Glutathione–Ascorbate Cycle Is an Early Warning Indicator of Toxicity of BDE-47 in Mangroves

Mangroves are often exposed to contamination by polybrominated diphenyl ethers (PBDEs) from wastewater discharges and solid waste dumping. As one of the most prevalent and toxic PBDE congeners in the environment, 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) and its oxidative stress deserves more attention. In plants, the glutathione–ascorbate (GSH-AsA) cycle plays an important role in the defensive processes against oxidative stress. However, the importance of this cycle in mangroves to defend against PBDE toxicity has not been reported. We conducted a study to evaluate the effects of BDE-47 on GSH-AsA cycle-related antioxidants in a mangrove species, namely Kandelia obovata Sheue, H.Y. Liu & J. Yong. An 8-wk hydroponic culture experiment was conducted with 1-yr-old seedlings of K. obovata exposed to five levels of BDE-47 contamination. At the two high BDE-47 levels (5 and 10 mg L−1), seedling growth, expressed as dry biomass of leaves and roots, was suppressed from Weeks 4 to 8. Parameters in the GSH-AsA cycle in roots and leaves changed significantly within the first week after exposure, indicating that they were more sensitive indicators to BDE-47 toxicity than growth. The suppression of seedling growth, expressed as final biomass production, at the end of the 8-wk experiment was positively correlated to the antioxidative responses in the first week, confirming the indicative roles of these antioxidants. This is the first study to demonstrate that GSH-AsA cycle-related antioxidants in mangrove plants are sensitive indicators of BDE-47 toxicity. These antioxidants, in particular, ascorbate and glutathione peroxidase, could provide early warning of the toxicity of PBDEs.