Reactive oxygen species (ROS) are formed in photosystem II (PSII) under various types of abiotic and biotic stresses. It is considered that ROS play a role in chloroplast-to-nucleus retrograde signaling, which changes the nuclear gene expression. However, as ROS lifetime and diffusion are restricted due to the high reactivity towards biomolecules (lipids, pigments, and proteins) and the spatial specificity of signal transduction is low, it is not entirely clear how ROS might transduce signal from the chloroplasts to the nucleus. Biomolecule oxidation was formerly connected solely with damage; nevertheless, the evidence appears that oxidatively modified lipids and pigments are be involved in chloroplast-to-nucleus retrograde signaling due to their long diffusion distance. Moreover, oxidatively modified proteins show high spatial specificity; however, their role in signal transduction from chloroplasts to the nucleus has not been proven yet. The review attempts to summarize and evaluate the evidence for the involvement of ROS in oxidative signaling in PSII.

• Keywords
• Chloroplast-to-nucleus retrograde signaling, Lipid peroxidation, Protein oxidation, Reactive oxygen species,
• MeSH
• Chloroplasts * metabolism   MeSH
• Photosystem II Protein Complex * metabolism   MeSH
• Lipids MeSH
• Oxidative Stress MeSH
• Reactive Oxygen Species metabolism   MeSH
• Signal Transduction physiology   MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Photosystem II Protein Complex * MeSH
• Lipids MeSH
• Reactive Oxygen Species MeSH

The Photosystem II reaction center is vulnerable to photoinhibition. The D1 and D2 proteins, lying at the core of the photosystem, are susceptible to oxidative modification by reactive oxygen species that are formed by the photosystem during illumination. Using spin probes and EPR spectroscopy, we have determined that both O2•- and HO• are involved in the photoinhibitory process. Using tandem mass spectroscopy, we have identified a number of oxidatively modified D1 and D2 residues. Our analysis indicates that these oxidative modifications are associated with formation of HO• at both the Mn4O5Ca cluster and the nonheme iron. Additionally, O2•- appears to be formed by the reduction of O2 at either PheoD1 or QA Early oxidation of D1:332H, which is coordinated with the Mn1 of the Mn4O5Ca cluster, appears to initiate a cascade of oxidative events that lead to the oxidative modification of numerous residues in the C termini of the D1 and D2 proteins on the donor side of the photosystem. Oxidation of D2:244Y, which is a bicarbonate ligand for the nonheme iron, induces the propagation of oxidative reactions in residues of the D-de loop of the D2 protein on the electron acceptor side of the photosystem. Finally, D1:130E and D2:246M are oxidatively modified by O2•- formed by the reduction of O2 either by PheoD1•- or QA•- The identification of specific amino acid residues oxidized by reactive oxygen species provides insights into the mechanism of damage to the D1 and D2 proteins under light stress.

• Keywords
• Photosystem II, mass spectrometry, photo inhibition, photosynthesis, reactive oxygen species,
• MeSH
• Amino Acids chemistry   metabolism   MeSH
• Antioxidants metabolism   MeSH
• Chlorides metabolism   MeSH
• Electron Spin Resonance Spectroscopy MeSH
• Photosystem II Protein Complex chemistry   metabolism   MeSH
• Mass Spectrometry MeSH
• Hydroxyl Radical metabolism   MeSH
• Oxygen metabolism   MeSH
• Molecular Conformation MeSH
• Models, Molecular MeSH
• Oxidation-Reduction * MeSH
• Reactive Oxygen Species metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Names of Substances
• Amino Acids MeSH
• Antioxidants MeSH
• Chlorides MeSH
• Photosystem II Protein Complex MeSH
• Hydroxyl Radical MeSH
• Oxygen MeSH
• Reactive Oxygen Species MeSH

The effect of various abiotic stresses on photosynthetic apparatus is inevitably associated with formation of harmful reactive oxygen species (ROS). In this review, recent progress on ROS production by photosystem II (PSII) as a response to high light and high temperature is overviewed. Under high light, ROS production is unavoidably associated with energy transfer and electron transport in PSII. Singlet oxygen is produced by the energy transfer form triplet chlorophyll to molecular oxygen formed by the intersystem crossing from singlet chlorophyll in the PSII antennae complex or the recombination of the charge separated radical pair in the PSII reaction center. Apart to triplet chlorophyll, triplet carbonyl formed by lipid peroxidation transfers energy to molecular oxygen forming singlet oxygen. On the PSII electron acceptor side, electron leakage to molecular oxygen forms superoxide anion radical which dismutes to hydrogen peroxide which is reduced by the non-heme iron to hydroxyl radical. On the PSII electron donor side, incomplete water oxidation forms hydrogen peroxide which is reduced by manganese to hydroxyl radical. Under high temperature, dark production of singlet oxygen results from lipid peroxidation initiated by lipoxygenase, whereas incomplete water oxidation forms hydrogen peroxide which is reduced by manganese to hydroxyl radical. The understanding of molecular basis for ROS production by PSII provides new insight into how plants survive under adverse environmental conditions.

• Keywords
• free oxygen radicals, heat inactivation, lipid peroxidation, photoinhibition, singlet oxygen,
• Publication type
• Journal Article MeSH
• Review MeSH

In the current study, singlet oxygen formation by lipid peroxidation induced by heat stress (40 °C) was studied in vivo in unicellular green alga Chlamydomonas reinhardtii. Primary and secondary oxidation products of lipid peroxidation, hydroperoxide and malondialdehyde, were generated under heat stress as detected using swallow-tailed perylene derivative fluorescence monitored by confocal laser scanning microscopy and high performance liquid chromatography, respectively. Lipid peroxidation was initiated by enzymatic reaction as inhibition of lipoxygenase by catechol and caffeic acid prevented hydroperoxide formation. Ultra-weak photon emission showed formation of electronically excited species such as triplet excited carbonyl, which, upon transfer of excitation energy, leads to the formation of either singlet excited chlorophyll or singlet oxygen. Alternatively, singlet oxygen is formed by direct decomposition of hydroperoxide via Russell mechanisms. Formation of singlet oxygen was evidenced by the nitroxyl radical 2,2,6,6-tetramethylpiperidine-1-oxyl detected by electron paramagnetic resonance spin-trapping spectroscopy and the imaging of green fluorescence of singlet oxygen sensor green detected by confocal laser scanning microscopy. Suppression of singlet oxygen formation by lipoxygenase inhibitors indicates that singlet oxygen may be formed via enzymatic lipid peroxidation initiated by lipoxygenase.

• MeSH
• Chlamydomonas reinhardtii metabolism   MeSH
• Lipoxygenase metabolism   MeSH
• Malondialdehyde metabolism   MeSH
• Lipid Peroxidation physiology   MeSH
• Heat-Shock Response physiology   MeSH
• Plant Proteins metabolism   MeSH
• Singlet Oxygen metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Lipoxygenase MeSH
• Malondialdehyde MeSH
• Plant Proteins MeSH
• Singlet Oxygen MeSH

Hydroxyl radical (HO•) production in photosystem II (PSII) was studied by electron paramagnetic resonance (EPR) spin-trapping technique. It is demonstrated here that the exposure of PSII membranes to heat stress (40 °C) results in HO• formation, as monitored by the formation of EMPO-OH adduct EPR signal. The presence of different exogenous halides significantly suppressed the EMPO-OH adduct EPR signal in PSII membranes under heat stress. The addition of exogenous acetate and blocker of chloride channel suppressed the EMPO-OH adduct EPR signal, whereas the blocker of calcium channel did not affect the EMPO-OH adduct EPR signal. Heat-induced hydrogen peroxide (H₂O₂) production was studied by amplex red fluorescent assay. The presence of exogenous halides, acetate and chloride blocker showed the suppression of H₂O₂ production in PSII membranes under heat stress. Based on our results, it is proposed that the formation of HO• under heat stress is linked to uncontrolled accessibility of water to the water-splitting manganese complex caused by the release of chloride ion on the electron donor side of PSII. Uncontrolled water accessibility to the water-splitting manganese complex causes the formation of H₂O₂ due to improper water oxidation, which leads to the formation of HO• via the Fenton reaction under heat stress.

• MeSH
• Chlorides metabolism   MeSH
• Electron Spin Resonance Spectroscopy methods   MeSH
• Photosystem II Protein Complex chemistry   metabolism   MeSH
• Hydroxyl Radical metabolism   MeSH
• Oxidation-Reduction MeSH
• Hydrogen Peroxide pharmacology   MeSH
• Spin Trapping methods   MeSH
• Spinacia oleracea chemistry   MeSH
• Heating MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Chlorides MeSH
• Photosystem II Protein Complex MeSH
• Hydroxyl Radical MeSH
• Hydrogen Peroxide MeSH