Chronic ionising radiation exposure is a main consequence of radioactive pollution of the environment. The development of functional genomics approaches coupled with morphological and physiological studies allows new insights into plant adaptation to life under chronic irradiation. Using morphological, reproductive, physiological, and transcriptomic experiments, we evaluated the way in which Arabidopsis thaliana natural accessions from the Chernobyl exclusion zone recover from chronic low-dose and acute high-dose γ-irradiation of seeds. Plants from radioactively contaminated areas were characterized by lower germination efficiency, suppressed growth, decreased chlorophyll fluorescence, and phytohormonal changes. The transcriptomes of plants chronically exposed to low-dose radiation indicated the repression of mobile genetic elements and deregulation of genes related to abiotic stress tolerance. Furthermore, these chronically irradiated natural accessions showed higher tolerance to acute 150 Gy γ-irradiation of seeds, according to transcriptome and phytohormonal profiles. Overall, the lower sensitivity of the accessions from radioactively contaminated areas to acute high-dose irradiation may come at the cost of their growth performance under normal conditions.

Plant growth response to γ-irradiation includes stimulating or inhibitory effects depending on plant species, dose applied, stage of ontogeny and other factors. Previous studies showed that responses to irradiation could depend on ABA accumulation and signaling. To elucidate the role of ABA in growth and photosynthetic responses to irradiation, lines Col-8, abi3-8 and aba3 -1 of Arabidopsis thaliana were used. Seeds were γ-irradiated using ⁶⁰Co in the dose range 50-150 Gy. It was revealed that the dose of 150 Gy affected germination parameters of aba3 -1 and Col-8 lines, while abi3-8 line was the most resistant to the studied doses and even showed faster germination at early hours after γ-irradiation at 50 Gy. These results suggest that susceptibility to ABA is probably more important for growth response to γ-irradiation than ABA synthesis. The photosynthetic functioning of 16-day-old plants mainly was not disturbed by γ-irradiation of seeds, and no indication of photosystem II photoinhibition was noticed, revealing the robustness of the photosynthetic system of A. thaliana. Glutathione peroxidase activity and ABA concentrations in plant tissues were not affected in the studied dose range. These results contribute to the understanding of germination and photosynthesis fine-tuning and of mechanisms of plant tolerance to ionizing radiation.

The development of adaptation strategies for crops under ever-changing climate conditions is a critically important food security issue. Studies of barley responses to ionising radiation showed that this evolutionarily ancient stress factor can be successfully used to identify molecular pathways involved in adaptation to a range of abiotic stressors. In order to identify potential molecular contributors to abiotic stress resilience, we examined the transcriptomic profiles of barley seedlings after exposure to γ-rays, electrons, and protons. A total of 553 unique differentially expressed genes with increased expression and 124 with decreased expression were detected. Among all types of radiation, the highest number of differentially expressed genes was observed in electron-irradiated samples (428 upregulated and 56 downregulated genes). Significant upregulation after exposure to the three types of radiation was shown by a set of ROS-responsive genes, genes involved in DNA repair, cell wall metabolism, auxin biosynthesis and signalling, as well as photosynthesis-related genes. Most of these genes are known to be involved in plant ROS-mediated responses to other abiotic stressors, especially with genotoxic components, such as heavy metals and drought. Ultimately, the modulation of molecular pathways of plant responses to ionising radiation may be a prospective tool for stress tolerance programmes.

The stimulation of growth and development of crops using ionising radiation (radiation hormesis) has been reported by many research groups. However, specific genes contributing to the radiation stimulation of plant growth are largely unknown. In this work, we studied the impact of the low-dose γ-irradiation of barley seeds on the growth dynamics and gene expression of eight barley cultivars in a greenhouse experiment. Our findings confirmed that candidate genes of the radiation growth stimulation, previously established in barley seedlings (PM19L-like, CML31-like, and AOS2-like), are significant in radiation hormesis throughout ontogeny. In γ-stimulated cultivars, the expression of these genes was aligned with the growth dynamics, yield parameters, and physiological conditions of plants. We identified contrasting cultivars for future gene editing and found that the γ-stimulated cultivar possessed some specific abiotic stress-responsive elements in the promotors of candidate genes, possibly revealing a new level of radiation hormesis effect execution. These results can be used in creating new productive barley cultivars, ecological toxicology of radionuclides, and eustress biology studies.

Crops are simultaneously affected by factors of different nature; therefore, it is important to study the separate and combined effects of technogenic stressors on plants. During seed germination, there is a transition from heterotrophic to autotrophic type of nutrition, which largely determines the further development of the plant, the size and quality of the crop. The impact of biotic and abiotic factors on seeds can significantly affect the passage of germination phases. In this work, for the first time, the dynamics of development in the first phases of germination of barley variety Nur under the conditions of separate and combined action of gamma radiation and heavy metal Pb(NO3)2 was studied in detail. The antagonistic effect of preliminary irradiation on the toxic effects of lead salt during germination was revealed. The aim of the work is to evaluate the influence of separate and combined effects of gamma radiation and lead, including possible synergistic and antagonistic effects of the interaction of stressors, on the dynamics of germination of spring barley seeds. The seeds of spring barley (Hordeum vulgare L.) of the Nur variety of the first reproduction of 2019 were used. The germination process was assessed visually for 70 hours, with detailed observation every 2 hours from the 18th to the 38th hour and every 4 hours from the 46th to the 70th hour. The seeds were irradiated with a dose of 20 Gy (dose rate 60 Gy/h) at the GUR-120 (60Co) unit (RIRAE, Obninsk). We also used the Pb(NO3)2 salt at a concentration of 2 mg/ml which inhibited the development of seedlings but did not lead to their death. In the control group, non-irradiated seeds were germinated in 7 ml of distilled water. In experimental group I, seeds irradiated at a dose of 20 Gy were germinated in the same volume of water. In experimental group II, non-irradiated seeds were germinated in water with the addition of Pb(NO3)2 at a concentration of 2 mg/ml; in experimental group III, the seeds were subjected to a combined action of g-irradiation and lead. In total, 800 seeds were studied, 200 seeds in each group. Seeds were germinated in a MIR-254 thermostat (Sanyo, Japan) in Petri dishes (20 pieces each), on a double layer of filter paper (Belaya Lenta, Russia), in the dark, at 20±0.5 °C. The germination process was divided into 6 main phases: “point’ — pecking, the appearance of the germinal root, roots 1 (K-1), “fork” — differentiation of the germinal root into several roots 1-2 mm long; roots 2 (K-2) — the initial growth of roots, their size is less than the length of the seed; roots 3 (K-3) — mature roots larger than the length of the seed, no sprout; sprout — the appearance of a coleoptile, the seed has several roots and a sprout less than half the length of the seed; seedling — the formation of a full-fledged sprout, having at least two roots larger than the length of the seed and a sprout larger than half the length of the seed.. The nonparametric Mann-Whitney test was used to compare mean values. The coefficient of interaction Kw was used as a quantitative measure of the deviation of the observed effect from the additive effect and classification of the effects of combined action into groups of additivity, synergy, and antagonism. Under g-irradiation of seeds, statistically significant differences from the control appeared in phases K-1 and K-3. Significant differences were noted in the “sprout” and “seedling” phases by the end of the observations. In general, g-irradiation at a dose of 20 Gy did not significantly disrupt the passage of microphenological phases in seeds. Treatment with Pb(NO3)2 at a concentration of 2 mg/ml slowed down seed germination, which manifested itself in a delay in the transition to each subsequent microphenological phase, as well as in a decrease in the proportion of seeds at late stages of development compared to the control. In addition, lead had a negative effect on the development of the root, almost completely excluding the K-3 phase from the development of the seedling. The combined effect of g-irradiation and lead also led to a slowdown in development, but in this variant, the proportion of seeds that reached the K-3 phase increased and approached the rate in the control, that is, g-irradiation at a dose of 20 Gy mitigated the toxic effect of lead. Therefore, a dose of 2 mg/ml Pb(NO3)2, regardless of the effect of g-irradiation, has an inhibitory effect on the development of seeds, but does not completely suppress it, only reducing the rate of development