Mycosporine-like amino acids in the marine dinoflagellate Gyrodinium dorsum: induction by ultraviolet irradiation

Cultures of the marine dinoflagellate Gyrodinium dorsum have been exposed to polychromatic radiation (photosynthetically active radiation and UV) from a solar simulator for up to 72 h. Different irradiance spectra in the ultraviolet are produced by inserting cut-off filters between lamp and samples. The mycosporine-like amino acid (MAA) content and composition are investigated by spectroscopic and chromatographic analysis. The study reveals that G. dorsum contains a complex mixture of several aminocyclohexenimine-MAAs and one aminocyclohexenone-MAA. UV irradiation around 320 nm induces an increase in the concentration of all MAAs in the samples. In contrast, exposure to short-wavelength UV-B radiation results in decreased overall MAA production. Furthermore, there is a spectral shift in the absorption of the MAA mixture towards shorter wavelengths, indicating that short-wavelength UV-B induces an altered MAA composition. The amount of MAAs is normalized to the chlorophyll a concentration.