PARENT SESSION
Posters P1B Photo-oxidative stress, photoinhibition. Abstracts (394-443)

Recovery from photoinhibition in the low-light adapted psychrophilic green alga, Chlamydomonas raudensis (uwo 241). Tessa Pocock^*,1, Dominic Rosso¹, Stefan Falk², Norman Huner¹, ¹ Department of Biology, London, Ontario, Canada²

ABSTRACT- Chlamydomonas raudensis (UWO 241) is a newly described species that was isolated from the permanently ice-covered Lake Bonney in Antarctica. In its natural environment, this psychrophile would never experience temperatures above 4-6 degrees C or light in excess of 15 umol during the austral summer. Photoinhibition and recovery experiments at its optimum growth temperature of 8 degrees C and at the non-permissive temperature of 29 degrees C were performed to determine if the photosynthetic apparatus in C. raudensis had maintained the capacity for photoprotection and recovery from high light stress. This psychrophile has lost the capacity to modulate the extent of photoinhibition even though it is able to induce the xanthophyll cycle and the D1 repair cycle. In contrast to C. reinhardtii, temperature had little to no effect on the quantum yield and the maximum extent of photoinhibition in the psychrophile. Despite the constraints placed on the protective and repair mechanisms at low temperatures, full recovery of PSII photochemistry and the maximum rate and photosynthetic efficiency of oxygen evolution occurred in parallel. Photoinhibition resulted in a 62% decrease in Fv/Fm and this recovered up to 70% of control values within the first 20 min and up to 80% of the control value after 2h at 8 degrees C. C. raudensis has maintained similar protective and repair mechanisms as C. reinhardtii despite the former having evolved and adapted to extremely low light. Recovery of PSII photochemistry and photoinhibition in C. raudensis was not dependent on the xanthophyll cycle. The D1 repair cycle was minimally involved in low-temperature recovery. Recovery up to 70% of control values occurred in the presence of lincomycin. Therefore, recovery in C. raudensis relies more on the temperature-independent and lincomycin-resistant mechanisms. The involvement of active and inactive PSII centres will be discussed.

KEY WORDS: Recovery, Photoinhibition, Photoprotection, Antarctica