Molecular Biology Division; Bhabha Atomic Research Centre, Mumbai 400085, India; Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India.
Molecular Biology Division; Bhabha Atomic Research Centre, Mumbai 400085, India; Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India.
Aquat Toxicol. 2021 Jul;236:105839. doi: 10.1016/j.aquatox.2021.105839. Epub 2021 Apr 18.
Selenium, an essential trace element for animals, poses a threat to all forms of life above a threshold concentration. The ubiquitously present cyanobacteria, a major photosynthetic biotic component of aquatic and other ecosystems, are excellent systems to study the effects of environmental toxicants. The molecular changes that led to beneficial or detrimental effects in response to different doses of selenium oxyanion Se(IV) were analyzed in the filamentous cyanobacterium Anabaena PCC 7120. This organism showed no inhibition in growth up to 15 mg/L sodium selenite, but above this dose i.e. 20-100 mg/L of Se(IV), both growth and photosynthesis were substantially inhibited. Along with the increased accumulation of non-protein thiols, a consistent reduction in levels of ROS was observed at 10 mg/mL dose of Se(IV). High dose of Se(IV) (above 20 mg/L) enhanced endogenous reactive oxygen species (ROS)/lipid peroxidation, and decreased photosynthetic capability. Treatment with 100 mg/L Se(IV) downregulated transcription of several photosynthesis pathways-related genes such as those encoding photosystem I and II proteins, phycobilisome rod-core linker protein, phycocyanobilin, phycoerythrocyanin-associated proteins etc. Interestingly, at a dose range of 10-15 mg/L Se(IV), Anabaena showed an increase in PSII photosynthetic yield and electron transport rate (at PSII), suggesting improved photosynthesis. Se was incorporated into the Anabaena cells, and Se-enriched thylakoid membranes showed higher redox conductivity than the thylakoid membranes from untreated cells. Overall, the data supports that modulation of photosynthetic machinery is one of the crucial mechanisms responsible for the dose-dependent contrasting effect of Se(IV) observed in Anabaena.
硒是动物必需的微量元素，超过阈值浓度会对所有生命形式构成威胁。广泛存在的蓝细菌是水生和其他生态系统中主要的光合生物组成部分，是研究环境毒物影响的理想系统。本研究在丝状蓝藻鱼腥藻 PCC 7120 中分析了导致硒氧阴离子 Se(IV)不同剂量下产生有益或有害影响的分子变化。该生物在高达 15mg/L 亚硒酸钠的浓度下生长没有受到抑制，但在此剂量以上，即 20-100mg/L 的 Se(IV)，生长和光合作用都受到了很大的抑制。随着非蛋白巯基含量的增加，在 10mg/mL Se(IV)剂量下观察到 ROS 水平持续降低。高剂量的 Se(IV)（高于 20mg/L）会增强内源性活性氧（ROS）/脂质过氧化，降低光合作用能力。用 100mg/L Se(IV)处理会下调几个光合作用途径相关基因的转录，如编码光系统 I 和 II 蛋白、藻胆体棒-核心连接蛋白、藻蓝胆素、藻红胆素相关蛋白等。有趣的是，在 10-15mg/L Se(IV)的剂量范围内，鱼腥藻表现出 PSII 光合作用产量和电子传递速率（在 PSII 处）的增加，表明光合作用得到改善。硒被纳入鱼腥藻细胞中，富硒类囊体膜的氧化还原电导率高于未经处理的细胞的类囊体膜。总的来说，这些数据表明，光合作用机制的调节是硒(IV)在鱼腥藻中观察到的剂量依赖性对比效应的关键机制之一。
