Low-dose Gamma Irradiation Causes Enhancement Of Stress Resistance And Biological Yield In Barley(Hordeum Vulgare)

Low-dose ⁶⁰Co-?irradiation can not only enhance stress tolerance in barley,but also promote growth development and increase crop yield,however,there is less research on the effect of ⁶⁰Co-?irradiation on barley.In this thesis,barley seeds were irradiated by ⁶⁰Co-?with doses of 50-300 Gy,the physiological indexes,chloroplast ultrastructure and stress-related gene expression in the subsequent seedlings were measured,hence,this study was carried out to investigate the effects of gamma irradiation on the physio-biochemical and molecular mechanism of barley seedlings to abiotic stress.At the same time,a two-year field experiment to explore the effect of⁶⁰Co-?irradiation on barley yield,the dynamic accumulation of dry matter in different irradiation groups and the photosynthetic characteristics of leaves at the filling stage were studied,the differences in dry matter transport and grain contribution between stems and leaves in the control group and the irradiation group were analyzed,and the purpose of exploring how ⁶⁰Co-?radiation can increase yield by regulating the efficient accumulation and transport of barley dry matter to reveal the rules of high barley yield.The main results of the study are:1.In response to the treatments with lead?Pb?/cadmium?Cd?,compared with the control seedlings,50 Gy gamma irradiation maximally promoted the seedling growth,however,the high-dose gamma irradiation treatment?100-300 Gy?all had negative effects on the plant growth parameters.Moreover,the activities of antioxidant enzyme?SOD,POD,CAT?and proline levels in 50 Gy gamma-irradiated seedlings were drastically higher than those in non-irradiated seedlings under lead/cadmium stress.Additionally,transmission electron microscopy results revealed that the 50 Gy gamma-irradiated seedlings exhibited improved chloroplasts ultra-structure compared with non-irradiated seedlings exposed to lead/cadmium stress.Notably,transcriptional expression analysis showed that 50 Gy gamma irradiation could significantly affect the expression of genes?HvHMT1?HvHMT2?HvHMT3 and HvHMT4?related to heavy metal transport and abscisic acid homeostasis under lead/cadmium stress,meanwhile down-regulating the expression of genes related to ABA degradation.Collectively,our results indicate that ⁶⁰Co-?irradiation enhances tolerance to heavy metal in barley seedlings.2.The results indicated that 50 Gy gamma irradiation pretreatment could markedly stimulate growth of seedlings under salt stress and alleviate the salt-induced oxidative stress?evidenced by lower malondialdehyde and hydrogen peroxide contents in irradiated seedlings?through elevating the antioxidant enzyme activities and proline level.Moreover,transmission electron microscopy results revealed that irradiation pretreatment could alleviate the salt damage to chloroplasts ultrastructure.Notably,transcriptional analysis showed that the expression of salt stress related genes were enhanced by irradiation pretreatment,such as Na⁺/H⁺antiporters?HvNHX1,HvNHX2,HvNHX3,HvNHX4?.3.The results showed that ⁶⁰Co-?radiation within 100 Gy promoted the growth of barley,while the height of barley was gradually reduced under 150 Gy irradiation,and the height of barley was significantly reduced under 200-300 Gy irradiation.The stem diameter under 50 Gy treatment was higher than that of the control at different growth stages,and 300 Gy irradiation had inhibitory effects on stem thickening.The effect of 50 Gy irradiation on the quantitative index of strong barley standard has a positive effect.4.The results showed that the content of chlorophyll in 50 Gy ⁶⁰Co gamma irradiation treatment continued to be high,and the content of chlorophyll varied with the other radiation doses.The values of photosynthesis under different irradiation treatments increased first and then decreased with the increase of days after anthesis.Two years of data showed that 50 Gy treatment can promote the growth of vegetative organs,not only increase the flag leaf chlorophyll content,delay plant senescence,but also can increase the leaf net photosynthetic rate?Pn?and the ability of the leaves to assimilate CO₂,thereby accumulating more photosynthetic products and laying a foundation for obtaining higher yield.5.These results indicated that among the different doses of gamma irradiation,only 50 Gy gamma irradiation pretreatment presented maximal beneficial effects on dry matter accumulation,while above the dose of 250 Gy,dry matter accumulation severely decreased compared with the control and therefore not suitable for to barley breeding,the effects of different irradiation treatments on contemporary barley were obvious and the impact on the next generation weakening trend.The contribution of dry matter to grain weight in pre-anthesis in gamma-irradiated?200-300 Gy?seedlings were drastically higher than those in non-irradiated seedlings,while the value of contribution rate in 50 Gy was significantly lower than that of the control,second from flag leaf?L2?and third from flag leaf?L3?had higher pre-anthesis dry matter transport properties.Under the conditions of 250 Gy,dry matter translocation?DMT?,dry matter translocation efficiency?DMTE?,and contribution of dry matter to grain weight?CDMT?of stems and sheaths were all higher in pre-anthesis,but the transport characteristics of stems and sheaths were the lowest under 50 Gy treatment,comparing different parts of the stem and sheath,the second from uppermost play a very important role in maintaining grain filling.and the contribution of post-anthesis dry matter to the grain at 50 Gy irradiation continued to be high,and the post-anthesis photosynthate production capacity was more important for grain yield formation,and therefore 50 Gy treatment with the highest yield.In conclusion,the results in this study show that ⁶⁰Co-?irradiation can effectively enhance stress tolerance in barley seedlings by elevating the antioxidant enzyme activities and proline level.protecting chloroplasts ultrastructure from adversity destruction and up-regulating the expression of genes associated with stress-related detoxification.Moreover,50 Gy gamma-irradiated seedlings showed improved production and productivity,during the whole growth period,low-dose⁶⁰Co-?irradiation can promote the vegetative growth of barley at the early stage and increase the biomass and storage capacity of the barley population at the later stage,by stabilizing the photosynthetic rate,improving efficiency for solar energy utilization,meeting the demand for grain assimilation.thus,it increases barley production.