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The practice of using wind and solar energy to generate electricity represents a solution that would be beneficial for the environment and ought to be explored. However, in order to ensure users' stability and continuous access to electricity, the increasing usage of renewable energy needs to align with the advancement of energy storage technologies. Redox flow batteries, which use an organic solution as the electrolyte and a proton exchange membrane as an ion exchange layer, are currently the subject of extensive research as one of the alternative renewable energy storage systems with the benefit of a techno economy. This study investigated the solubility of organic solution, namely 2,2,6,6-Tetramethylpiperidinyloxy or 2,2,6,6-Tetramethylpiperidine 1-oxyl (TEMPO) and methyl viologen (MV) in various essential electrolyte solutions such as NaCl, KCl, KOH, and H2SO4 that can be used as electrolytes of all organic redox flow battery (AORFB) system to produce high energy density and charging and discharging capacity. The result shows the optimum condition for effective charge transfer in AORFB is TEMPO catholyte and MV anolytes in the 0.08 M H2SO4electrolyte solution. Additionally, a correlation between the acquisition of electrolyte solutions on TEMPO catalyst and MV anolytes was discovered by the data. Electrolyte solution can improve electrical conductivity in TEMPO solution, which in turn can improve the efficiency of AORFB charging and discharging. Contrarily, MV anolytes exhibit a different pattern where the addition of electrolyte solutions reduces their electrical conductivity. RFBs systems with the aforementioned catholyte and anolyte can be used to store solar energy with a maximum current of 0.6 A for 35 minutes. Storage effectiveness is characterized by a change in colour in the catholyte and anolyte. The findings firming the possibility of using AORFB as one of the alternative energy storage systems that can accommodate the intermittence of the renewable energy input resource.

ADP-ribosylation (ADPRylation) is a mechanism which post-translationally modifies proteins in eukaryotes in order to regulate a broad range of biological processes including programmed cell death, cell signaling, DNA repair, and responses to biotic and abiotic stresses. Poly(ADP-ribosyl) polymerases (PARPs) play a key role in the process of ADPRylation, which modifies target proteins by attaching ADP-ribose molecules. Here, we investigated whether and how PARP1 and PARylation modulate responses of Nicotiana benthamiana plants to methyl viologen (MV)-induced oxidative stress. It was found that the burst of reactive oxygen species (ROS), cell death, and loss of tissue viability invoked by MV in N. benthamiana leaves was significantly delayed by both the RNA silencing of the PARP1 gene and by applying the pharmacological inhibitor 3-aminobenzamide (3AB) to inhibit PARylation activity. This in turn reduced the accumulation of PARylated proteins and significantly increased the gene expression of major ROS scavenging enzymes including SOD (NbMnSOD; mitochondrial manganese SOD), CAT (NbCAT2), GR (NbGR), and APX (NbAPX5), and inhibited cell death. This mechanism may be part of a broader network that regulates plant sensitivity to oxidative stress through various genetically programmed pathways. [ABSTRACT FROM AUTHOR]

Under nitrogen deprivation (-N), cyanobacterium Synechocystis sp. PCC 6803 exhibits growth arrest, reduced protein content, and remarkably increased glycogen accumulation. However, producing glycogen under this condition requires a two-step process with cell transfer from normal to -N medium. Metabolic engineering and chemical treatment for rapid glycogen accumulation can bypass the need for two-step cultivation. For example, recent studies indicate that individually disrupting hydrogen (H2) or poly(3-hydroxybutyrate) (PHB) synthesis, or treatment with methyl viologen (MV), effectively increases glycogen accumulation in Synechocystis. Here we explore the effects of disrupted H2 or poly(3-hydroxybutyrate) synthesis, together with MV treatment to on enhanced glycogen accumulation in Synechocystis grown in normal medium. Wild-type cells without MV treatment exhibited low glycogen content of less than 6% w/w dry weight (DW). Compared with wild type, disrupting PHB synthesis combined with MV treatment did not increase glycogen content. Disrupted H₂ production without MV treatment yielded up to 11% w/w DW glycogen content. Interestingly, when combined, disrupted H2 production with MV treatment synergistically enhanced glycogen accumulation to 51% and 59% w/w DW within 3 and 7 days, respectively. Metabolomic analysis suggests that MV treatment mediated the conversion of proteins into glycogen. Metabolomic and transcriptional-expression analysis suggests that disrupted H2 synthesis under MV treatment positively influenced glycogen synthesis. Disrupted H₂ synthesis under MV treatment significantly increased NADPH levels. This increased NADPH content potentially contributed to the observed enhancements in antioxidant activity against MV-induced oxidants, O2 evolution, and metabolite substrates levels for glycogen synthesis in normal medium, ultimately leading to enhanced glycogen accumulation in Synechocystis. Key message: Combining disrupted hydrogen-gas synthesis and the treatment by photosynthesis electron-transport inhibitor significantly enhance glycogen production in cyanobacteria. [ABSTRACT FROM AUTHOR]

Flavodiiron proteins Flv1/Flv3 accept electrons from photosystem (PS) I. In this work we investigated light adaptation mechanisms of Flv1-deficient mutant of Synechocystis PCC 6803, incapable to form the Flv1/Flv3 heterodimer. First seconds of dark–light transition were studied by parallel measurements of light-induced changes in chlorophyll fluorescence, P700 redox transformations, fluorescence emission at 77 K, and OCP-dependent fluorescence quenching. During the period of Calvin cycle activation upon dark–light transition, the linear electron transport (LET) in wild type is supported by the Flv1/Flv3 heterodimer, whereas in Δflv1 mutant activation of LET upon illumination is preceded by cyclic electron flow that maintains State 2. The State 2–State 1 transition and Orange Carotenoid Protein (OCP)-dependent non-photochemical quenching occur independently of each other, begin in about 10 s after the illumination of the cells and are accompanied by a short-term re-reduction of the PSI reaction center (P700+). ApcD is important for the State 2–State 1 transition in the Δflv1 mutant, but S-M rise in chlorophyll fluorescence was not completely inhibited in Δflv1/ΔapcD mutant. LET in Δflv1 mutant starts earlier than the S–M rise in chlorophyll fluorescence, and the oxidation of plastoquinol (PQH2) pool promotes the activation of PSII, transient re-reduction of P700+ and transition to State 1. An attempt to induce state transition in the wild type under high intensity light using methyl viologen, highly oxidizing P700 and PQH2, was unsuccessful, showing that oxidation of intersystem electron-transport carriers might be insufficient for the induction of State 2–State 1 transition in wild type of Synechocystis under high light. [ABSTRACT FROM AUTHOR]

The photosynthesis-induced accumulation of reactive oxygen species in chloroplasts can lead to oxidative stress, triggering changes in protein synthesis, degradation, and the assembly/disassembly of protein complexes. Using shot-gun proteomics, we identified methyl viologen-induced changes in protein abundance in wild-type Arabidopsis and oxidative stress-hypersensitive fsd1-1 and fsd1-2 knockout mutants, which are deficient in IRON SUPEROXIDE DISMUTASE 1 (FSD1). The levels of proteins that are localized in chloroplasts and the cytoplasm were modified in all lines treated with methyl viologen. Compared with the wild-type, fsd1 mutants showed significant changes in metabolic protein and chloroplast chaperone levels, together with increased ratio of cytoplasmic, peroxisomal, and mitochondrial proteins. Different responses in proteins involved in the disassembly of photosystem II–light harvesting chlorophyll a / b binding proteins were observed. Moreover, the abundance of PATELLIN 4, a phospholipid-binding protein enriched in stomatal lineage, was decreased in response to methyl viologen. Reverse genetic studies using patl4 knockout mutants and a PATELLIN 4 complemented line indicate that PATELLIN 4 affects plant responses to oxidative stress by effects on stomatal closure. [ABSTRACT FROM AUTHOR]

Time‐dependent density functional theory (TDDFT) was applied to gain insights into the electronic and vibrational spectroscopic properties of an important electron transport mediator, methyl viologen (MV2+). An organic dication, MV2+ has numerous applications in electrochemistry that include energy conversion and storage, environmental remediation, and chemical sensing and electrosynthesis. MV2+ is easily reduced by a single electron transfer to form a radical cation species (MV•+), which has an intense UV–visible absorption near 600 nm. The redox properties of the MV2+/MV•+ couple and light‐sensitivity of MV•+ have made the system appealing for photo‐electrochemical energy conversion (e.g., solar hydrogen generation from water) and the study of photo‐induced charge transfer processes through electronic absorption and resonance Raman spectroscopic measurements. The reported work applies leading TDDFT approaches to investigate the electronic and vibrational spectroscopic properties of MV2+ and MV•+. Using a conventional hybrid exchange functional (B3‐LYP) and a long‐range corrected hybrid exchange functional (ωB97X‐D3), including with a conductor‐like polarizable continuum model to account for solvation, the electronic absorption and resonance Raman spectra predicted are in good agreement with experiment. Also analyzed are the charge transfer character and natural transition orbitals derived from the TDDFT vertical excitations calculated. The findings and models developed further the understanding of the electronic properties of viologens and related organic redox mediators important in renewable energy applications and serve as a reference for guiding the interpretation of electronic absorption and Raman spectra of the ions. [ABSTRACT FROM AUTHOR]

Brassinosteroids are plant hormones that play an important role in the regulation of the growth, development, and stress responses in plants, particularly, in the induction of tolerance to oxidative stress. It is known that the oxidative stress in plants, which consists in a sharp accumulation of reactive oxygen species (ROS), is induced by a methyl viologen herbicide. Since calcium plays an important role in the transduction of brassinosteroid signals in plant cells and closely interacts with a ROS network in the cells, the role of calcium in the modulation of ROS balance by brassinosteroids was studied using 35S::AtCAX1 transgenic tobacco plants. It was established that 35S::AtCAX1 tobacco plants with an artificial calcium deficiency in the cytosol are more sensitive to the oxidative damage induced by the effect of methyl viologen. The level of lipid peroxidation and oxidized glutathione was higher; however, the activation of superoxide dismutase and glutathione reductase was lower in mutated plants. In 35S::AtCAX1 plants, the effect of brassinosteroids on the induction of the oxidative state changes. A partial restoration of the chlorophyll level, weakening of lipid peroxidation, and a decrease in the level of oxidized glutathione, as well as the activation of superoxide dismutase and glutathione reductase, induced by brassinosteroids were less pronounced in the transgenic plants. The results of the analysis of gene coexpression, protein–protein interactions, and posttranslational modifications in silico confirm that brassinosteroids regulate the mechanisms of tobacco plant response to the effect of methyl viologen using calcium-dependent signaling processes, contributing to the formation of a balance of reactive oxygen species. [ABSTRACT FROM AUTHOR]

Widely used in biomedical and bioanalytical applications, the detonation nanodiamonds (NDs) are generally considered to be biocompatible and non-toxic to a wide range of eukaryotic cells. Due to their high susceptibility to chemical modifications, surface functionalisation is often used to tune the biocompatibility and antioxidant activity of the NDs. The response of photosynthetic microorganisms to redox-active NDs is still poorly understood and is the focus of the present study. The green microalga Chlamydomonas reinhardtii was used to assess the potential phytotoxicity and antioxidant activity of NDs hosting hydroxyl functional groups at concentrations of 5–80 μg NDs/mL. The photosynthetic capacity of microalgae was assessed by measuring the maximum quantum yield of PSII photochemistry and the light-saturated oxygen evolution rate, while oxidative stress was assessed by lipid peroxidation and ferric-reducing antioxidant capacity. We demonstrated that hydroxylated NDs might reduce cellular levels of oxidative stress, protect PSII photochemistry and facilitate the PSII repair under methyl viologen and high light associated stress conditions. Factors involved in this protection may include the low phytotoxicity of hydroxylated NDs in microalgae and their ability to accumulate in cells and scavenge reactive oxygen species. Our findings could pave the way for using hydroxylated NDs as antioxidants to improve cellular stability in algae-based biotechnological applications or semi-artificial photosynthetic systems. [ABSTRACT FROM AUTHOR]

Overcoming the intrinsic low activity of most photoinduced oxidase mimics has been extremely challenging. In this work, we developed a methyl viologen (MV2+) mediated strategy to enhance the oxidase-like activity of fluorescein. The presence of MV2+ gives it a high affinity for TMB with a low Michaelis-Menten constant (K m) of 0.053 mM, which is about 2.8 times lower than that of fluorescein and with a remarkable catalytic constant (K cat) as 0.2490 s−1, which is 3 times as high as that of fluorescein. Fluorescein diacetate (FDA) without oxidase-like activity can be hydrolyzed in situ to produce fluorescein in the presence of carboxylesterases (CaE). Based on the inhibition of CaE activity by organophosphorus pesticides (OP), a novel colorimetric signal biosensor was established with a wide linear range from 1.0 to 200 ng/mL. This work not only provides a convenient and feasible strategy for enhancing the activity of photoinduced oxidase mimics but also blazes a new pathway for the sensitive detection of OP. A simple, cost-effective, and sensitive colorimetric method for the quantitative detection of MP based on the photo-mediated oxidase-like activity of fluorescein-MV2+. [Display omitted] • The biosensor successfully achieved the detection of MP. • The sensor exhibits outstanding sensitivity and selectivity with acceptable results in real sample analysis. • MV2+ as an efficient electron mediator effectively enhances the oxidase-like activity of fluorescein. • The presence of MV2+ gives fluorescein a high affinity for TMB and a remarkable catalytic constant. [ABSTRACT FROM AUTHOR]

A novel pH-responsive crystalsomes has been developed using acetal-functionalized pillar[5]arenes (AP[5]) and methyl viologen (MV) through host-guest interactions. The successful synthesis of AP[5] was confirmed via 1H-NMR spectroscopy, while the formation of the host-guest complex between AP[5] and MV was also verified using ¹H-NMR. The supramolecular assemblies formed at a 1:1 molar ratio of AP[5] to MV exhibited remarkable colloidal stability, a negative surface charge, and a high association constant.An acetal-functionalized pillara[5]arenes (AP[5]) crystalsomes were fabricated to reduce the toxicity of pemetrexed (PMX) in off-target sites and deliver the therapeutic doses to the active sites. Extensive characterization of the crystalsomes was performed, revealing their morphology and crystalline structure through SEM and TEM imaging. WAXS analysis confirmed the crystalline nature of the assemblies, and SAED patterns indicated that the crystalsome shell consisted of lamellae resembling single crystals with polymer chains oriented parallel to the interface. To enhnace the targeting capabilities, the surface of the crystalsomes was modified with biotin by conjugating viologen with biotin (MV-BT), aiming to target biotin receptors overexpressed on tumor cells. These biotin -modified crystalsomes (PMX-BT@CLs) were designed to be acid-labile facilitating the release of encapsulated drugs upon cellular internalization, as confirmed by confocal laser scanning microscopy (CLSM). In vivo , studies demonstrated that the PMX-loaded crystalsomes remained in circulation for extended period, showing improved pharmacokinetics. The area under the curve (AUC) of PMX-BT@CLs was approxiately 3.9 times higher than that of the free drug. Additionally, the relative tumor volume was found to be about 3.5 times lower in the group treated with biotin-modified crystalsomes compared to those treated with free PMX. The mean survival time was also significantly enhanced in the PMX-BT@CLs group. This study underscores the potential of using host-guest motifs in drug delivery app;ications, demonstrating the PMX can effectively targted to tumor sites with minimal off-target toxicity. [Display omitted] • pH-sensitive acetal functionalized host (pillara[5]arene (P[5])) were synthesized. • Crystalsomes were fabricated to reduce the toxicity of pemetrexed in off-target sites. • Guest-biotin (MV-BT) were conjugated to target overexpressed biotin receptor. [ABSTRACT FROM AUTHOR]

Considering the unfavorable impacts of methyl viologen-induced oxidative stress (MV1-2, 50 and 500 µM) on growth, gas exchange (intercellular CO2 concentration, carbon assimilation rate, stomatal conductance, transpiration rate), the efficiency of PSII photochemistry and gene expressions of proteins related to photosystems, antioxidant capacity, and the content/histochemical staining of reactive oxygen species (ROS) markers, the experiment was conducted to evaluate the possible mechanisms of sodium hydrosulfide hydrate (a hydrogen sulfide donor, 500 µM NaHS) and its scavenger/inhibitor (hypotaurine, 50 µM and hydroxylamine, 100 µM) in Arabidopsis thaliana for 24 h. NaHS alleviated stress-reduced growth (4.2-fold increase for MV2 + NaHS) and improved the gas exchange parameters. NaHS was capable of improving the photosynthetic ability under 50 µM MV through sustaining photochemical activity in PSII and photochemical conversion efficiency as evident by transcript levels of psbA, psbD, psaA, and psaB. Stress-caused oxidative damage was scavenged by POX (a 90% increase). However, this action was not enough, suggested by increased ROS accumulation, lipid peroxidation (a 165% induction) and lipoxygenase activity (2.4-fold increase), and loss of membrane integrity. Meanwhile, NaHS successfully eliminated these responses against MV, evidenced by weak histochemical staining of ROS and lesser lipid peroxidation and membrane damage. The synchronized activities of both SOD and CAT triggered by NaHS were responsible for decreasing H2O2 content (by 57.4% decrease for MV2 + NaHS) in response to MV stress. After stress exposure, NaHS utilized the ascorbate–glutathione (AsA-GSH) cycle for removing H2O2. Arabidopsis subjected to MV1 plus NaHS exhibited the advanced levels of AsA regeneration (by 15.3% increase) and the redox state of GSH. Interestingly, NaHS under the high MV concentration did not maintain the re-establishment of GSH homeostasis and redox state of GSH in spite of the induced AsA/DHA (dehydroascorbate). NaHS could protect Arabidopsis from oxidative stress, likely by regulating growth, gas exchange, and photosynthetic performance, inducing expression levels of genes associated with photosystems and regulating antioxidant capacity, and redox balance for AsA and GSH. [ABSTRACT FROM AUTHOR]

One of the challenges of using carbon nanotubes electronics is achieving precise control of the conductivity type. It is particularly difficult to obtain the n-type conductive nanotubes. One of the most common methods of CNTs modification allowing to change their conductivity type is chemical functionalization. This paper describes the results of studies on non-covalent modification of randomly oriented single-walled carbon nanotubes (SWCNT) layers with methyl viologen (MV), which allows for the change of the conductivity of SWCNT from p - to n -type. The properties of pristine and MV-modified SWCNT have been compared using Scanning Electron Microscopy, Raman spectroscopy, and X-ray Photoelectron Spectroscopy. The SWCNT conductivity type change was confirmed by photo-conductance under ultraviolet illumination and measurements in the field effect transistor configuration. [Display omitted] [ABSTRACT FROM AUTHOR]

Molecule aggregation in solution is acknowledged to be universal and can regulate the molecule's physiochemical properties, which however has been rarely investigated in electrochemistry. Herein, an electrochemical method is developed to quantitatively study the aggregation behavior of the target molecule methyl viologen dichloride. It is found that the oxidation state dicationic ions stay discrete, while the singly‐reduced state monoradicals yield a concentration‐dependent aggregation behavior. As a result, the molecule's energy level and its redox potential can be effectively regulated. This work does not only provide a method to investigate the molecular aggregation, but also demonstrates the feasibility to tune redox flow battery's performance by regulating the aggregation behavior. [ABSTRACT FROM AUTHOR]

Gold nanoparticles-modified silver nanorod (AuNPs@AgNR) arrays were fabricated as surface-enhanced Raman spectroscopy (SERS) substrates. The coffee ring effect of the AuNPs@AgNR was explored as a preconcentration method for enriching the target analytes and increasing the "hot spots." Furthermore, methyl viologen (MV) as a toxic herbicide used in agricultural production was successfully determined to investigate the application of the coffee ring effect on AuNPs@AgNR arrays and density functional theory (DFT) was employed to calculate its vibrational modes of corresponding characteristic peaks. Good linearity was obtained in the range 0.10–100 mg/L, and the limit of detection (LOD) of MV was estimated to be 0.01 mg/L, which was lower than the US maximum residue limits (MRLs). This method was also applied to practical detection of MV in river water and apple peel with LODs of 0.10 mg/L and 0.05 mg/L, respectively. SERS results suggest that the coffee ring on AuNPs@AgNR arrays provides a promising way for monitoring environmental pollution and food safety caused by pesticides. [ABSTRACT FROM AUTHOR]

Two-stage cultivation is effective for glycogen production by cyanobacteria. Cells were first grown under adequate nitrate supply (BG11) to increase biomass and subsequently transferred to nitrogen deprivation (–N) to stimulate glycogen accumulation. However, the two-stage method is time-consuming and requires extensive energy. Thus, one-stage cultivation that enables both cell growth and glycogen accumulation is advantageous. Such one-stage method could be achieved using a chemical triggering glycogen storage. However, there is a limited study on such chemicals. Here, nine compounds previously reported to affect cyanobacterial cellular functions were examined in Synechocystis sp. PCC 6803. 2-Phenylethanol, phenoxyethanol, 3-(3,4-dichlorophenyl)-1,1-dimethylurea and methyl viologen can stimulate glycogen accumulation. The oxidative stress agent, methyl viologen significantly increased glycogen levels up to 57% and 69% [w/w dry weight (DW)] under BG11 and –N cultivation, respectively. One-stage cultivation where methyl viologen was directly added to the pre-grown culture enhanced glycogen storage to 53% (w/w DW), compared to the 10% (w/w DW) glycogen level of the control cells without methyl viologen. Methyl viologen treatment reduced the contents of total proteins (including phycobiliproteins) but caused increased transcript levels of glycogen synthetic genes and elevated levels of metabolite substrates for glycogen synthesis. Metabolomic results suggested that upon methyl viologen treatment, proteins degraded to amino acids, some of which could be used as a carbon source for glycogen synthesis. Results of oxygen evolution and metabolomic analysis suggested that photosynthesis and carbon fixation were not completely inhibited upon methyl viologen treatment, and these two processes may partially generate upstream metabolites required for glycogen synthesis. [ABSTRACT FROM AUTHOR]

Leaf senescence accompanied by yellowing and Rubisco degradation occurs prematurely in response to various stresses. However, signaling pathways between stress perception and senescence responses are not understood fully, although previous studies suggest the involvement of reactive oxygen species (ROS). While investigating the physiological functions of autophagy in Physcomitrium patens using wild-type (WT) and autophagy-deficient atg5 strains, we found that Physcomitrium colonies senesce prematurely under dark or nitrogen-deficient conditions, with atg5 senescing earlier than WT. In the present study, we measured cellular H2O2, and examined whether H2O2 mediates premature senescence in Physcomitrium colonies. Methyl viologen, an ROS generator, increased cellular H2O2 levels and caused senescence-like symptoms. H2O2 levels were also elevated to the same plateau levels in WT and atg5 under dark or nitrogen-deficient conditions. The ROS scavenger N-acetylcysteine and the ROS source inhibitor carbonyl cyanide m-chlorophenylhydrazone inhibited the increase in H2O2 levels as well as senescence. Upon transfer to a nitrogen-deficient medium, H2O2 levels increased earlier in atg5 than in WT by ~18 h, whereas atg5 yellowed earlier by >2 days. We conclude that the increased H2O2 levels under dark or nitrogen-deficient conditions mediate premature senescence in Physcomitrium but do not explain the different senescence responses of WT and atg5 cells. [ABSTRACT FROM AUTHOR]

—Action potential (AP) of excitable plant cells is an important signaling event that can differentially alter physicochemical and physiological processes in various parts of the same cell. In giant cells of characean algae, the AP propagation has minor effect on photosynthetic electron transport in areas with high activity of plasmalemmal H+-pump but inhibits linear electron flow in regions featuring high passive H+/OH− conductance of the plasma membrane (PM). Uneven spatial distributions of local periplasmic and cytoplasmic pH facilitate the operation of distinct (CO 2 -dependent and O 2 -mediated) pathways of photoinduced electron flow, which presumably accounts for differential influence of AP on photosynthesis. The excitation of Chara australis cell in the presence of methyl viologen (MV), a redox mediator with the prooxidant action, provides a convenient model system to clarify the influence of voltage-dependent ion fluxes across PM on photosynthetic activity of chloroplasts. This study shows that permeation of MV to their target sites in chloroplasts is restricted by PM in resting cells, but MV easily passes through ionic channels opened during the PM depolarization. This gated permeation of MV gives rise to strong non-photochemical quenching, decrease in the effective quantum yield of linear electron flow, apparent O 2 uptake, and, finally, the enhanced ROS production, as detected by the fluorescent probe dichlorofluorescein. Taken together, the results indicate that the AP generation in the presence of MV acts as trigger for instant redirection of photosynthetic linear electron flow from CO 2 -dependent route to the path of O 2 reduction with the eventual formation of H 2 O 2 as a dominant and most stable ROS form. • Excitation of Chara cell opens membrane channels permeable to methyl viologen (MV2+). • Entry of MV upon excitation redirects electron flow and quenches the F m ′ fluorescence. • Inhibition of thylakoid ΔpH by nigericin mitigated the F m ′ quenching upon cell excitation. • Switching of linear electron flow to MV-mediated path is further evidenced by O 2 uptake. • Cell excitation in the presence of MV promotes ROS accumulation after a lag period. [ABSTRACT FROM AUTHOR]

A series of bis‐(4'‐pyridylethynyl)arenes (arene=benzene, tetrafluorobenzene, and anthracene) were synthesized and their bis‐N‐methylpyridinium compounds were investigated as a class of π‐extended methyl viologens. Their structures were determined by single crystal X‐ray diffraction, and their photophysical and electrochemical properties (cyclic voltammetry), as well as their interactions with DNA/RNA were investigated. The dications showed bathochromic shifts in emission compared to the neutral compounds. The neutral compounds showed very small Stokes shifts, which are a little larger for the dications. All of the compounds showed very short fluorescence lifetimes (<4 ns). The neutral compound with an anthracene core has a quantum yield of almost unity. With stronger acceptors, the analogous bis‐N‐methylpyridinium compound showed a larger two‐photon absorption cross‐section than its neutral precursor. All of the dicationic compounds interact with DNA/RNA; while the compounds with benzene and tetrafluorobenzene cores bind in the grooves, the one with an anthracene core intercalates as a consequence of its large, condensed aromatic linker moiety, and it aggregates within the polynucleotide when in excess over DNA/RNA. Moreover, all cationic compounds showed highly specific CD spectra upon binding to ds‐DNA/RNA, attributed to the rare case of forcing the planar, achiral molecule into a chiral rotamer, and negligible toxicity toward human cell lines at ≤10 μM concentrations. The anthracene‐analogue exhibited intracellular accumulation within lysosomes, preventing its interaction with cellular DNA/RNA. However, cytotoxicity was evident at 1 μM concentration upon exposure to light, due to singlet oxygen generation within cells. These multi‐faceted features, in combination with its two‐photon absorption properties, suggest it to be a promising lead compound for development of novel light‐activated theranostic agents. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Microalgae are known to be a potential resource of high-value metabolites that can be used in the growing field of biotechnology. These metabolites constitute valuable compounds with a wide range of applications that strongly enhance a bio-based economy. Among these metabolites, astaxanthin is considered the most important secondary metabolite, having superior antioxidant properties. For commercial feasibility, microalgae with enhanced astaxanthin production need to be developed. In this study, the tropical green microalgae strain, Coelastrum sp., isolated from the environment in Malaysia, was incubated with methyl viologen, a reactive oxygen species (ROS) reagent that generates superoxide anion radicals (O2-) as an enhancer to improve the accumulation of astaxanthin. The effect of different concentrations of methyl viologen on astaxanthin accumulation was investigated. The results suggested that the supplementation of methyl viologen at low concentration (0.001 mM) was successfully used as a ROS reagent in facilitating and thereby increasing the production of astaxanthin in Coelastrum sp. at a rate 1.3 times higher than in the control.

Leaf-type ferredoxin-NADP(H) oxidoreductase, encoded by AtLFNR1 gene in Arabidopsis, extensively exists in chloroplast stroma and thylakoids and is responsible for the reduction of NADP+ to NADPH in PSI. To investigate the relationship between the characteristics of chlorophyll a fluorescence transients OJIP and the function of AtLFNR1 protein, the fluorescence rise kinetics OJIP curves of AtLFNR1 mutant leaves were determined. It is observed that AtLFNR1 mutant has a lower level of variable fluorescence intensity relative to wild type, especially the J-step and the IP-phase. The JIP-test analysis suggests that the loss of AtLFNR1 function decreases clearly the oxidation rate of plastocyanin as well as PSI reaction center, damages slightly PSII antenna size and pigment assemblies, but stimulates distinctly the photosynthetic activity of PSII. Such multiple effects contribute to the change of shape characteristics of the OJIP transient curve in AtLFNR1 mutant.

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.

SUMMARY: Calcium (Ca2+) is widely recognized as a key second messenger in mediating various plant adaptive responses. Here we show that calcineurin B‐like interacting protein kinase CIPK9 along with its interacting partner VDAC3 identified in the present study are involved in mediating plant responses to methyl viologen (MV). CIPK9 physically interacts with and phosphorylates VDAC3. Co‐localization, co‐immunoprecipitation, and fluorescence resonance energy transfer experiments proved their physical interaction in planta. Both cipk9 and vdac3 mutants exhibited a tolerant phenotype against MV‐induced oxidative stress, which coincided with the lower‐level accumulation of reactive oxygen species in their roots. In addition, the analysis of cipk9vdac3 double mutant and VDAC3 overexpressing plants revealed that CIPK9 and VDAC3 were involved in the same pathway for inducing MV‐dependent oxidative stress. The response to MV was suppressed by the addition of lanthanum chloride, a non‐specific Ca2+ channel blocker indicating the role of Ca2+ in this pathway. Our study suggest that CIPK9‐VDAC3 module may act as a key component in mediating oxidative stress responses in Arabidopsis. [ABSTRACT FROM AUTHOR]

To explore the effect of the presence of a self-assembled monolayer (SAM) of an alkyl thiol derivative as an underlayer of a Nafion film, redox reaction of methyl viologen (MV) at the Au/SAM/Nafion (1 µm-thick) interface was characterized using the results of the voltammetric and electroreflectance measurements. The perfluorinated SAM slowed the kinetics of the interfacial electron transfer process compared to a Au/Nafion electrode, whereas 1-dodecanethiol SAM accelerated it. However, both the SAMs decreased the voltammetric current by half. Importance of the approach to underlay a SAM was discussed.

The toxicity of methyl viologen (MV) to organisms is mainly due to the oxidative stress caused by reactive oxygen species produced from cell response. This study mainly investigated the response of Synechocystis sp. PCC 6803 to MV by combining transcriptomic and metabolomic analyses. Through transcriptome sequencing, we found many genes responding to MV stress, and analyzed them by weighted gene co-expression network analysis (WGCNA). Meanwhile, many metabolites were also found by metabolomic analysis to be regulated post MV treatment. Based on the analysis results of Kyoto encyclopedia of genes and genomes (KEGG) of the differentially expressed genes (DEGs) in the transcriptome and the differential metabolites in the metabolome, the dynamic changes of genes and metabolites involved in ten metabolic pathways in response to MV were analyzed. The results indicated that although the oxidative stress caused by MV was the strongest at 6 h, the proportion of the upregulated genes and metabolites involved in these ten metabolic pathways was the highest. Photosynthesis positively regulated the response to MV-induced oxidative stress, and the regulation of environmental information processing was inhibited by MV. Other metabolic pathways played different roles at different times and interacted with each other to respond to MV. This study comprehensively analyzed the response of Synechocystis sp. PCC 6803 to oxidative stress caused by MV from a multi-omics perspective, with providing key data and important information for in-depth analysis of the response of organisms to MV, especially photosynthetic organisms. Key points: • Methyl viologen (MV) treatment caused regulatory changes in genes and metabolites. • Proportion of upregulated genes and metabolites was the highest at 6-h MV treatment. • Photosynthesis and environmental information processing involved in MV response. [ABSTRACT FROM AUTHOR]

The study concerns the preparation of Rh nanoparticles (NPs) by room-temperature, methyl viologen (MV2+) mediated electrochemical reduction of RhCl3 in the presence of poly(N-vinylpyrrolidone) (PVP, 40000 Da) and nanocellulose (NC, d = 57±36 nm) at a controlled potential of generation of MV·+ radical cations in aqueous medium. When a theoretical amount of electricity is passed, the mediator is not consumed, while Rh(III) is quantitatively reduced to Rh(0). The reduction results in the Rh@PVP (141–191 nm in size) and Rh@PVP/NC nanocomposites dispersed in the solution bulk. The Rh@PVP/NC nanocomposite represents PVP globules (42±13 nm in size) with encapsulated ultrasmall spherical Rh NPs (1.3±0.4 nm in size) bound to the surface of NC fibers. The Rh nanocomposites exhibited high catalytic activity in the model reaction, viz., reduction of p-nitrophenol with sodium borohydride in aqueous medium. The catalytic activity increased in the presence of cetyltrimethylammonium chloride (CTAC). [ABSTRACT FROM AUTHOR]

Leaf senescence accompanied by yellowing and Rubisco degradation occurs prematurely in response to various stresses. However, signaling pathways between stress perception and senescence responses are not understood fully, although previous studies suggest the involvement of reactive oxygen species (ROS). While investigating the physiological functions of autophagy in Physcomitrium patens using wild-type (WT) and autophagy-deficient atg5 strains, we found that Physcomitrium colonies senesce prematurely under dark or nitrogen-deficient conditions, with atg5 senescing earlier than WT. In the present study, we measured cellular H2O2, and examined whether H2O2 mediates premature senescence in Physcomitrium colonies. Methyl viologen, an ROS generator, increased cellular H2O2 levels and caused senescence-like symptoms. H2O2 levels were also elevated to the same plateau levels in WT and atg5 under dark or nitrogen-deficient conditions. The ROS scavenger N-acetylcysteine and the ROS source inhibitor carbonyl cyanide m-chlorophenylhydrazone inhibited the increase in H2O2 levels as well as senescence. Upon transfer to a nitrogen-deficient medium, H2O2 levels increased earlier in atg5 than in WT by ~18 h, whereas atg5 yellowed earlier by >2 days. We conclude that the increased H2O2 levels under dark or nitrogen-deficient conditions mediate premature senescence in Physcomitrium but do not explain the different senescence responses of WT and atg5 cells.

Oxidative stress can significantly impair the plants growth and development. It can be triggered by various biotic and abiotic factors. The study analyzed durum wheat genotypes aiming at identifying the forms characterized by increased tolerance to stress induced by methyl viologen (paraquat). The presence of paraquat in the medium caused the majority of analyzed forms to reduce the weight and length of the shoot part of seedling. In addition, inhibition of the root system development compared to control forms was observed. In some of the forms studied, oxidative stress caused chlorosis. Six different types of responses to oxidative stress were found. Most genotypes (58.8%) showed a reduction in seedling weight and length, irrespective of the paraquat concentration used. Nine genotypes resistant to stressor (CYP, MEX × 2, ETH, FRA, ITA, POL, SUN, TUN) were identified, which constituted 6.1% of the examined forms.

Despite the increased interest in exploring the potential of algal biomass production for food stock and renewable energy, very little work has been done in developing reliable screening protocols to enable the identification of species that are best suited to mass cultivation outdoors. Nannochloropsis is an algal genus identified as a potential source of lipids due to its ability to accumulate large quantities of these compounds, especially under nutrient-limiting conditions. The objective of the current work was to use two species of this genus, Nannochloropsis oceanica and N. oculata, as model organisms to develop a protocol that will allow the evaluation of their capacity to yield high biomass productivity under outdoor conditions. Growing the alga under different light intensities and measuring growth rate as well as a range of photosynthetic parameters based on light response curves and variable fluorescence highlighted significant differences between the two species. Our data show that N. oceanica cells have a better capacity to respond to higher light intensities, as reflected by growth measurements, photosynthetic electron transport rates, and oxygen evolution as well as their response to the very high photon flux densities expected in outdoor culture. On the other hand, N. oculata showed a higher tolerance to oxidative stress as reflected in its resistance to the reactive oxygen species generating compounds Rose Bengal (RB) and methyl viologen (MV). Based on the above evidence, we suggest that N. oceanica may perform better than N. oculata when grown under high light conditions typically found outdoors in summer, while N. oculata may perform better than N. oceanica under oxidative stress conditions usually found in outdoor cultures exposed to a combination of high light and low temperature commonly occurring in winter time. [ABSTRACT FROM AUTHOR]

Different salts of 1,1′-dimethyl-4,4′-bipyridinium which known as methyl viologen compounds (MVX 2) (where X= iodide (I‾, MVI 2), perchlorate (ClO 4 ‾, MVC 2) and tetraphenylborate anion (BPh 4 ‾, MVT 2)) were prepared and characterized using 1H NMR, 13C NMR, elemental analysis and mass spectroscopy. The impact of these viologen salts on the thermal decomposition of ammonium perchlorate was investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and mass spectroscopy. The obtained results revealed that the high-temperature decomposition (HTD) temperature of MVX 2 :AP mixtures (5:100 (w/w)) significantly decreases by 121 ◦C, 151 ◦C and 112 ◦C compared to pure AP in MVC 2 , MCI 2 and MVT 2 , respectively. Moreover, the apparent released heat of AP decomposition in these mixtures grows up from 574.2 J g−1 for the pure AP to 2108, 1965 and 1564 J g−1 for MVC 2 , MCI 2 and MVT 2 , respectively. Furthermore, the calculation of the kinetic parameters confirms that the activation energy of HTD of AP was significantly decreased from 142.9 to 124.9, 138.9 and 131.2 KJ mol−1, upon mixing with MVC 2 , MVI 2 and MVT 2 respectively. The rate constant of AP decomposition at the peak temperatures of these mixtures was higher than that at the peak temperature of pure AP. The evolved gas analysis using mass spectrometry shows that the decomposition of pure AP mainly results in ClO 3, ClO 2, HClO 4, ClO , Cl 2, HCl, N 2 O and O 2 , while the major gaseous products of the 5:100 (w/w) mixture of MVX 2 salts with AP were detected as N 2 , NO, N 2 O, O 2 , Cl 2 , ClO, ClO 2 , ClO 3 , HClO 4 , HCl and 4, 4′-Bipyridine (Bpy). The amounts of Bpy in decomposition products of AP/MVX 2 mixtures follow the order of MVC 2 >MVI 2 >MVT 2 , which surprisingly is in accordance with the catalytic activity of these compounds. • Employment of I‾, ClO4‾ and BPh4‾ salts of methyl viologen as catalyst for thermal decomposition of ammonium perchlorate. • The observation of high catalytic effects of the investigated compounds specially the perchlorate salt of methyl viologen. • Exploration of mechanism of catalyzed thermal decomposition of ammonium perchlorate by thermal and mass spectrometry methods. [ABSTRACT FROM AUTHOR]

The WRKY transcription factors (TFs) are integral parts of signaling pathways that regulate many processes, such as senescence, seed dormancy, seed germination, and resistance to abiotic and biotic stresses. Stress-related functions of WRKY6 have been characterized in Arabidopsis and other plant species, but its role has not been identified in apple. Here, we cloned WRKY6 genes from Malus prunifolia. Two homologues MpWRKY6a and MpWRKY6b found in this species were members of Group II WRKY6 TFs. They were localized to the cell nucleus. MpWRKY6a can bind to W-boxes. Compared with the untransformed wild type plants, MpWRKY6a-overexpressing Arabidopsis plants were more sensitive to methyl jasmonate (MeJA) and less sensitive to methyl viologen and abscisic acid (ABA), which suggests its role in responses to oxidative stress and MeJA or ABA signaling. The results fill a gap in the WRKY6 function in apple and provide basis for resistance improvement of Malus.

Abstract Background Oxidative stress is considered to be involved in growth retardation of plants when they are exposed to a variety of biotic and abiotic stresses. Despite its potential importance in improving crop production, comparative studies on oxidative stress tolerance between rice (Oryza sativa L.) cultivars are limited. This work describes the difference in term of oxidative stress tolerance between 72 rice cultivars. Methods 72 rice cultivars grown under naturally lit greenhouse were used in this study. Excised leaf discs were subjected to a low concentration of methyl viologen (paraquat), a chemical reagent known to generate reactive oxygen species in chloroplast. Chlorophyll fluorescence analysis using a two-dimensional fluorescence meter, ion leakage analysis as well as the measurement of chlorophyll contents were used to evaluate the oxidative stress tolerance of leaf discs. Furthermore, fluorescence intensities were finely analyzed based on new fluorescence theories that we have optimized. Results Treatment of leaf discs with methyl viologen caused differential decrease of maximum quantum yield of photosystem II (Fv/Fm) between cultivars. Decrease of Fv/Fm was also closely correlated with increase of ion leakage and decrease of chlorophyll a/b ratio. Fv/Fm was factorized into photochemical and non-photochemical parameters to classify rice cultivars into sensitive and tolerant ones. Among the 72 compared rice cultivars, the traditional cultivar Co13 was identified as the most tolerant to oxidative stress. Koshihikari, a dominant modern Japonica cultivar in Japan as well as IR58, one of the modern Indica breeding lines exhibited a strong tolerance to oxidative stress. Conclusions Close correlation between Fv/Fm and chlorophyll a/b ratio provides a simple method to estimate oxidative stress tolerance, without measurement of chlorophyll fluorescence with special equipment. The fact that modern cultivars, especially major cultivars possessed tolerance to oxidative stress suggests that oxidative stress tolerance is one of the agricultural traits prerequisite for improvement of modern rice cultivars. Data presented in this study would enable breeding of rice cultivars having strong tolerance to oxidative stress.

Rcd1 (radical-induced cell death1) is an Arabidopsis thaliana mutant, which exhibits high tolerance to paraquat [methyl viologen (MV)], herbicide that interrupts photosynthetic electron transport chain causing the formation of superoxide and inhibiting NADPH production in the chloroplast. To understand the biochemical mechanisms of MV-resistance and the role of RCD1 in oxidative stress responses, we performed metabolite profiling of wild type (Col-0) and rcd1 plants in light, after MV exposure and after prolonged darkness. The function of RCD1 has been extensively studied at transcriptomic and biochemical level, but comprehensive metabolite profiling of rcd1 mutant has not been conducted until now. The mutant plants exhibited very different metabolic features from the wild type under light conditions implying enhanced glycolytic activity, altered nitrogen and nucleotide metabolism. In light conditions, superoxide production was elevated in rcd1, but no metabolic markers of oxidative stress were detected. Elevated senescence-associated metabolite marker levels in rcd1 at early developmental stage were in line with its early-senescing phenotype and possible mitochondrial dysfunction. After MV exposure, a marked decline in the levels of glycolytic and TCA cycle intermediates in Col-0 suggested severe plastidic oxidative stress and inhibition of photosynthesis and respiration, whereas in rcd1 the results indicated sustained photosynthesis and respiration and induction of energy salvaging pathways. The accumulation of oxidative stress markers in both plant lines indicated that MV-resistance in rcd1 derived from the altered regulation of cellular metabolism and not from the restricted delivery of MV into the cells or chloroplasts. Considering the evidence from metabolomic, transcriptomic and biochemical studies, we propose that RCD1 has a negative effect on reductive metabolism and rerouting of the energy production pathways. Thus, the altered, highly active reductive metabolism, energy salvaging pathways and redox transfer between cellular compartments in rcd1 could be sufficient to avoid the negative effects of MV-induced toxicity.

Owing to their sessile life habit, plants are continuously subjected to a broad range of environmental stresses. During periods of (a)biotic stresses, reactive oxygen species (ROS) levels can rise excessively, leading to oxidative stress. Glutathione reductase (GR) plays an important role in scavenging the ROS and maintenance of redox potential of the cell during oxidative stress. To enhance ROS scavenging capacity, and hence stress tolerance, the Arabidopsis thalianaGR2 (AtGR2) gene was expressed from the tobacco plastid (chloroplast) genome, the main source of ROS production in plant photosynthetic tissues, in this study. Leaves of transplastomic tobacco plants had about seven times GR activity and 1.5 times total glutathione levels compared to wild type. These transplastomic tobacco plants showed no discernible phenotype and exhibited more tolerance to methyl viologen-induced oxidative stress than wild-type control plants. The results indicate that introducing AtGR2 in chloroplasts is an efficient approach to increase stress tolerance. This study also provides evidence that increasing antioxidant enzyme via plastid genome engineering is an alternative to enhance plant’s tolerance to stressful conditions.

The design and exploration of advanced materials as a durable multifunctional electrocatalyst toward sustainable energy generation and storage development is the most perdurable challenge in the domain of renewable energy research. Herein, a facile in situ solvothermal approach has been adopted to prepare a methylviologen-regulated crystalline metal phosphonate compound, [C 12 H 14 N 2 ][Ni(C 11 H 11 N 2 )(H 2 hedp) 2 ] 2 •6H 2 O ( NIT1 ), (H 4 hedp = 1-hydroxyethane 1,1-diphosphonic acid) and well characterized by several techniques. The as-prepared NIT1 displays excellent bifunctional electrocatalytic activity with dynamic stability toward oxygen evolution reaction (η 10 = 288 mV) and hydrogen evolution reaction (η 10 = 228 mV) in alkaline (1.0 M KOH) and acidic mediums (0.5 M H 2 SO 4 ), respectively. Such a low overpotential and Tafel slope (68 mV/dec for OER; 56 mV/dec for HER) along with long-term durability up to 20 h of NIT1 make it superior to benchmark the electrocatalyst and various nonprecious metal-based catalysts under similar experimental condition. Further, the electrochemical supercapacitor measurements (in three-electrode system) reveal that the NIT1 electrode possesses much higher specific capacity of 187.6 C g -1 at a current density of 2 A g -1 (272 C g -1 at 5 mV s -1 ) with capacitance retention of 75.2% over 10,000 cycles at 14 A g -1 (Coulombic efficiency > 99%) in 6 M KOH electrolyte medium. Finally for a practical application, an asymmetric supercapacitor device (coin cell) is assembled by NIT1 material. The as-fabricated device delivers the maximum energy density of 39.4 Wh kg -1 at a power density of 450 W kg -1 and achieves a wide voltage window of 1.80 V. Notably, the device endures a remarkable cycle performance with cyclic retention of 92% (Coulombic efficiency > 99%) even after 14,000 charge/discharge cycles at 10 A g -1 . Nevertheless, the extraordinary electrochemical activities toward OER and HER as well as the high-performance device fabrication for LED illumination of such a noble metal-free lower-dimensional charge-transfer compound are truly path breaking and would be promising for the development of advanced multifunctional materials.

Photocatalytic hydrogen production using an inorganic bio-hybrid system can contribute to the proficient utilization of light energy, but it would necessitate the development of novel approaches for preparing a new hydrogen-producing biocatalyst. In this study, we developed a hybrid system to produce hydrogen, whereby the highly efficient light-harvesting inorganic semiconductor (TiO 2) was mixed with Escherichia coli to form a biocatalyst with the addition of an electron mediator (MV2+) under different visible light irradiation. Under this hybrid system, the hydrogen production by E. coli was light intensity-dependent showing maximum production at 2000 W m−2, with a 2-fold increase in the hydrogen production compared to that without TiO 2. The experiments on the continued cycle of hydrogen production revealed that the production could be continued for at least 3 cycles of 5 h incubation for each. A possible pathway utilizing glucose for hydrogen production by the hybrid system was proposed based on the analysis of the levels of metabolites. A feasibility study was also conducted using natural sunlight for hydrogen production by the hybrid system. Overall results demonstrated that whole cells of E. coli could be employed for photocatalytic hydrogen production where the intactness of the E. coli was retained under experimental conditions. • Photogenerated electron from the NPs has ability to interact with bacterial cell. • The combination of photocatalyst and biocatalyst enhances hydrogen production. • TiO 2 /MV2+/ E. coli hybrid system produces more hydrogen compared with control. • Use of natural sunlight is feasible for photocatalytic biohydrogen production. [ABSTRACT FROM AUTHOR]

Rcd1 (radical-induced cell death1) is an Arabidopsis thaliana mutant, which exhibits high tolerance to paraquat [methyl viologen (MV)], herbicide that interrupts photosynthetic electron transport chain causing the formation of superoxide and inhibiting NADPH production in the chloroplast. To understand the biochemical mechanisms of MV-resistance and the role of RCD1 in oxidative stress responses, we performed metabolite profiling of wild type (Col-0) and rcd1 plants in light, after MV exposure and after prolonged darkness. The function of RCD1 has been extensively studied at transcriptomic and biochemical level, but comprehensive metabolite profiling of rcd1 mutant has not been conducted until now. The mutant plants exhibited very different metabolic features from the wild type under light conditions implying enhanced glycolytic activity, altered nitrogen and nucleotide metabolism. In light conditions, superoxide production was elevated in rcd1 , but no metabolic markers of oxidative stress were detected. Elevated senescence-associated metabolite marker levels in rcd1 at early developmental stage were in line with its early-senescing phenotype and possible mitochondrial dysfunction. After MV exposure, a marked decline in the levels of glycolytic and TCA cycle intermediates in Col-0 suggested severe plastidic oxidative stress and inhibition of photosynthesis and respiration, whereas in rcd1 the results indicated sustained photosynthesis and respiration and induction of energy salvaging pathways. The accumulation of oxidative stress markers in both plant lines indicated that MV-resistance in rcd1 derived from the altered regulation of cellular metabolism and not from the restricted delivery of MV into the cells or chloroplasts. Considering the evidence from metabolomic, transcriptomic and biochemical studies, we propose that RCD1 has a negative effect on reductive metabolism and rerouting of the energy production pathways. Thus, the altered, highly active reductive metabolism, energy salvaging pathways and redox transfer between cellular compartments in rcd1 could be sufficient to avoid the negative effects of MV-induced toxicity. [ABSTRACT FROM AUTHOR]

Voltammetric parameters are studied to confirm the antioxidant activity of citric acid towards reduced form of methyl viologen dication (1, 1'-dimethyl-4, 4'-bipyridinium, MV2+, also known as paraquat). In this study the kinetics of the reaction of citric acid with reduced form of methyl viologen is also reported. Out of two oxidative peaks (i.e. MVo to MV++ and MV++ to MV+2) the first peak is almost removed after interaction with citric acid. Shifting in second cathodic peak potential is also obvious and possibility of citric acid to scavenge or making adduct with paraquat is identified. Some real samples (fruit juices) as a rich source of citric acid are also studied. This study presents a simple, relevant and fast voltammetric method by which quick quantitation and monitoring of antioxidant/ scavenging activity of food, herbs and other spices towards paraquat poisoning is possible. It may constitute a new wave of treatment or therapy for the disease caused by paraquat. [ABSTRACT FROM AUTHOR]

Leaf-type ferredoxin-NADP(H) oxidoreductase, encoded by AtLFNR1 gene in Arabidopsis, extensively exists in chloroplast stroma and thylakoids and is responsible for the reduction of NADP+ to NADPH in PSI. To investigate the relationship between the characteristics of chlorophyll a fluorescence transients OJIP and the function of AtLFNR1 protein, the fluorescence rise kinetics OJIP curves of AtLFNR1 mutant leaves were determined. It is observed that AtLFNR1 mutant has a lower level of variable fluorescence intensity relative to wild type, especially the J-step and the IP-phase. The JIP-test analysis suggests that the loss of AtLFNR1 function decreases clearly the oxidation rate of plastocyanin as well as PSI reaction center, damages slightly PSII antenna size and pigment assemblies, but stimulates distinctly the photosynthetic activity of PSII. Such multiple effects contribute to the change of shape characteristics of the OJIP transient curve in AtLFNR1 mutant. [ABSTRACT FROM AUTHOR]