中文摘要：

由于臭氧层逐渐变薄,到达地球表面UV-B辐射不断增加,因UV-B辐射改变的太阳光谱将会对陆地植物造成不同程度的伤害。本试验以高粱龙杂5为材料,对二叶一心高粱进行四种剂量UV-B处理,恢复2d采用光合仪测定光合参数,并取样测定抗氧化酶活性。随着UV-B剂量的升高,高粱叶片褐化损伤加重,植株矮化,鲜重和干重显著降低;花青素含量显著升高,叶绿素和类胡萝卜素含量显著减少,净光合速率和叶绿素荧光参数显著下降。同时,随UV-B剂量升高,高粱幼苗气孔导度、胞间CO_2浓度和蒸腾速率表现为＂降-升-降＂变化;POD和CAT活性呈现＂降-升-降＂变化;SOD和GR活性呈现＂降-升＂变化,APX和GPX呈现＂升-降-升＂变化。在供试的四种剂量中,UV-B处理6h（相当2.4J·m^-2）的高粱幼苗净光合急剧下降,其他光合指标以及抗氧化酶活性也表现出明显转折。结果表明,增强的UV-B辐射直接导致高粱光合色素、净光合速率和叶绿素荧光参数的改变;高粱抗氧化系统对高、低剂量UV-B响应机制不同,其中ASA-GSH循环对低剂量UV-B反应更敏感,高剂量UV-B辐射不仅破坏高粱光合作用,而且启动植物酶促和非酶抗氧化系统,导致叶片褐化坏死,植株生物量累积减少、株高矮化,甚至死亡。

英文摘要：

The UV-B radiation on the surface of our planet has been enhanced due to gradual thinning of ozone layer.The change of solar spectrum UV-B radiation will cause damage to all kinds of terrestrial plants at certain degree.In this paper,taking breeding sorghum（Sorghum bicolor（L.Moench））variety Longza No.5 as sample,40μW·cm~（-2） UV-B radiation treatment was conducted on sorghum seedlings at two-leaf and one-heart stage and different time courses;then after a 2d recovering,photosynthetic parameters were measured with a photosynthetic apparatus;the activities of antioxidant enzymes were detected as well.Our results revealed that,as the dosages of UV-B increasing,leaf browning injury was aggravated,plants dwarfing and significantly were reduced fresh weight and dry weight were observed;anthocyanin content was significantly increased;chlorophyll and carotenoid content significantly were reduced and net photosynthetic rate and chlorophyll fluorescence parameters were decreased.Meanwhile,with the increase in UV-B dosages,stomatal conductance,intercellular CO_2 concentration and transpiration rate showed＂down-up-down＂trend;the activities of SOD and GR presented＂down-up＂changes;activities of POD and CAT demonstrated＂down-up-down＂,and APX,GPX showed an ＂up-down-up＂pattern.It is worth to note that,under the four-dose treatment,a sharp decline in net photosynthesis in sorghum seedlings was observed at 6h UV-B treatment（equals to 2.4J·m~（-2））,and an obvious turning point was also found for other photosynthetic parameters and activities of antioxidant enzymes at the same time point.In summary,the results indicated that the enhanced UV-B radiation directly accounted for the damages in photosynthesis system including photosynthetic pigment content,net photosynthetic rate and chlorophyll fluorescence parameters of sorghum;the antioxidant system showed different responses to UV-B radiation below or above 6h treatment：ASA-GSH cycle was more sensitive to low-dose UV-B radiation,while high-dose U