• 关键词：蓝藻结皮  UV-B辐射  超微结构  光合活性  叶绿素a  伪枝藻素  胞外多糖  N-乙酰半胱氨酸

• 基金项目：淡水生态与生物技术国家重点实验室项目(No.2008FBZ21);武汉市科技局与内蒙古自治区发改委重大科技产业化专项(No.200720112031);河南省高等学校青年骨干教师资助计划;信阳师范学院高层次人才科研启动基金项目;信阳师范学院青年骨干教师资助计划项目

• 饶本强
• 1. 中国科学院水生生物研究所, 淡水生态与生物技术国家重点实验室, 武汉 430072; 2. 信阳师范学院生命科学学院, 信阳 464000

• 吴沛沛
• 1. 中国科学院水生生物研究所, 淡水生态与生物技术国家重点实验室, 武汉 430072; 2. 中国科学院研究生院, 北京 100039

• AlainDAUTA
• Laboratoired′ Ecologie Fonctionnelleet Environnement, Université Paul Sabatier, 118 route de Narbonne, 31062 TOULOUSE Cedex 9, France

• 李敦海
• 中国科学院水生生物研究所, 淡水生态与生物技术国家重点实验室, 武汉 430072

• 刘永定
• 中国科学院水生生物研究所, 淡水生态与生物技术国家重点实验室, 武汉 430072

• 摘要：UV-B辐射是野外蓝藻结皮经常面临的一种环境胁迫因子.报道了温室条件下UV-B辐射对蓝藻结皮形态、生理和超微结构特征的影响.在本研究中,首先通过接种具鞘微鞘藻和爪哇伪枝藻形成初始蓝藻结皮,接着以初始蓝藻结皮为材料进行3种辐射处理:光合有效辐射、UV-B辐射+光合有效辐射和N-乙酰半胱氨酸+UV-B辐射+光合有效辐射.在各种辐射处理的第0、1、3、6、9和20天分别测定蓝藻结皮的光合活性(F_v//F_m)、叶绿素a、伪枝藻素和胞外多糖含量.同时采用扫描电镜观察辐射处理下结皮的超微结构特征.此外,对结皮的表观形态如结皮颜色、厚度、干重等进行了测定.结果表明UV-B辐射对蓝藻结皮具有持续而明显的负面效应.与对照结皮相比,UV-B辐射下结皮的表观形态受到不利影响,结皮F_v//F_m被完全抑制,单位重量的叶绿素a含量和胞外多糖含量显著降低,而伪枝藻素含量并未受到UV-B辐射抑制,其含量则出现大量增加.电镜观察表明,UV-B辐射导致蓝藻结皮的超微结构遭到明显破坏,表现为藻丝体数量减少,缢缩成条索状,对沙粒的缠绕减弱等.研究还表明,N-乙酰半胱氨酸能够较好地保护UV-B辐射下结皮的光合活性,增加结皮的叶绿素a含量和胞外多糖含量,并有利于结皮表观形态的恢复.本研究探索了蓝藻结皮对UV-B辐射的响应,对于进一步理解蓝藻结皮对UV-B辐射的耐受限度以及应用蓝藻结皮进行荒漠化治理具有重要的理论与实际意义.

• Abstract：UV-Bradiation may be an environmental stress commonly experienced by cyanobacterial crusts growing in desert areas. Here we report the effects of UV-Bradiation on the morphological and physiological changes and ultrastructural characteristics of cyanobacterial crusts. In this study,firstly the initial cyanobacterial crusts were formed by inoculating Microcoleus vaginatusGom. and Scytonema javanicum(Ktz.) Born et Flah onto loose sand in Petri dishes. Then,the initial cyanobacterial crusts were exposed to three different radiation treatments as follows:photosynthetically active radiation (PAR),UV-B+PARand N-acetylcysteine (NAC) +UV-B+PAR. On the 1st,3rd,6th,9th,12th and 20th days during the UV-Bradiation experiments,photosynthetic activities (optimal quantum yield,F_v//F_m),chlorophyll a,scytonemin and exopolysaccharide (EPS) contents of the crusts were examined. Crust color,crust shape,crust thickness and crust pHas well as crust dry weight were all determined. We also observed the ultrastructure properties of the cyanobacterial crusts under PARand UV-B+PARtreatments by means of scanning electron microscopy (SEM). The results indicated that the applied UV-Bdose had long-lasting negative effects on the cyanobacterial crusts. F_v//F_m of the cyanobacterial crusts was completely inhibited by UV-Bradiation,which meant UV-Bradiation had evident photoinhibition effects on the crusts. Chlorophyll acontent of the crust treated with UV-Bradiation was significantly lower than that of the crust under control conditions. In the case of UV-Bexposure,scytonemin of the cyanobacterial crusts was not inhibited by UV-Band on the contrary UV-Binduced a marked increase in scytonemin. Furthermore,the EPS content of the crust under UV-Btreatment presented a significant decline as compared to the control crust (p<0.05). Obvious destruction of ultrastructures was observed from the cyanobacterial crust subjected to UV-Bstress,and many changes in morphological characteristics of the crust under UV-Bradiation were also detected. Further,our results showed that NAC addition could provide effective protection to the photosynthetic activity of the crust under UV-Bradiation and the levels of chlorophyll aand EPSwere also promoted due to NACaddition,which meant that NAC might function as an effective antioxidant and could protect the cyanobacterial crust from oxidant stress induced by UV-Bradiation. The aim of this study was to discuss the responses of cyanobacterial crusts to UV-Bradiation and to improve understanding of toleration restriction of the crusts against UV-Bradiation,which may provide academic and practical significances for cyanobacterial crust applications in desertification control.

• Key words：cyanobacterial crusts  UV-B radiation  ultrastructures  photosynthetic activities  chlorophyll a  scytonemin  exopolysaccharide  N-acetylcysteine

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