Abstract
When dark-adapted cells of the Chlamydomonas reinhardtii mutant strain F15 + deficient in Photosystem I are illuminated by a single saturating flash (2 μs duration), a transitory O 2 uptake process is observed. This O 2 uptake transient was recorded by using either an amperometric or a mass spectrometric technique. The light-induced signal was inhibited by DCMU, but insensitive to DBMIB, which is known to block the electron transport between the plastoquinone pool and the cytochrome (cyt) b 6 f complex. A similar O 2 uptake signal was observed in a mutant strain (FuD6) deficient in the cytochrome b 6 f complex. We conclude from these data that when the photosynthetic electron transport is impaired after the plastoquinones, flash illumination induces an electron transport from Photosystem II to O 2; this transfer involves the quinones of the plastoquinone pool, but not the cytochrome b 6 f complex. The Photosystem II-dependent O 2 uptake transient is shown to be inhibited by both antimycin A and myxothiazol which were recently reported to inhibit chlororespiration (avenel and Peltier (1991) Photosynth. Res. 28, 141–148). We therefore suggest the involvement of chlororespiratory electron carriers in this process and propose that flash-induced Photosystem II activity transitorily increases the chlororespiratory electron flow. By studying the effect of DCMU on the flash-induced O 2 signal recorded in wild-type Chlamydomonas cells, we show that such a stimulation of chlororespiration by Photosystem II also occurs when both photosystems are active but develops slower than its inhibition by Photosystem I.
Published Version
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