Effects Of O₃ On Antioxidant System Activities And Resistance Gene Expression In Soybean

Elevated tropospheric ozone?O₃?caused severe damages to crop production including soybean?Glycine max?Linn.?Merr.?in the worldwide scale.In order to study the response mechanism of soybean under ozone stress and the mechanism of self-repair after ozone stress,Liaodou 23 was used as experimental materials,and the different concentrations of ozone(CK,80,200 nmol·mol^-1)were set in experiment.The changes of ROS level,membrane lipid peroxidation,ascorbic acid?AsA?and glutathione?GSH?level,antioxidative enzymes activities,and antioxidant genes expression levels of leaves were studied in the experiments.In addition,we measured the effects of ozone fumigation time and concentration on soybean agronomic traits in the long-term and short-term treatment.The results show that.1.Effects of long/short-term fumigation on soybean growth and yieldThe leaf area,plant height,above-ground biomass,underground biomass and100-grain weight index of soybean were reduced by 26.01%,10.13%,25.96%,63.52%and 15.49%respectively compared with CK under long-term 200 nmol·mol^-1treatment.However,short-term 200 nmol·mol^-11 ozone significantly decreased leaf area and subsurface biomass of soybean compared with CK.It showed that short-term high-ozone-stressed plants did not cause changes in agronomic traits.Long-term fumigation of ozone(80 nmol·mol^-1)resulted in a significant increase in the number of soybean pods per plant and the number of grains per plant relative to the control group,while there were no significant differences between ozone group and CK under the short-term fumigation.The results showed that the long-term treatment of80 nmol·mol^-11 increased the number of soybean pods and the number of grains per plant,while there were no difference between the short-term ozone treatment.2.Antioxidant system activity and stress resistance gene expression in soybean during O₃ stress periodROS and MDA levels in soybean leaves were increased during the fumigation of200 nmol·mol^-1,and the ratios of AsA/DHA and GSH/GSSG were decreased,and the activities of CAT,APX,GR,DHAR and MDHAR were at a lower level;80nmol·mol^-11 group did not induce the continuous increase of ROS and MDA levels in soybean leaves,the ratio of AsA/DHA and GSH/GSSG increased,and the activities of antioxidant enzymes increased.These results indicated that the fumigation of 200nmol·mol^-11 leads to deeper membrane lipid peroxidation and the inhibition of antioxidant system in soybean leaves;the fumigation of 80 nmol·mol^-1in the short term did not cause ROS bursts and membrane lipid peroxidation,and the antioxidant capacity was enhanced.Ozone fumigation with different concentrations(80 and 200nmol·mol^-1)led to the up-regulation firstly and then down-regulation of CAT gene family,SOD gene family,APX and GR expression.These results showed that short-term ozone treatment?36h?will induce stress gene expression.3.Antioxidant system activity and stress resistance gene expression of soybean in recovery period200 nmol·mol^-11 ozone fumigation caused damages to soybean.During the recovery experiment,ROS and MDA contents in soybean leaves of the treated group gradually decreased,and membrane lipid peroxidation level was decreased,but it did not drop to CK level after 72 hours.The levels of AsA and AsA-GSH cycle metabolic efficiency increased compared with control,and the expression of CAT gene family,SOD gene family,and APX were increased.These results indicated that 200nmol·mol^-11 ozone-stressed soybean plants can repair the previous damages in an appropriate environment through active regulation of their physiological and molecular levels.The repair speed and degree of recovery are affected by the ozone concentration.In conclision,in order to remove ROS to protect plants from oxidative stress damage,the expression of antioxidant enzymes in soybean leaves were up-regulated under 80 nmol·mol^-11 treatment,and the activities of antioxidant enzyme were also increased.The ROS contents in soybean leaves were increased under 200 nmol·mol^-1treatment,and the accumulation of ROS could lead to oxidative stress and the decrease of antioxidant capacity,resulted in membrane lipid peroxidation.Although ozone fumigation increased the expression of related antioxidant enzyme genes,the activities of multiple antioxidant enzymes did not consistent with their gene expression.The increase of ROS contents as well as the level of membrane lipid peroxidation induced by high-level ozone fumigation were gradually alleviated during the recovery period.The activities of antioxidant enzyme and gene expression in soybean leaves were increased under 200 nmol·mol^-1,resulted in the decreased of active oxygen as well as the level of membrane lipid peroxidation.