Effect Of Ozone Concentration Increasing Near The Ground On Antioxidant System Of Parent And Offspring Soybean Leaves

Surface ozone is a kind of biologically harmful atmospheric pollutant,which has attracted worldwide attention in plant and ecosystem services due to its universality,strong oxidation and plant toxicity.Therefore,the study on the stress mechanism and antioxidant system of field crops under elevated ozone concentration gradient is helpful to reveal the application problems of crop planting.The purpose of this study was to detect the antioxidant capacity of soybean（Glycine max）leaves,and set three ozone concentrations[CK:control,45ppb;T1:（80±10）ppb;T2:（120±10）ppb]to study the effects of ozone on grain yield and oxidative stress parameters of soybean cultivar’Tiefeng 21’.In order to analyze the changes and differences of growth,physiology and related antioxidant system of soybean leaves in the process of ozone fumigation,the progeny after the first year of stress were compared with the leaves of two consecutive generations of soybean plants after fumigation.It provides a reference for the yield research of continuous soybean varieties under the background of ozone exposure.1.During ozone exposure,soybean leaves showed membrane lipid peroxidation,and a large number of reactive oxygen species were generated and accumulated.Especially,the content increased rapidly in the late stage,reaching the peak at high concentrations at podding stage,with an increase of 88.2%and 92.4%,respectively（P<0.05）.Ozone treatment resulted in the first increase and then decrease of reduced ascorbic acid and reduced glutathione,and the contents of oxidized ascorbic acid and oxidized glutathione continued to increase.Soybean leaves de novo synthesized antioxidants to alleviate oxidative stress by regulating the transformation pathway in the ascorbic acid-glutathione cycle.Reduced oxidized ascorbic acid and reduced/oxidized glutathione first increased and then decreased,and total antioxidant content increased.The response of antioxidant system was related to ozone stress concentration and the accumulation of reactive oxygen species and antioxidants in plants2.In the early stage of O₃ treatment,the activities of peroxidase in parental generation and offspring generation leaves and ascorbate peroxidase and glutathione reductase in ASC-GSH cycle were increased,and in the late stage,they were lower than those of CK with the increase of O₃ fumigation concentration and fumigation time.O₃ inhibited the significantly decreased activities of superoxide dismutase,catalase monodehydroascorbate reductase and dehydroascorbate reductase.It was speculated that the response of antioxidant enzyme system was related to O₃ stress concentration and ROS accumulation in plants.Although plants alleviate the increase of ROS by actively regulating the antioxidant system,it still causes the further accumulation of ROS and the weakening of enzyme activity.3.The effects of ozone on yield factors,including grain number per plant,pod number per plant,grain weight per plant and 100-grain weight were significant.Among them,seed number per plant of parental soybean decreased most,which were 27.9%and 37.5%respectively（P<0.05）.The decrease of grain weight per plant of progeny soybean reached the maximum,which was 30.9%and 39.8%,respectively（P<0.05）.Ozone treatment also caused the conversion rate of ABTS+and DPPH free radicals in soybean extract decreased with time.The results of iron reduction antioxidant capacity test also showed that the damage of ozone gradually increased with time,and the total reducing power reached the lowest at podding stage,which was reduced by 23.4%（P<0.05）.However,low concentration ozone treatment enhanced the antioxidant capacity of soybean,which indicated that soybean had strong tolerance to ozone,and showed rapid regulation in antioxidant system,which could establish and maintain a new balance of redox state in the short term.4.Compared with the parental generation,the antioxidant capacity of the offspring exposed to O₃ did not have a significant indigenous effect or further decline.Compared with the offspring,soybeans exposed to O₃ in the first year could establish a new balance of redox state more quickly.It was speculated that the offspring after multiple cropping were more likely to produce and accumulate ROS when exposed to O₃ in the second growing season.However,soybean plants start the defense system,stimulate the activity of antioxidant enzymes,regulate the ASC-GSH cycle,increase the content of antioxidant substances to maintain the stability of intracellular redox state,and detoxify ROS to ensure the growth of individuals.Therefore,although most of them show a decreasing trend of resistance,the difference is not significant.Therefore,soybean has a certain ability to adapt to the environment with elevated O₃ concentration,which is related to exposure time and concentration,so it may adapt to the environment with increasing O₃ concentration in the future.