Jiangtao Wang

The oxidative stress and antioxidant defense response of Prorocentrum donghaiense induced by the cell-free filtrate of Gymnodinium catenatum cultures were investigated. Biomarkers of P. donghaiense, including the levels of intracellular reactive oxygen species (ROS), malondialdehyde (MDA), total protein, ascorbate (ASA), reduced glutathione (GSH) and the activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) were measured following 48 and 96 hours of exposure to the cell-free filtrate of G. catenatum, which significantly inhibited the growth of P. donghaiense with relative growth inhibition rates of 21.2%–52.6%, and led to a marked increase in intracellular ROS (57.2%–102%) and MDA, indicating the occurrence of lipid peroxidation. In response to the allelopathy from G. catenatum, the antioxidant system of P. donghaiense was activated with significantly increased activities of SOD, CAT and APX, as well as elevated ASA and GSH levels. Although ROS levels declined at 96 h compared with their peak at 48 h, they still remained significantly elevated compared to the control, indicating that oxidative stress persisted despite the activation of defensive responses. Transcriptomic analysis revealed significant upregulation of antioxidant genes of SOD1 (copper-zinc superoxide dismutase 1), SOD2 (manganese superoxide dismutase 2), GPX4 (glutathione peroxidase 4), PRDX5 (peroxiredoxin 5) and GST (glutathione S-transferase), and the downregulation of photosynthesis-related genes, which demonstrated that G. catenatum allelopathy suppresses P. donghaiense growth by inducing oxidative stress, and the GSH-ASA cycle might be the core antioxidant defense pathway for P. donghaiense.