| Tropospheric ozone(O3)is one of the most important air pollutants.The concentration of O3 in East Asia has increased dramatically.Acute O3 have a negative impact on plants,resulting in reduced crops and forests worldwide.In order to understand the response mechanism of Ginkgo biloba to short-term O3 stress,this study used Ginkgo biloba leaves as experimental materials,fumigation in open-top chamber(OTCs),treated under three O3 concentrations of 80 nmol-mol-’,120 nmol·mol-1 and 200 nmol.mol-1.To investigate the response of O3 treatment to antioxidant system activity and stress resistance gene expression in leaves,the present study measured the changes of reactive oxygen species(ROS),membrane peroxidation(MDA),ascorbic acid(AsA),antioxidant enzyme activities and the expression of stress resistance genes in MAPKs signaling pathway.The main findings are as follows,(1)After acute O3 fumigation,the ROS of Ginkgo biloba leaves oxidized and erupted.The content of hydrogen peroxide(H2O2)and superoxide radical(O2)in the O3 group were significantly higher than that of the CK.The malondialdehyde content(MDA)of 120 and 200 nmol·mol-1 group increased with the treatment time,which had a certain cumulative effect;after O3 stress 8 h,the activities of catalase(CAT),glutathione reductase(GR)and monodehydroascorbate reductase(MDHAR)were increased in the 80,120 and 200 nmol-mol-1 group and the superoxide gasification enzyme(SOD)and dehydroascorbate reductase(DHAR)activities of 200 nmol·mol-1 group increased after 12 h.With the prolongation of fumigation time,the antioxidant system was destroyed and antioxidant enzyme activity was reduced.O3 fumigation for 32-56 h,SOD,CAT,MDHAR,DHAR and GR activities decreased,APX activity increased with increasing O3 concentration,there is no significant difference between 80 nmol·mol-1 and CK in enzyme activities.80 and 120 nmo·mol-1 group has increasesd the content of As A and AsA/DHA ratio;200 nmol·mol-1 group inhibited the production of AsA and decreased the antioxidant capacity of AsA.(2)After O3 fumigation 0-8 h,the expression levels of CAT,APX2,Cu/Zn-SOD and Mn-SOD in leaves were up-regulated,and the expressions of APX1 and Fe-SOD were up-regulated after 32-56 h.In different periods of O3 stress,the expression levels of individual genes in the gene family are different,and the responsible regulatory regions are also different.In addition,there is no uniformity between the rise or fall of gene expression and the regulation of enzyme activity.After acute O3 fumigation for 12 h,MAPK gene expression was up-regulated,MAPK signal pathway was activated,fumigation was 56 h,MAPK and p38 gene expressions were up-regulated,WRKY31 expression was increased,and MAPK signal pathway was activated.At this time,a large amount of ROS in plants accumulation,membrane lipid peroxidation degree aggravated,high concentration O3 group enzyme activities imbalance,ROS as a signal molecule to activate MAPKs,and thus regulate plant resistance to O3.In summary,during the acute O3 fumigation,H2O2 and O2·-were produced in the leaves of Ginkgo biloba,and excessive ROS were accumulated.H2O2 was used as a signal molecule to transmit external stimuli into the cells.The relative expression of p38 and WRKY31 increased,and the MAPK signal was activated.The pathway leads to the up-regulation of the relative expression of the stress-resistant genes,and initiates the defense system.The antioxidant enzyme activities and AsA content of leaves were increased,thereby improving the ability of the Ginkgo biloba to detoxify ROS,maintaining the balance of the intracellular redox reaction and the stability of the cell membrane structure.It also enhance the tolerance of Ginkgo biloba to O3 stress.However,with the prolongation of fumigation time,the antioxidant system of Ginkgo biloba was destroyed,and antioxidant enzyme activities were also reduced. |
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