Department of Biological Sciences North Carolina State University, Raleigh, NC, 27695, USA.
Sci Rep. 2018 May 8;8(1):7172. doi: 10.1038/s41598-018-24087-7.
Nitrogenous compounds enter the environment through various anthropogenic sources. Among these are nitrate (NO) and nitrite (NO) which can oxidize the heme moiety of hemoglobin and reduce the oxygen-carrying capacity of the molecule resulting in toxicity. Of the two anions, nitrite is more toxic. Hemoglobin levels are influenced by environmental conditions; thus, we hypothesized that hemoglobin levels would influence the toxicity of nitrite with low hemoglobin levels resulting in enhanced toxicity and high hemoglobin levels resulting in reduced toxicity. We tested this hypothesis by elevating hemoglobin levels with pyriproxyfen treatment and lowering hemoglobin levels using siRNA in Daphnia magna. Exposure to pyriproxyfen significantly elevated hemoglobin mRNA levels and induced copper coloration of the organisms, indicative of increased hemoglobin protein accumulation. siRNA treatment significantly reduced hemoglobin mRNA levels in both untreated and pyriproxyfen-treated organisms and attenuated copper coloration. Pyriproxyfen treatment increased the tolerance of daphnids to the acute toxicity of nitrite approximately 2-fold while siRNA treatment significantly decreased the tolerance of daphnids to nitrite toxicity. Results indicate that increased hemoglobin levels increase the tolerance of daphnids to nitrite toxicity which may serve to protect daphnids in environments subject to hemoglobin-elevating hypoxia or elevated temperatures.
氮化合物通过各种人为来源进入环境。其中包括硝酸盐（NO）和亚硝酸盐（NO），它们可以氧化血红蛋白的血红素部分，降低分子的携氧能力，从而导致毒性。在这两种阴离子中，亚硝酸盐的毒性更大。血红蛋白水平受环境条件的影响；因此，我们假设血红蛋白水平会影响亚硝酸盐的毒性，低血红蛋白水平会导致毒性增强，高血红蛋白水平会导致毒性降低。我们通过用吡虫啉处理来提高血红蛋白水平，并在大型溞中使用 siRNA 降低血红蛋白水平来验证这一假设。吡虫啉处理显著提高了血红蛋白 mRNA 水平，并诱导了生物体的铜色，表明血红蛋白蛋白积累增加。siRNA 处理显著降低了未处理和吡虫啉处理生物体的血红蛋白 mRNA 水平，并减弱了铜色。吡虫啉处理使大型溞对亚硝酸盐急性毒性的耐受性增加了约 2 倍，而 siRNA 处理则显著降低了大型溞对亚硝酸盐毒性的耐受性。结果表明，血红蛋白水平的升高增加了大型溞对亚硝酸盐毒性的耐受性，这可能有助于在血红蛋白升高的缺氧或高温环境中保护大型溞。
