Effects Of Enhanced UV-B Radiation On Antioxidant And Photosynthetic Characteristics Of Two Species Of Hippophae L.

The ozone layer has been subjected to artificial chemical disturbances for nearly 40years?Portmann et al.,2012?.According to statistics,the global ozone concentration has decreased by 2%-3%in the past 20 years,the reduction in the Antarctic region has reached 50%,and the ozone layer cavity continues to expand?Fang Ying et al.,2018?,this change leads to enhanced UV-B?280-320 nm?radiation reaching the Earth's surface.The high UV-B radiation areas such as mountains and plateaus has been radiated much stronger than other regions in the same latitude.The Qinghai-Tibet Plateau is not only the third pole of the world,but also one of the strong centers of ozone depcrement?Xue ZH et al.,2018;Liu W&Li Wl,2001?.Therefore,UV-B radiation and its enhancement problems are particularly prominent.It is of great value to understand the physiological and ecological response mechanism of plants resisting UV-B radiation by studying on the relationship between UV-B enhanced radiation and biology in using living organisms distributed there as materials.In this paper,H.neurocarpa,a unique woody plant of the Qinghai-Tibet Plateau,and its related species,H.rhamnoides ssp.sinensis,are used as materials.Under UV-B enhanced radiation intensity of 62?W·cm^-2,leaf morphology observation and determination of oxidative damage,antioxidant physiology and photosynthetic characteristics of two species of Hippophae L.seedlings at different treatment time had been done,the effects of enhanced UV-B radiation on oxidative damage and antioxidant physiology and photosynthetic characteristics of two species of Hippophae L.seedlings had been studied.The aim is to preliminarily reveal the physiological response and adaptation mechanism of Hippophae L.and other plants growing on the Tibetan Plateau to UV-B radiation.This will also help us to further understand the adaptation of woody plants to UV-B radiation.At the same time,it provides a theoretical reference for the protection,development and utilization of Hippophae L.resources.The results are summarized as follows:?1?Enhanced UV-B radiation caused leaf curling of both Hippophae L.seedling leaves after 4 days of radiation,among them,H.neurocarpa is extended with radiation time,also showed leaf edge fading and mild wilting,however,other obvious changes have not been observed in H.rhamnoides ssp.sinensis.?2?The enhancement of UV-B radiation significantly increased the H₂O₂ content in the leaves of H.neurocarpa.The content of H₂O₂ in H.rhamnoides ssp.sinensis seedlings increased first and then decreased.The MDA content associated with it showed a consistent trend with a significant increase in radiation time in both Hippophae L.species.?3?In the antioxidant enzyme system,with the prolongation of UV-B radiation time,the CAT activity of H.neurocarpa was significantly improved,their POD and APX activities are significantly inhibited.And CAT,APX and POD activities of H.rhamnoides ssp.sinensis increased in UV-B radiation within 1-4 d,in the later stages of radiation,there are different degrees of decline,and the POD has the largest drop.There was no significant change in the SOD activity of the two Hippophae L..?4?Enhanced UV-B radiation is beneficial to the accumulation of total flavonoids in the leaves of H.neurocarpa and H.rhamnoides ssp.sinensis seedlings,and during the radiation,the total flavonoid content of H.neurocarpa is generally higher than that of H.rhamnoides ssp.sinensis.Studying on the antioxidant activity of two kinds of Hippophae L.,in addition to the control,the total flavonoids of H.rhamnoides ssp.sinensis had higher clearance rate of DPPH free radicals than H.neurocarpa.?5?With the extension of UV-B radiation time,Chlorophyll a,Chlorophyll b,total Chlorophyll and Carotenoid content of H.neurocarpa seedlings decreased significantly,Chlorophyll a/b increased first and then decreased,the chlorophyll a,b and total chlorophyll content of H.rhamnoides ssp.Sinensis show changes of promotion or no significant difference,Chlorophyll a/b and carotenoid content increase with the extension of radiation time.?6?Under enhanced UV-B radiation,exposure over time leads to Initial fluorescence?Fo?,Maximum fluorescence?Fm?,PSII maximum photochemical efficiency?Fv/Fm?,Actual photochemical efficiency??PSII?,Electron transfer rate?ETR?,and Photochemical quenching coefficient?qP?of H.neurocarpa decreased and Non-photochemical quenching coefficient?NPQ?increased.Initial fluorescence?Fo?,Maximum fluorescence?Fm?,PSII maximum photochemical efficiency?Fv/Fm?of H.rhamnoides ssp.Sinensis decreased,but it shows promotion or no significant effect to its Actual photochemical efficiency??PSII?,Electron transfer rate?ETR?,Photochemical quenching coefficient?qP?and Non-photochemical quenching coefficient?NPQ?.The results showed that there were significant differences in the response of H.neurocarpa and H.rhamnoides ssp.sinensis to enhanced UV-B radiation.The damage or inhibition of H.neurocarpa was more obvious than that of H.rhamnoides ssp.sinensis.