Effects Of Elevated O₃ On Antioxidant System And Protein Expression Of MAPKs Signal Pathway In Ginkgo Biloba Leaves

To study the responses of Ginkgo Biloba (G.B) on high concentration of ozone in astomsphere, we applied the 3 year-old G.B as the experimental material in the OTCs (open top chambers), and ozone concentration in the natural condition as the control group. The study set 80 nmol·mol-1,160 nmol·mol-1, and 200 nmol·mol-1 three ozone concentration gradients to study the damage of the accumulation ofH2O2 and O2- produced from ozone fumigation to the G.B leaves and the effects of degree of membrane lipid peroxidation, as well as the influence on the activity of antioxidant enzymesincluding CAT, SOD, APX, MDAR, DHAR, GR and so on. The study used Western-Blot to study the effect of high concentration ozone on MAPKs signaling pathway and the relationship between ROS, antioxidase and MAPK signal pathway.The results show:(1) The GB leaves under 80 nmol·mol-1 ozone fumigation suffered less damage during the whole treatment; and the foliar injury of the high concentration ozone (160 nmol·mol-1 and 200 nmol·mol-1) to G.B leaves showed the positive correlation with the treatment period and ozone concentration. (2) ROS of 80 nmol·mol-1 ozone concentration maintained a low level; the GB leaves released O2- faster, the content of MDA increased, the activity of SOD, CAT, APX, MDAR, DHAR and GR which can scavenge ROS increased and the content of H2O2 decreased. In the late stage (>20d), the activities of CAT, SOD, APX, DHAR,, MDAR, GR and other enzyme decreased, O2- production rate and H2O2 content increased significantly, and MDA content increased. (3) The increase of ozone concentration resulted in a large number of the accumulation of ROS, leaded to expression of the related protein JNK、ASK1 and p38 in the MAPKs signal pathway. Active ASK1 was the same upstream of JNK protein kinase and p38MAPK protein kinase, resulting in JNK and p38 MAPK phosphorylation expression, and activating the JNK and p38MAPK signal pathways in GB leave cells.Thus, short-term high concentrations of ozone can cause the enhancement of anti-oxidation system in G.B. leaves and decrease the accumulation of ROS. Long-term high concentrations of ozone can induce the accumulation of ROS, resulting reduction in antioxidant enzymes activities and led to aggravation in lipid peroxidation, activate the expression of ASK1, JNK and p38protein kinase in MAPKs signaling pathways of the G.B leaves.