Can Mycosporine-Like Amino Acids Act as Multifunctional Compounds in Gymnodinium catenatum (Dinophyceae)?

MAAs originating from Gymnodinium catenatum were subjected to H2 O2 oxidation, light and heat. Shinorine and porphyra-334 were the more resistant to all treatments, mycosporine-glycine (MYGL) was the least resistant to oxidation and heat, whereas palythene and M-370 were the least resistant to light. MYGL and M-311 were similarly resistant to photodegradation and oxidation in the dark and low temperature, but M-311 was more resistant to oxidation under light or heat. The ratio M-370/M-365 changed from 29:1 to 6:1 ratio after 240 h of exposure to fluorescent light, indicating that M-365 could represent the M-370 cis-isomer. The role of MAAs as antioxidants and/or osmolytes was evaluated by studying effects of abrupt salinity reduction. Both increases or decreases in concentrations were observed and were dependent on the MAA initial concentration and its chemical structure. The relative increase in MAAs with a known antioxidant capacity (MYGL, palythene) followed an exponential decay trend related to initial concentration. The relative decrease in highly polar MAAs (shinorine, porphyra-334, M-332) with a suspected osmolyte role followed a rise to a maximum with the increase in initial concentration. Whether or not MAAs play a significant role in osmoregulation, their loss can occur upon hypoosmotic shock.