Combined toxic effects of anatoxin-a and microcystin-LR on submerged macrophytes and biofilms.

Hazardous substances, such as anatoxin-a and microcystin-LR, are released into the aquatic environment during cyanobacterial blooms, causing significant ecological risk. To assess the toxic effects of anatoxin-a, microcystin-LR and their combined exposure on submerged macrophytes and biofilms, Vallisneria natans was exposed to solutions containing different concentrations of anatoxin-a and microcystin-LR (0.05-5.00 μg L^-1). Results showed that Vallisneria natans was sensitive to anatoxin-a of 0.05 μg L^-1, and antagonistic effects were induced at combined microcystin-LR and anatoxin-a exposure. Single and combined exposure effectively induced antioxidant responses such as promoted activities of superoxide dismutase, peroxidase and catalase, as well as increased glutathione S-transferase, glutathione and malondialdehyde content. In addition, anatoxin-a and microcystin-LR could also be absorbed by Vallisneria natans and trigger plant defense responses, generating increased concentrations of the phytohormones abscisic acid and strigolactones. Moreover, the abundances and structure of the microbial community in periphyton biofilms were altered by combined anatoxin-a and microcystin-LR exposure. The enhanced concentration of N-acylated-l-homoserine lactone indicated that the assessed cyanotoxins had a significant influence on quorum-sensing in biofilm microbial communities. These results demonstrated that anatoxin-a and microcystin-LR at environmentally relevant concentrations could disrupt homeostasis, induce effective defense mechanisms of Vallisneria natans and alter biofilms in aquatic ecosystems.