Control of misses in oxygen evolution by the oxido-reduction state of plastoquinone in Dunaliella tertiolecta

Abstract

The way misses happen in oxygen evolution is subject to debate (Govindjee et al. 1985). We recently observed a linear lowering of the miss probability with the flash number (Meunier and Popovic 1989). Therefore, we investigated in Dunaliella tertiolecta the link between the average miss probability and the redox state of plastoquinone after n flashes. The effect of flashes was to oxidize the plastoquinone pool; we found that the oxidation of plastoquinone highly correlated (linear regression: R (2)=0.996) with the lowering of the miss probability. The flash frequency was found to affect both the miss probability and the redox state of plastoquinone. When pre-flashes were given using a high flash frequency (10 Hz), the plastoquinone pool was oxidized and misses were low; however, if long dark intervals between flashes were used, the oxidizing effect of flashes was lost and the misses were high. We could not explain our results by assuming equal misses over all S-states; but unequal misses, caused by deactivations, were coherent with our results. We deduced that chlororespiration was responsible for the reduction of plastoquinone in the dark interval between flashes. We compared oxygen evolution with and without benzoquinone, using a low flash frequency (0.5 Hz) for maximum misses. Benzoquinone lowered the misses from 34% to 3%, and raised the amplitude of oxygen evolution by more than a factor of two (2). From this we deduced that the charge carrier "C" postulated to explain misses (Lavorel and Maison-Peteri 1983) did not account for more than 3% of miss probability in Dunaliella tertiolecta. These results indicate that the misses in oxygen evolution are controlled by the redox state of plastoquinone, through deactivations.

Evidence for a linear variation of the miss and single hit S-state probabilities with the flash number, measured by oxygen evolution in Dunaliella tertiolecta

“…Our results show a steady linear variation of the miss probability, correlated to a steady, progressive oxidation of plastoquinone (Meunier and Popovic 1989). However, those reported by Lavorel and Lemasson 1976) show erratic or semi-oscillatory (period 2) variations.…”

“…If the oxygen production is averaged over any five other precedent flashes, excepted when the third flash is included, the result is smaller than one. This shows We investigated in another work (Meunier and Popovic 1989) the effects of flashes on the plastoquinone pool. Using a 10 Hz flash frequency, as in the 02 evolution measurements, we observed that flashes oxidized the plastoquinone pool.…”

Oxygen-evolving system and secondary quinonic acceptors are highly reduced in dark adapted Euglena cells: A thermoluminescence study

“…The large oscillations, displaying a periodicity of four, are obviously associated to electron fluxes through acceptor and donor sides of PS II which lead to both reoxidation of the plastoquinones molecules and changes in the distribution of the S-states. This modest effect of the pBQ treatment on the pattern of O2-emission differed from that obtained with Chlorella in anaerobic conditions (Greenbaum and Mauzerall 1976) and with Dunaliela in aerobiosis (Meunier and Popovic 1990). In these two materials, addition of pBQ restored oscillations of 02-emission not existing in control dark-adapted cells.…”

Interaction of the photosynthetic and respiratory electron transport chains producing slow O2 signals under flashing light in Synechocystis sp. PCC 6803

“…It is possible to control the lifetime of $3 by keeping the PS II electron acceptors oxidized (Styring and Rutherford 1987;Meunier and Popovic 1990). This is especially true in thylakoid preparations, and at low temperatures, long-lived $3 (stable for a few minutes) that is affected by ADRY agents has been observed (Schmid et al 1994).…”