Influence of y-irradiation and lead on the dynamics of germination of spring barley seeds

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.