Detection of hydrogen peroxide in Photosystem II (PSII) using catalytic amperometric biosensor

Bioactive Compounds and Their Impact on Protein Modification in Human Cells

Reactive oxygen species (ROS) represent a group of molecules with a signaling role that are involved in regulating human cell proliferation and differentiation. Increased ROS concentrations are often associated with the local nonspecific oxidation of biological macromolecules, especially proteins and lipids. Free radicals, in general, may randomly damage protein molecules through the formation of protein-centered radicals as intermediates that, in turn, decay into several end oxidation products. Malondialdehyde (MDA), a marker of free-radical-mediated lipid oxidation and cell membrane damage, forms adducts with proteins in a nonspecific manner, leading to the loss of their function. In our study, we utilized U-937 cells as a model system to unveil the effect of four selected bioactive compounds (chlorogenic acid, oleuropein, tomatine, and tyrosol) to reduce oxidative stress associated with adduct formation in differentiating cells. The purity of the compounds under study was confirmed by an HPLC analysis. The cellular integrity and changes in the morphology of differentiated U-937 cells were confirmed with confocal microscopy, and no significant toxicity was found in the presence of bioactive compounds. From the Western blot analysis, a reduction in the MDA adduct formation was observed in cells treated with compounds that underlaid the beneficial effects of the compounds tested.

Hydrogen Peroxide Variation Patterns as Abiotic Stress Responses of Egeria densa

In vegetation management, understanding the condition of submerged plants is usually based on long-term growth monitoring. Reactive oxygen species (ROS) accumulate in organelles under environmental stress and are highly likely to be indicators of a plant's condition. However, this depends on the period of exposure to environmental stress, as environmental conditions are always changing in nature. Hydrogen peroxide (H2O2) is the most common ROS in organelles. The responses of submerged macrophytes, Egeria densa, to high light and iron (Fe) stressors were investigated by both laboratory experiments and natural river observation. Plants were incubated with combinations of 30-200 μmol m-2 s-1 of photosynthetically active radiation (PAR) intensity and 0-10 mg L-1 Fe concentration in the media. We have measured H2O2, photosynthetic pigment concentrations, chlorophyll a (Chl-a), chlorophyll b (Chl-b), carotenoid (CAR), Indole-3-acetic acid (IAA) concentrations of leaf tissues, the antioxidant activity of catalase (CAT), ascorbic peroxidase (APX), peroxidase (POD), the maximal quantum yield of PSII (Fv Fm -1), and the shoot growth rate (SGR). The H2O2 concentration gradually increased with Fe concentration in the media, except at very low concentrations and at an increased PAR intensity. However, with extremely high PAR or Fe concentrations, first the chlorophyll contents and then the H2O2 concentration prominently declined, followed by SGR, the maximal quantum yield of PSII (Fv Fm -1), and antioxidant activities. With an increasing Fe concentration in the substrate, the CAT and APX antioxidant levels decreased, which led to an increase in H2O2 accumulation in the plant tissues. Moreover, increased POD activity was proportionate to H2O2 accumulation, suggesting the low-Fe independent nature of POD. Diurnally, H2O2 concentration varies following the PAR variation. However, the CAT and APX antioxidant activities were delayed, which increased the H2O2 concentration level in the afternoon compared with the level in morning for the same PAR intensities. Similar trends were also obtained for the natural river samples where relatively low light intensity was preferable for growth. Together with our previous findings on macrophyte stress responses, these results indicate that H2O2 concentration is a good indicator of environmental stressors and could be used instead of long-term growth monitoring in macrophyte management.

Facile fabrication of GCE/Nafion/Ni composite, a robust platform to detect hydrogen peroxide in basic medium via oxidation reaction

Nickel particles alone can oxidize hydrogen peroxide but confronts extreme stability problem which imparts a barrier to act as sensor. The porous Nafion bed on glassy carbon electrode (GCE) surface provides the sureness of incorporating of Ni particles which was further exploited as an electrochemical sensor for H₂O₂ detection through oxidative degradation process. The simple electrochemical incorporation of Ni particles along the pores of Nafion improves the stability of the sensor significantly. The oxidative pathway of hydrogen peroxide on GCE/Nafion/Ni was probed by analyzing mass transfer dependent linear sweep voltammograms both in static and rotating modes along with chronoamperometry. An electron transfer step determines the overall reaction rate with k°= 2.72 × 10^-4 cm s^-1, which is supported by the values of transfer coefficient (β) in between (0.68-0.75). Sensing performance was evaluated by recording differential pulse voltammograms (DPVs) with the linear detection limit (LOD) of 1.8 μM and linear dynamic range (LDR) of 5-500 μM. Real samples from industrial sources were successfully quantified with excellent reproducibility mark GCE/Nafion/Ni electrode as an applicable sensor.

Synthesizing Electrodes Into Electrochemical Sensor Systems

Electrochemical sensors that can determine single/multiple analytes remain a key challenge in miniaturized analytical systems and devices. In this study, we present in situ synthesis and modification of gold nanodendrite electrodes to create an electrochemical system for the analysis of hydrogen peroxide. The sensor system consisted of the reference and counter electrodes as well as the working electrode. Electrochemical reduction of graphene oxide, ErGO, on the thin-film gold and gold nanodendrite working electrodes was used to achieve an efficient sensor interface for the adsorption of a biomimetic electrocatalytic sensor material, Mn(III) meso-tetra(N-methyl-4-pyridyl) porphyrin complex, with as high as 10^-10 mol cm^-2 surface coverage. The sensor system demonstrated a detection limit of 0.3 µM H₂O₂ in the presence of oxygen. Electrochemical determination of hydrogen peroxide in plant material in the concentration range from 0.09 to 0.4 µmol (gFW)^-1 using the electrochemical sensor system was shown as well as in vivo real-time monitoring of the hydrogen peroxide dynamics as a sign of abiotic stress (intense sunlight). Results of the electrochemical determination were in good agreement with the results of biochemical analysis with the spectrophotometric detection. We anticipate that this method can be extended for the synthesis and integration of multisensor arrays in analytical microsystems and devices for the quantification and real-time in vivo monitoring of other analytes and biomarkers.

Reactive Oxygen Species Imaging in U937 Cells

The U937 cell culture is a pro-monocytic, human histiocytic lymphoma cell line. These monocytes can differentiate into either macrophages or dendritic cells (antigen-presenting cells) depending on the initiators. The U937 cells activated in the presence of phorbol 12-myristate 13-acetate (PMA) change their morphology into macrophage-like cells creating pseudopodia and adhering generously. Macrophages are known to produce reactive oxygen species (ROS) mostly during phagocytosis of foreign particles, an important non-specific immune response. Recently, we have focused on the role of hydroxyl radical (HO^∙) and provide evidence on its importance for differentiation in U937 cells. Based on electron paramagnetic resonance (EPR) spectroscopy combined with confocal laser scanning microscopy (CLSM), formation of HO^∙ was confirmed within the cells undergoing differentiation and/or apoptosis during the PMA treatment. This study aims to increase our knowledge of ROS metabolism in model cell lines used in human research.

Reactive Oxygen Species as a Response to Wounding: In Vivo Imaging in Arabidopsis thaliana

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.

Protein Carbonylation As a Biomarker of Heavy Metal, Cd and Pb, Damage in Paspalum fasciculatum Willd. ex Flüggé

Heavy metal tolerant plants have phytoremediation potential for the recovery of contaminated soils, and the characterization of their metabolic adaptation processes is an important starting point to elucidate their tolerance mechanisms at molecular, biochemical and physiological levels. In this research, the effects of Cd and Pb on growth and protein carbonylation in tissues of Paspalum fasciculatum exposed to 30 and 50 mg·Kg⁻¹ Cd and Pb respectively were determined. P. fasciculatum seedlings exposed to metals grew more than controls until 60 days of cultivation and limited their oxidative effects to a reduced protein group. Carbonyl indexes in leaf and root proteins reached a significant increase concerning their controls in plants exposed 30 days to Cd and 60 days to Pb. From the combined approach of Western Blot with Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE) and protein analysis by Matrix Asisted Laser Desorption/Ionisation-Time Of Flight (MALDI-TOF/TOF) mass spectrometry, chloroplastic proteins were identified into the main oxidative stress-inducible proteins to Cd and Pb, such as subunits α, γ of ATP synthetase, Chlorophyll CP26 binding protein, fructose-bisphosphate aldolase and long-chain ribulose bisphosphate carboxylase (RuBisCO LSU). Cd generated damage in the photosynthetic machinery of the leaves of P. fasciculatum into the first 30 days of treatment; five of the oxidized proteins are involved in photosynthesis processes. Moreover, there was a proteolytic fragmentation of the RuBisCO LSU. Results showed that intrinsic tolerance of P. fasciculatum to these metals reached 60 days in our conditions, along with the bioaccumulating appreciable quantities of metals in their roots.

Drought Tolerance of Soybean (Glycine max L. Merr.) by Improved Photosynthetic Characteristics and an Efficient Antioxidant Enzyme Activities Under a Split-Root System

Water deficiency significantly affects photosynthetic characteristics. However, there is little information about variations in antioxidant enzyme activities and photosynthetic characteristics of soybean under imbalanced water deficit conditions (WDC). We therefore investigated the changes in photosynthetic and chlorophyll fluorescence characteristics, total soluble protein, Rubisco activity (RA), and enzymatic activities of two soybean varieties subjected to four different types of imbalanced WDC under a split-root system. The results indicated that the response of both cultivars was significant for all the measured parameters and the degree of response differed between cultivars under imbalanced WDC. The maximum values of enzymatic activities (SOD, CAT, GR, APX, and POD), chlorophyll fluorescence (Fv/Fm, qP, ɸPSII, and ETR), proline, RA, and total soluble protein were obtained with a drought-tolerant cultivar (ND-12). Among imbalanced WDC, the enhanced net photosynthesis, transpiration, and stomatal conductance rates in T2 allowed the production of higher total soluble protein after 5 days of stress, which compensated for the negative effects of imbalanced WDC. Treatment T4 exhibited greater potential for proline accumulation than treatment T1 at 0, 1, 3, and 5 days after treatment, thus showing the severity of the water stress conditions. In addition, the chlorophyll fluorescence values of FvFm, ɸPSII, qP, and ETR decreased as the imbalanced WDC increased, with lower values noted under treatment T4. Soybean plants grown in imbalanced WDC (T2, T3, and T4) exhibited signs of oxidative stress such as decreased chlorophyll content. Nevertheless, soybean plants developed their antioxidative defense-mechanisms, including the accelerated activities of these enzymes. Comparatively, the leaves of soybean plants in T2 displayed lower antioxidative enzymes activities than the leaves of T4 plants showing that soybean plants experienced less WDC in T2 compared to in T4. We therefore suggest that appropriate soybean cultivars and T2 treatments could mitigate abiotic stresses under imbalanced WDC, especially in intercropping.

Oxygenic Photoreactivity in Photosystem II Studied by Rotating Ring Disk Electrochemistry

Protein film photoelectrochemistry has previously been used to monitor the activity of photosystem II, the water-plastoquinone photooxidoreductase, but the mechanistic information attainable from a three-electrode setup has remained limited. Here we introduce the four-electrode rotating ring disk electrode technique for quantifying light-driven reaction kinetics and mechanistic pathways in real time at the enzyme-electrode interface. This setup allows us to study photochemical H₂O oxidation in photosystem II and to gain an in-depth understanding of pathways that generate reactive oxygen species. The results show that photosystem II reacts with O₂ through two main pathways that both involve a superoxide intermediate to produce H₂O₂. The first pathway involves the established chlorophyll triplet-mediated formation of singlet oxygen, which is followed by its reduction to superoxide at the electrode surface. The second pathway is specific for the enzyme/electrode interface: an exposed antenna chlorophyll is sufficiently close to the electrode for rapid injection of an electron to form a highly reducing chlorophyll anion, which reacts with O₂ in solution to produce O₂^•-. Incomplete H₂O oxidation does not significantly contribute to reactive oxygen formation in our conditions. The rotating ring disk electrode technique allows the chemical reactivity of photosystem II to be studied electrochemically and opens several avenues for future investigation.

Plant Science View on Biohybrid Development

Biohybrid consists of a living organism or cell and at least one engineered component. Designing robot-plant biohybrids is a great challenge: it requires interdisciplinary reconsideration of capabilities intimate specific to the biology of plants. Envisioned advances should improve agricultural/horticultural/social practice and could open new directions in utilization of plants by humans. Proper biohybrid cooperation depends upon effective communication. During evolution, plants developed many ways to communicate with each other, with animals, and with microorganisms. The most notable examples are: the use of phytohormones, rapid long-distance signaling, gravity, and light perception. These processes can now be intentionally re-shaped to establish plant-robot communication. In this article, we focus on plants physiological and molecular processes that could be used in bio-hybrids. We show phototropism and biomechanics as promising ways of effective communication, resulting in an alteration in plant architecture, and discuss the specifics of plants anatomy, physiology and development with regards to the bio-hybrids. Moreover, we discuss ways how robots could influence plants growth and development and present aims, ideas, and realized projects of plant-robot biohybrids.

Simultaneous Real-Time Monitoring of Oxygen Consumption and Hydrogen Peroxide Production in Cells Using Our Newly Developed Chip-Type Biosensor Device

All living organisms bear its defense mechanism. Immune cells during invasion by foreign body undergoes phagocytosis during which monocyte and neutrophil produces reactive oxygen species (ROS). The ROS generated in animal cells are known to be involved in several diseases and ailments, when generated in excess. Therefore, if the ROS generated in cells can be measured and analyzed precisely, it can be employed in immune function evaluation and disease detection. The aim of the current study is to introduce our newly developed chip-type biosensor device with high specificity and sensitivity. It comprises of counter electrode and working electrodes I and II. The counter electrode is a platinum plate while the working electrodes I and II are platinum microelectrode and osmium-horseradish peroxidase modified gold electrode, respectively which acts as oxygen and hydrogen peroxide (H₂O₂) detection sensors. Simultaneous measurement of oxygen consumption and H₂O₂ generation were measured in animal cells under the effect of exogenous addition of differentiation inducer, phorbol 12-myristate 13-acetate. The results obtained showed considerable changes in reduction currents in the absence and presence of inducer. Our newly developed chip-type biosensor device is claimed to be a useful tool for real-time monitoring of the respiratory activity and precise detection of H₂O₂ in cells. It can thus be widely applied in biomedical research and in clinical trials being an advancement over other H₂O₂ detection techniques.

Production of Reactive Oxygen Species by Photosystem II as a Response to Light and Temperature Stress

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.

Production of Reactive Oxygen Species by Photosystem II as a Response to Light and Temperature Stress

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.