Effects Of Long-time Elevated O₃ On Physiological Characters And Antioxidant Genes Expression In Ginkgo Biloba

Recently,the ozone concentration in ground level has a rapid increase and evidently affects urban plants.Ginkgo Biloba?G.B?is common for road greening in China.In the study,we used five-year-old G.B as experimental matirial to fumigate continuously for two years,and to study the effects of long-term ozone fumigation on the growth,physiological characteristics and antioxidant genes expression of G.B.In the experiment the Open-Top Chambers?OTCs?method was used,the concentration of atmospheric ozone in natural conditions?around 40 nmol·mol-1?was used as control,and the treatment groups were set at 120 nmol·mol-1 and 200 nmol·mol-1.In the study,we observed the injury symptoms of leaves,the growth indicators we measured including the germination rate,the infection rate next year,the increase of plant height,basal diameter,leaf area and branch length of G.B,the physiological indicators such as catalase?CAT?,superoxide dismutase?SOD?,ascorbic acid peroxidase?APX?,monodehydroascorbate reductase?MDAR?,dehydroascorbate reductase?DHAR?,glutathione reductase?GR?,and malonaldehyde?MDA?content,and some antioxidant genes expression such as CAT?Cu/Zn-SOD?Mn-SOD?Fe-SOD?APX?glutathione mercaptotransferase?GST?and peroxidase?POD?.The purpose of this study was to investigate the effects of long-term ozone fumigation on G.B and accumulated data for studying the effects of climate change on trees.The results showed that?1?Comparing with the control,long-term ozone fumigation caused significant damage to the leaves,and with the increase of ozone concentration and fumigation time,the damage was more evident.?2?Comparing with the control,long-term 200 nmol·mol-1 ozone fumigation could significantly inhibit the germination rate of G.B and increase the rate of disease,120 nmol·mol-1ozone group had no evident change.The plant morphological characteristics of G.B were restrained,and the higher the ozone concentration was,the more obvious the differences were.?3?Comparing with the control,long-term ozone fumigation could significantly increase reactive oxygen?ROS?level and antioxidase activities,in the early period?<40 d?,the production rate of O2-.and the content of H2O2 were at lower level,the activity of CAT?SOD and APX decreased.In the later period?>40 d?,the ROS level increased gradually,and the activities of CAT?SOD and APX decreased after increasing to the maximum.At the prime stage?<20 d?,MDAR,DHAR and GRincreased significantly,with the increasing of O₃ concentration,the activity increasing was more obvious.With the time of fumigation increasing?>20 d?,the activities of APX,MDAR,DHAR and GR decrased gradually,the content of MDA increased gradually.?4?Comparing with the control,long-term ozone fumigation can significantly increase the expression of antioxidant genes,in the early stage?<40 d?,the expression of CAT,Cu/Zn-SOD,Mn-SOD increased gradually and were relevant significantly to corresponding antioxidase activities,APX and Fe-SOD decreased,GST and POD increased significantly at the ozone concentration of 120 nmol·mol-1and were inhibited at 200 nmol·mol-1,later incrased gradually.Therefore,under long-term ozone fumigation the growth of G.B was inhibited,the ROS level had a large accumulation,the degree of lipid peroxidation increased,the activitiy of antioxidant enzymes increased firstly and then decreased,which had consistent change with the expression of the antioxidant genes,and the antioxidant enzymes activitiy and antioxidant genes were inhibited when the fumigation time and concentration increased.