ADAPTATION OF A PSYCHROPHILIC FRESHWATER DINOFLAGELLATE TO ULTRAVIOLET RADIATION 1 Ulrike Obertegger, 2 Federica Camin IASMA Research and Innovation Centre-Fondazione Edmund Mach- Via E. Mach 2 —38010 San Michele all’Adige, Trentino, Italy Graziano Guella University of Trento-Department of Physics, Bioorganic Chemistry Lab, via Sommarive 14—38123 Povo, Trentino, Italy and Giovanna Flaim IASMA Research and Innovation Centre-Fondazione Edmund Mach- Via E. Mach 2—38010 San Michele all’Adige, Trentino, Italy Little is known about the UV photobiology of psy- chrophilic dinoflagellates, particularly in freshwater systems. We addressed the life strategies of Borghiella dodgei Moestrup, Gert. Hansen et Daugbjerg to cope with ambient levels of ultraviolet radiation (UVR) under cold conditions. Several physiological parame- ters related to growth, metabolism, and UVR protec- tion were determined for 4 d in UVR-exposed and control cells by applying stable isotope analysis, spectrophotometry, and liquid chromatography– mass spectrometry (LC ⁄ MS). In UVR-exposed cells, assimilation of 15 N and 13 C and content of chl 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 preexposure levels. Both in UVR-exposed and control cells, no lipid peroxidation of galactolipids was observed. How- ever, in UVR-exposed cells, content of galactolipids was higher and linked to an increase in monogalac- tosyldiacylglycerols (MGDGs). We concluded that Borghiella’s adaptation to UVR depended on a gen- eral metabolic enhancement and efficient scaveng- ing of oxygen radicals to mitigate and counteract damage. While Borghiella seemed 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. Key index words: catalase; diatoxanthin; galactoli- pids; psychrophiles; stable isotopes; UVR Abbreviations: DD, diadinoxanthin; DGDG, diga- lactosyldiacylglycerol; DN, dinoxanthin; DT, diatoxanthin; ESI, electrospray ion source; LC ⁄ MS, liquid chromatography–mass spectrometry; MGDG, monogalactosyldiacylglycerol; ns, not significant; PDA, photo diode array; PUFA, polyunsaturated fatty acid; t R, retention time; UVR, ultraviolet radiation; V–PDB, Vienna–Pee Dee Belemnite Adaptation of a psychrophilic freshwater dinoflagellate to UVR. Early life experienced higher levels of UVR than those that are presently impinging on Earth, and organisms have developed various defense mechanisms to cope with this stressor (Hessen 2008). In fact, UVR is harmful to biological systems at many levels. At the cellular level, UVR directly affects DNA with repercussions on many transcript products and cell processes (Karentz et al. 1991) and leads to the formation of reactive oxygen spe- cies (ROS) that attack DNA, proteins, and lipids (Halliwell and Gutteridge 1999). Therefore, UVR influences algae in several ways, such as growth reduction (de Bakker et al. 2005), reduced or increased uptake of inorganic nutrients (Do ¨hler and Biermann 1987, Braune and Do ¨hler 1996, Korbee et al. 2010), reduced swimming speed (Ekelund 1991), increased cell volume (Van Donk and Hessen 1995), and altered fatty acid composition (Leu et al. 2007). The extent of these changes is species spe- cific and depends on the efficiency of protection strategies, such as repair, detoxification, and protein turnover, which restore functions lost by UVR dam- age. Photoreactivation, nucleotide excision repair, and recombinational repair are known cellular mechanisms that remedy DNA damage (Karentz et al. 1991). ROS can be detoxified by antioxidative enzymes such as catalase, superoxide dismutase, ascorbate peroxidase, and glutathione reductase (Asada 1994). Furthermore, photoprotective com- pounds, such as mycosporine-like amino acids (MAAs) and carotenoids, effectively quench ROS (Asada 1994). In dinoflagellates, apart from UV protection through MAAs (e.g., Gyrodinium dorsum, Klisch and Ha ¨der 2002; Borghiella dodgei, Flaim et al. 2010), photodamage is also avoided through the de-epoxidation of the xanthophyll diadinoxanthin 1 Received 12 August 2010. Accepted 2 February 2011. 2 Author for correspondence: e-mail ulrike.obertegger@iasma.it; obertegger@gmx.net. J. Phycol. 47, 811–820 (2011) Ó 2011 Phycological Society of America DOI: 10.1111/j.1529-8817.2011.01025.x 811