Higher Reduced State of Fe/S-Signals, with the Suppressed Oxidation of P700, Causes PSI Inactivation in Arabidopsis thaliana

Abstract

Environmental stress increases the risk of electron accumulation in photosystem I (PSI) of chloroplasts, which can cause oxygen (O2) reduction to superoxide radicals and decreased photosynthetic ability. We used three Arabidopsis thaliana lines: wild-type (WT) and the mutants pgr5hope1 and paa1-7/pox1. These lines have different reduced states of iron/sulfur (Fe/S) signals, including Fx, FA/FB, and ferredoxin, the electron carriers at the acceptor side of PSI. In the dark, short-pulse light was repetitively illuminated to the intact leaves of the plants to provide electrons to the acceptor side of PSI. WT and pgr5hope1 plants showed full reductions of Fe/S during short-pulse light and PSI inactivation. In contrast, paa1-7/pox1 showed less reduction of Fe/S and its PSI was not inactivated. Under continuous actinic-light illumination, pgr5hope1 showed no P700 oxidation with higher Fe/S reduction due to the loss of photosynthesis control and PSI inactivation. These results indicate that the accumulation of electrons at the acceptor side of PSI may trigger the production of superoxide radicals. P700 oxidation, responsible for the robustness of photosynthetic organisms, participates in reactive oxygen species suppression by oxidizing the acceptor side of PSI.

Enhanced Reduction of Ferredoxin in PGR5-Deficient Mutant of Arabidopsis thaliana Stimulated Ferredoxin-Dependent Cyclic Electron Flow around Photosystem I

“…The accumulation of electrons in PSI is evident in the reduction of electron carriers at the acceptor side of PSI, including the Fe/S-series, Fx, F A /F B , and Fd. This accumulation triggers the reduction of O 2 to produce O 2 − , and the O 2 − subsequently degrades Fe/S compounds, leading to the inactivation of PSI [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ].…”

“…Although CO 2 assimilation could potentially proceed at an ATP supply-limited rate under photorespiratory conditions, the issue arises when NADPH starts to accumulate. The accumulation of electrons at the acceptor side of PSI, manifesting as the reduction of electron carriers such as Fe/S-clusters, is known to induce ROS production [ 19 ]. It is crucial to alleviate the accumulation of NADPH, and this is where the function of Fd-CEF becomes significant.…”

“…Fd-CEF necessitates Fd as the electron donor to effectively reduce oxidized PQ [ 3 ]. Typically, the redox state of Fd remains constant in response to decreases in both the net CO 2 assimilation rate and the photosynthetic linear electron flow under constant actinic light intensity [ 19 , 24 , 25 , 26 ]. Our recent findings revealed an augmented reduction of Fd in a PGR5-less mutant ( pgr5 hope1 ) of Arabidopsis thaliana due to the inhibited oxidation of P700 in PSI [ 19 ].…”

“…Typically, the redox state of Fd remains constant in response to decreases in both the net CO 2 assimilation rate and the photosynthetic linear electron flow under constant actinic light intensity [ 19 , 24 , 25 , 26 ]. Our recent findings revealed an augmented reduction of Fd in a PGR5-less mutant ( pgr5 hope1 ) of Arabidopsis thaliana due to the inhibited oxidation of P700 in PSI [ 19 ]. Subsequently, we conducted a comparative analysis of Fd-CEF activity between the wild type (WT) and pgr5 hope1 to elucidate the influence of the Fd redox state in vivo.…”

Long-Term Alleviation of the Functional Phenotype in Chlorophyll-Deficient Wheat and Impact on Productivity: A Semi-Field Phenotyping Experiment

“…The combination of these alterations is responsible for a tendency toward the over-reduction of the acceptor side of PSI, potentially leading to a significant rate of PSI inactivation [ 20 ]. A chronic overreduction of the electron transport chain can be extremely harmful for plants and even threaten their survival [ 21 ]. Nevertheless, the chlorophyll-depleted wheat mutants cope with the electron-flow deregulation through the accumulation of PSI end electron acceptors (ferredoxin and ferredoxin-NADP + -oxidoreductase, FNR) and, in addition, the enhancement of the electron-sink alternative to photosynthesis and photorespiration [ 15 , 16 ].…”