CITAB-Centre for Research and Technology of Agro-Environment and Biological Sciences, Sustainable Agro-Food Chains Research Group/Department of Biology and Environment, University of Trás-os-Montes and Alto Douro, Apartado 1013, 5001-801 Vila Real, Portugal.
Aquat Toxicol. 2011 Jan 25;101(2):367-76. doi: 10.1016/j.aquatox.2010.11.011. Epub 2010 Nov 27.
Herbicide contamination of aquatic ecosystems is a serious global environmental concern. Several herbicides enhance the intracellular formation of reactive oxygen species, and can lead to the damage of macromolecules and to a decrease of oxidant defenses in a wide range of non-target microorganisms including cyanobacteria. The effects of molinate (a thiocarbamate herbicide used for controlling grassy weeds in rice fields) on the activities of antioxidant enzymes such as superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, and glutathione S-transferase were evaluated in Nostoc muscorum, a freshwater cyanobacterium with a significant spread in Portuguese rice fields. These were determined in N. muscorum cultures acutely (72h) exposed to concentrations ranging from 0.75 to 2mM of molinate. This study also analyzed the effects of molinate on: (1) the nonenzymatic antioxidant contents (reduced and oxidized glutathione, carotenoids, and proline), (2) the oxidative cell damage measured in terms of lipid peroxidation (MDA level) and electrolyte leakage (intactness of plasma membrane), and (3) the total fatty acid profile. The results showed that the activities of all antioxidant enzymes decreased dramatically with the rising concentration of molinate after 72h. Time-dependent and concentration-dependent increase in MDA and enhanced cell membrane leakage were indicative of lipid peroxidation, formation of free radicals and oxidative damage. Compared to control, 72-h herbicide exposure increased lipid peroxidation by 5.4%, 19% and 28% with 0.75, 1.5 and 2mM of molinate, respectively. Similarly, herbicide stress induced an increase in electrolyte leakage (5.8%, 29.5% and 30.2% above control, with 0.75, 1.5 and 2mM of molinate, respectively). The increased production of proline at higher molinate concentrations (the values rose above control by 45%, 95% and 156% with 0.75, 1.5 and 2mM, respectively) indicated the involvement of this osmoprotectant in a free radical scavenging mechanism. Moreover, a radical decline in both glutathione pool, carotenoids and saturated fatty acids were also observed. The results of the present study lead us to conclude that: (1) both enzymatic and nonenzymatic antioxidative defense system of N. muscorum are dramatically affected by molinate, (2) the herbicide induces peroxidation, (3) it contributes to an increase of the unsaturation level of cell membrane fatty acids. These evidences should be taken in account when using N. muscorum as an environmental indicator species in studies of herbicide biotransformation and biomarker response as well as in environmental monitoring programmes.
水生生态系统中的除草剂污染是一个严重的全球环境问题。几种除草剂会增强细胞内活性氧的形成，并且可以导致包括蓝藻在内的多种非靶标微生物中的大分子物质的损伤和抗氧化防御的降低。本研究评估了灭草喹（一种用于稻田除草的硫代氨基甲酸酯类除草剂）对淡水蓝藻念珠藻（Nostoc muscorum）中超氧化物歧化酶、过氧化氢酶、抗坏血酸过氧化物酶、谷胱甘肽还原酶和谷胱甘肽 S-转移酶等抗氧化酶活性的影响。这些酶在念珠藻培养物中被急性（72 小时）暴露于 0.75 至 2mM 的灭草喹浓度范围内进行测定。本研究还分析了灭草喹对以下方面的影响：（1）非酶抗氧化剂含量（还原型和氧化型谷胱甘肽、类胡萝卜素和脯氨酸）；（2）用脂质过氧化（MDA 水平）和电解质泄漏（质膜完整性）来衡量的氧化细胞损伤；（3）总脂肪酸谱。结果表明，72 小时后，随着灭草喹浓度的升高，所有抗氧化酶的活性均显著下降。MDA 水平的时间依赖性和浓度依赖性增加以及细胞膜泄漏的增强表明了脂质过氧化、自由基形成和氧化损伤。与对照相比，用 0.75、1.5 和 2mM 的灭草喹处理 72 小时后，分别使脂质过氧化增加了 5.4%、19%和 28%。同样，除草剂胁迫诱导了电解质泄漏的增加（分别比对照增加了 5.8%、29.5%和 30.2%，用 0.75、1.5 和 2mM 的灭草喹处理）。在较高的灭草喹浓度下脯氨酸的产量增加（分别比对照增加了 45%、95%和 156%，用 0.75、1.5 和 2mM 的灭草喹处理）表明这种渗透保护剂参与了自由基清除机制。此外，还观察到谷胱甘肽池、类胡萝卜素和饱和脂肪酸的含量显著下降。本研究的结果表明：（1）灭草喹对念珠藻的酶促和非酶促抗氧化防御系统均有显著影响；（2）除草剂诱导了过氧化作用；（3）它有助于增加细胞膜脂肪酸的不饱和度。在使用念珠藻作为除草剂生物转化和生物标志物反应以及环境监测计划中的环境指示物种时，应考虑到这些证据。
