Afromontane forests are an important part of the KwaZulu Natal region of southern Africa, having a distinctive flora with a high proportion of endemic species, and lichens are keystone members. Unlike other continental areas, KwaZulu Natal climate change is predicted to increase rainfall and cloudiness. In the present study, hydrated Afromontane lichens from both exposed and shaded microhabitats were given either constant [100 µmol(photon) m-2 s-1] or fluctuating [0, 200, 0 µmol(photon) m-2 s-1] light for 8 h a day for 3 d and changes monitored in nonphotochemical quenching (NPQ) and rates of photosynthetic electron transport. In sun but not shade collections, NPQ strongly increased following treatment with constant and fluctuating light. It seems likely that CO2 fixation may be reduced in moist thalli, and the increase in NPQ may reduce ROS formation during exposure to light while hydrated. Sun lichens can readily modify their NPQ in response to increased cloudiness and rainfall expected in KwaZulu Natal.

• Klíčová slova
• chlorophyll fluorescence, photobionts, reactive oxygen species, stress,
• MeSH
• aklimatizace * fyziologie   MeSH
• fotosyntéza * fyziologie   MeSH
• klimatické změny * MeSH
• lišejníky * fyziologie   účinky záření   MeSH
• transport elektronů MeSH
• tropické klima MeSH
• Publikační typ
• časopisecké články MeSH

Robust oxygenic photosynthesis requires a suite of accessory factors to ensure efficient assembly and repair of the oxygen-evolving photosystem two (PSII) complex. The highly conserved Ycf48 assembly factor binds to the newly synthesized D1 reaction center polypeptide and promotes the initial steps of PSII assembly, but its binding site is unclear. Here we use cryo-electron microscopy to determine the structure of a cyanobacterial PSII D1/D2 reaction center assembly complex with Ycf48 attached. Ycf48, a 7-bladed beta propeller, binds to the amino-acid residues of D1 that ultimately ligate the water-oxidising Mn4CaO5 cluster, thereby preventing the premature binding of Mn2+ and Ca2+ ions and protecting the site from damage. Interactions with D2 help explain how Ycf48 promotes assembly of the D1/D2 complex. Overall, our work provides valuable insights into the early stages of PSII assembly and the structural changes that create the binding site for the Mn4CaO5 cluster.

• MeSH
• elektronová kryomikroskopie MeSH
• fotosystém II (proteinový komplex) * metabolismus   MeSH
• kyslík metabolismus   MeSH
• mangan metabolismus   MeSH
• sinice * metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fotosystém II (proteinový komplex) * MeSH
• kyslík MeSH
• mangan MeSH

Marine phytoplankton produce and scavenge Reactive Oxygen Species, to support cellular processes, while limiting damaging reactions. Some prokaryotic picophytoplankton have, however, lost all genes encoding scavenging of hydrogen peroxide. Such losses of metabolic function can only apply to Reactive Oxygen Species which potentially traverse the cell membrane outwards, before provoking damaging intracellular reactions. We hypothesized that cell radius influences which elements of Reactive Oxygen Species metabolism are partially or fully dispensable from a cell. We therefore investigated genomes and transcriptomes from diverse marine eukaryotic phytoplankton, ranging from 0.4 to 44 μm radius, to analyze the genomic allocations encoding enzymes metabolizing Reactive Oxygen Species. Superoxide has high reactivity, short lifetimes and limited membrane permeability. Genes encoding superoxide scavenging are ubiquitous across phytoplankton, but the fractional gene allocation decreased with increasing cell radius, consistent with a nearly fixed set of core genes for scavenging superoxide pools. Hydrogen peroxide has lower reactivity, longer intracellular and extracellular lifetimes and readily crosses cell membranes. Genomic allocations to both hydrogen peroxide production and scavenging decrease with increasing cell radius. Nitric Oxide has low reactivity, long intracellular and extracellular lifetimes and readily crosses cell membranes. Neither Nitric Oxide production nor scavenging genomic allocations changed with increasing cell radius. Many taxa, however, lack the genomic capacity for nitric oxide production or scavenging. The probability of presence of capacity to produce nitric oxide decreases with increasing cell size, and is influenced by flagella and colony formation. In contrast, the probability of presence of capacity to scavenge nitric oxide increases with increasing cell size, and is again influenced by flagella and colony formation.

• MeSH
• fytoplankton genetika   metabolismus   MeSH
• genomika MeSH
• oxid dusnatý * metabolismus   MeSH
• peroxid vodíku metabolismus   MeSH
• reaktivní formy kyslíku metabolismus   MeSH
• superoxidy * metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• oxid dusnatý * MeSH
• peroxid vodíku MeSH
• reaktivní formy kyslíku MeSH
• superoxidy * MeSH

Plants growing in nature often experience fluctuating irradiance. However, in the laboratory, the dynamics of photosynthesis are usually explored by instantaneously exposing dark-adapted plants to constant light and examining the dark-to-light transition, which is a poor approximation of natural phenomena. With the aim creating a better approximation, we exposed leaves of pea (Pisum sativum) to oscillating light and measured changes in the functioning of PSI and PSII, and of the proton motive force at the thylakoid membrane. We found that the dynamics depended on the oscillation period, revealing information about the underlying regulatory networks. As demonstrated for a selected oscillation period of 60 s, the regulation tries to keep the reaction centers of PSI and PSII open. We present an evaluation of the data obtained, and discuss the involvement of particular processes in the regulation of photosynthesis. The forced oscillations provided an information-rich fingerprint of complex regulatory networks. We expect future progress in understanding these networks from experiments involving chemical interventions and plant mutants, and by using mathematical modeling and systems identification and control tools.

• Klíčová slova
• Pisum sativum, Fluctuating light, forced oscillations, pea, photosynthesis, photosystem I and II, proton motive force, regulation,
• MeSH
• fotosyntéza fyziologie   MeSH
• fotosystém I (proteinový komplex) metabolismus   MeSH
• fotosystém II (proteinový komplex) * metabolismus   MeSH
• hrách setý * metabolismus   MeSH
• listy rostlin metabolismus   MeSH
• rostliny metabolismus   MeSH
• světlo MeSH
• transport elektronů fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fotosystém I (proteinový komplex) MeSH
• fotosystém II (proteinový komplex) * MeSH

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.

• Klíčová slova
• Chloroplast-to-nucleus retrograde signaling, Lipid peroxidation, Protein oxidation, Reactive oxygen species,
• MeSH
• chloroplasty * metabolismus   MeSH
• fotosystém II (proteinový komplex) * metabolismus   MeSH
• lipidy MeSH
• oxidační stres MeSH
• reaktivní formy kyslíku metabolismus   MeSH
• signální transdukce fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH
• Názvy látek
• fotosystém II (proteinový komplex) * MeSH
• lipidy MeSH
• reaktivní formy kyslíku MeSH

Iron superoxide dismutase 1 (FSD1) was recently characterized as a plastidial, cytoplasmic, and nuclear enzyme with osmoprotective and antioxidant functions. However, the current knowledge on its role in oxidative stress tolerance is ambiguous. Here, we characterized the role of FSD1 in response to methyl viologen (MV)-induced oxidative stress in Arabidopsis thaliana. In accordance with the known regulation of FSD1 expression, abundance, and activity, the findings demonstrated that the antioxidant function of FSD1 depends on the availability of Cu2+ in growth media. Arabidopsis fsd1 mutants showed lower capacity to decompose superoxide at low Cu2+ concentrations in the medium. Prolonged exposure to MV led to reduced ascorbate levels and higher protein carbonylation in fsd1 mutants and transgenic plants lacking a plastid FSD1 pool as compared to the wild type. MV induced a rapid increase in FSD1 activity, followed by a decrease after 4 h long exposure. Genetic disruption of FSD1 negatively affected the hydrogen peroxide-decomposing ascorbate peroxidase in fsd1 mutants. Chloroplastic localization of FSD1 is crucial to maintain redox homeostasis. Proteomic analysis showed that the sensitivity of fsd1 mutants to MV coincided with decreased abundances of ferredoxin and photosystem II light-harvesting complex proteins. These mutants have higher levels of chloroplastic proteases indicating an altered protein turnover in chloroplasts. Moreover, FSD1 disruption affects the abundance of proteins involved in the defense response. Collectively, the study provides evidence for the conditional antioxidative function of FSD1 and its possible role in signaling.

• Klíčová slova
• Arabidopsis, FSD1, copper, ferredoxin, methyl viologen, oxidative stress, proteomics, superoxide dismutase,
• Publikační typ
• časopisecké články MeSH

Foundations of photosynthesis research have been established mainly by studying the response of plants to changing light, typically to sudden exposure to a constant light intensity after dark acclimation or light flashes. This approach remains valid and powerful, but can be limited by requiring dark acclimation before time-domain measurements and often assumes that rate constants determining the photosynthetic response do not change between dark and light acclimation. We show that these limits can be overcome by measuring plant responses to sinusoidally modulated light of varying frequency. By its nature, such frequency-domain characterization is performed in light-acclimated plants with no need for prior dark acclimation. Amplitudes, phase shifts, and upper harmonic modulation extracted from the data for a wide range of frequencies can target different kinetic domains and regulatory feedbacks. The occurrence of upper harmonic modulation reflects nonlinear phenomena, including photosynthetic regulation. To support these claims, we measured chlorophyll fluorescence emission of the green alga Chlorella sorokiniana in light that was sinusoidally modulated in the frequency range 1000-0.001 Hz. Based on these experimental data and numerical as well as analytical mathematical models, we propose that frequency-domain measurements can become a versatile tool in plant sensing.

• MeSH
• biosenzitivní techniky * MeSH
• Chlorella metabolismus   MeSH
• fotosyntéza * MeSH
• světlo * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem 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.

• Klíčová slova
• EPR, mass spectrometry, photosystem II, reactive oxygen species, tocopherol,
• MeSH
• alfa-tokoferol chemie   metabolismus   MeSH
• aminokyseliny chemie   metabolismus   MeSH
• Arabidopsis enzymologie   genetika   účinky záření   MeSH
• fotosyntéza fyziologie   účinky záření   MeSH
• fotosystém II (proteinový komplex) chemie   genetika   metabolismus   MeSH
• hydroxylový radikál chemie   metabolismus   MeSH
• interakční proteinové domény a motivy MeSH
• intramolekulární transferasy chemie   genetika   metabolismus   MeSH
• konformace proteinů, alfa-helix MeSH
• konformace proteinů, beta-řetězec MeSH
• kyslík chemie   metabolismus   MeSH
• molekulární modely MeSH
• mutace MeSH
• oxidace-redukce MeSH
• superoxidy chemie   metabolismus   MeSH
• světlo MeSH
• termodynamika MeSH
• Thermosynechococcus enzymologie   genetika   účinky záření   MeSH
• tylakoidy enzymologie   genetika   účinky záření   MeSH
• vazba proteinů MeSH
• vazebná místa MeSH
• železo chemie   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• alfa-tokoferol MeSH
• aminokyseliny MeSH
• fotosystém II (proteinový komplex) MeSH
• hydroxylový radikál MeSH
• intramolekulární transferasy MeSH
• kyslík MeSH
• superoxidy MeSH
• tocopherol cyclase MeSH Prohlížeč
• železo MeSH

Reactive oxygen species (ROS) are signaling molecules essential for plant responses to abiotic and biotic stimuli as well as for multiple developmental processes. They are produced as byproducts of aerobic metabolism and are affected by adverse environmental conditions. The ROS content is controlled on the side of their production but also by scavenging machinery. Antioxidant enzymes represent a major ROS-scavenging force and are crucial for stress tolerance in plants. Enzymatic antioxidant defense occurs as a series of redox reactions for ROS elimination. Therefore, the deregulation of the antioxidant machinery may lead to the overaccumulation of ROS in plants, with negative consequences both in terms of plant development and resistance to environmental challenges. The transcriptional activation of antioxidant enzymes accompanies the long-term exposure of plants to unfavorable environmental conditions. Fast ROS production requires the immediate mobilization of the antioxidant defense system, which may occur via retrograde signaling, redox-based modifications, and the phosphorylation of ROS detoxifying enzymes. This review aimed to summarize the current knowledge on signaling processes regulating the enzymatic antioxidant capacity of plants.

• Klíčová slova
• antioxidant enzymes, calcium, mitogen-activated protein kinases, oxidative stress, plants, reactive oxygen species, signaling, stress,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

Reactive oxygen species (ROS) have been recognized as important signaling compoundsof major importance in a number of developmental and physiological processes in plants. Theexistence of cellular compartments enables efficient redox compartmentalization and ensuresproper functioning of ROS-dependent signaling pathways. Similar to other organisms, theproduction of individual ROS in plant cells is highly localized and regulated bycompartment-specific enzyme pathways on transcriptional and post-translational level. ROSmetabolism and signaling in specific compartments are greatly affected by their chemicalinteractions with other reactive radical species, ROS scavengers and antioxidant enzymes. Adysregulation of the redox status, as a consequence of induced ROS generation or decreasedcapacity of their removal, occurs in plants exposed to diverse stress conditions. During stresscondition, strong induction of ROS-generating systems or attenuated ROS scavenging can lead tooxidative or nitrosative stress conditions, associated with potential damaging modifications of cellbiomolecules. Here, we present an overview of compartment-specific pathways of ROS productionand degradation and mechanisms of ROS homeostasis control within plant cell compartments.

• Klíčová slova
• cell wall, chloroplasts, cytoplasmic membrane, cytosol, glyoxysomes, mitochondria, peroxisomes, plant cell, reactive oxygen species,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH