| The principal ultraviolet radiation absorbance occurs in the stratospheric ozone layer in earth's atmosphere.The destruction of this layer,which is caused by ozone depletion,has lead to an increase in solar UV-B radiation(280-320 nm)reaching the earth's surface and produced potentially biological effect for plant in the earth.In this experiment,three different ages Eucommia ulmoides seedlings were used as experimental materials to study the effects on the photosynthesis,antioxidant enzyme system,free radical accumulation,UV-absorbing substances and secondary metabolites of Eucommia ulmoides seedlings under the different intensities of UV-B radiation.We revealed the adapted mechanism of physiological characteristics in Eucommia ulmoides seedlings under enhanced UV-B radiation and stress release.The main results are as follows:(1)The photosynthetic capacity of different three ages Eucommia ulmoides seedlings,which main indicator were Net photosynthetic rate(Pn),Stomatal conductance(Cond),Transpiration rate(Tr)and the Maximum photosynthetic efficiency of Light System II(Fv/Fm)and Actual Photosynthetic Efficiency of Light System ?(Y(II))were significantly decreased by enhanced UV-B radiation(P<0.05).The contents of chlorophyll and carotenoids in Eucommia ulmoides decreased with increasing UV-B in one-year and three-year old,and the content of chlorophyll in Eucommia ulmoides increased with low UV-B intensity in five-year's.(2)The UV-B radiation treatment induced the accumulation of soluble protein in the Eucommia ulmoides seedlings,reduced the content of soluble sugar in one-year old and three-year old Eucommia ulmoides seedlings(P<0.05),and not affect on five-year old seedlings(P>0.05).(3)The UV-B radiation treatment reduced the activities of ascorbate peroxide(APX),catalase(CAT),peroxidase(POD),while increased the activities of superoxide dismutase(SOD)in one-year old and three-year old Eucommia ulmoides seedlings(P<0.05),and not affect on five-year old seedlings.(4)Our results showed that the contents of MDA,H2O2,O2(?)and NO in Eucommia ulmoides seedlings were significantly increased by enhanced UV-B radiation(P<0.05).(5)Enhanced UV-B radiation significantly increased the activities of phenylalanine ammonia-lyase(PAL)and the content of flavonoid,total phenols,tannins,genipin,chlorgenic acid and geniposide in three ages of Eucommia ulmoides seedlings(P<0.05).The contents of aucubin and geniposidic acid in three ages of Eucommia ulmoides seedlings were decreased.Compared to the variation of secondary metabolites in different ages Eucommia ulmoides seedlings,the contents of genipin and chlorogenic acid in the secondary metabolites were highest at the seedling stage(one-year old),the contents of geniposidic acid,aucubin and geniposide were highset at the five-year old Eucommia ulmoides seedlings(P<0.05).(6)After one year recovery,the leaf area and branches quantity of Eucommia ulmoides seedlings increased with UV-B radiation intensity,the water content did not significantly changed,resulting in increasing leaf biomass.The photosynthetic indicators gradually recovery,chlorogenic acid and genipin had significantly improved,but UV-B radiation treatment negative affect the recovery of aucubin,geniposide and geniposidic acid.In summary,because of the results demonstrate that free radicals were increased sharply and antioxidase activities decreased,plant was damaged.On the other hand,Eucommia ulmoides seedlings will mitigate the damage to plants caused by UV-B through their defense system,such as secondary metabolism.After calculation of membership function,we found that five-year old Eucommia ulmoides seedlings are more resistant to UV-B radiation and through one year recovery,the photosynthetic index of Eucommia ulmoides seedlings almost returned,some of the metabolites have been improved effectively. |
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