Uptake of the cyanobacterial neurotoxin, anatoxin-a, and alterations in oxidative stress in the submerged aquatic plant Ceratophyllum demersum

• Interactions between anatoxin-a and aquatic plants are not well-understood.
• The influence of anatoxin-a uptake on tocopherol contents and lipid peroxidation in C. demersum was investigated.
• Four tocopherol forms that alleviate anatoxin-a-induced lipid peroxidation increase in response to the rapid uptake of toxin in C. demersum.
• Anatoxin-a uptake and its metabolism can cause alterations in the oxidative stress status of aquatic plants.

The prevalence of cyanobacterial blooms in fresh water bodies worldwide has become a serious environmental problem. The blooms can increase the occurrence of cyanobacterial neurotoxin, anatoxin-a, and this toxin can interact with aquatic plants and other pivotal components of aquatic ecosystems. Despite this, several questions regarding the uptake of the toxin by aquatic plants and its association with toxic effects still remain. This study investigated the uptake of anatoxin-a in relation to alterations in oxidative stress, estimated by changes in lipid peroxidation and tocopherol contents (alpha-, beta-, gamma-, and delta-tocopherol), in the submerged aquatic plant, Ceratophylum demersum, at environmentally relevant concentrations. Exposure to five different concentrations of anatoxin-a (0.005, 0.05, 0.5, 5 and 50 μg l−1) for 24 h increased concentrations in C. demersum in a dose-dependent manner. All four forms of tocopherols were elevated at low concentrations of anatoxin-a (0.005. 0.05. 0.5 and 5 μg l−1). However, a decline in the four tocopherol forms along with a high level of lipid peroxidation was observed at 50 μg l−1 exposure dose. During 336-h exposure to 15 μg l−1 anatoxin-a, rapid toxin uptake during the first 24 h and subsequent steady accumulation of the toxin were observed. The four tocopherol forms increased in response to anatoxin-a uptake, attaining their maximum levels together with a significant increase of lipid peroxidation after 12 or 24 h. After 24-h exposure, the four tocopherol forms decreased gradually without recovery. The results clearly indicate that anatoxin-a uptake can cause a disturbance of the oxidative stress in the aquatic plant, and depending on the concentration and exposure duration, oxidative damage occurs.