Comparative Study of Defense Strategies against UV-Induced Damage in an Antarctic Diatom (Thalassiosira sp.) and a Sub-Antarctic Phytoflagellate (Ateromonas sp.).

HERNANDO M., MALANGA G., PUNTARULO S. Y FERREYRA G.

Reports on Polar and Marine Research. Evolution of Antarctic Fauna

Año: 2008; p. 243 - 253

During January of 1999, unialgal cultures of the marine diatom Thalassiosira sp., isolated from natural phytoplankton assemblages at Potter Cove (62°14´S, 58°38´W, Antarctica) were exposed to solar ultraviolet radiation (UVR, 280-400 nm) to study the long-term acclimation of this species to such radiations. Before the start of the experiments, the cultures were pre-exposed during 10 days to solar ultraviolet radiation A (UVA, 315 – 400 nm) + Photosynthetic Available Radiation (PAR, 400 – 700 nm). Samples were then exposed during 6 days to three radiation treatments (i.e., PAR+UVR; PAR+UVAR and only PAR, defined as UVB, UVA and PAR treatments, respectively). Growth rate was inhibited by ultraviolet radiation B (UVBR, 280 – 315 nm) and UVAR in the first exposure day and only for UVBR in second one. No UVR inhibition was observed in 3rd day. No significant differences were observed between days in the content of lipid soluble antioxidants (α-tocopherol and β-carotene ) on algae exposed to PAR. The content of α-tocopherol showed a significant decrease during the exponential growth period (until day 3) of the algae exposed to the UVB and UVA treatments. The content of β-carotene did not show significant differences neither between treatments nor between days (P> 0.05). Cellular concentration of MAA´s showed significant increases until day 3, being higher in the UVB treatment, compared with the UVA and PAR ones. When mechanisms of photo-protection were considered, the relative importance of MAA´s concentration was significant (P < 0.05) in the UVB and UVA treatments in relation to α tocopherol. It was showed a positive relation between higher MAA´s cell concentration and higher growth rate. The growth rates in the three treatments were similar between the third and the last days of the experiment. This suggests that cells were able to cope with UV damage, and that the only significant effect was a delay in the starting time of exponential growth. Overall, our results suggest that UVR damage/repair balance in the studied species involves the combined action of several internal factors in the cell, being more important in this case the synthesis of MAA´s.