| Summary: | Hexavalent chromium (Cr(VI)) is a harmful environmental pollutant, which is widely distributed in the marine environment. However, the mechanisms underlying Cr-induced oxidative stress and reproductive toxicity in clams remain largely unknown. The objective of this study was to explore the acute toxic effects of Cr(VI) and estimate the applicability of male clam Geloina coaxans as a bioindicator in mangrove ecosystems. In this study, G. coaxans were exposed to 4.34, 8,69, 17.38 and 34.76 mg/L Cr(VI) for 24, 48 and 72 h. The activities of catalase (CAT), glutathione S-transferase (GST) and the content of malondialdehyde (MDA) were determined. The gene expression of CAT, GST, autophagy-related gene 5 (ATG5), cyclin B3 and spermatogenesis associated protein 4 (SAP4) were measured by RT-qPCR. Furthermore, histological alteration of the gonad and sperm was observed by light microscopy and transmission electron microscopy. The results showed that Cr(VI) exposure induced the accumulation of MDA and activities of enzymes. Cr(VI) exposure also inhibited the mRNA expression of ATG5, cyclin B3 and SAP4 in a dose-dependent manner, which might suggest that Cr(VI) caused reproductive toxicity by affecting gene expression. Significant changes in the histological structure of gonad were observed. The results demonstrate that Cr(VI) significantly affected functional and molecular parameters in Geloina coaxans, and indicate that gonad represents the target of exposure to Cr(VI).
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