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

The role of tocopherol in preventing oxidative damage at the cyanobacterial Photosystem II from Synechocystis sp. PCC 6803. Ninja Backasch^*,1, Jens Appel¹, Matthias Schultze¹, Rüdiger Schulz-Friedrich¹, ¹ Botanisches Institut, Kiel, Germany

ABSTRACT- In contrast to the situation in higher plants the deletion of the gene enconding 4-hydroxyphenylpyruvate dioxygenase (hpd) in Synechocystis leads to a tocopherol lacking mutant without affecting the plastoquinone biosynthesis [1]. In the wildtyp of Synechocystis light, glucose and carbon dioxide can influence the tocopherol biosynthesis. Under higher light intensities, increasing the oxidative stress at Photosystem II (PS II), more tocopherol is synthesized. Cultures growing photomixotrophically, shifting the ratio of PSII/PSI towards PS I compared to cultures growing photoautotrophically, contained less tocopherol than those grown photoautotrophically. Carbon dioxide deficiency, slowing down the dark reaction of photosynthesis, which causes oxidative stress at PS II, leads to higher amounts of tocopherol in Synechocystis. Additonally a PS II free mutant of Synechocystis contained almost no tocopherol at all. Fluorescence experiments which quantify the portion of functional PS II showed, that PS II is degraded successively in the hpd-mutant under high light conditions. In the wildtyp the number of intact PS II remained constant over the time. All the data support the hypothesis, that tocopherol prevents oxidative damage at PS II. In contrast to experiments in Chlamydomonas reinhardtii [2], our model allows a distinct differentiation of tocopherol from plastoquinone effects and the results indicate that the tocopherol biosynthesis is correlated with the amount of oxidative stress at PS II. References[1] Daehnhardt, D., Falk, J., Appel, J., van der Kooij, T.A.W., Schulz-Friedrich, R. and Krupinska, K. (2002) FEBS Lett. 523, 177-181 [2] Trebst, A., Depka, B. and Hollaender-Czytko, H. (2002) FEBS Letters 516, 156-160

KEY WORDS: photosystem II, tocopherol, plastoquinone, oxidative stress