The long-term exposure of cyanotoxin, cylindrospermopsin, on the macrophyte Lemna trisulca

The increase in frequency and prevalence of cylindrospermopsin (CYN)-producing cyanobacteria blooms have become a growing problem worldwide. Therefore, the long-term effects of CYN on the physiological processes of the macrophyte, Lemna trisulca, were examined. During a 5-day exposure to a range of CYN concentrations (0.5, 1 and 5 μg ml−1), the low levels of stress experienced by L. trisulca stimulated its growth rate and photosynthesis and led to an increase in the synthesis of photosynthetic pigments. In turn, it was shown that a 3-week exposure to the highest tested CYN concentration (5 μg ml−1) resulted in the inhibition of biomass accumulation (by 7.6%) compared with that of the control plants, but necrosis and chlorosis were not observed. A negative correlation with the concentration of carotenoids was also observed, which may suggest that the antioxidant mechanisms of L. trisulca are effective only up to a certain CYN concentration. An increase in protein content in the tissues of macrophytes treated with concentrations of CYN ranging from 0.5 to 5 μg ml−1 indicates that the toxin did not inhibit protein synthesis but increased the metabolism of L. trisulca, potentially to provide energy for defence. The toxin also affects the homeostasis of mineral ions in cells. This is the first description of the physiological response of L. trisulca to the long-term effects of a wide range of CYN concentrations.