Adaptation of a psychrophilic freshwater dinoflagellate to ultraviolet radiation: study with IRMS

Summary • Little is known about the UV photobiology of psychrophilic dinoflagellates, particularly in freshwater systems. We address the life strategies of Borghiella dodgei to cope with ambient levels of ultraviolet radiation (UVR) under cold conditions. • Several physiological parameters related to growth, metabolism, and UVR protection were determined for 4 days in UVR-exposed and control cells by applying stable isotope analysis, spectrophotometry, and liquid chromatography–mass spectrometry. • In UVR-exposed cells, assimilation of 15N and 13C and content of chlorophyll a and carotenoids, specifically diatoxanthin with respect to dinoxanthin and diadinoxanthin, were increased; furthermore, catalase activity showed a cyclic pattern with a strong increase after UVR exposure but a rapid return to pre-exposure levels. Both in UVR-exposed and control cells, no lipid peroxidation of galactolipids was found. However, in UVR-exposed cells, content of galactolipids was higher and linked to an increase in monogalactosyldiacylglycerols (MGDGs). • We conclude that Borghiella`s adaptation to UVR depends on a general metabolic enhancement and efficient scavenging of oxygen radicals to mitigate and counteract damage. While Borghiella seems to be well adapted to ambient UVR, the interactive effects of higher temperature and UVR on psychrophilic species in front of climate change merit further investigation.