Respiration Interacts With Photosynthesis Through the Acceptor Side of Photosystem I, Reflected in the Dark-to-Light Induction Kinetics of Chlorophyll Fluorescence in the Cyanobacterium Synechocystis sp. PCC 6803

Abstract

In cyanobacteria, the photosynthetic prokaryotes, direct interaction between photosynthesis and respiration exists at plastoquinone (PQ) pool, which is shared by the two electron transport chains. Another possible point of intersection of the two electron transport chains is NADPH, which is the major electron donor to the respiratory chain as well as the final product of the photosynthetic chain. Here, we showed that the redox state of NADPH in the dark affected chlorophyll fluorescence induction in the cyanobacterium Synechocystis sp. PCC 6803 in a quantitative manner. Accumulation of the reduced NADPH in the dark due to the defect in type 1 NAD(P)H dehydrogenase complex in the respiratory chain resulted in the faster rise to the peak in the dark-to-light induction of chlorophyll fluorescence, while depletion of NADPH due to the defect in pentose phosphate pathway resulted in the delayed appearance of the initial peak in the induction kinetics. There was a strong correlation between the dark level of NADPH determined by its fluorescence and the peak position of the induction kinetics of chlorophyll fluorescence. These results indicate that photosynthesis interacts with respiration through NADPH, which enable us to monitor the redox condition of the acceptor side of photosystem I by simple measurements of chlorophyll fluorescence induction in cyanobacteria.

First in vivo analysis of the regulatory protein CP12 of the model cyanobacterium Synechocystis PCC 6803: Biotechnological implications

“…Using this technique, also employed by many other groups (for examples see Assil-Companioni et al, 2020 ; Ogawa et al, 2021 ), we have analyzed in vivo the kinetics of light-induced NADPH formation (in conditions where the Calvin cycle is not active) and subsequent dark consumption in the WT strain and CP12 mutants. Practically, cells were exposed to several 1 min cycles of 0.5 s actinic light (λ 630nm ) of sufficient intensity (340 μmoles photons m −2 s −1 ) to trigger total photoproduction of NADPH ( Kauny and Sétif, 2014 ; Sétif et al, 2020 ) followed by 55 s darkness to monitor NADPH decays.…”

Glycogen synthesis prevents metabolic imbalance and disruption of photosynthetic electron transport from photosystem II during transition to photomixotrophy in Synechocystis sp. PCC 6803

“…In the presence of glucose, none of the strains exhibited light‐induced increase in NAD(P)H fluorescence, indicating strong reduction of NADP+ already in the dark via the OPP shunt (Ogawa et al ., 2021). In contrast to the ∆PGM and ∆AGP mutants, the WT strain actively used NAD(P)H pools as evidenced by the fast decay of the signal upon the light–dark transition, followed by a subsequent recovery of NAD(P)H fluorescence close to dark‐adapted levels.…”

Light‐driven redox biocatalysis on gram‐scale in Synechocystis sp. PCC 6803 via an in vivo cascade

“…As a consequence, the CBB cycle activity may be significantly decreased upon NADPH withdrawal, in turn reinforcing the NADPH:ATP imbalance due to lacking ATP sink (Cano et al ., 2018). This then also may harm the photosynthetic machinery, for example, its regeneration and oxidative stress management, finally leading to a decrease in light reaction rates and thus fostering NADPH limitation (Brandenburg and Klähn, 2020; Mallén‐Ponce et al ., 2021; McFarlane et al ., 2019; Ogawa et al ., 2021). Thus, the NADPH:ATP imbalance caused by extensive NADPH withdrawal may shut down the photosynthetic electron supply, resulting in a metabolic stalemate.…”