Effects Of Excess UV-B Irradiation On Physiological And Biochemical Responses In Three Species Of Saussurea On Eastern Of Qinghai-Tibetan Plateau

Since1984, when the British scientists found the ozone hole over the Antarctica, the destruction of ozonosphere and increase of UV irradiation has attracted many scientists and acquired lots of attentions. While, recent studies show that the Qinghai-Tibet Plateau as a highly sensitive areas of the global atmospheric crisis, its UV radiation intensity is also increasing. The Qinghai-Tibetan plateau is also one of modern distributive centers of the genus of Saussurea of Compositae, Saussurea distributing in this area as a common species will inevitably under the influence of ultraciolet enhancement. In this study, an experiment using by ultraviolet spectrophotometry was conducted to investigated the effects of UV-B irradiation on germination and physiological characteristics in three Saussurea species distribute in eastern Qinghai-Tibetan plateau, S. hieracioides Hook. f., S. arenaria Maxim. and S. nigrescens Maxim. The physiological indexes including chlorophy content, MDA content, hdrogen peroxide （H2O2） content, superoxide anion （·O₂^-） content, soluble sugar content, soluble protein content, UV-B-absorbing compounds content and antionxidant enzyme activity such as superoxide dismutase （SOD） and catlase （CAT） acticity. Through the statistical analysis of experimental data of response about three Saussurea under excess UV-B irradiation stress provides information for protection of alpine meadow under the background of global atmospheric crisis over the eastern of Qinghai-Tibetan Plateau.Three Saussurea species seeds treated with different UV-B radiation （2,4,6,8hours） compared with that without radiation processing, the results show that:（1） Three Saussurea seeds germination appeared hysteretic phenomenon under UV-B radiation treatment, and compared with the without radiation treatment control group the germination index showed a significant reduction beside with the increase of the duration of action, the germination index decline gradually.（2） Three Saussurea species seed germination was reduced significantly under UV-B radiation treatment, the slope of the curve that S. nigrescens seed germination decreased with the UV-B radiation processing time was the smallest.The physiological characteristic of three Saussurea species seedlings under UV-B radiation treatment and the untreated control seedlings were measured in four stages （0,5,10,15day）, the results showed that:（1） The content of chlorophyll a and chlorophyll b in three Saussurea seedling were lower than the control group in various stages of processing, and the content of chlorophyll a and chlorophyll b decreased with the increased processing time, the slope of the curve that S. hieracioides chlorophyll a and chlorophyll b decreased with the radiation time was minimum the content of carotenoid in three Saussurea seedling increased with radiation processing time, the slope of the curve S. hieracioides carotenoid content increased with the irradiation time was maximum.（2） Since the UV-B radiation processing time increased three Saussurea species seedlings were damaged, the content of MDA, H2O2and O-2were increased With the increase of the irradiation time, the slope of the curve that S. hieracioides MDA, H2O2and O-2content increased was minimum.（3） Counter with the damage caused by UV-B radiation, the SOD activity of three Saussurea seedlings were enhanced after UV-B radiation treatment, the slope of the curve that S. nigrescens SOD activity increased with the irradiation time was minimum. In addition to S. nigrescens, the other two species of Saussurea catalase activity were enhanced with the increase of the irradiation time.（4） The content of soluble sugar in three Saussurea species seedlings under UV-B radiation stress increased, of which the slope of the curve that S. hieracioides soluble sugar content increased with the irradiation time was maximum. In addition to S. nigrescens, the other two species of Saussurea soluble protein content increased with increasing irradiation time.（5） Compared to the control group the content of UV-absorbing compounds in S. hieracioides did not change significantly with the increase of UV-B irradiation treatment time. The slope of the curve that S. arenaria UV-absorbing compounds content increased with irradiation time was greater than S. nigrescens’s.The above experimental results showed that the ability to resistance UV-B irradiation damage of S. hieracioides and S. arenaria is stronger than S. nigrescens.