Phytotoxic effects of Perfluorooctane sulfonate on the physiological responses of the seaweed Gracilaria lemaneiformis

Perfluorooctane sulfonate (PFOS) is a man-made persistent organic pollutant that is commonly found in coastal ecosystems. However, there is limited knowledge about its impact on seaweed. In this study, Gracilaria lemaneiformis were cultured in the incubators to examine growth, antioxidant system, soluble substances, amino acid metabolism, and Chlorophyll a fluorescence transient (OJIP) in response to PFOS exposure at concentrations ranging from 0 to 50.0 mg L⁻¹. The results showed that the specific growth rate decreased in a concentration-dependent manner after 6 days, with a significant decrease observed only at 50.0 mg L⁻¹ (p < 0.05). However, the malondialdehyde contents remained stable across different PFOS concentrations, indicating the strong antioxidant ability to the oxidative stress induced by PFOS exposure. This may be due to the combined impact of enzymatic (e.g., catalase and peroxidase) and non-enzyme (e.g., carotenoid, phycoerythrin, and phycocyanin) antioxidants. Furthermore, analysis of amino acid metabolism after 6 days of exposure revealed that the accumulation of specific amino acids, such as arginine (Arg), citrulline (Cit), and ornithine (Orn), played a vital role in improving resistance to PFOS toxicity. Additionally, the electron transport after the reduction of plastoquinone A (Q_A⁻) was highly sensitive to PFOS exposure. Based on the JIP-test analysis, it was inferred that PFOS potentially hinders the transport of electrons by binding to the plastoquinone B (Q_B) site of protein D₁ in the PSII reaction center. These findings will provide valuable insights into the potential influence of PFOS on seaweed cultivation, ultimately contributing to the better utilization of seaweed sources.