The ichthyotoxic dinoflagellate Lingulodinium polyedrum has a cyst phase in its reproduction cycle, although environmental factors as oscillations in the light:dark cycle, temperature and the presence of xenobiotics also induce the encystment process. Morphological modifications and changes in the membrane composition result in the increase of the cellular density leading to the cyst deposition on marine sediments, which comprises a strategy for the unicellular organism to avoid adverse growth conditions. Although the molecular mechanism of algal encystment is poorly understood, strong evidences associate increased rates of reactive oxygen species (ROS) production with unfavorable environmental conditions in photoautotrophs. Thus, the aim of this work is to study the encystment kinetic of the dinoflagellate Lingulodinium polyedrum induced by nano- to micromolar concentrations of hydrogen peroxide (H₂O₂) and nitric oxide (·NO), conceived as essential redox signaling molecules in several eukaryotic cells. The induction of cyst formation in L. polyedrum was biphasic (peaks after 1 h and 48 h) and dose-dependent to sodium nitroprussiate concentrations (SNP), an aqueous soluble ·NO-donor. Maximum rates of encystment (number of cysts/total number of cells) were observed with addition of 50 mM SNP to the microalgal cultures: 24.7% and 18.2% after 1 h and 48 h, respectively. Concentrations of H₂O₂ lower than 5 mM did not induce cyst formation in microalgal cultures. On the other hand, a gradual increase of cyst percentage was observed upon 10 mM H₂O₂ treatment, achieving a 100% encystment threshold after 5 h. Contrarily, microalgal exposure to 50 mM H₂O₂ provoked a much earlier massive induction of encystment (100%) within only 30 min.
Financial support: CNPq, FAPESP (Brazil); IFS (Sweden).