The Mehler reaction in Chlamydomonas during photosynthetic induction and steady-state photosynthesis in wild-type and in a mitochondrial mutant

The effects of fast O2-removal on electron transport rate (ETR), measured by chlorophyll fluorescence, were investigated in C. reinhardtii. In wild-type, O2-removal caused a strong decrease in ETR during photosynthetic induction due to the absence of Mehler reaction. Light-saturation curves of the O2-dependent electron flow were established in different conditions. O2-dependent electron flow was triggered within a few seconds and amounted to up to 80 % of total electron flow during photosynthetic induction in algae grown on minimal medium, while it represented less than 15 % at steady-state. It was significantly weaker in the presence of acetate and in a mutant devoided of mitochondrial complexes I and III. Measurements of the light-induced changes of 820nm transmission in the s time-range show that in wild-type the O2-dependent electron flow leads to complete re-oxidation of PSI donor side in saturating light.