Radiation Hormesis in Barley Manifests as Changes in Growth Dynamics Coordinated with the Expression of PM19L-like, CML31-like, and AOS2-like

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.

Growth, antioxidant system, and phytohormonal status of barley cultivars contrasting in cadmium tolerance

Cadmium leads to disturbance of plant growth, and the manifestation of toxicity can vary greatly in different genotypes within one species. In this work we studied the effect of Cd on growth, antioxidant enzyme activity, and phytohormonal status of four barley cultivars (cvs. Simfoniya, Mestnyj, Ca 220702, Malva). According to the earlier study on seedlings, these cultivars were contrast in tolerance to Cd: Simfoniya and Mestnyj are Cd-tolerant and Ca 220702 and Malva are Cd-sensitive. The results presented showed that barley plants accumulated more Cd in straw than in grain. Tolerant cultivars accumulated significantly less Cd in grain than sensitive ones. The leaf area appeared to be a growth parameter susceptible to Cd treatment. The significant differences in leaf area values depended on Cd contamination and were not associated with cultivars' tolerance. Tolerance of cultivars was contingent on the activity of the antioxidant defense system. Indeed, activity of enzymes decreased in sensitive cultivars Ca 220702 and Malva under Cd stress. In contrast, in tolerant cultivars, increased activity of guaiacol peroxidase was revealed. The concentrations of abscisic acid and salicylic acid mostly increased as a result of Cd treatment, while the concentrations of auxins and trans-zeatin either decreased or did not change. The results obtained indicate that antioxidant enzymes and phytohormones play an important role in the response of barley plants to elevated concentrations of cadmium; however, these parameters are not able to explain the differentiation of barley cultivars in terms of tolerance to cadmium at the seedling stage. Therefore, barley intraspecific polymorphism for cadmium resistance is determined by the interplay of antioxidant enzymes, phytohormones, and other factors that require further elucidation.

Multifaceted effects of chronic radiation exposure in Japanese red pines from Fukushima prefecture

Despite many studies carried out to date, the long-term effects of chronic exposure on plants and animals inhabiting the territories affected by the Fukushima Dai-Ichi NPP accident remain the subject of scientific discussions. Our investigations were performed on Japanese red pine, the native tree species that is widely spread in the radioactive contaminated areas. Earlier observations revealed the radiation-induced cancellation of the apical dominance in young trees of this species. To understand the mechanism of such transformation, we evaluated the morphometric parameters of needles, the frequency of cytogenetic abnormalities, and the concentrations of the major classes of phytohormones in several natural populations of young red pine trees growing under different exposure conditions in Fukushima prefecture. No significant relationships between the morphometric parameters of needles and dose rates at the experimental sites were revealed. The frequencies of aberrant cells in the needle's intercalary meristem and the frequencies of cancellation of the apical dominance in the young pine populations in the radioactive contaminated areas were significantly higher than in the reference population. However, only cytogenetic abnormalities increased with the dose rate. We have not found the relation between the frequency of cytogenetic abnormalities in needles and cancellation of the apical dominance in the individual trees. In this paper, for the first time, it is shown that chronic radiation exposure changes the concentration ratio of the major classes of phytohormones in the needles of Japanese red pine. Given the complete lack of information about the most important regulatory system of plants in chronically irradiated populations, this study fills a substantial gap in our knowledge. Finally, our findings indicated that the most probable causes of the cancellation of apical dominance observed in chronically exposed Japanese red pines are radiation damage to the apical meristems of the trees and changes in their phytohormonal balance.