Salicylate pollutants (SAs) poses a serious threat to marine ecosystems as emerging contaminants. However, the toxic effects of SAs on marine phytoplankton, as well as the potential mechanisms and their ecological risks linked with them, are remain largely unknown. In this study, we aimed to evaluate the toxic effects of salicylic acid (SA) and its 5-substituted derivatives (5-sSA) on the marine diatom Phaeodactylum tricornutum, as well as the potential molecular mechanism involved in the toxicity. Physiological assays conducted on P. tricornutum revealed significant changes in photosynthetic pigments, chlorophyll fluorescence parameters, and antioxidant enzyme activities. The results showed that exposure of P. tricornutum to SAs caused a significant decline in chlorophyll contents and damage to the photosystem II (PSII) core resulting in the decline of photosynthesis. Although the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were enhanced, oxidative damage occurred. Transcriptome analysis showed that a large number of differentially expresses genes (DEGs) were significantly enriched in metabolic pathways such as porphyrin metabolism, terpenoid backbone biosynthesis, and carbon fixation in photosynthetic organisms after SA and 5-BrSA treatments. In addition, key genes in transcriptomic metabolic pathways were further analyzed and validated using weighted correlation network analysis (WGCNA) and real-time fluorescence quantitative PCR (qPCR). Considering the above results, SAs mainly inhibit the processes of photosynthesis by repressing the expression of genes involved in secondary metabolite synthesis and photosynthetic carbon sequestration pathways, thus exerting toxic effects on algal cells. The results of the study will provide key data for understanding the ecological risk and toxicity mechanisms of SA pollutants.

中文翻译：

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水杨酸及其衍生物对硅藻 Phaeodactylum tricornutum 的急性毒性：物理生化和转录组学见解


水杨酸盐污染物 （SAs） 作为新兴污染物对海洋生态系统构成严重威胁。然而，SAs 对海洋浮游植物的毒性作用，以及与之相关的潜在机制及其生态风险，在很大程度上仍然未知。在本研究中，我们旨在评估水杨酸 （SA） 及其 5-取代衍生物 （5-sSA） 对海洋硅藻 Phaeodactylum tricornutum 的毒性作用，以及参与毒性的潜在分子机制。对 P. tricornutum 进行的生理测定显示光合色素、叶绿素荧光参数和抗氧化酶活性发生显着变化。结果表明，三角松暴露于 SAs 导致叶绿素含量显著下降，光系统 II （PSII） 核心受损，导致光合作用下降。尽管超氧化物歧化酶 （SOD） 、过氧化物酶 （POD） 和过氧化氢酶 （CAT） 的活性增强，但发生了氧化损伤。转录组分析显示，SA 和 5-BrSA 处理后，光合生物体内卟啉代谢、萜类骨架生物合成和碳固定等代谢途径中显著富集了大量差异表达基因 （DEGs）。此外，使用加权相关网络分析 （WGCNA） 和实时荧光定量 PCR （qPCR） 进一步分析和验证转录组代谢途径中的关键基因。考虑到上述结果，SAs 主要通过抑制参与次生代谢物合成和光合碳封存途径的基因表达来抑制光合作用过程，从而对藻类细胞产生毒性作用。 研究结果将为理解 SA 污染物的生态风险和毒性机制提供关键数据。