The Response Of Antioxidant Protection System Of Lespedeza Davurica To The Combined Stress Of Drought And UV-B Radiation

Lespedezadavurica is the native plants of the Loess Plateau, we simulated drought stress,UV-B radiation and the combination of two stresses in this paper. We studied the dynamicchange of the activities of superoxide dismutase, peroxidase, catalase and ascorbateperoxidase(APX),as well as the contents of superoxide anion radical, malonaldehyde,ascorbic acid and carotenoid in leaves of Lespedeza davurica under different stresses, explorethe changes of these indicators in time and space law under different stress conditions, andconducted a comprehensive evaluation antioxidant capacity of a variety of stress conditionsbased on anti-oxidation protection system by the membership function method to explore theability of adaption to adversity environment.The conclusions were shown as follows,1．The effects of antioxidation protection system under drought stress and re-wateringWith the stress time, the activities of SOD,POD,APX and POD in leaves weresignificantly higher in the water-stressed plants compared to well-watered plants. The activityof SOD increased with the increased of drought stress intensity,,while activities of CAT,APXdecreased,however, activity of POD initially decreased and then increased after6days; Aboutanti-oxidants, the Car content in leaves were significantly higher in the water-stressed plantscompared to well-watered plants, however, the AsA content didn't change significantly, AsAcontent initially decreased and then increased. Production of O₂-increased by drought stresstreatment, the MDA content increased. In addition, with the increase of drought stressintensity, MDA content in the first6days increased and after that the changes of eachtreatment group was not significant, however, the O₂-content was decreased; Afterre-watering, the activities of APX and CAT, the content of Car and O₂-ware all increased,and the others were all decreased. We comprehensively evaluated the antioxidant capacity ofthis plant by the subordinate function under drought stress, and the result was:DR₁>DR₂>CK.2．The effects of antioxidation protection system under enhanced UV-B radiationDuring the whole treatment time, enhanced UV-B radiation decreased the SOD and PODactivities and increased APX and POD activities. The activities of SOD, POD and CATdecreased with the increase of UV-B radiation intensity. During the first9days treatment,APX activity became higher with the increase of radiation intensity, after9days treatment, APX activity was lower with the increase of radiation intensity; UV-B radiation increased theAsA content, decreased the Car content, and both of them decreased with the radiationintensity increased. Production of O₂-and MDA content increased by UV-B radiationtreatment. In addition, O₂-and MDA increased with increasing radiation intensity. AfterUV-B radiation was removed, SOD activity, POD activity and Ascorbic acid content weredecreased,the others were all increased. We comprehensively evaluated the antioxidantcapacity of this plant by the subordinate function under UV-B radiation, and the result was:T₂>T₁>T0.3．The effects on antioxidation protection system by enhanced UV-B radiation under differentdrought stressesEnhanced UV-B radiation under well-watered make the activity of SOD, POD activityinitially increased and then decreased, CAT activity gradually increased, and APX activityfirst decreased and then increased, compared with the drought stress only, SOD activitydecreased, APX and POD activity increased activity, CAT activity did not occur verysignificant change under the combination stresses, the activity of SOD, POD, CAT activityincreased with the increase in the intensity of UV-B radiation, however, the APX activityinitially decreased and then increased with the increase on the intensity of UV-B radiation.AsA content and anthocyanin content increased by enhanced UV-B radiation under droughtstress, increased, but Car contents very significantly reduced by enhanced the high UV andsignificantly increased by enhanced the low UV under drought stress. After6days treatment,MDA content under the combination stresses is lower than the drought stress only, O₂.-content changed not significantly under the combination stresses, and then, the O₂.-contentwas significantly increased by enhanced low UV-B radiation.SOD activity and CAT activity was reduced by enhanced UV-B radiation undermoderately drought stressed, APX activity and POD activity increased under the combinationof drought and UV-B radiation, SOD activity by enhanced low UV-B radiation wassignificantly lower than the drought stress only; However, with the increase on the intensityof UV-B radiation, POD activity decreased,the APX activity and CAT activity increased; Byenhanced UV-B radiation under drought stress, the AsA content higher than the control andthe carotenoid content lower than the control, with the increase of radiation intensity, AsAcontent first increased and then decreased, and Car contents decreased. During6days on thelow UV-B radiation, anthocyanin content was significantly higher than controls. Within6days stressed, MDA content is lower than the drought stress only under the combinedstress.Under the combined stresses O₂.-content first increased and then decreased.When enhanced UV-B radiation under severely drought stress,SOD activity was lower than the control group and POD activity was higher than the control by enhanced UV-Bradiation under drought stress, and the POD activity decreases with the increase of radiationintensity from9to15days, CAT activity is reduced with the reduction of the radiationintensity, APX activity under the combined stress of low UV was higher than the controlwhile APX activity under the high UV combined stress was lower than the control. Comparedwith the control, AsA content did not change significantly under the combined stress, the Carcontent under enhanced high dose UV-B radiation was significantly increase,however theCar content under enhanced low dose UV-B radiation was significantly lower than thedrought stress only from9to12days. From0to6days, anthocyanins content was increasedby the combined stress of high UV and anthocyanins content was decreased by the combinedstress of low UV, MDA content was significantly lower than the control under the combinedof drought stress and UV-B radiation. O₂.–Content under the combined stress was lower thanthe control.We comprehensively evaluated the antioxidant capacity of this plant by thesubordinate function under the conbined stress of UV-B radiation and drought, and the resultwas: when enhanced UV-B radiation under well-watered, T₂+DR₁> T₁+DR₁> DR₁; whenenhanced UV-B radiation under moderately drought stress, T₁+DR₂> DR₂> T₂+DR₂;when enhanced UV-B radiation under severely drought stress, T₁+DR₃> T₂+DR₃> DR₃.4．The comprehensive evaluation of resistance of Lespedeza davurica.Comprehensive evaluation indicates that①Lespedeza davurica has higher droughtresistant and the antioxidant capacity of this plant in the moderate stress was higher than thatin severely stress, moderate stress may be more suitable for the growth of the plants.②Compared to the control, enhanced UV-B radiation reduces the antioxidant capacity ofLespedeza davurica, and the antioxidant was lower and lower with the increase of theintensity of UV-B radiation.③When enhanced UV-B radiation under moderately andseverely drought stress, it was helpful to improve the drought resistance of plants byenhanced UV-B radiation, when enhanced UV-B radiation under well-watered, droughtresistance of Lespedeza davurica increased with the increase of UV-B radiationintensity.When enhanced UV-B radiation under severely drought stress, drought resistance ofLespedeza davurica decreased with the increasing UV-B radiation intensity. When enhancedUV-B radiation under moderately drought stress, the increase of low-dose UV-B radiationwas conducive to improve the drought resistance of Lespedeza davurica, however, increasethe high-dose UV-B radiation decreased slightly the ability to adapt to drought stress.