PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Effects of UVB radiation on the D1 protein of natural phytoplankton. Josee Bouchard^*,1, Suzanne Roy², Douglas Campbell¹, ¹ Institut des Sciences de la Mer de Rimouski - UQAR, Rimouski, Québec, Canada² Department of Biology and Coastal Wetlands Institute, Mount Allison University, Sackville, New Brunswick, Canada

ABSTRACT- Ultraviolet-B (UV-B; 280-320 nm) effects were examined in phytoplankton communities from Rimouski (Canada), Ubatuba (Brazil) and Ushuaia (Argentina). Two light treatments were tested: ambient solar radiation, and ambient with additional UV-B from lamps, corresponding to a 60% ozone depletion scenario at each site. The experiments were performed outdoors using 1800 L pump-mixed mesocosms. In all three cases, algal biomass and optimal quantum yield (Fv/Fm) were not significantly affected by the UV-B addition, suggesting that UV-protective or repair mechanisms were active. We tested for the role of the D1 protein, critical in the repair of photosystem II (PSII) centres, by using short-term, small-volume surface incubations in the presence or absence of lincomycin, an inhibitor of the synthesis of chloroplast encoded proteins such as D1 protein. In these incubations damage to the PSII was detected using fluorescence and the D1 protein by detected immunochemically. At all sites inhibition of D1 protein synthesis with lincomycin (no repair) consistently resulted in rapid decrease in D1 pools generally paralleled by decreases in Fv/Fm. Rates of D1 degradation were generally similar under NUVB and HUVB but were faster at tropical Ubatuba where irradiance (PAR and UVR) was greater than at the two other sites. In the presence of D1 protein synthesis (repair occurring) changes in D1 pools generally occurred in parallel with changes in Fv/Fm but not always. At all sites D1 turnover (degradation and synthesis occurring) was faster under HUVB compared to NUVB. Our results suggest that HUVB exposure in field populations had more effect on D1 synthesis than on the D1 degradation rate. D1 turnover was much faster at tropical Ubatuba where high water temperature allowed faster D1 biosynthesis.

KEY WORDS: Ultraviolet radiation, D1 protein, Phytoplankton, Optimal quantum yield