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

Photoacclimation of Thalassiosira pseudonana and Heterosigma akashiwo: Changes in photosynthetic activity and energy dissipation processes. Philippe Juneau^*,1, Paul Harrison¹, Beverley Green¹, ¹ Department of Botany, University of British Columbia, Vancouver, BC, Canada

ABSTRACT- Phytoplankton have developed strategies that optimise light harvesting and photosynthetic electron transport when changes in irradiance occur. Although the acclimation processes of the photosynthetic apparatus of diatoms, such as Thalassiosira pseudonana, have been already studied, no information concerning the acclimation processes of the toxic raphidophyte Heterosigma akashiwo is available. By using Pulse-Amplitude-Modulated (PAM) fluorometry we assessed the change of the energy dissipation processes when low (40 uE m^-2 s^-1) and moderate (160 uE m^-2 s^-1) light grown algae were transfer to higher light intensity for 1 to 9 hours. We found that energy dissipation processes of both moderated-light grown phytoplankton species are affected similarly to acclimation to high light intensities, however, H. akashiwo showed strong decrease in the photochemical activity sooner than T. pseudonana. Low-light grown algae seem to be more sensitive to high irradiance than the moderated-light grown algae, since the photosynthetic activity decreased more rapidly. In parallel with the decrease in the photosynthetic activity, the non-photochemical processes increased importantly in both species. Acclimation of T. pseudonana and H. akashiwo was also analysed by measuring the pigment content (analysis are underway). This permitted us to assess modification of light-harvesting complex and xanthophyll cycle pigments during the acclimation to high light intensities. Photoacclimation processes of these two algal species are discussed in term of their evolutionary pathways and ecological importance.

KEY WORDS: Photoacclimation, Photosynthesis, Chlorophyll a/c algae