增强的UV-B辐射对高粱幼苗光合和抗氧化系统的影响

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。

Effects of Enhanced Ultraviolet B Irradiation on Photosynthetic and Antioxidant System of Sorghum Seedlings

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 (Sorghumbicolor (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 2 d recovering,photo-synthetic 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 inj ury was aggravated,plants dwarfing and signifi-cantly 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 de-creased.Meanwhile,with the increase in UV-B dosages,stomatal conductance,intercellular CO2 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 6 h UV-B treatment (equals to 2.4 J·m-2 ),and an obvious turning point was also found for other photosynthetic parameters and activities of antioxidant en-zymes 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 6 h treatment:ASA-GSH cycle was more sensitive to low-dose UV-B radiation,while high-dose UV-B radiation not only undermined the photo-synthesis system,but also triggered plant enzymatic and non-enzymatic antioxidant systems,resulting in leaf browning and nec-rosis,biomass accumulation reduction,plant dwarfing and even death.