolism during seed development

Starting in 2007, we have grown soybean (Glycine max [L.] Merr. variety Soniachna) and flax (Linum usitatissimum, L. variety Kyivskyi) in the radio-contaminated Chernobyl area and analyzed the seed proteomes. In the second-generation flax seeds, we detected a 12% increase in oil content. To characterize the bases for this increase, seed development has been studied. Flax seeds were harvested in biological triplicate at 2, 4, and 6 weeks after flowering and at maturity from plants grown in nonradioactive and radio-contaminated plots in the Chernobyl area for two generations. Quantitative proteomic analyses based on 2-D gel electrophoresis (2-DE) allowed us to establish developmental profiles for 199 2-DE spots in both plots, out of which 79 were reliably identified by tandem mass spectrometry. The data suggest a statistically significant increased abundance of proteins associated with pyruvate biosynthesis via cytoplasmic glycolysis, L-malate decarboxylation, isocitrate dehydrogenation, and ethanol oxidation to acetaldehyde in early stages of seed development. This was followed by statistically significant increased abundance of ketoacyl-[acylcarrier protein] synthase I related to condensation of malonyl-ACP with elongating fatty acid chains. On the basis of these and previous data, we propose a preliminary model for plant adaptation to growth in a radio-contaminated environment. One aspect of the model suggests that changes in carbon assimilation and fatty acid biosynthesis are an integral part of plant adaptation.

Proteomic insights into intra- and intercellular plant-bacteria symbiotic association during root nodule formation

Over the last several decades, there have been a large number of studies done on the all aspects of legumes and bacteria which participate in nitrogen-fixing symbiosis. The analysis of legume-bacteria interaction is not just a matter of numerical complexity in terms of variants of gene products that can arise from a single gene. Bacteria regulate their quorum-sensing genes to enhance their ability to induce conjugation of plasmids and symbiotic islands, and various protein secretion mechanisms; that can stimulate a collection of chain reactions including species-specific combinations of plant-secretion isoflavonoids, complicated calcium signaling pathways and autoregulation of nodulation mechanisms. Quorum-sensing systems are introduced by the intra- and intercellular organization of gene products lead to protein-protein interactions or targeting of proteins to specific cellular structures. In this study, an attempt has been made to review significant contributions related to nodule formation and development and their impacts on cell proteome for better understanding of plant-bacterium interaction mechanism at protein level. This review would not only provide new insights into the plant-bacteria symbiosis response mechanisms but would also highlights the importance of studying changes in protein abundance inside and outside of cells in response to symbiosis. Furthermore, the application to agriculture program of plant-bacteria interaction will be discussed.

Seeds in Chernobyl: the database on proteome response on radioactive environment

Two serious nuclear accidents during the last quarter century (Chernobyl, 1986 and Fukushima, 2011) contaminated large agricultural areas with radioactivity. The database "Seeds in Chernobyl" (http://www.chernobylproteomics.sav.sk) contains the information about the abundances of hundreds of proteins from on-going investigation of mature and developing seed harvested from plants grown in radioactive Chernobyl area. This database provides a useful source of information concerning the response of the seed proteome to permanently increased level of ionizing radiation in a user-friendly format.

Seeds in Chernobyl: the database on proteome response on radioactive environment

Two serious nuclear accidents during the last quarter century (Chernobyl, 1986 and Fukushima, 2011) contaminated large agricultural areas with radioactivity. The database "Seeds in Chernobyl" (http://www.chernobylproteomics.sav.sk) contains the information about the abundances of hundreds of proteins from on-going investigation of mature and developing seed harvested from plants grown in radioactive Chernobyl area. This database provides a useful source of information concerning the response of the seed proteome to permanently increased level of ionizing radiation in a user-friendly format.