Histological and Transcriptomic Analyses Reveal Potential Mechanisms Underlying BDE-47-Induced Leaf Damage in the Mangrove Seedlings of Avicennia marina

2,2′,4,4′-Tetrabromodiphenyl ether (BDE-47) is a persistent organic pollutant detected in coastal environments. The effects of BDE-47 on mangrove plants at the molecular and histological levels remain elusive. In this study, seedlings of the man-grove species Avicennia marina were exposed to BDE-47 at concentrations of 0, 1 and 10 ng L-1 for 20 days under hydroponic conditions. Leaf growth parameters, anatomical structures, and transcriptomic profiles were examined. At 1 ng L-1 BDE-47, no signif-icant changes were observed in leaf growth or vascular tissue morphology. However, transcriptome analysis showed significant enrichment of differentially expressed genes in the linoleic acid metabolism pathway, indicating that A. marina initiates early stress perception via enhanced stress perception and signal transduction, trigger adaptive defense responses to low-level BDE-47 exposure, and circumvent growth inhibition. At 10 ng L-1 BDE-47, leaf area, width, length, and fresh weight were all reduced. In addi-tion, histological examination revealed vascular bundle sheath atrophy, impaired xy-lem and phloem development, reduced parenchyma cell diameter, and a decreased proportion of intercellular space. Transcriptomic analysis at 10 ng L^-1 exposure identi-fied significant enrichment of differentially expressed genes in the circadian rhythm and spliceosome pathways, indicating that the pollutant's toxicity has progressed from local metabolic disruption to perturbation of the plant's core regulatory network. Overall, our findings reveal distinct response patterns of A. marina leaves to BDE-47 exposure at environmentally relevant concentrations, initially elucidate the adaptive defense mechanism and underlying molecular basis of toxic effects in mangrove plants under low-concentration BDE-47 exposure, and provide critical scientific support for the ecological risk assessment and conservation of coastal mangrove wetlands.