State transitions in Chlamydomonas reinhardtii. The role of the Mehler reaction in state 2-to-state 1 transition

The light intensity-dependent transition to state 1 of dark-adapted anaerobic state 2 Chlamydomonas reinhardtii cells is stimulated by oxygen and by other electron acceptors for photosystem I, such as oxaloacetate and methylviologen. This suggests that the transition to state 1 requires the oxidatio...

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Veröffentlicht in:Plant physiology (Bethesda) 2005-02, Vol.137 (2), p.492-499
Hauptverfasser: Forti, G, Caldiroli, G
Format: Artikel
Sprache:eng
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Zusammenfassung:The light intensity-dependent transition to state 1 of dark-adapted anaerobic state 2 Chlamydomonas reinhardtii cells is stimulated by oxygen and by other electron acceptors for photosystem I, such as oxaloacetate and methylviologen. This suggests that the transition to state 1 requires the oxidation of the intersystem chain by photosystem I photochemistry. On the other hand, the mere oxidation in the dark of the chain--by addition of O₂--leads only to a slow and incomplete transition. The light-driven stimulation by O₂ of the state 1 transition is saturated at an O₂ concentration of 15 to 20 [micro]M, definitely higher than that of respiration. We suggest that this may represent the affinity for oxygen of the Mehler reaction, a conclusion that is confirmed by the observations that mitochondrial respiration is apparently not involved in modulating state 2-to-state 1 transition. The catalysis of the state 2-to-state 1 transition upon illumination of anaerobically adapted algae might represent, therefore, a relevant physiological role of this process in C. reinhardtii.
ISSN:0032-0889
1532-2548
DOI:10.1104/pp.104.048256