Biochemical and growth performance of the aquatic macrophyte Azolla filiculoides to sub-chronic exposure to cylindrospermopsin

Physiological and biochemical effects of cylindrospermopsin (CYN), a cyanobacterial toxin that inhibits protein synthesis and released during a harmful cyanobacterial bloom, has been overlooked in plants. Therefore, at the present research, the toxic effects (physiological and biochemical) of a crude extract containing CYN were assessed in the aquatic fern Azolla filiculoides exposed to three concentrations (0.05, 0.5 and 5 μg CYN mL−1). At 5 μg CYN mL−1, fern growth rate has showed a drastic decrease (0.001 g g−1 day−1) corresponding to a 99.8 % inhibition, but at the concentrations of 0.05 and 0.5 μg CYN mL−1 the growth rate was similar to the control plants. Growth rate also indicated a IC50 of 2.9 μg CYN mL−1. Those data point to the presence of other compounds in the crude extract may stimulate the fern growth and/or the fern is tolerant to CYN. Chlorophyll (a and b), carotenoids and protein content as well as the activities of glutathione reductase (GR) and glutathione-S-transferase (GST) has increased at 5 μg CYN mL−1 which may indicate that photosynthesis and protein synthesis are not affected by CYN and the probable activation of defense and detoxifying mechanisms to overcome the effects induced by the presence of CYN. Low uptake of cylindrospermopsin (1.314 μg CYN g−1 FW) and low bioconcentration factor (0.401) point towards to a safe use of A. filiculoides as biofertilizer and as food source, but also indicate that the fern is not suitable for CYN phytoremediation.