Fluorescent in vivo imaging of reactive oxygen species and redox potential in plants

Advances in Fluorescence-based Probes for Abiotic Stress Detection in Plants

Abiotic stress poses significant challenges to the ecological environment and global food security. Early and accurate diagnosis of abiotic stress is essential for modern agriculture. Recently, fluorescence sensing technology has emerged as a valuable tool for monitoring abiotic stress due to its ease of use and capability for spatiotemporal visualization. These probes specifically bind to abiotic stress biomarkers, facilitating the detection of stress responses and advancing related biological research. However, there is a lack of comprehensive reviews on fluorescence probe for abiotic stress, which limits progress in this area. This review outlines the biological markers of abiotic stress, discusses the types and design principles of fluorescence probe, and reviews research on detecting plant responses to such stress. Its goal is to inspire the rational design of fluorescence probe for plant bioimaging, promote early diagnosis of abiotic stress, and enhance the understanding of plant defense mechanisms at the molecular level, ultimately providing a scientific basis for stress management in agriculture.

Development of a near-infrared fluorescent probe for in situ monitoring of hydrogen peroxide in plants

In plants, hydrogen peroxide (H2O2), one of the significant reactive oxygen species, plays a dual function. Investigating its concentration is essential for understanding its production and scavenging mechanisms in plants. In this study, a near-infrared fluorescent probe (Cy-Bo) was developed, which is based on the hemicyanine compound. By introducing indole salts into the oxygenated anthraquinone structure, the conjugated system is expanded, enabling the probe to emit long-wavelength fluorescence in the near-infrared region, thereby minimizing interference from other biomolecules in plant tissues (λex = 650 nm, λem = 720 nm). As for the specific recognition of H2O2, the pinacol phenylborate ester was selected to be the recognition group. It shows good linearity (R2 = 0.998) in the concentration range of 0.5-100 μM, with a detection limit of 0.07 μM. Furthermore, this probe Cy-Bo has been used for in vivo fluorescence imaging in plants due to its good bio-penetration and in-situ imaging capabilities. The results reveal a significant increase in H2O2 concentration in Arabidopsis thaliana under progressively increasing drought, high-temperature, and salt stress. This tool provides a non-invasive, in situ imaging method for detecting H2O2 in plants, which has a fast response, easy operation, and high sensitivity. It enables visual monitoring of H2O2 fluctuations and aids in advancing physiological and pathological studies related to H2O2.

The salty tango of brine composition and UV photochemistry effects on Halobacterium salinarum cell envelope biosignature preservation

Hypersaline environments, including brines and brine inclusions of evaporite crystals, are currently of great interest due to their unique preservation properties for the search for terrestrial and potentially extraterrestrial biosignatures of ancient life. However, much is still unclear about the specific effects that dictate the preservation properties of brines. Here we present the first insights into the preservation of cell envelope fragments in brines, characterizing the relative contributions of brine composition, UV photochemistry, and cellular macromolecules on biosignature preservation. Cell envelopes from the model halophile Halobacterium salinarum were used to simulate dead microbial cellular remains in hypersaline environments based on life as we currently know it. Using different Early Earth and Mars analogue brines, we show that acidic and NaCl-dominated brine compositions are more predisposed to preserving complex biosignatures from UV degradation, but that the composition of the biological material also influences this preservation. Furthermore, a combinatory effect between chaotropicity and photochemistry occurs, with the relative importance of each being brine-specific. These results provide an experimental framework for biosignature detection in hypersaline environments, emphasizing the need for laboratory simulations to evaluate preservation properties of each potential brine environment, on Earth and elsewhere in the solar system.

Diverse Fluorescent Probe Concepts for Detection and Monitoring of Reactive Oxygen Species

World-wide research on reactive oxygen species (ROS) continues to reveal new information about the role and impact of ROS on human health and disease. ROS are generated in live cells as a byproduct of aerobic metabolism. Physiological concentrations of cellular ROS are important for signaling and homeostasis, but excessive generation of ROS causes apoptotic and necrotic cell death and various health disorders. Fluorescence technology is a powerful tool to detect, monitor, and image cellular ROS. The present review provides an overview of diverse organic dye-based fluorescent probe concepts that involve modifications of traditional fluorescent dyes utilizing basic principles of dye chemistry and photophysics. Fluorescence responses of the probes and their specificity towards ROS are discussed through analyses of their photophysical and photochemical parameters. We also provide an outlook on future directions of ROS-responsive fluorescent dyes, which could enable the design and development of advanced probes for gaining deeper insights into redox biology.

New insights on antibacterial mode of action of blue-light photoactivated berberine and curcumin-antibiotic combinations against Staphylococcus aureus

Antimicrobial photodynamic inactivation (aPDI), using photosensitisers in combination with antibiotics, is a promising multi-target strategy to address antibiotic resistance, particularly in wound infections. This study aimed to elucidate the antibacterial mode of action of combinations of berberine (Ber) or curcumin (Cur) with selected antibiotics (Ber-Ab or Cur-Ab) under blue light irradiation (420 nm) against Staphylococcus aureus, including methicillin-resistant (MRSA) and methicillin-susceptible (MSSA) strains. Multiple physiological parameters were assessed using complementary assays (fluorometry, epifluorescence microscopy, flame emission and atomic absorption spectroscopy, zeta potential, flow cytometry, and the plate agar method) to examine the effect on ROS production, membrane integrity, DNA damage, motility and virulence factors of S. aureus. Results indicated that blue light photoactivated Ber-Ab and Cur-Ab combinations led to substantial ROS generation, even at low concentrations, causing oxidative stress that severely impacted bacterial membrane integrity (approximately 90 % in MRSA and 40 % in MSSA). Membrane destabilization was further confirmed by elevated intercellular potassium release (≈ 2.00 and 2.40 µg/mL in MRSA and MSSA, respectively). Furthermore, significant DNA damage was observed in both strains (≈ 50 %). aPDI treatment with blue light also reduced S. aureus pathogenicity by impairing motility and inhibiting key virulence factors such as proteases, lipases, and gelatinases, all of which play key roles in the infectious process. Overall, Ber-Ab combinations demonstrated the highest efficacy across all parameters tested, highlighting for the first time the multi-target therapeutic potential of this phytochemical-based aPDI strategy to combat antibiotic-resistant S. aureus infections and improve wound infection treatment outcomes.

Identification of senescence rejuvenation mechanism of Magnolia officinalis extract including honokiol as a core ingredient

Reactive oxygen species (ROS) contribute to aging by mainly damaging cellular organelles and DNA. Although strategies to reduce ROS production have been proposed as important components of anti-aging therapy, effective mechanisms to lower ROS levels have not yet been identified. Here, we screened natural compounds frequently used as cosmetic ingredients to find substances that reduce ROS levels. Magnolia officinalis (M. officinalis) extract significantly lowered the levels of ROS in senescent fibroblasts. A novel mechanism by which M. officinalis extract restores mitochondrial function to reduce ROS, a byproduct of inefficient electron transport, was discovered. The reduction of ROS by M. officinalis extracts reversed senescence-associated phenotypes and skin aging. Then, honokiol was demonstrated as a core ingredient of M. officinalis extract that exhibits antioxidant effects. Honokiol functions as an oxygen radical scavenger through redox processes, also significantly reduced ROS levels by restoring mitochondrial function. In summary, our study identified a novel mechanism by which M. officinalis extract reverses aging and skin aging by reducing ROS through restoring mitochondrial function. These new findings will not only expand our understanding of aging and associated diseases, but also provide new approaches to anti-aging treatments.

Promising tools into oxidative stress: A review of non-rodent model organisms

Oxidative stress is a crucial concept in redox biology, and significant progress has been made in recent years. Excessive levels of reactive oxygen species (ROS) can lead to oxidative damage, heightening vulnerability to various diseases. By contrast, ROS maintained within a moderate range plays a role in regulating normal physiological metabolism. Choosing suitable animal models in a complex research context is critical for enhancing research efficacy. While rodents are frequently utilized in medical experiments, they pose challenges such as high costs and ethical considerations. Alternatively, non-rodent model organisms like zebrafish, Drosophila, and C. elegans offer promising avenues into oxidative stress research. These organisms boast advantages such as their small size, high reproduction rate, availability for live imaging, and ease of gene manipulation. This review highlights advancements in the detection of oxidative stress using non-rodent models. The oxidative homeostasis regulatory pathway, Kelch-like ECH-associated protein 1-Nuclear factor erythroid 2-related factor 2 (Keap1-Nrf2), is systematically reviewed alongside multiple regulation of Nrf2-centered pathways in different organisms. Ultimately, this review conducts a comprehensive comparative analysis of different model organisms and further explores the combination of novel techniques with non-rodents. This review aims to summarize state-of-the-art findings in oxidative stress research using non-rodents and to delineate future directions.

Assessment of the Antioxidant and Photoprotective Properties of Cornus mas L. Extracts on HDF, HaCaT and A375 Cells Exposed to UVA Radiation

The influence of UV radiation on skin discoloration, skin aging and the development of skin cancer is widely known. As a part of this study, the effect of extracts from three varieties of Cornus mas L. (C. mas L.) on skin cells exposed to UVA radiation was assessed. The analyses were performed on both normal and cancer skin cells. For this purpose, the potential photoprotective effects of the obtained extracts (aqueous and ethanolic) was assessed by performing two cytotoxicity tests (Alamar blue and Neutral red). Additionally, the antioxidant capacity was compared using three different assays. The 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) probe was used to evaluate the intracellular level of free radicals in cells exposed to the simultaneous action of UVA radiation and dogwood extracts. Additionally, the ability to inhibit excessive pigmentation was determined by assessing the inhibition of melanin formation and tyrosinase activity. The obtained results confirmed the strong antioxidant properties of dogwood extracts and their photoprotective effect on normal skin cells. The ability to inhibit the viability of melanoma cells was also observed. Additionally, a reduction in oxidative stress in skin cells exposed to UVA radiation and a strong inhibition of melanin formation and tyrosinase activity have been demonstrated. This study shows that dogwood extract could be a valuable cosmetic raw material that can play both a photoprotective and antihyperpigmentation role in cosmetic preparations.

Responses of Dunaliella sp. AL-1 to chromium and copper: Biochemical and physiological studies

Microalgae have gained recognition as versatile candidates for the remediation of heavy metals (HMs). This study investigated the biosorption potential of Dunaliella sp. AL1 for copper (Cu(II)) and hexavalent chromium (Cr(VI)) in aqueous solutions. The marine microalga Dunaliella sp. AL1 was exposed to half-sublethal concentrations of both metals in single and bimetallic systems, and responses in algal growth, oxidative stress, photosynthetic pigment production, and photosynthetic performance were evaluated. Cu and/or Cr exposure increased the generation of reactive oxygen species (ROS) in microalgae cells but did not impact algal growth. In terms of photosynthesis, there was a decrease in chlorophylls and carotenoids production in the microalgae culture treated with Cr, either alone or in combination with Cu. The study recorded promising metal removal efficiencies: 26.67%-20.11% for Cu and 94.99%-95.51% for Cr, in single and bimetallic systems, respectively. FTIR analysis revealed an affinity of Cu and Cr ions towards aliphatic/aldehyde C-H, N-H bending, and phosphate groups, suggesting the formation of complex bonds. Biochemical analysis of microalgae biomass collected after the removal of Cr alone or in combination with Cu showed a significant decrease in total carbohydrate content and soluble protein levels. Meanwhile, higher lipid accumulation was recorded and evidenced by BODIPY 505/515 staining. Fatty acid composition analysis by GC revealed a modulation in lipid composition, with a decrease in the ratio of unsaturated fatty acids (UFA) to saturated fatty acids (SFA), in response to Cu, Cr, and Cu-Cr exposure, indicating the suitability of the biomass for sustainable biofuel production.

Heat-stress-induced ROS in maize silks cause late pollen tube growth arrest and sterility

The reproductive phase of plants is highly sensitive to ambient temperature stresses. To investigate sensitivity of female reproductive organs in grass crops during the pollination phase, we exposed the elongated stigma (silk) of maize to ambient environment at the silking stage. Moderate heat stress causes cell death of silk hair cells but did not affect early pollen tube growth inside the silk. Late pollen tube growth arrest was observed, leading to sterility. Heat stress causes elevated levels of reactive oxygen species (ROS) in silks, whose levels can be reduced by scavengers partly restoring pollen tube growth and fertility. A number of biological processes including hydrogen peroxide catabolic processes and bHLH transcription factor genes are downregulated by heat stress, while some NAC transcription factor genes are strongly upregulated. In conclusion, this study now provides a basis to select genes for engineering heat-stress-tolerant grass crops during the pollination phase.

A practical guide to the discovery of biomolecules with biostimulant activity

The growing demand for sustainable solutions in agriculture, which are critical for crop productivity and food quality in the face of climate change and the need to reduce agrochemical usage, has brought biostimulants into the spotlight as valuable tools for regenerative agriculture. With their diverse biological activities, biostimulants can contribute to crop growth, nutrient use efficiency, and abiotic stress resilience, as well as to the restoration of soil health. Biomolecules include humic substances, protein lysates, phenolics, and carbohydrates have undergone thorough investigation because of their demonstrated biostimulant activities. Here, we review the process of the discovery and development of extract-based biostimulants, and propose a practical step-by-step pipeline that starts with initial identification of biomolecules, followed by extraction and isolation, determination of bioactivity, identification of active compound(s), elucidation of mechanisms, formulation, and assessment of effectiveness. The different steps generate a roadmap that aims to expedite the transfer of interdisciplinary knowledge from laboratory-scale studies to pilot-scale production in practical scenarios that are aligned with the prevailing regulatory frameworks.

Reactive oxygen species: Multidimensional regulators of plant adaptation to abiotic stress and development

Reactive oxygen species (ROS) are produced as undesirable by-products of metabolism in various cellular compartments, especially in response to unfavorable environmental conditions, throughout the life cycle of plants. Stress-induced ROS production disrupts normal cellular function and leads to oxidative damage. To cope with excessive ROS, plants are equipped with a sophisticated antioxidative defense system consisting of enzymatic and non-enzymatic components that scavenge ROS or inhibit their harmful effects on biomolecules. Nonetheless, when maintained at relatively low levels, ROS act as signaling molecules that regulate plant growth, development, and adaptation to adverse conditions. Here, we provide an overview of current approaches for detecting ROS. We also discuss recent advances in understanding ROS signaling, ROS metabolism, and the roles of ROS in plant growth and responses to various abiotic stresses.

Tonic ErbB signaling underlies TGFβ-induced activation of ERK and is required for lens cell epithelial to myofibroblast transition

Fibrosis is a major, but incompletely understood, component of many diseases. The most common vision-disrupting complication of cataract surgery involves differentiation of residual lens cells into myofibroblasts. In serum-free primary cultures of lens epithelial cells (DCDMLs), inhibitors of either ERK or of ErbB signaling prevent TGFβ from upregulating both early (fibronectin) and late (αSMA) markers of myofibroblast differentiation. TGFβ stimulates ERK in DCDMLs within 1.5 h. Kinase inhibitors of ErbBs, but not of several other growth factor receptors in lens cells, reduce phospho ERK to below basal levels in the absence or presence of TGFβ. This effect is attributable to constitutive ErbB activity playing a major role in regulating the basal levels pERK. Additional studies support a model in which TGFβ-generated reactive oxygen species serve to indirectly amplify ERK signaling downstream of tonically active ErbBs to mediate myofibroblast differentiation. ERK activity is in turn essential for expression of ErbB1 and ErbB2, major inducers of ERK signaling. By mechanistically linking TGFβ, ErbB, and ERK signaling to myofibroblast differentiation, our data elucidate a new role for ErbBs in fibrosis and reveal a novel mode by which TGFβ directs lens cell fate.

Characterization of cellular toxicity induced by sub-lethal inorganic mercury in the marine microalgae Chlorococcum dorsiventrale isolated from a metal-polluted coastal site

Mercury (Hg) is a global pollutant that affects numerous marine aquatic ecosystems. We isolated Chlorococcum dorsiventrale Ch-UB5 microalga from coastal areas of Tunisia suffering from metal pollution and analyzed its tolerance to Hg. This strain accumulated substantial amounts of Hg and was able to remove up to 95% of added metal after 24 and 72 h in axenic cultures. Mercury led to lesser biomass growth, higher cell aggregation, significant inhibition of photochemical activity, and appearance of oxidative stress and altered redox enzymatic activities, with proliferation of starch granules and neutral lipids vesicles. Such changes matched the biomolecular profile observed using Fourier Transformed Infrared spectroscopy, with remarkable spectral changes corresponding to lipids, proteins and carbohydrates. C. dorsiventrale accumulated the chloroplastic heat shock protein HSP70B and the autophagy-related ATG8 protein, probably to counteract the toxic effects of Hg. However, long-term treatments (72 h) usually resulted in poorer physiological and metabolic responses, associated with acute stress. C. dorsiventrale has potential use for Hg phycoremediation in marine ecosystems, with the ability to accumulating energetic reserves that could be used for biofuel production, supporting the notion of using of C. dorsiventrale for sustainable green chemistry in parallel to metal removal.

Fluorescent-Dye-Labeled Amino Acids for Real-Time Imaging in Arabidopsis thaliana

Amino acid is the main transport form of reduced nitrogen in plants. To investigate the uptake and source–sink translocation process of plants to help understand their physiological roles and transport mechanisms, we designed and synthesized three fluorescent-dye-labeled amino acids as tools to visualize amino acid transportation in Arabidopsis thaliana; these amino acids consist of amino acids linked to the fluorophore nitrobenzoxadiazole (NBD) with excellent optical properties. Furthermore, we incubated Arabidopsis thaliana with these NBD fluorescent-dye-labeled amino acids for real-time imaging along with fluorescence enhancement for 24 h. The results showed that Arabidopsis thaliana could absorb them directly from the roots to the leaves. Therefore, our fluorescent-dye-labeled amino acids provide a de novo tool and strategy for visualizing amino acid absorption and transportation in plants.

Live Imaging in Planarians: Immobilization and Real-Time Visualization of Reactive Oxygen Species

Imaging of living animals allows the study of metabolic processes in relation to cellular structures or larger functional entities. To enable in vivo imaging during long-term time-lapses in planarians, we combined and optimized existing protocols, resulting in an easily reproducible and inexpensive procedure. Immobilization with low-melting-point agarose eliminates the use of anesthetics, avoids interfering with the animal during imaging-functionally or physically-and allows recovering the organisms after the imaging procedure. As an example, we used the immobilization workflow to image the highly dynamic and fast-changing reactive oxygen species (ROS) in living animals. These reactive signaling molecules can only be studied in vivo and mapping their location and dynamics during different physiological conditions is crucial to understand their role in developmental processes and regeneration. In the current protocol, we describe both the immobilization and ROS detection procedure. We used the intensity of the signals together with pharmacological inhibitors to validate the signal specificity and to distinguish it from the autofluorescent nature of the planarian.

Reactive oxygen species function as signaling molecules in controlling plant development and hormonal responses

Reactive oxygen species (ROS) serve as second messengers in plant signaling pathways to remodel plant growth and development. New insights into how enzymatic ROS-producing machinery is regulated by hormones or localized during development have provided a framework for understanding the mechanisms that control ROS accumulation patterns. Signaling-mediated increases in ROS can then modulate the activity of proteins through reversible oxidative modification of specific cysteine residues. Plants also control the synthesis of antioxidants, including plant-specialized metabolites, to further define when, where, and how much ROS accumulate. The availability of sophisticated imaging capabilities, combined with a growing tool kit of ROS detection technologies, particularly genetically encoded biosensors, sets the stage for improved understanding of ROS as signaling molecules.

Intertwined Roles of Reactive Oxygen Species and Salicylic Acid Signaling Are Crucial for the Plant Response to Biotic Stress

One of the earliest hallmarks of plant immune response is production of reactive oxygen species (ROS) in different subcellular compartments, which regulate plant immunity. A suitable equilibrium, which is crucial to prevent ROS overaccumulation leading to oxidative stress, is maintained by salicylic acid (SA), a chief regulator of ROS. However, ROS not only act downstream of SA signaling, but are also proposed to be a central component of a self-amplifying loop that regulates SA signaling as well as the interaction balance between different phytohormones. The exact role of this crosstalk, the position where SA interferes with ROS signaling and ROS interferes with SA signaling and the outcome of this regulation, depend on the origin of ROS but also on the pathosystem. The precise spatiotemporal regulation of organelle-specific ROS and SA levels determine the effectiveness of pathogen arrest and is therefore crucial for a successful immune response. However, the regulatory interplay behind still remains poorly understood, as up until now, the role of organelle-specific ROS and SA in hypersensitive response (HR)-conferred resistance has mostly been studied by altering the level of a single component. In order to address these aspects, a sophisticated combination of research methods for monitoring the spatiotemporal dynamics of key players and transcriptional activity in plants is needed and will most probably consist of biosensors and precision transcriptomics.

Inhibition of peroxidases and oxidoreductases is crucial for avoiding false-positive reactions in the localization of reactive oxygen species in intact barley root tips

NBT and HE may be efficiently used for the detection of superoxide, while DCDHF-DA and DHR123 for the detection of peroxynitrite in intact barley root tips, only if PRXs and oxidoreductases are inhibited to avoid false-positive reactions. Strong peroxidase (PRX) and oxidoreductase activities were observed in the barley root tips that were markedly inhibited by NaN₃. Rapid and strong nitro-blue tetrazolium chloride (NBT) reduction is associated mainly with the vital functions of root cells but not with superoxide formation. In turn, the inhibition of root surface redox activity by NaN₃ strongly reduced the formation of formazan, but its slight accumulation, observed in the root elongation zone, was a result of NADPH oxidase-mediated apoplastic superoxide formation. A longer staining time period with NBT was required for the detection of antimycin A-mediated superoxide formation inside the cells. This antimycin A-induced superoxide was clearly detectable by hydroethidine (HE) after the inhibition of PRXs by NaN₃, and it was restricted into the root transition zone. TEMPOL, a superoxide scavenger, strongly inhibited both NBT reduction and HE oxidation in the presence of NaN₃. Similarly, the DCDHF-DA and DHR123 oxidation was markedly reduced after the inhibition of apoplastic PRXs by NaN₃ and was detectable mainly in the root transition zone. This fluorescence signal was not influenced by the application of pyruvate but was strongly reduced by urea, a peroxynitrite scavenger. The presented results suggest that if the root PRXs and oxidoreductases are inhibited, both NBT and HE detect mainly superoxide, whereas both DCDHF-DA and DHR123 may be efficiently used for the detection of peroxynitrite in intact barley root tips. The inhibition of PRXs and oxidoreductases is crucial for avoiding false-positive reactions in the localization of reactive oxygen species in the intact barley root tip.

Measuring ROS and redox markers in plant cells

Reactive oxygen species (ROS) are produced throughout plant cells as a by-product of electron transfer processes. While highly oxidative and potentially damaging to a range of biomolecules, there exists a suite of ROS-scavenging antioxidant strategies that maintain a redox equilibrium. This balance can be disrupted in the event of cellular stress leading to increased ROS levels, which can act as a useful stress signal but, in excess, can result in cell damage and death. As crop plants become exposed to greater degrees of multiple stresses due to climate change, efforts are ongoing to engineer plants with greater stress tolerance. It is therefore important to understand the pathways underpinning ROS-mediated signalling and damage, both through measuring ROS themselves and other indicators of redox imbalance. The highly reactive and transient nature of ROS makes this challenging to achieve, particularly in a way that is specific to individual ROS species. In this review, we describe the range of chemical and biological tools and techniques currently available for ROS and redox marker measurement in plant cells and tissues. We discuss the limitations inherent in current methodology and opportunities for advancement.

The latest HyPe(r) in plant H2O2 biosensing

HyPer7 senses minute amounts of H₂O₂ independent of pH and the glutathione redox potential and enables detection of physiological H₂O₂ fluxes within the cytosol and between subcellular compartments.

Electroanalysis at a Single Giant Vesicle Generating Enzymatically a Reactive Oxygen Species

In the framework of artificial or synthetic cell development, giant liposomes are common basic structures. Their enclosed membrane allows encapsulating proteins, DNA, reactants, etc., while its phospholipid nature allows some exchanges with the surrounding medium. Biochemical reactions induced inside giant liposomes or vesicles are often monitored or imaged by fluorescence microscopy techniques. Here, we show that electrochemistry performed with ultramicroelectrodes is perfectly suitable to monitor an enzymatic reaction occurring in a single giant unilamellar vesicle. Glucose oxidase (GOx) was microinjected inside individual vesicles containing 1 mM glucose. H₂O₂ was thus generated in the vesicle and progressively diffused across the membrane toward the surrounding environment. An ultramicroelectrode sensitive to H₂O₂ (black platinum-modified carbon surface) was placed next to the membrane and provided a direct detection of the hydrogen peroxide flux generated by the enzyme activity. Electrochemistry offered a highly sensitive (in situ detection), selective (potential applied at the electrode), time-resolved analysis (chronoamperometry) of the GOx activity over an hour duration, without modifying the internal giant unilamellar vesicles (GUV) medium. These results demonstrate that electroanalysis with microsensors is well adapted and complementary to fluorescence microscopy to sense enzymatic activities, for instance, generating reactive oxygen species, at single vesicles further used to develop artificial cells.

Rhizobium leguminosarum Glutathione Peroxidase Is Essential for Oxidative Stress Resistance and Efficient Nodulation

Glutathione (GSH) plays a key role in regulating the cellular Redox Homeostasis, and appears to be essential for initiation and development of root nodules. Glutathione peroxidase (Gpx) catalyzes the reduction of H₂O₂ and organic hydroperoxides by oxidation of GSH to oxidized GSH (GSSG), which in turn is reduced by glutathione reductase (GR). However, it has not been determined whether the Rhizobium leguminosarum Gpx or GR is required during symbiotic interactions with pea. To characterize the role of glutathione-dependent enzymes in the symbiotic process, single and double mutants were made in gpxA (encoding glutathione peroxidase) and gshR (encoding glutathione reductase) genes. All the mutations did not affect the rhizobial growth, but they increased the sensitivity of R. leguminosarum strains to H₂O₂. Mutant in GpxA had no effect on intracellular GSH levels, but can increase the expression of the catalase genes. The gshR mutant can induce the formation of normal nodules, while the gpxA single and double mutants exhibited a nodulation phenotype coupled to more than 50% reduction in the nitrogen fixation capacity, these defects in nodulation were characterized by the formation of ineffective nodules. In addition, the gpxA and gshR double mutant was severely impaired in rhizosphere colonization and competition. Quantitative proteomics using the TMT labeling method was applied to study the differential expression of proteins in bacteroids isolated from pea root nodules. A total of 27 differentially expressed proteins were identified in these root bacteroids including twenty down-regulated and seven up-regulated proteins. By sorting the down-regulated proteins, eight are transporter proteins, seven are dehydrogenase, deoxygenase, oxidase, and hydrolase. Moreover, three down-regulating proteins are directly involved in nodule process.

Morphological, Physiological and Molecular Markers for Salt-Stressed Plants

Plant growth and development is adversely affected by different kind of stresses. One of the major abiotic stresses, salinity, causes complex changes in plants by influencing the interactions of genes. The modulated genetic regulation perturbs metabolic balance, which may alter plant's physiology and eventually causing yield losses. To improve agricultural output, researchers have concentrated on identification, characterization and selection of salt tolerant varieties and genotypes, although, most of these varieties are less adopted for commercial production. Nowadays, phenotyping plants through Machine learning (deep learning) approaches that analyze the images of plant leaves to predict biotic and abiotic damage on plant leaves have increased. Here, we review salinity stress related markers on molecular, physiological and morphological levels for crops such as maize, rice, ryegrass, tomato, salicornia, wheat and model plant, Arabidopsis. The combined analysis of data from stress markers on different levels together with image data are important for understanding the impact of salt stress on plants.

Reactive Oxygen Species Link Gene Regulatory Networks During Arabidopsis Root Development

Plant development under altered nutritional status and environmental conditions and during attack from invaders is highly regulated by plant hormones at the molecular level by various signaling pathways. Previously, reactive oxygen species (ROS) were believed to be harmful as they cause oxidative damage to cells; however, in the last decade, the essential role of ROS as signaling molecules regulating plant growth has been revealed. Plant roots accumulate relatively high levels of ROS, and thus, maintaining ROS homeostasis, which has been shown to regulate the balance between cell proliferation and differentiation at the root tip, is important for proper root growth. However, when the balance is disturbed, plants are unable to respond to the changes in the surrounding conditions and cannot grow and survive. Moreover, ROS control cell expansion and cell differentiation processes such as root hair formation and lateral root development. In these processes, the transcription factor-mediated gene expression network is important downstream of ROS. Although ROS can independently regulate root growth to some extent, a complex crosstalk occurs between ROS and other signaling molecules. Hormone signals are known to regulate root growth, and ROS are thought to merge with these signals. In fact, the crosstalk between ROS and these hormones has been elucidated, and the central transcription factors that act as a hub between these signals have been identified. In addition, ROS are known to act as important signaling factors in plant immune responses; however, how they also regulate plant growth is not clear. Recent studies have strongly indicated that ROS link these two events. In this review, we describe and discuss the role of ROS signaling in root development, with a particular focus on transcriptional regulation. We also summarize the crosstalk with other signals and discuss the importance of ROS as signaling molecules for plant root development.

Reactive Oxygen Species in Plant Interactions With Aphids

Reactive oxygen species (ROS) such as hydrogen peroxide and superoxide are produced in plants in response to many biotic and abiotic stressors, and they can enhance stress adaptation in certain circumstances or mediate symptom development in others. The roles of ROS in plant-pathogen interactions have been extensively studied, but far less is known about their involvement in plant-insect interactions. A growing body of evidence, however, indicates that ROS accumulate in response to aphids, an economically damaging group of phloem-feeding insects. This review will cover the current state of knowledge about when, where, and how ROS accumulate in response to aphids, which salivary effectors modify ROS levels in plants, and how microbial associates influence ROS induction by aphids. We will also explore the potential adaptive significance of intra- and extracellular oxidative responses to aphid infestation in compatible and incompatible interactions and highlight knowledge gaps that deserve further exploration.

Vascular Bundles Mediate Systemic Reactive Oxygen Signaling during Light Stress

Systemic signaling and systemic acquired acclimation (SAA) are essential for plant survival during episodes of environmental stress. Recent studies highlighted a key role for reactive oxygen species (ROS) signaling in mediating systemic responses and SAA during light stress in Arabidopsis (Arabidopsis thaliana). These studies further identified the RESPIRATORY BURST OXIDASE HOMOLOG D (RBOHD) protein as a key player in mediating rapid systemic ROS responses. Here, we report that tissue-specific expression of RBOHD in phloem or xylem parenchyma cells of the rbohD mutant restores systemic ROS signaling, systemic stress-response transcript expression, and SAA to a local treatment of light stress. We further demonstrate that RBOHD and RBOHF are both required for local and systemic ROS signaling at the vascular bundles of Arabidopsis. Taken together, our findings highlight a key role for RBOHD-driven ROS production at the vascular bundles of Arabidopsis in mediating light stress-induced systemic signaling and SAA. In addition, they suggest that the integration of ROS, calcium, electric, and hydraulic signals, during systemic signaling, occurs at the vascular bundles.

Lipid Peroxidation Assay Using BODIPY-Phenylbutadiene Probes: A Methodological Overview

The assessment of reactive oxygen species has increasing importance in biomedical sciences, due to their biological role in signaling pathways and induction of cell damage at low and high concentrations, respectively. Detection of lipid peroxidation with sensing probes such as some BODIPY dyes has now wide application in studies using fluorescent microplate readers, flow cytometry, and fluorescence microscopy. Two phenylbutadiene derivatives of BODIPY are commonly used as peroxidation probes, non-oxidized probes and oxidized products giving red and green fluorescence, respectively. Peculiar features of lipoperoxidation and BODIPY dye properties make this assessment a rather complex process, not exempt of doubts and troubles. Color changes and fluorescence fading that are not due to lipid peroxidation must be taken into account to avoid misleading results. As a characteristic feature of lipoperoxidation is the propagation of peroxyl radicals, pitfalls and advantages of a delayed detection by BODIPY probes should be considered.

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.

Reactive oxygen species detection-approaches in plants: Insights into genetically encoded FRET-based sensors

The generation of reactive oxygen species (ROS) (and their reaction products) in abiotic stressed plants can be simultaneous. Hence, it is very difficult to establish individual roles of ROS (and their reaction products) in plants particularly under abiotic stress conditions. It is highly imperative to detect ROS (and their reaction products) and ascertain their role in vivo and also to point their optimal level in order to unveil exact relation of ROS (and their reaction products) with the major components of ROS-controlling systems. Förster Resonance Energy Transfer (FRET) technology enables us with high potential for monitoring and quantification of ROS and redox variations, avoiding some of the obstacles presented by small-molecule fluorescent dyes. This paper aims to: (i) introduce ROS and overview ROS-chemistry and ROS-accrued major damages to major biomolecules; (ii) highlight invasive and non-invasive approaches for the detection of ROS (and their reaction products); (iii) appraise literature available on genetically encoded ROS (and their reaction products)-sensors based on FRET technology, and (iv) enlighten so far unexplored aspects in the current context. The studies integrating the outcomes of the FRET-based ROS-detection approaches with OMICS sciences (genetics, genomics, proteomics, and metabolomics) would enlighten major insights into real-time ROS and redox dynamics, and their signaling at cellular and subcellular levels in living cells.

Illuminating human disease: The potential of in vivo imaging for preclinical research and diagnostics

New in vivo imaging technologies, including optical methods to observe biological processes in real time, show great promise for preclinical research and diagnostics of human diseases.

Selective Immobilization of Fluorescent Proteins for the Fabrication of Photoactive Materials

The immobilization of fluorescent proteins is a key technology enabling to fabricate a new generation of photoactive materials with potential technological applications. Herein we have exploited superfolder green (sGFP) and red (RFP) fluorescent proteins expressed with different polypeptide tags. We fused these fluorescent proteins to His-tags to immobilize them on graphene 3D hydrogels, and Cys-tags to immobilize them on porous microparticles activated with either epoxy or disulfide groups and with Lys-tags to immobilize them on upconverting nanoparticles functionalized with carboxylic groups. Genetically programming sGFP and RFP with Cys-tag and His-tag, respectively, allowed tuning the protein spatial organization either across the porous structure of two microbeads with different functional groups (agarose-based materials activated with metal chelates and epoxy-methacrylate materials) or across the surface of a single microbead functionalized with both metal-chelates and disulfide groups. By using different polypeptide tags, we can control the attachment chemistry but also the localization of the fluorescent proteins across the material surfaces. The resulting photoactive material formed by His-RFP immobilized on graphene hydrogels has been tested as pH indicator to measure pH changes in the alkaline region, although the immobilized fluorescent protein exhibited a narrower dynamic range to measure pH than the soluble fluorescent protein. Likewise, the immobilization of Lys-sGFP on alginate-coated upconverting nanoparticles enabled the infrared excitation of the fluorescent protein to be used as a green light emitter. These novel photoactive biomaterials open new avenues for innovative technological developments towards the fabrication of biosensors and photonic devices.

Disruption of putative short-chain acyl-CoA dehydrogenases compromised free radical scavenging, conidiogenesis, and pathogenesis of Magnaporthe oryzae

Short-chain acyl-CoA dehydrogenase (Scad) mediated β-oxidation serves as the fastest route for generating essential energies required to support the survival of organisms under stress or starvation. In this study, we identified three putative SCAD genes in the genome of the globally destructive rice blast pathogen Magnaporthe oryzae, named as MoSCAD1, MoSCAD2, and MoSCAD3. To elucidate their function, we deployed targeted gene deletion strategy to investigate individual and the combined influence of MoSCAD genes on growth, stress tolerance, conidiation and pathogenicity of the rice blast fungus. First, localization and co-localization results obtained from this study showed that MoScad1 localizes to the endoplasmic reticulum (ER), MoScad2 localizes exclusively to the mitochondria while MoScad3 partially localizes to the mitochondria and peroxisome at all developmental stages of M. oryzae. Results obtained from this investigation showed that the deletion of MoSCAD1 and MoSCAD2 caused a minimal but significant reduction in the growth of ΔMoscad1 and ΔMoscad2 strains, while, growth characteristics exhibited by the ΔMoscad3 strain was similar to the wild-type strain. Furthermore, we observed that deletion of MoSCAD2 resulted in drastic reduction in conidiation, delayed conidia germination, triggered the development of abnormal appressorium and suppressed host penetration and colonization efficiencies of the ΔMoscad1 strain. This study provides first material evidence confirming the possible existence of ER β-oxidation pathway in M. oryzae. We also infer that mitochondria β-oxidation rather than peroxisomal and ER β-oxidation play an essential role in the vegetative growth, conidiation, appressorial morphogenesis and progression of pathogenesis in M. oryzae.

Quantitative ROS bioreporters: A robust toolkit for studying biological roles of ROS in response to abiotic and biotic stresses

While the accumulation of reactive oxygen species (ROS) through spontaneous generation or as the by-products of aerobic metabolism can be toxic to plants, recent findings demonstrate that ROS act as signaling molecules that play a critical role in adapting to various stress conditions. Tight regulation of ROS homeostasis is required to adapt to stress and survive, yet in vivo spatiotemporal information of ROS dynamics are still largely undefined. In order to understand the dynamics of ROS changes and their biological function in adapting to stresses, two quantitative ROS transcription-based bioreporters were developed. These reporters use ROS-responsive promoters from RBOHD or ZAT12 to drive green fluorescent protein (GFP) expression. The resulting GFP expression is compared to a constitutively expressed mCherry that is contained on the same cassette with the ROS-responsive promoter: This allows for the generation of ratiometric images comparing ROS changes (GFP) to the constitutively expressed mCherry. Both reporters were used to assess ROS levels to oxidative stress, salt stress, and the pathogen defense elicitor flg22. These bioreporters showed increases in the ratio values of GFP to mCherry signals between 10 and 30 min poststress application. Such stress-associated ROS signals correlated with the induction of abiotic/biotic stress responsive markers such as RbohD, ZAT12, SOS2 and PR5 suggesting these ROS bioreporters provide a robust indicator of increased ROS related to stress responses. Based upon the spatiotemporal response patterns of signal increase, ZAT12 promoter-dependent ROS (Zat12p-ROS) bioreporter appears to be suitable for cellular mapping of ROS changes in response to abiotic and biotic stresses.

The fluorescent protein sensor roGFP2-Orp1 monitors in vivo H2 O2 and thiol redox integration and elucidates intracellular H2 O2 dynamics during elicitor-induced oxidative burst in Arabidopsis

Hydrogen peroxide (H₂ O₂ ) is ubiquitous in cells and at the centre of developmental programmes and environmental responses. Its chemistry in cells makes H₂ O₂ notoriously hard to detect dynamically, specifically and at high resolution. Genetically encoded sensors overcome persistent shortcomings, but pH sensitivity, silencing of expression and a limited concept of sensor behaviour in vivo have hampered any meaningful H₂ O₂ sensing in living plants. We established H₂ O₂ monitoring in the cytosol and the mitochondria of Arabidopsis with the fusion protein roGFP2-Orp1 using confocal microscopy and multiwell fluorimetry. We confirmed sensor oxidation by H₂ O₂ , show insensitivity to physiological pH changes, and demonstrated that glutathione dominates sensor reduction in vivo. We showed the responsiveness of the sensor to exogenous H₂ O₂ , pharmacologically-induced H₂ O₂ release, and genetic interference with the antioxidant machinery in living Arabidopsis tissues. Monitoring intracellular H₂ O₂ dynamics in response to elicitor exposure reveals the late and prolonged impact of the oxidative burst in the cytosol that is modified in redox mutants. We provided a well defined toolkit for H₂ O₂ monitoring in planta and showed that intracellular H₂ O₂ measurements only carry meaning in the context of the endogenous thiol redox systems. This opens new possibilities to dissect plant H₂ O₂ dynamics and redox regulation, including intracellular NADPH oxidase-mediated ROS signalling.