Comparative strategies against UV-induced damage in an Antarctic diatom (Thalassiosira sp.) and a Sub-Antarctic phytoflagellate (Asteromonas sp.).

HERNANDO M; MALANGA G; PUNTARULO S; FERREYRA G

Reports on Polar and Marine Research. The Antarctic ecosystem of Potter Cove King-George Island (Isla 25 de Mayo)

Año: 2008; p. 243 - 254

During the past decades, spring-time stratospheric ozone depletion over the Antarctic and the Southern Ocean has resulted in enhanced levels of ultraviolet- B (UVB, 280-315 nm) radiation reaching the earth´s surface. One of the main difficulties to evaluate the potential ecological impact on natural phytoplankton of increased in UVB is that UV sensitivity is species specific UVR induced effects on phytoplankton include the reduction of growth and photosynthetic rates. Several biological effects of UVB involve endogenous photosensitization and formation of reactive oxygen species. The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions.   Cells were exposed in parallel to three irradiance treatments: PAR (control, 400- 700 nm), UVA (PAR + Ultraviolet-A radiation, UVA, 315-400 nm) and UVB (PAR + UVA + UVB). Cylindrical UV-transparent quartz flasks were used for phytoplankton exposure. For the UVA treatment, the bottles were covered with Mylar foil (DuPont country, which has 50% transmission at 323 nm) and PAR controls were performed with cylindrical Plexiglass flasks (UF3) (Röhm & Haas Darmstadt, Germany) which cutt off all UV radiation. Three replicate samples were used for each of the treatments and controls. Culture medium was added to the different treatments at the beginning of the experiment. Samples (80 ml) were taken out daily at 9 a.m. to determine chl-a concentration, cell number and the content of MAA´s for Asteromonas sp. where samples were analysed at the beginning and at day 5 of experiment. The content of α-tocopherol and β-carotene was measured at the beginning of the experiment, and at days 1, 3 and 5 of exposure.   A significant result coming forth from this experiment is that UVR-induced damage affected the starting time of exponential growth, but not final biomass accumulation nor growth during the exponential phase in neither of the studied species. Observation suggests that cells were able to cope with UV, and that the only significant effect was the delay in the timing of exponential growth. Overall, our results support the idea that UVR damage/repair balance involves the combined action of several internal factors in the cell. However, our results showed different mechanisms in the algae groups studied. On the Sub-Antarctic Asteromonas sp. the production of tocopherols plays a key role in UV protection. On the other hand, in the Thalassiosira sp Antarctica the MAA´s synthesis was the most effective internal factor for photoprotection.