Reaction-controlled phase transfer catalysis for styrene epoxidation to styrene oxide with aqueous hydrogen peroxide

The epoxidation of styrene catalyzed by a reaction-controlled phase transfer catalyst [(C18H37(30%)+C16H33(70%))N(CH3)(3))(3)](3)-[PW4O16] with H2O2 in a biphasic medium was investigated. Under certain conditions, the selectivity for styrene oxide was 95%, the conversion of styrene based on H2O2 was 85%, and the reaction time was less than 1 h. During the reaction, this catalyst powder formed soluble active species by the action of H2O2, was recovered as a precipitate, and was reused after H2O2 was used up. After two times recycling, the catalyst kept almost the same activity.

由农杆菌介导将葡萄糖氧化酶基因转入水稻

过氧化氢（Hydrogen peroxide,H2O2）是植物和病原微生物互作中快速合成的一种早期活性氧类（reactive oxygen species, ROS ），它在植物受到病原微生物侵染后引发的一系列防御反应中起着非常重要的作用，因此通过外源基因导入提高植物体内过氧化氢的含量，可以增强植物的广谱抗病性。葡萄糖氧化酶（glucose oxidase, GO）可以催化β-D-葡萄糖氧化生成过氧化氢和葡萄糖酸，此酶已在数种细菌和真菌中检测到，但在植物和动物中仍未发现。为了尝试将此酶应用于水稻广谱抗病基因工程，本研究将葡萄糖氧化酶基因插入具有潮霉素抗性选择标记的双元载体pCAMBIA1301，新构建为水稻高效表达载体pCAG1301。将此质粒导入根癌农杆菌（Agrobacterium tumefaciens ）菌株LBA4404后,转化粳稻(Oryza sativa )品种日本晴(Nipponbare)成熟胚来源的愈伤组织和幼胚，并由筛选出的潮霉素抗性愈伤组织分化再生植株。对所得到的潮霉素抗性植株的Southern杂交分析表明GO基因已整合到受体基因组,为单拷贝或双拷贝插入。利用过氧化氢与淀粉-碘化钾反应显蓝色的特性检测到了转基因植株产生的过氧化氢，证实GO基因表达产生的葡萄糖氧化酶已经在水稻中发挥功能，这是将GO基因转入单子叶植物的首例报道。 基于过氧化氢诱导的植物防御反应没有种属专一性的优点，可以预期所得转基因水稻植株很可能对水稻的多种病原菌具有良好的抗性。已完成的抗病性鉴定表明，所得转基因水稻植株对稻瘟病具有良好的抗性。

果实成熟衰老与抗病性的调控机制研究

　　果实为开花植物所特有的发育器官，在种子的成熟和传播过程中发挥着重要作用。同时，肉质果实中含有丰富的营养物质，包括纤维素、维生素、抗氧化剂等，成为人们饮食的重要组成部分。由于果实的成熟衰老和抗病性直接影响果品的质量和市场价值，因此，研究果实成熟衰老和抗病性的调控机制具有重要的理论意义和应用前景。本文主要利用蛋白质组学的方法，探讨外源化学物质抑制果实成熟衰老和诱导抗病性的调控机制。 1. 硅对果实的抗病性诱导：用硅酸钠（1%）处理采后的甜樱桃果实，再接种褐腐病原菌（Molinilia fracticola），置于20C下，观测贮藏期间果实的发病率，并分析硅处理后诱导的主要蛋白质及调控机制。研究结果表明：硅酸钠处理可显著抑制贮藏期间褐腐病的发生，其抑病机理与硅诱导PR-蛋白的表达，提高果实的抗氧化水平，减轻由病原菌侵染造成的氧化胁迫相关。同时，硅处理还能保护细胞骨架结构，有利于增强果实对病原菌入侵的抵抗力。 2. 水杨酸对果实的抗病性诱导：用水杨酸（SA，2mM）在果园处理三种成熟度的甜樱桃果实，然后接种青霉病原菌（Penicillium expansum）观察其发病情况，并取样分析参与抗病性应答的主要蛋白质及调控机制。试验结果表明：SA处理能显著降低青霉病的发病率和抑制病斑扩展，而且SA对低成熟度甜樱桃果实的抗性诱导效果更好。在八成熟的果实中，有5个热激蛋白和4个脱氢酶蛋白被SA诱导，这些蛋白参与了糖酵解和三羧酸循环。抗氧化蛋白和PR蛋白主要参与较低成熟度果实的抗性应答，而热激蛋白和脱氢酶在较高成熟度果实的抗性应答中更明显，SA诱导的抗性与代谢途径相关。 　　3. 草酸对果实的抗性诱导：用5mM的草酸处理冬枣果实后，接种青霉菌（P. expansum），观察果实发病情况，测定果实相关的生理指标，分析参与果实抗性应答的主要蛋白质及调控机制。结果表明：草酸能明显延缓冬枣果实的衰老，提高果实对青霉菌的抗性。草酸处理能抑制果实乙烯的释放量和呼吸强度，延缓叶绿素的降解，减少乙醇积累。利用蛋白质组学的研究方法证实了在25个参与了草酸处理应答的蛋白中，胱硫醚-β-合酶结构域包含蛋白（CBB domain-containing protein）和3个与光合作用相关蛋白[二磷酸核酮糖羧化酶/加氧酶（Ribulose bisphosphate carboxylase/oxygenase activase, chloroplast precursor），二磷酸核酮糖羧化酶/加氧酶大亚基结合蛋白（RuBisCO large subunit-binding protein subunit beta, chloroplast precursor），植物光系统Ⅱ放氧复合蛋白2（PSII oxygen-evolving complex protein 2）]的表达量上调，乙醇脱氢酶的表达量出现下调。草酸处理还提高了与乙烯合成前体相关蛋白的表达，抑制了ACC合成酶的活性。草酸提高果实抗病的机制与延缓果实成熟衰老和保持果实抗性有关。 4. 果实衰老的调控机制：采用高氧（100%）和低氧（2-3%）处理苹果果实，观察果实衰老的进程，并基于蛋白质组学的研究方法，探讨苹果果实衰老与线粒体蛋白质组的关系。结果表明，在苹果衰老过程中有22个蛋白的表达量发生变化，这些蛋白主要参与了三羧酸循环，电子传递，碳代谢和胁迫应答。高氧处理能诱导氧化胁迫，加速了果实的衰老。质谱鉴定结果证明：在高氧胁迫下，超氧化物歧化酶（manganese superoxide dismutase，MnSOD）和线粒体外膜通道蛋白（porin) 的表达量降低，MnSOD的活性受到抑制，由此提高了线粒体中超氧阴离子的含量，增加了蛋白质的氧化损伤。 此外，高氧处理改变了porin的功能，导致了线粒体膜的透势发生变化，从而引起外膜损伤。由此阐明了活性氧在果实的成熟衰老调控中的重要作用。

水稻幼苗脱黄化过程以及灌浆期茎的蛋白质组学研究

水稻既是我国三大粮食作物之一，又是基因组学研究的模式材料，在生产实践和科学研究中都占有极其重要的地位。基因组学研究取得的巨大成就以前所未有的深度和广度推动了生命科学各个研究领域的飞速发展。水稻基因组的破译是水稻科学研究的重要里程碑，同时也宣告了功能基因组学时代的到来。蛋白质组学是研究细胞内全部蛋白质的动态表达及其相互关系的新兴学科，是功能基因组学研究的重要组成部分和战略制高点。 本论文采用高分辨率的蛋白质双向电泳分离技术和高通量的蛋白质质谱分析技术以及生物信息学等手段，开展水稻灌浆期茎蛋白质组表达模式和水稻幼苗脱黄化过程的比较蛋白质组学研究，探讨茎生长发育规律和水稻应答光信号相关蛋白质及其网络调控机制，是学科前沿与实际应用的有机结合，在科研和生产实践中都具有重要的意义。 首先，分别构建了灌浆期水稻顶端茎段和水稻黄化幼苗的蛋白质组表达谱。并对其中185个目的蛋白点进行了MALDI-TOF/MS分析和数据库检索鉴定。共有149个蛋白质得到了鉴定，蛋白质鉴定的成功率为80.5％。这些被鉴定的蛋白质分属118个基因的表达产物，根据它们功能可以分为13种不同的类别，其中绝大多数为能量产生和代谢以及抗性相关的蛋白质。 在水稻灌浆期顶端茎段表达的蛋白质中，与能量和物质代谢相关的蛋白质例如ATPase、磷酸丙糖异构酶，6－磷酸葡萄糖异构酶等占有很高比例，说明茎段组织中具有很强的代谢活动。与生长发育相关的蛋白质包括beta-tubulins、无机焦磷酸酶（inorganic pyrophosphatase）、液泡质子ATP酶（vacuolar proton-ATPase）以及UDP葡萄糖焦磷酸酶等的大量累积，显示出顶端茎段细胞分裂和生长迅速;同时，贮存多糖和结构多糖也在旺盛合成。G蛋白、GDP释放抑制因子等信号传导蛋白以及苯丙氨酸氨解酶、谷胱苷肽S转移酶（glutathione S-transferase，GST）、抗坏血酸过氧化酶（ascorbate peroxidase，APX）以及超氧化物歧化酶（superoxide dismutase，SOD）等抗性相关蛋白质在该时期丰度表达，表明在灌浆期水稻顶端茎段能够迅速感受并传递外界信号，从而使得其在遭受胁迫时能够立刻启动抗逆防御系统，最大限度地降低不利环境对种子发育的影响。 在黑暗中萌发和生长的水稻黄化幼苗随着光照时间（0~24小时）的延长，能通过双向电泳后检测到的蛋白质逐渐变少，24小时后趋于稳定，相当于正常光照条件下生长的水稻幼苗蛋白质组表达谱。进一步分析表明，在黄化苗中，分解代谢及能量产生相关的蛋白如丙糖磷酸异构酶、琥珀酰辅酶A连接酶、异戊酰辅酶A脱氢酶与ATPase等的表达量比较丰富;另外，还可能启动了脂肪酸的α氧化分解途径，以供黑暗中生长所需的物质和能量。当黄化幼苗光照后，与光合作用及物质合成相关的一些蛋白质表达量增加，而那些分解代谢相关酶类则有所下降。同时，鸟核苷酸结合蛋白β亚基类似蛋白、20S proteasome以及Bowman Birk trypsin inhibitor等信号传递及抗性相关蛋白随着光照时间的延长而减少，说明黑暗胁迫条件下水稻幼苗启动了相关的抗逆途径。叶绿素合成途径中的蛋白酶胆色素原脱氨基酶和金属鳌合酶在脱黄化过程中表达量有所下降，可能是因为叶绿素合成产物具有反馈抑制作用。 本研究首次利用蛋白质组学方法来解析水稻灌浆期茎蛋白质组表达模式和水稻黄化幼苗响应光因子的蛋白质组变化情况，鉴定了一些有价值的蛋白质，并得到了它们的表达特点和相关数据，为更好地理解水稻顶端茎秆的生长特点和功效、水稻应答黑暗胁迫和光形态建成以及光合作用机理等提供了分子证据。

一氧化氮在磷酸盐调节拟南芥根系形态变化中的作用

磷缺乏已成为制约世界农业生产的重要因子。植物根系的大小和形态是决定植物吸收土壤磷能力的重要因素，而且根系的生长发育与磷素的分布及其有效性密切相关。关于磷酸盐调节植物根系生长研究已有很多报道，但其生理和分子机制仍不清楚。一氧化氮 (NO) 是一种重要的气体信号分子，参与调控植物的生长发育和对多种逆境胁迫的应答反应。本文选用拟南芥为实验材料，研究探讨了NO与缺磷诱导的拟南芥根系形态变化之间的关系，主要结果如下： 用正常磷水平 (1 mM) 和低磷水平 (1 µM) 处理拟南芥幼苗，发现低磷抑制主根伸长，刺激侧根发生。外源NO供体销普纳 (SNP) 也抑制主根、刺激侧根生长，与低磷诱导根系形态变化相似。NO清除剂c-PTIO和一氧化氮合成酶 （NOS）抑制剂L-NNA均可部分减缓由低磷引起的对主根生长的抑制和对侧根的刺激作用。暗示低磷诱导的拟南芥根系形态的变化可能与NO含量的降低有关。 利用NO荧光标记物DAF-FM和激光共聚焦显微成像技术，本研究发现缺磷6 h和24 h后根细胞内源NO含量显著增加，而且NOS 抑制剂能减少低磷诱导的根细胞NO含量的增加。与正常供磷处理相比，低磷处理6 h和24 h，拟南芥根中编码与NO合成相关的基因（AtNOA1）的表达量增加，缺磷24 h后根中NOS酶活性升高。为了明确低磷诱导的NO 增加是否与硝酸还原酶（NR）介导的NO合成有关，本论文进一步研究了低磷对拟南芥硝酸还原酶活性和编码NR基因 （AtNR1和AtNR2）表达的影响。研究发现低磷处理6 h和24 h后和AtNR1和AtNR2基因的表达均没有变化，且蛭石中生长的拟南芥缺磷1个月后NR活性也没有发生变化;拟南芥的NR双突变体nia1，nia2在低磷处理24 h后，其根中的内源NO含量表现出与野生型相同的增加。因此这些研究结果表明，缺磷后拟南芥根细胞NO的含量增加主要由于NOS的活性升高，而与NR介导的NO合成无关。 已有资料表明低磷诱导植物根细胞内源过氧化氢（H2O2）分布和含量的变化。本论文研究了低磷处理对用H2O2标记物CM-H2DCFDA标记不同磷处理下的拟南芥根中的H2O2。研究发现，缺磷6 h根中H2O2的分布无明显变化，缺磷24 h后H2O2呈斑块状分布，且多集中在根尖伸长区。缺磷24 h后，叶片中的抗氧化保护酶—超氧化物歧化酶（SOD）、过氧化物酶（POD）和过氧化氢酶（CAT）活性没有明显变化。说明缺磷24 h 后产生的H2O2没有引起氧化胁迫，而是作为一种信号分子，与NO相互作用共同介导低磷胁迫的应答反应。关于NO与H2O2在低磷诱导的根形态变化中的信号转导过程还有待进一步研究。

Effect of beta-glucan on activity of antioxidant enzymes and Mx gene expression in virus infected grass carp

The effects of beta-glucan, an immunostimulatory agent, on the superoxide dismutase (SOD) and catalase (CAT) activities of erythrocytes and Mx gene expression were studied from grass carp that were challenged with grass carp hemorrhage virus (GCHV). The SOD and CAT activities in erythrocytes and Mx gene expression in spleen from the fish were detected by spectrophotometry and RT-PCR, respectively. Negative control fish were injected with PBS; positive control groups were injected with either P-glucan or GCHV only; and the experimental groups were pre-injected with beta-glucan 15 days prior to injection with GCHV. The results show that the SOD and CAT activities were higher in fish injected with beta-glucan for 15 days than the negative control group injected with PBS. The SOD and CATactivities significantly decreased when the fish were challenged with GCHV, but it was higher in the group pre-treated with beta-glucan than in infected fish not pre-treated, 15 days after GCHV infection. Mx gene expression levels increased during the early stages (at 12 h and 36 h) of GCHV infection, and it remained at higher levels from the 6th till the 10th day in the beta-glucan pre-treated group, but it was failing from the 6th day in the beta-glucan untreated group. The GCHV-infected group pre-treated with P-glucan had a higher survival rate (60%) than the group not pre-treated with P-glucan (20%), suggesting that beta-glucan possesses or enhances anti-viral responses. (C) 2009 Elsevier Ltd. All rights reserved.

Ultraviolet-B exposure induces photo-oxidative damage and subsequent repair strategies in a desert cyanobacterium Microcoleus vaginatus Gom.

Biological soil crusts are important in reversing desertification. Ultraviolet radiation, however, may be detrimental for the development of soil crusts. The cyanobacterium Microcoleus vaginatus can be a dominant species occurring in desert soil crusts all over the world. To investigate the physico-chemical consequences of ultraviolet-B radiation on M. vaginatus, eight parameters including the contents of chlorophyll a, reactive oxygen species, malondialdehyde and proline, as well as the activities of photosynthesis, superoxide dismutase (EC 1.15.1.1), peroxiclase (EC 1.11.1.7) and catalase (EC 1.11.1.6) were determined. As shown by the results of determinations, ultraviolet-B radiation caused decreases both in contents of chlorophyll a and in ratios of variable fluorescence over maximum fluorescence that indicate the growth and photosynthesis of M. vaginatus, besides, increases both in levels of reactive oxygen species and in contents of malondialdehyde and proline, while intensified activities of superoxide dismutase, peroxiclase and catalase reflecting the abilities of enzymatic preventive substances to oxidative stress of the treated cells. Therefore, ultraviolet-B radiation affects the growth of M. vaginatus and leads to oxidative stress in cells. Under ultraviolet-B radiation, the treated cells can improve their antioxidant abilities to alleviate oxidative injury. The change trends of reactive oxygen species, superoxide dismutase, peroxiclase and catalase are synchronous. These results suggest that a balance between the antioxidant system and the reactive oxygen species content may be one part of a complex stress response pathway in which multiple environmental factors including ultraviolet-B radiation affect the Survival of M. vaginatus. (C) 2009 Elsevier Masson SAS. All rights reserved.

Allelopathic mechanism of pyrogallol to Microcystis aeruginosa PCC7806 (Cyanobacteria): From views of gene expression and antioxidant system

Pyrogallol is a potent allelochemical on Microcystis aeruginosa, but its allelopathic mechanism is not fully known. In order to explore this mechanism, gene expressions for prx, mcyB, psbA, recA, grpE, fabZ under pyrogallol stress were studied, and activities of the main antioxidant enzymes were also measured. The results showed that expression of grpE and recA showed no significant change under pyrogallol stress, while psbA and mcyB were up-regulated at 4 mg L-1. Both prx and fabZ were up-regulated even under exposure to 1 mg L-1 pyrogallol concentration. The activities of superoxide dismutase (SOD) and catalase (CAT) were enhanced under pyrogallol stress. Levels of malodialdehyde (MDA) at 2 and 4 mg L-1 pyrogallol were significantly higher than those of the controls. It was concluded that oxidant damage is an important mechanism for the allelopathic effect of pyrogallol on M. aeruginosa. (c) 2009 Elsevier Ltd. All rights reserved.

Oxidative stress response after prolonged exposure of domestic rabbit to a lower dosage of extracted microcystins

Oxidative stress response after prolonged exposure to a low dose of microcystins (MCs) was studied in liver, kidney and brain of domestic rabbits. Rabbits were treated with extracted MCs (mainly MC-LR and MC-RR) at a dose of 2 MC-LReq. mu g/kg body weight or saline solution every 24 h for 7 or 14 days. During the exposure of MCs, increase of lipid peroxidation (LPO) levels were detected in all the organs studied, while antioxidant enzymes responded differently among different organs. The enzyme activities Of Superoxide dismutase (SOD). catalase (CAT) and glutathione reductase (GR) in liver decreased in the MCs treated animals. In brain, there were obvious changes in glutathione peroxidase (GPx) and GR, while only CAT was obviously influenced in kidney. Therefore, daily exposure at a lower dosage of MCs, which mimicked a natural route of MCs. could also induce obvious oxidative stress in diverse organs of domestic rabbits. The oxidative stress induced by MCs in brain was as serious as in liver and kidney, suggesting that brain may also be a target of MCs in mammals. And it seems that animals may have more time to metabolize the toxins or to form an adaptive response to reduce the adverse effects when exposed to the low dose of MCs. (C) 2008 Elsevier B.V. All rights reserved.

Time-Dependent Oxidative Stress Responses of Crucian Carp (Carassius auratus) to Intraperitoneal Injection of Extracted Microcystins

This study was conducted to investigate time-dependent changes in oxidative enzymes in liver of crucian carp after intraperitoneally injection with extracted microcystins 600 and 150 mu g kg(-1) body weight. The results showed that activities of antioxidant enzymes, including superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase generally exhibited a rapid increase in early phase (1-3 h post injection), but gradually decreased afterwards (12-48 h) compared with the control, with an evident time-dependent effect. These zigzag changes over time contributed a better understanding on oxidative stress caused by microcystins in fish.

Effects of dietary ascorbic acid supplementation on the growth performance, immune and stress response in juvenile Leiocassis longirostris Gunther exposed to ammonia

This experiment was designed to investigate the effect of dietary supplemental ascorbic acid (AA) on the feed intake, growth, serum lysozyme, hepatic superoxide dismutase (SOD) and handling stress response in Chinese longsnout catfish (Leiocassis longirostris Gunther) exposed to three levels of unionized ammonia nitrogen (UIA-N). Juvenile Chinese longsnout catfish were reared in 54 fibreglass tanks with a 3 x 3 factorial design treatment consisting of three supplemental AA levels in ascorbyl 2-monophosphate (38, 364 and 630 mg AA equivalent kg(-1) diet) and three UIA-N concentrations [0.004 (the control), 0.037 and 0.292 mg L-1]. The fish were sampled on the 11th, 32nd and 60th day. On the 62nd day, the remaining fish were subjected to an acute stress by being held in a dipnet out of water for 60 s, and sampled at 30 min post handling. The results showed that the specific growth rate (SGR) in 32 days significantly decreased with increased water UIA-N (P=0.0476) but was not affected by dietary supplemental AA (P > 0.05). After 60 days, SGR, feeding rate (FR) and feed conversion efficiency (FCE) significantly increased with increased dietary supplemental AA (P < 0.001) while remaining unaffected by water UIA-N (P > 0.05). There was no significant interaction between dietary AA and UIA-N for growth responses (P > 0.05). The serum lysozyme activity on the 11th day and the hepatic SOD activity on the 32nd day were significantly affected at high (0.292 mg L-1) water UIA-N. On the 62nd day, the increase in cortisol resulting from acute stress significantly decreased by higher UIA-N (P=0.038). It is suggested that Chinese longsnout catfish displayed an adaptive response after long-term UIA-N exposure, and AA had beneficial effects on the growth and feed intake of catfish and alleviated the negative effects of chronic ammonia stress. A chronically higher ammonia level shows a tendency to inhibit the cortisol response to another acute stressor.

Effects of dietary manganese on growth and tissue manganese concentrations of juvenile gibel carp, Carassius auratus gibelio

A 68-day growth trial was conducted in a flow-through system to determine the effect of dietary manganese levels on growth and tissue manganese concentration of juvenile gibel carp (Carassius auratus gibelio). Seven purified diets containing 7.21, 8.46, 9.50, 10.50, 13.03, 19.72 and 22.17 mg manganese (as manganic sulfate) per kilogram diet were fed to triplicate groups of fish (initial weight 3.21 +/- 0.01 g). The results showed that dietary manganese levels did not significantly affect feed intake of the fish. Specific growth rate, feed efficiency, total hepatic superoxide dismutase activity, carcass and skeletal manganese concentration increased significantly with increased dietary manganese(P < 0.05) while condition factor decreased significantly(P < 0.05). It was concluded that dietary requirement of manganese was 13.77 mg Mn per kilogram diet. Carcass and skeletal manganese concentration could also be used to evaluate the manganese requirement. Total hepatic superoxide dismulase activity was not a sensitive indicator for dietary requirement.

Allelopathic effects on Scenedesmus obliquus by two submerged macrophytes Najas minor and Potamogeton malaianus

The allelopathic effects of two submerged macrophytes, Najas minor and Potamogeton malaianus, on growth, photosynthesis and antioxidant systems of Scenedesmus obliquus were assessed in coexistence experiments. The growth of S. obliquus was significantly suppressed by the two macrophytes. Moreover, P. malaianus showed the stronger growth inhibition effect on S. obliquus than N. minor. P. malaianus obviously inhibited the photosynthetic rate of S. obliquus, while N. minor had no inhibitory effect. Lipid peroxidation and three antioxidant enzymes activities (superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD)) of S. obliquus were investigated at the end of the co-cultures. The two macrophytes significantly enhanced the malondialdehyde (MDA) content, a product of lipid peroxidation, in S. obliquus. Activities of the three antioxidant enzymes of S. obliquus were simultaneously stimulated in P. malaianus treatment, while no significant variation of POD activity was observed in N. minor treatment. The results indicated that the two macrophytes N. minor and P. malaianus had significant allelopathic effects on S. obliquus. However, the two macrophytes influenced S. obliquus in different ways.

The response of antioxidant systems in Nostoc sphaeroides against UV-B radiation and the protective effects of exogenous antioxidants

UV radiation is one of many harmful factors found in space that are detrimental to organisms on earth in space exploration. In the present work, we examined the role of antioxidant system in Nostoc sphaeroides Kutz (Cyanobacterium) and the effects of exogenously applied antioxidant molecules on its photosynthetic rate under UV-B radiation. It was found that UV-B radiation promoted the activity of antioxidant system to protect photosystem 11 (PSII) and exogenously applied antioxidant: sodium nitroprusside (SNP) and N-acetylcysteine (NAC) had an obvious protection on PSII activity under UV-B radiation. The activity of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7) and content of NIDA (malondialdehyde) and ASC (ascorbate) were improved by 0.5 mM and 1 mM SNP, but 0.1 mM SNP decreased the activity of antioxidant system. Addition of exogenous NAC decreased the activity of SOD, POD, CAT and the content MDA and ASC. In contrast, exogenously applied NAC increased GSH content. The results suggest that exogenous SNP and NAC may protect algae by different mechanisms: SNP may play double roles as both sources of reactive free radicals as well as ROS scavengers in mediating the protective role of PSII on algae under UV-B radiation. On the other hand, NAC functions as an antioxidant or precursor of glutathione, which could protect PSII directly from UV-B radiation. (c) 2007 COSPAR, Published by Elsevier Ltd. All rights reserved.