At low intensity, certain stress conditions may have a positive effect on growth and development of plants (eustress). Growth stimulation of barley plants after gamma irradiation of seeds in low doses was observed as an increase in root and shoot lengths. Hydrogen peroxide concentrations in shoots of irradiated plants were significantly higher than in control, while the opposite effect was observed in the roots. To elucidate the molecular basis of growth stimulation after gamma irradiation of barley seeds, we performed the transcriptomic analysis of barley embryos at different stages of seed germination. The transcriptomic data were correlated with morphological parameters and the hydrogen peroxide levels in irradiated and control plants. These data indicate that the growth stimulation by low‐dose irradiation involves the transcriptional control of genes related to phytohormones, antioxidant system, late embryogenesis abundant proteins and cell wall components, with possible involvement of jasmonate and ABA signalling. Gamma irradiation of seeds at dose 100 Gy caused significant growth inhibition and promoted expression changes in transcripts related to cell cycle arrest, DNA damage repair and antioxidant system.
Gamma (γ)-irradiation of plants at low doses can provoke a broad range of growth-stimulating effects. In order to reveal universal target genes that are involved in molecular pathways of radiation hormesis establishment, we studied nine barley cultivars for their tolerance to γ-irradiation of seeds. Four morphological traits were assessed in barley seedlings after γ-irradiation of seeds at 20 Gy. Nine cultivars were sorted according to the sensitivity to irradiation as γ-stimulated, “no morphological effect”, or γ-inhibited. Gene expression of 17 candidate genes was evaluated for the 7 most contrasting cultivars. Changes in expression of barley homologues of PM19L and CML31 were suggested as possible determinants of radiation hormesis effect. The possible role of jasmonate signaling in roots in radiation growth stimulations was revealed. Morphological analysis and gene expression study showed that the genetic background of a cultivar plays an important role in eustress responses to low-dose γ-irradiation of seeds.
Low-dose γ-irradiation can stimulate plant growth and development; however, the knowledge on the molecular mechanisms of such stimulation is yet fragmented. Irradiation of seeds leads to the mobilisation of endosperm resources and reallocation of available nitrogen to facilitate development. Based on the metabolomic analysis, several metabolites possibly involved in radiation stimulation were studied using the HPLC approach in barley cultivars after γ-irradiation of seeds. The comparison of changes in metabolite concentrations and changes in morphological traits after irradiation revealed seven metabolites that may be involved in the growth stimulation after γ-irradiation of barley seeds. Among them are free amino acids, such as γ-aminobutyric acid, β-alanine, arginine, lysine, glutamine, methionine, and a signalling compound methylglyoxal.
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.
Barley is the main forage crop in the Russian Federation. Barley grain is also used for food and brewery (Filippov, 2013). It is common knowledge that low doses of gamma irradiation can have a stimulating effect on the growth and development of plants, in particular barley. However, there is a lack of knowledge about the molecular pathways responsible for the formation of the stimulation effect after low-dose seed irradiation. The use of varieties with different radio sensitivity to low-dose gamma irradiation will allow studying specific molecular mechanisms to form a stimulating irradiation effect. Such knowledge could further help in the development of varieties with a large stable productivity over the years and with high resistance to biotic and abiotic stressors. In 2019 there was conducted a gamma irradiation of the original seeds of nine winter and spring barley varieties developed in the FSBSI “Agricultural Research Center “Donskoy” in order to assess intensity of the response on low-dose ionizing irradiation based on changes in the morphological parameters of irradiated and unirradiated plants. The original seeds of each barley variety were irradiated at the FSBSI “All-Russian Research Institute of Radiology and Agroecology” by the gamma device “GUR-120” with 60Со radiation sources at a dose of 20 Gy (dose rate of 60 Gy/hour). The statistical data processing was performed by the Microsoft Office Excel 2019. The morphological analysis of the length and weight of roots and sprouts made it possible to establish the presence or absence of the stimulating irradiation effect on the studied indicators of the varieties and to conduct their subsequent ranking according to the value of the radiobiological effect. There have been identified the winter and spring barley varieties with different sensitivity to a dose of 20 Gy. The stimulating irradiation effect was established in such varieties as “Foks 1”, “Ratnik”, “Yerema” and “Master”. The variety “Leon” had an inhibitory irradiation effect.
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