Key Laboratory of Agro-ecological Processes in Subtropical Region/Changsha Research Station for Agricultural and Environmental Monitoring, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan 410125, PR China; College of Resources and Environment, Hunan Agricultural University, Changsha, Hunan 410128, PR China.
Key Laboratory of Agro-ecological Processes in Subtropical Region/Changsha Research Station for Agricultural and Environmental Monitoring, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan 410125, PR China.
Sci Total Environ. 2022 Nov 20;848:157596. doi: 10.1016/j.scitotenv.2022.157596. Epub 2022 Jul 27.
High-strength ammonium (NH), the main characteristic of swine wastewater, poses a significant threat to the rural ecological environment. As a novel phytoremediation technology, Myriophyllum aquaticum wetlands have high tolerance and removal rate of NH. Glutamine synthetase (GS), a pivotal enzyme in nitrogen (N) metabolism, is hypothesized to play an important role in the tolerance of M. aquaticum to high NH. Herein, the responses of M. aquaticum to GS inhibition by 0.1 mM methionine sulfoximine (MSX) under 15 mM NH were investigated. After 5 days, visible NH toxicity symptoms were observed in MSX-treated plants. Compared with the control, the NH accumulation in the leaves increased by 20.99 times, while that of stems and roots increased by 3.27 times and 47.76 %, suggesting that GS inhibition had a greater impact on the leaves. GS inhibition decreased pigments in the leaves by 8.64 %-41.06 %, triggered oxidative stress, and affected ions concentrations in M. aquaticum. The concentrations of glutamine (Gln) and asparagine decreased by 63.46 %-97.43 % and 12.37 %-76.41 %, respectively, while the concentrations of most other amino acids increased after 5 days of MSX treatment, showing that GS inhibition reprogrammed the amino acids synthesis. A decrease in Gln explains the regulations of N-related genes, including increased expression of AMT in roots and decreased expression of GS, GOGAT, GDH, and AS, which would cause further NH accumulation via promoting NH uptake and decreasing NH assimilation in M. aquaticum. This study revealed for the first time that GS inhibition under high NH condition can lead to phytotoxicity in M. aquaticum due to NH accumulation. The physiological and molecular responses of the leaves, stems, and roots confirmed the importance of GS in the high NH tolerance of M. aquaticum. These findings provide new insights into NH tolerance mechanisms in M. aquaticum and a theoretical foundation for the phytoremediation of high NH-loaded swine wastewater.
高浓度铵（NH）是猪废水中的主要特征，对农村生态环境构成重大威胁。作为一种新型的植物修复技术，水蕹菜湿地对 NH 具有较高的耐受性和去除率。谷氨酰胺合成酶（GS）是氮（N）代谢中的关键酶，被认为在水蕹菜对高 NH 的耐受性中发挥重要作用。本研究中，在 15 mM NH 条件下，通过 0.1 mM 甲硫氨酸亚砜（MSX）抑制 GS 活性，研究了水蕹菜对其的响应。5 天后，MSX 处理的植物出现明显的 NH 毒性症状。与对照组相比，叶片中的 NH 积累增加了 20.99 倍，而茎和根中的 NH 积累分别增加了 3.27 倍和 47.76%，表明 GS 抑制对叶片的影响更大。GS 抑制使叶片中的色素减少了 8.64%-41.06%，引发氧化应激，并影响水蕹菜中的离子浓度。谷氨酰胺（Gln）和天冬酰胺的浓度分别降低了 63.46%-97.43%和 12.37%-76.41%，而 MSX 处理 5 天后，大多数其他氨基酸的浓度增加，表明 GS 抑制重新编程了氨基酸合成。Gln 的减少解释了与 N 相关基因的调控，包括根中 AMT 的表达增加和 GS、GOGAT、GDH 和 AS 的表达减少，这会通过促进 NH 吸收和减少水蕹菜中 NH 的同化来导致进一步的 NH 积累。本研究首次揭示，在高 NH 条件下抑制 GS 会导致水蕹菜因 NH 积累而产生植物毒性。叶片、茎和根的生理和分子响应证实了 GS 在水蕹菜高 NH 耐受性中的重要性。这些发现为水蕹菜 NH 耐受性机制提供了新的见解，并为高 NH 负荷猪废水的植物修复提供了理论基础。
