Responses Of Antioxidative System In Ginkgo Biloba Leaves On Elevated Ozone

Ozone is known as one of the important greenhouse gas and a photochemicaloxidant in the earth’s troposphere as a result of natural processes. There are anincreasing number of ozone concentrations in the atmosphere in recent150years,especially in urban areas of China. High concentrations of O3have a highly toxiceffect on the plant. The Ginkgo biloba (GB) is the last remaining member of theGinkgoaceae family, which once included a lot of species. It is famous for “livingfossil” and “the panda of plant kingdom”. Ginkgo biloba is one of the mainly usedstreet trees for urban greening in many cities, and it also has highly ornamental andeconomic value. Under adverse conditions, a variety of antioxidant systems exist in plants canreduce the damage causing by reactive oxygen species produced in the plant. We analyzedplant resistance mechanism deeply, which provided much valuable information andlaid a foundation for effectively improving stress resistance in plant.In order to reveal the effect of the high concentrations of O3on Ginkgo bilobaleaves antioxidant system, we selected the5-year-old Ginkgo biloba to analyze thechanges of reactive oxygen production, antioxidant content, antioxidative enzymesactivities, and membrane lipid peroxidation under the high concentrations of O3stress(80,160nmol·mol-1) at cellular and molecular level in Open-Top Chambers (OTCs).And for further details about which signaling pathways were activated by highconcentrations of O3, we eamined for JNK, p38and ASK1pathway activation bywestern blot and immunolocalization of the phosphory-lated p38MAPK, JNK andASK1kinases in ginkgo biloba leaves.The results clearly indicate that superoxide free radical production rate wasincreased and CAT, SOD, APX, MDAR, DHAR and GR activities were increased,while H2O2and MDA contents were decreased by the ozone fumigation treatment (80and160nmol mol-1) for10d and20d. However, the superoxide free radicalproduction rate and H2O2as well as MDA contents were increased, while CAT、SOD、APX、MDAR、GR activities decreased and DHAR activities increased by the ozonefumigation treatment (80and160nmol mol-1) for30d,40d and50d. APX activityhad been in decline when ozone concentration went up to160nmol mol-1. Thereforewe concluded that the activities of antioxidantive enzymes were increased in Ginkgobiloba under ozone stress within10-20d. However, the activities of antioxidantivesystem decreased, and membranous content increased, which indicated the increasingactivities of antioxidantive system could not resist the long term (20-50d) highconcentrations of O3stress. At the same time, the induction of kinases by O3wastested by western blot. A clear induction of a band corresponding to JNK protein ofGinkgo biloba leaves were treated with high concentration of ozone fumigation (160 nmol mol-1), while the p38MAPK and ASK1protein all could be detected when theatmospheric ozone concentration went up to80nmol mol-1at least. Our studyconcluded that the accumulation of H2O2in the Ginkgo biloba leaves under ozonestress can induced phosphorylation of the ASK1kinase. Because the ASK1kinase isa common upstream molecule in both JNK and p38MAPK signaling passways, theobserved phosphorylation of the JNK kinase is in agreement with p38kinaseactivation of the stress-activated ASK1by high concentrations of O3stress, than theymaybe activated the JNK and p38MAPK signaling pathways in Ginkgo biloba leavesunder high concentrations of O3(80,160nmol·mol-1) stress. And JNK signalingpathway could be activated when ozone concentrations rised to160nmol·mol-1in theatmospheric.According to the result of study, O3is causing foliar injury, the reactive oxygenspecies enhanced, and antioxidant enzymes activities increased and the degree ofmembrane lipid peroxidation deepening, especially under high concentrations of O3(160nmol·mol-1) stress. Western blot showed that the JNK, p38MAPK and ASK1signaling pathways maybe activated by high concentrations of O3in Ginkgo bilobaleaves, depended on the phosphorylation of these kinases expression whether or not.