IMPACT OF TEMPERATURE-ACCLIMATION ON PHOTOSYNTHESIS IN THE TOXIC RED-TIDE DINOFLAGELLATE ALEXANDRIUM FUNDYENSE (CA28)

This study assessed the impact of temperature on the photosynthetic ac tivity in the dinoflagellate Alexandrium fundyense (Ca28) for cultures grown at 75 mu mol photons m(-2) s(-1) over a range of temperatures. Increasing light intensity under static temperatures caused a 5-fold d ecrease in the maximum quantum yield for photosystem II (PSII) (F-v/F- m). Carbon fixation rates mirrored high-light depressions in F-v/F-m. Cells in the presence of streptomycin showed an 83% recovery in F-v/F- m; therefore, only a minor proportion of the decline in F-v/F-m was at tributable to PSII damage by bright light. For cells transferred to hi gher temperatures, F-v/F-m was less sensitive to high light, decreasin g only 20-40% compared to the 80-90% decrease observed for cells incub ated at their ambient growth temperature. For cells shifted to higher temperatures, the rapid recovery phase of F-v/F-m was not present; the refore, cells did not initiate downregulation of PSII. Higher capacity to maintain electron transport, as indicated by the quantum yields, w as confirmed by enhanced carbon fixation. Shifts to lower temperatures significantly increased PSTI sensitivity to high light. Overall, thes e relationships reflect the synergy between photosynthetic light and d ark reactions which are differentially impacted by changes in temperat ure.