Effects Of Elevated Ozone On Antioxidant Enzymes And Defensin Gene Expression In Ginkgo Biloba

Ozone is now considered to be the second most important gaseous pollutant in our environment.To date,unsustainable resource utilization has turned this secondary pollutant into a prime threat to plants on earth.High Ozone has a strongly adverse effect on forest ecosystem.Moreover,about 30%of forest has been repressed by this gaseous pollutant.To study the effects of ozone in ginkgo leaves on transcriptional level,we applied 3-year-old ginkgo in OTCs as materials.12 OTCs was filled with ozone of 4 concentrations each of triplicate:control,80nmol·mol^-1,160 nmol·mol^-1,and 200 nmol·mol^-1.The foliar injury of ozone on ginkgo was investigated and documented.Then the production rate and contents of reactive oxygen species was measured in labs.Most importantly,the RT-PCR analysis of antioxidant enzymes genes and defensin genes in ginkgo leaves were conducted.The results showed that:?1?Leaves to control and 80 nmol·mol^-11 O₃showed no significant changes from color to stipples in the whole fumigation span.However,the foliar injury on ginkgo to 160 nmol·mol^-11 and 200 nmol·mol^-11 was getting worse as time went on,and the degree of injure to 200 nmol·mol^-11 was strong than to 160 nmol·mol^-1in every harvesting time.?2?The production rate of O₂^-.stayed in low levels and didn't increased significantly until 20th day.The production rate of O₂^-.to high ozone was higher than control and 80 nmol·mol^-1.Moreover,due to the inefficient scavenging mechanisms of O₂^-.,there was another increase in later fumigation.The time of increasing O₂^-.to high concentrations of ozone was the 30th day.Whereas the time of increase to control and 80 nmol·mol^-1was the 40th day,later and lower than those to ozone concentrations of 160nmol·mol^-11 and 200 nmol·mol^-1.The H₂O₂ contents showed an oxidative burst and reached a peak at 10th day.The rapid increase of H₂O₂ contents activated the scavenging system of H₂O₂ in ginkgo leaves,then caused a significant decrease in H₂O₂ contents the 20th day.Although H₂O₂ contents to control and 80 nmol·mol^-11 of ozone were higher than to 160 nmol·mol^-11 and 200 nmol·mol^-1,the situations inverted as time went on.?3?As for the transcriptive levels of antioxidant enzymes genes,CAT gene was quite sensitive to the change of H₂O₂ contents.It showed a rapid increase at 10th day of fumigation and then decreased significantly at 20th day.There was another increase of CAT gene in transcriptional levels at the 40th day,just consistent with the changes of H₂O₂ contents.Although at the 60th day of fumigation the H₂O₂ contents decreased,the CAT gene in transcriptional levels kept on increasing.Another unexpected detection was that CAT gene in transcriptional levels to 160 nmol·mol^-11 was higher than 200 nmol·mol^-1.The APX gene in transcriptional levels showed a slight increase as time went on.Moreover the transcriptional levels of APX gene to high concentrations of ozone were higher than to control and 80 nmol·mol^-11 just as expected.While similar to CAT transcription levels the 60th day,the APX transcription levels to 200 nmol·mol^-11 was lower than160 nmol·mol^-1.The GbD transcription levels increased in every harvesting time.And more excitingly,the GbD transcription levels rose as the increase of ozone concentrations.Just like an indication of harm on ginkgo leaves,GbD transcription levels depended on the cumulative effect of both concentration and duration of ozone exposure.