Exogenous methyl jasmonate activates the jasmonic acid signaling pathway in <i>Chlorella</i> sp. to alleviate 2,2′,4,4′‐tetrabromodiphenyl ether stress

Exogenous application of methyl jasmonate (MeJA), a plant stress-responsive hormone, has been suggested to improve plant resistance, but its protective role in marine microalgae under pollutant exposure remains poorly understood. This study investigated the cytoprotective effects of MeJA on the marine green microalga Chlorella sp. exposed to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), a highly biotoxic dibrominated diphenyl ether. Exposure to BDE-47 (0.075 mg · L^-1) significantly impaired cellular structure, inhibited growth, and induced oxidative stress, as evidenced by reactive oxygen species (ROS) overproduction, membrane lipid peroxidation, G2/M phase arrest, and DNA damage. Cotreatment with 0.1 μM MeJA was associated with a significant reduction in adverse effects (p < 0.05), with observed lower ROS levels and elevated activities of key antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT). Additionally, MeJA-treated cells exhibited increased endogenous jasmonic acid (JA) content and upregulated lipoxygenase (LOX) activity and allene oxide synthase (AOS) content, both enzymes involved in JA biosynthesis. Partial least squares structural equation modeling suggested a potential link between MeJA-activated JA biosynthesis and antioxidant enzyme induction, indicating a self-amplifying ROS scavenging mechanism that may counteract BDE-47 toxicity. The findings have provided insights into the use of plant hormones to enhance microalgae tolerance to environmental pollutants, with potential applications in microalgae cultivation and biotechnology.