Reduction-Induced Suppression of Electron Flow (RISE) Is Relieved by Non-ATP-Consuming Electron Flow in PCC 7942.

Photosynthetic organisms oxidize P700 to suppress the production of reactive oxygen species (ROS) in photosystem I (PSI) in response to the lower efficiency of photosynthesis under high light and low CO conditions. Previously, we found a positive relationship between reduction of plastoquinone (PQ) pool and oxidation of P700, which we named reduction-induced suppression of electron flow (RISE). In the RISE model, we proposed that the highly reduced state of the PQ pool suppresses Q-cycle turnover to oxidize P700 in PSI.

Land plants drive photorespiration as higher electron-sink: comparative study of post-illumination transient O -uptake rates from liverworts to angiosperms through ferns and gymnosperms.

In higher plants, the electron-sink capacity of photorespiration contributes to alleviation of photoinhibition by dissipating excess energy under conditions when photosynthesis is limited. We addressed the question at which point in the evolution of photosynthetic organisms photorespiration began to function as electron sink and replaced the flavodiiron proteins which catalyze the reduction of O at photosystem I in cyanobacteria. Algae do not have a higher activity of photorespiration when CO assimilation is limited, and it can therefore not act as an electron sink.

Oxidation of P700 in Photosystem I Is Essential for the Growth of Cyanobacteria.

The photoinhibition of photosystem I (PSI) is lethal to oxygenic phototrophs. Nevertheless, it is unclear how photodamage occurs or how oxygenic phototrophs prevent it. Here, we provide evidence that keeping P700 (the reaction center chlorophyll in PSI) oxidized protects PSI.

Diversity in photosynthetic electron transport under [CO]-limitation: the cyanobacterium Synechococcus sp. PCC 7002 and green alga Chlamydomonas reinhardtii drive an O-dependent alternative electron flow and non-photochemical quenching of chlorophyll fluorescence during CO-limited photosynthesis.

Some cyanobacteria, but not all, experience an induction of alternative electron flow (AEF) during CO-limited photosynthesis. For example, Synechocystis sp. PCC 6803 (S.

Reduction-Induced Suppression of Electron Flow (RISE) in the Photosynthetic Electron Transport System of Synechococcus elongatus PCC 7942.

Accumulation of electrons under conditions of environmental stress produces a reduced state in the photosynthetic electron transport (PET) system and causes the reduction of O by PSI in the thylakoid membranes to produce the reactive oxygen species superoxide radical, which irreversibly inactivates PSI. This study aims to elucidate the molecular mechanism for the oxidation of reaction center Chl of PSI, P700, after saturated pulse (SP) light illumination of the cyanobacterium Synechococcus elongatus PCC 7942 under steady-state photosynthetic conditions. Both P700 and NADPH were transiently oxidized after SP light illumination under CO-depleted photosynthesis conditions.

FLAVODIIRON2 and FLAVODIIRON4 proteins mediate an oxygen-dependent alternative electron flow in Synechocystis sp. PCC 6803 under CO2-limited conditions.

This study aims to elucidate the molecular mechanism of an alternative electron flow (AEF) functioning under suppressed (CO2-limited) photosynthesis in the cyanobacterium Synechocystis sp. PCC 6803. Photosynthetic linear electron flow, evaluated as the quantum yield of photosystem II [Y(II)], reaches a maximum shortly after the onset of actinic illumination.

O2-dependent large electron flow functioned as an electron sink, replacing the steady-state electron flux in photosynthesis in the cyanobacterium Synechocystis sp. PCC 6803, but not in the cyanobacterium Synechococcus sp. PCC 7942.

To determine whether alternative electron flow (AEF) can replace the photosynthetic electron flow in cyanobacteria, we used an open O2-electrode system to monitor O2-exchange over a long period. In air-grown Synechocystis sp. PCC 6803 (S.