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

Photosystem II (PSII) is an intrinsic membrane protein complex that functions as a light-driven water:plastoquinone oxidoreductase in oxygenic photosynthesis. Electron transport in PSII is associated with formation of reactive oxygen species (ROS) responsible for oxidative modifications of PSII proteins. In this study, oxidative modifications of the D1 and D2 proteins by the superoxide anion (O2•-) and the hydroxyl (HO•) radicals were studied in WT and a tocopherol cyclase (vte1) mutant, which is deficient in the lipid-soluble antioxidant α-tocopherol. In the absence of this antioxidant, high-resolution tandem mass spectrometry was used to identify oxidation of D1:130E to hydroxyglutamic acid by O2•- at the PheoD1 site. Additionally, D1:246Y was modified to either tyrosine hydroperoxide or dihydroxyphenylalanine by O2•- and HO•, respectively, in the vicinity of the nonheme iron. We propose that α-tocopherol is localized near PheoD1 and the nonheme iron, with its chromanol head exposed to the lipid-water interface. This helps to prevent oxidative modification of the amino acid's hydrogen that is bonded to PheoD1 and the nonheme iron (via bicarbonate), and thus protects electron transport in PSII from ROS damage.

• Keywords
• EPR, mass spectrometry, photosystem II, reactive oxygen species, tocopherol,
• MeSH
• alpha-Tocopherol chemistry   metabolism   MeSH
• Amino Acids chemistry   metabolism   MeSH
• Arabidopsis enzymology   genetics   radiation effects   MeSH
• Photosynthesis physiology   radiation effects   MeSH
• Photosystem II Protein Complex chemistry   genetics   metabolism   MeSH
• Hydroxyl Radical chemistry   metabolism   MeSH
• Protein Interaction Domains and Motifs MeSH
• Intramolecular Transferases chemistry   genetics   metabolism   MeSH
• Protein Conformation, alpha-Helical MeSH
• Protein Conformation, beta-Strand MeSH
• Oxygen chemistry   metabolism   MeSH
• Models, Molecular MeSH
• Mutation MeSH
• Oxidation-Reduction MeSH
• Superoxides chemistry   metabolism   MeSH
• Light MeSH
• Thermodynamics MeSH
• Thermosynechococcus enzymology   genetics   radiation effects   MeSH
• Thylakoids enzymology   genetics   radiation effects   MeSH
• Protein Binding MeSH
• Binding Sites MeSH
• Iron chemistry   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
• alpha-Tocopherol MeSH
• Amino Acids MeSH
• Photosystem II Protein Complex MeSH
• Hydroxyl Radical MeSH
• Intramolecular Transferases MeSH
• Oxygen MeSH
• Superoxides MeSH
• tocopherol cyclase MeSH Browser
• Iron MeSH

Oxidative modification of proteins in photosystem II (PSII) exposed to high light has been studied for a few decades, but the characterization of protein radicals formed by protein oxidation is largely unknown. Protein oxidation is induced by the direct reaction of proteins with reactive oxygen species known to form highly reactive protein radicals comprising carbon-centered (alkyl) and oxygen-centered (peroxyl and alkoxyl) radicals. In this study, protein radicals were monitored in Arabidopsis exposed to high light by immuno-spin trapping technique based on the detection of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) nitrone adducts using the anti-DMPO antibody. Protein radicals were imaged in Arabidopsis leaves and chloroplasts by confocal laser scanning microscopy using fluorescein conjugated with the anti-DMPO antibody. Characterization of protein radicals by standard blotting techniques using PSII protein specific antibodies shows that protein radicals are formed on D1, D2, CP43, CP47, and Lhcb3 proteins. Protein oxidation reflected by the appearance/disappearance of the protein bands reveals that formation of protein radicals was associated with protein fragmentation (cleavage of the D1 peptide bonds) and aggregation (cross-linking with another PSII subunits). Characterization of protein radical formation is important for better understating of the mechanism of oxidative modification of PSII proteins under high light.

• Keywords
• aggregate, fragment, hydroxyl radical, photosystem II, protein, protein radical, reactive oxygen species, singlet oxygen,
• Publication type
• Journal Article MeSH

Mechanical injury or wounding in plants can be attributed to abiotic or/and biotic causes. Subsequent defense responses are either local, i.e. within or in the close vicinity of affected tissue, or systemic, i.e. at distant plant organs. Stress stimuli activate a plethora of early and late reactions, from electric signals induced within seconds upon injury, oxidative burst within minutes, and slightly slower changes in hormone levels or expression of defense-related genes, to later cell wall reinforcement by polysaccharides deposition, or accumulation of proteinase inhibitors and hydrolytic enzymes. In the current study, we focused on the production of reactive oxygen species (ROS) in wounded Arabidopsis leaves. Based on fluorescence imaging, we provide experimental evidence that ROS [superoxide anion radical (O2 •-) and singlet oxygen (1O2)] are produced following wounding. As a consequence, oxidation of biomolecules is induced, predominantly of polyunsaturated fatty acid, which leads to the formation of reactive intermediate products and electronically excited species.

• Keywords
• Arabidopsis, confocal microscopy, fluorescent probes, mechanical injury, wounding,
• Publication type
• Journal Article MeSH