Photoinhibition of Photosystem I Provides Oxidative Protection During Imbalanced Photosynthetic Electron Transport in Arabidopsis thaliana

Abstract

Photosynthesis involves the conversion of sunlight energy into stored chemical energy, which is achieved through electron transport along a series of redox reactions. Excess photosynthetic electron transport might be dangerous due to the risk of molecular oxygen reduction, generating reactive oxygen species (ROS) over-accumulation. Avoiding excess ROS production requires the rate of electron transport to be coordinated with the capacity of electron acceptors in the chloroplast stroma. Imbalance between the donor and acceptor sides of photosystem I (PSI) can lead to inactivation, which is called PSI photoinhibition. We used a light-inducible PSI photoinhibition system in Arabidopsis thaliana to resolve the time dynamics of inhibition and to investigate its impact on ROS production and turnover. The oxidation state of the PSI reaction center and rates of CO 2 fixation both indicated strong and rapid PSI photoinhibition upon donor side/acceptor side imbalance, while the rate of inhibition eased during prolonged imbalance. PSI photoinhibition was not associated with any major changes in ROS accumulation or antioxidant activity; however, a lower level of lipid oxidation correlated with lower abundance of chloroplast lipoxygenase in PSI-inhibited leaves. The results of this study suggest that rapid activation of PSI photoinhibition under severe photosynthetic imbalance protects the chloroplast from over-reduction and excess ROS formation.

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“…While ROS play an important role in plant signaling, excessive accumulation of ROS may cause oxidative damage towards plant cells, which leads metabolic homeostasis impairment. For instance, excessive ROS production caused by absorption of excessive sunlight by the light-harvesting complex resulted in photoinhibition of PSI 29 . Hence, it is vital to maintain cellular homeostasis in the plant during enhancement of photosynthetic activity.…”

The Rice Plastidial Phosphorylase Participates Directly In Both Sink And Source Processes

“…As recycling of reduced PSI acceptors is lowered, the availability of oxidized PSI acceptors further decreases. Reduction of PSI in the absence of available oxidized acceptors poses a severe problem because PSI has sufficient redox potential to reduce molecular oxygen and generate reactive oxygen species (ROS) when oxidized ferredoxin and NADP + are not available [32,47,48]. Alternatively, under hypothesis II, the increased cold-sensitivity could be the result of the deceleration of the electron flux into PSI from the upstream components (i.e.…”

“…This is achieved by two main mechanisms. First, linear electron flow to PSI is lowered to keep it oxidized as oxidized PSI can effectively dissipate light energy [48][49][50].…”

“…Second, cyclic electron flow is generated around the PSI to regenerate and maintain oxidized acceptors [48,50]. If the decreased donor side limitation in the Pho1ΔL80 plants indicates an increased linear electron flow into PSI, the inability to control this under cold can become problematic.…”

“…Under low temperature growth conditions, the L80 region of Pho1 may be required in how Pho1 modulates PSI activity and diminishes the formation of ROS, and its deleterious effects on photosynthesis. Hence, the association of Pho1 with PsaC may play an active role in the photoinhibition mechanism of PSI when photosynthetic electron transport becomes imbalanced under suboptimal growth conditions [48].…”