Formation of singlet oxygen and protection against its oxidative damage in Photosystem II under abiotic stress

Effects of Drought Stress on Abscisic Acid Content and Its Related Transcripts in Allium fistulosum-A. cepa Monosomic Addition Lines

Climate change has resulted in an increased demand for Japanese bunching onions (Allium fistulosum L., genomes FF) with drought resistance. A complete set of alien monosomic addition lines of A. fistulosum with extra chromosomes from shallot (A. cepa L. Aggregatum group, AA), represented as FF + 1A-FF + 8A, displays a variety of phenotypes that significantly differ from those of the recipient species. In this study, we investigated the impact of drought stress on abscisic acid (ABA) and its precursor, β-carotene, utilizing this complete set. In addition, we analyzed the expression levels of genes related to ABA biosynthesis, catabolism, and drought stress signal transduction in FF + 1A and FF + 6A, which show characteristic variations in ABA accumulation. A number of unigenes related to ABA were selected through a database using Allium TDB. Under drought conditions, FF + 1A exhibited significantly higher ABA and β-carotene content compared with FF. Additionally, the expression levels of all ABA-related genes in FF + 1A were higher than those in FF. These results indicate that the addition of chromosome 1A from shallot caused the high expression of ABA biosynthesis genes, leading to increased levels of ABA accumulation. Therefore, it is expected that the introduction of alien genes from the shallot will upwardly modify ABA content, which is directly related to stomatal closure, leading to drought stress tolerance in FF.

Singlet oxygen signalling and its potential roles in plant biotic interactions

Singlet oxygen (SO) is among the most potent reactive oxygen species, and readily oxidizes proteins, lipids and DNA. It can be generated at the plant surface by phototoxins in the epidermis, acting as a direct defense against pathogens and herbivores (including humans). SO can also accumulate within mitochondria, peroxisomes, cytosol and the nucleus through multiple enzymatic and nonenzymatic processes. However, the majority of research on intracellular SO generation in plants has focused on transfer of light energy to triplet oxygen by photopigments from the chloroplast. SO accumulates in response to diverse stresses that perturb chloroplast metabolism, and while its high reactivity limits diffusion distances, it participates in retrograde signalling through the EXECUTER1 sensor, generation of carotenoid metabolites and possibly other unknown pathways. SO thereby reprogrammes nuclear gene expression and modulates hormone signalling and programmed cell death. While SO signalling has long been known to regulate plant responses to high-light stress, recent literature also suggests a role in plant interactions with insects, bacteria and fungi. The goals of this review are to provide a brief overview of SO, summarize evidence for its involvement in biotic stress responses and discuss future directions for the study of SO in defense signalling.

Are tomato plants co-exposed to heat and salinity able to ensure a proper carbon metabolism? - An insight into the photosynthetic hub

Abiotic stress combinations, such as high temperatures and soil/water salinization, severely threaten crop productivity worldwide. In this work, an integrative insight into the photosynthetic metabolism of tomato plants subjected to salt (100 mM NaCl) and/or heat (42 °C; 4 h/day) was performed. After three weeks, the stress combination led to more severe consequences on growth and photosynthetic pigments than the individual stresses. Regarding the photochemical efficiency, transcript accumulation and protein content of major actors (CP47 and D1) were depleted in all stressed plants, although the overall photochemical yield was not negatively affected under the co-exposure. Gas-exchange studies revealed to be mostly affected by salt (single or combined), which harshly compromised carbon assimilation. Additionally, transcript levels of stress-responsive genes (e.g., HsfA1 and NHX2) were differentially modulated by the single and combined treatments, suggesting the activation of stress-signature responses. Overall, by gathering an insightful overview of the main regulatory hub of photosynthesis, we show that the impacts on the carbon metabolism coming from the combination of heat and salinity, two major conditioners of crop yields, were not harsher than those of single stresses, indicating that the growth impairment might be attributed to a proficient distribution of resources towards defense mechanisms.

Astaxanthin: Past, Present, and Future

Astaxanthin (AX), a lipid-soluble pigment belonging to the xanthophyll carotenoids family, has recently garnered significant attention due to its unique physical properties, biochemical attributes, and physiological effects. Originally recognized primarily for its role in imparting the characteristic red-pink color to various organisms, AX is currently experiencing a surge in interest and research. The growing body of literature in this field predominantly focuses on AXs distinctive bioactivities and properties. However, the potential of algae-derived AX as a solution to various global environmental and societal challenges that threaten life on our planet has not received extensive attention. Furthermore, the historical context and the role of AX in nature, as well as its significance in diverse cultures and traditional health practices, have not been comprehensively explored in previous works. This review article embarks on a comprehensive journey through the history leading up to the present, offering insights into the discovery of AX, its chemical and physical attributes, distribution in organisms, and biosynthesis. Additionally, it delves into the intricate realm of health benefits, biofunctional characteristics, and the current market status of AX. By encompassing these multifaceted aspects, this review aims to provide readers with a more profound understanding and a robust foundation for future scientific endeavors directed at addressing societal needs for sustainable nutritional and medicinal solutions. An updated summary of AXs health benefits, its present market status, and potential future applications are also included for a well-rounded perspective.

IGFBP1 Sustains Cell Survival during Spatially-Confined Migration and Promotes Tumor Metastasis

Cell migration is a pivotal step in metastatic process, which requires cancer cells to navigate a complex spatially-confined environment, including tracks within blood vessels and in the vasculature of target organs. Here it is shown that during spatially-confined migration, the expression of insulin-like growth factor-binding protein 1 (IGFBP1) is upregulated in tumor cells. Secreted IGFBP1 inhibits AKT1-mediated phosphorylation of mitochondrial superoxide dismutase (SOD2) serine (S) 27 and enhances SOD2 activity. Enhanced SOD2 attenuates mitochondrial reactive oxygen species (ROS) accumulation in confined cells, which supports tumor cell survival in blood vessels of lung tissues, thereby accelerating tumor metastasis in mice. The levels of blood IGFBP1 correlate with metastatic recurrence of lung cancer patients. This finding reveals a unique mechanism by which IGFBP1 sustains cell survival during confined migration by enhancing mitochondrial ROS detoxification, thereby promoting tumor metastasis.

Proton transfer triggered in-situ construction of C=N active site to activate PMS for efficient autocatalytic degradation of low-carbon fatty amine

Removal of low-carbon fatty amines (LCFAs) in wastewater treatment poses a significant technical challenge due to their small molecular size, high polarity, high bond dissociation energy, electron deficiency, and poor biodegradability. Moreover, their low Brønsted acidity deteriorates this issue. To address this problem, we have developed a novel base-induced autocatalytic technique for the highly efficient removal of a model pollutant, dimethylamine (DMA), in a homogeneous peroxymonosulfate (PMS) system. A high reaction rate constant of 0.32 min^-1 and almost complete removal of DMA within 12 min are achieved. Multi-scaled characterizations and theoretical calculations reveal that the in situ constructed C=N bond as the crucial active site activates PMS to produce abundant ¹O₂. Subsequently, ¹O₂ oxidizes DMA through multiple H-abstractions, accompanied by the generation of another C=N structure, thus achieving the autocatalytic cycle of pollutant. During this process, base-induced proton transfers of pollutant and oxidant are essential prerequisites for C=N fabrication. A relevant mechanism of autocatalytic degradation is unraveled and further supported by DFT calculations at the molecular level. Various assessments indicate that this self-catalytic technique exhibits a reduced toxicity and volatility process, and a low treatment cost (0.47 $/m³). This technology has strong environmental tolerance, especially for the high concentrations of chlorine ion (1775 ppm) and humic acid (50 ppm). Moreover, it not only exhibits excellent degradation performance for different amine organics but also for the coexisting common pollutants including ofloxacin, phenol, and sulforaphane. These results fully demonstrate the superiority of the proposed strategy for practical application in wastewater treatment. Overall, this autocatalysis technology based on the in-situ construction of metal-free active site by regulating proton transfer will provide a brand-new strategy for environmental remediation.

Photo-chemical aspects of iron complexes exhibiting photo-activated chemotherapy (PACT)

Iron is the trace element of natural selection by the biological systems due to its versatile coordination chemistry, and is recently explored for medicinal and diagnostic applications. Photo-activated states of iron complexes exhibiting substitution, dissociation, isomerization reactions, intramolecular redox reactions or energy transfer to other molecules have attracted the attention across the globe for the potent applications in photo-chemotherapy. There is a significant advancement on the development of iron-based complexes for photochemotherapeutic applications. Here in we reviewed the photo-activated states and photochemistry of iron complexes, and recent advances made in the area of photochemotherapy of iron complexes relevant to the photochemistry of iron complexes.

Viable protoplast formation of the coral endosymbiont alga Symbiodinium spp. in a microfluidics platform

Symbiodiniaceae is an important dinoflagellate family which lives in endosymbiosis with reef invertebrates, including coral polyps, making them central to the holobiont. With coral reefs currently under extreme threat from climate change, there is a pressing need to improve our understanding on the stress tolerance and stress avoidance mechanisms of Symbiodinium spp. Reactive oxygen species (ROS) such as singlet oxygen are central players in mediating various stress responses; however, the detection of ROS using specific dyes is still far from definitive in intact Symbiodinium cells due to the hindrance of uptake of certain fluorescent dyes because of the presence of the cell wall. Protoplast technology provides a promising platform for studying oxidative stress with the main advantage of removed cell wall, however the preparation of viable protoplasts remains a significant challenge. Previous studies have successfully applied cellulose-based protoplast preparation in Symbiodiniaceae; however, the protoplast formation and regeneration process was found to be suboptimal. Here, we present a microfluidics-based platform which allowed protoplast isolation from individually trapped Symbiodinium cells, by using a precisely adjusted flow of cell wall digestion enzymes (cellulase and macerozyme). Trapped single cells exhibited characteristic changes in their morphology, cessation of cell division and a slight decrease in photosynthetic activity during protoplast formation. Following digestion and transfer to regeneration medium, protoplasts remained photosynthetically active, regrew cell walls, regained motility, and entered exponential growth. Elevated flow rates in the microfluidic chambers resulted in somewhat faster protoplast formation; however, cell wall digestion at higher flow rates partially compromised photosynthetic activity. Physiologically competent protoplasts prepared from trapped cells in microfluidic chambers allowed for the first time the visualization of the intracellular localization of singlet oxygen (using Singlet Oxygen Sensor Green dye) in Symbiodiniaceae, potentially opening new avenues for studying oxidative stress.

Photosystem II photochemical adjustment of tall fescue against heat stress after melatonin priming

High temperature is the key factor restricting the survival of tall fescue. Extreme summer hot events arise from global warming further increases this risk. As a candidate chemical priming agent previously reported, melatonin offers innovative solution to improve heat resistance of plants. However, the mechanistic insight remains ill-defined, especially in PSII photochemical reactions. In this study, we investigated the effect of melatonin priming on photosynthetic electron transport of PS II against heat stress in tall fescue. Results showed that melatonin weakened the electron transfer efficiency of PS II per light reaction center (RC) at donor-side and receptor-side, while increased the number of RC per unit cross-sectional area. The quenching analysis further revealed that the proportion of photochemical quenching, Y(II), increased by melatonin. Considering the enriched chl a and nonevent oxidative damage, we argued that inefficient but more abundant RC introduced by melatonin protected the PSII from oxidative damage under heat stress. Notably, these effects were dependent on melatonin concentration but not temperature, an optimal application concentration (50 μmol/L) was uncovered. Besides, melatonin decreased NPQ and encouraged reverse reaction of the xanthophyll cycle. We proposed that melatonin prevents the production of excessive excitation energy. In brief, melatonin plays a distinctive role in regulating photoelectric conversion of PSII of tall fescue under heat stress, increased its survival rate after heat shock.

Drought tolerance assessment of citron watermelon (Citrullus lanatus var. citroides (L.H. Bailey) Mansf. ex Greb.) accessions based on morphological and physiological traits

Long-term cultivation of citron watermelon under water-constrained environments in sub-Saharan Africa resulted in the selection and domestication of highly tolerant genotypes. However, information on the magnitude of variation for drought tolerance in citron watermelon is limited for the effective selection of suitable genotypes for breeding. The objective of this study was to determine variation for drought tolerance among South African citron watermelon landrace accessions for selection and use as genetic stock for drought-tolerance breeding in this crop and closely-related cucurbit crops. Forty genetically differentiated citron watermelon accessions were grown under non-stress (NS) and drought-stress (DS) conditions under glasshouse environment. Data of physiological (i.e., leaf gas exchange and chlorophyll fluorescence parameters) and morphological traits (i.e., shoot and root system architecture traits, and fruit yield) were collected and subjected to various parametric statistical analyses. The accessions varied significantly for assessed traits under both NS and DS conditions which aided classification into five groups, namely; A (highly drought-tolerant), B (drought-tolerant), C (moderate drought-tolerant), D (drought-sensitive) and E (highly drought-sensitive). Drought-tolerant genotypes produced more fruit yield with less water compared with drought-sensitive genotypes. Several physiological and morphological parameters correlated with fruit yield under DS condition namely: instantaneous water-use efficiency (r = 0.97), leaf dry weight (r = 0.77), total root length (r = 0.46) and root dry weight (r = 0.48). The following accessions, namely: WWM-46, WWM-68, WWM-41(A), WWM-15, WWM-64, WWM-57, WWM-47, WWM-37(2), WWM-79, WWM-05 and WWM-50) were identified as highly drought-tolerant and recommended for drought-tolerance breeding in this crop or related cucurbit crops such as sweet dessert watermelon.

Triplet-driven chemical reactivity of β-carotene and its biological implications

The endoperoxides of β-carotene (βCar-EPOs) are regarded as main products of the chemical deactivation of ¹O₂ by β-carotene, one of the most important antioxidants, following a concerted singlet-singlet reaction. Here we challenge this view by showing that βCar-EPOs are formed in the absence of ¹O₂ in a non-concerted triplet-triplet reaction: ³O₂ + ³β-carotene → βCar-EPOs, in which ³β-carotene manifests a strong biradical character. Thus, the reactivity of β-carotene towards oxygen is governed by its excited triplet state. βCar-EPOs, while being stable in the dark, are photochemically labile, and are a rare example of nonaromatic endoperoxides that release ¹O₂, again not in a concerted reaction. Their light-induced breakdown triggers an avalanche of free radicals, which accounts for the pro-oxidant activity of β-carotene and the puzzling swap from its anti- to pro-oxidant features. Furthermore, we show that βCar-EPOs, and carotenoids in general, weakly sensitize ¹O₂. These findings underlie the key role of the triplet state in determining the chemical and photophysical features of β-carotene. They shake up the prevailing models of carotenoid photophysics, the anti-oxidant functioning of β-carotene, and the role of ¹O₂ in chemical signaling in biological photosynthetic systems. βCar-EPOs and their degradation products are not markers of ¹O₂ and oxidative stress but of the overproduction of extremely hazardous chlorophyll triplets in photosystems. Hence, the chemical signaling of overexcitation of the photosynthetic apparatus is based on a ³chlorophyll-³β-carotene relay, rather than on extremely short-lived ¹O₂.

How does interspecific competition modify the response of grass plants against herbicide treatment? A hierarchical concentration-response approach

Ecological interactions are rarely taken into account in environmental risk assessment. The objective of this work was to assess how interspecific competition affects the way plant species react to herbicides and more specifically how it modifies the concentration-response curves that can be built using ecotoxicological bioassays. To do this, we relied on the results of ecotoxicological bioassays on six herbaceous species exposed to isoproturon under two conditions: in presence and in absence of a competitor. At the end of the experiments, eleven endpoints were measured. We modelled these data using a hierarchical modelling framework designed to assess the effects of competition on each of the four parameters of the concentration response curves (e.g. the level of response at the control or the concentration at the inflection point of the curve) simultaneously for the six species. The modelled effects could be of three types, 1) competition had no effect on the parameter, 2) competition had the same effect on the parameter for all species and 3) competition had a different effect on the parameter for each species. Our main hypothesis was that different species would react differently to competition. Results showed that about a half of the estimated parameters showed a modification under competition pressure among which only a fourth showed a species-specific effect, the three other fourth showing the same effect between the different species. Our initial hypothesis was thus not supported as species tended to react in the same way to competition. The competition effect on plants was mainly negative, thus showing that they were more affected by isoproturon under competition pressure. This study therefore establishes how competition modifies plant responses to chemical stress and how this interaction varies from one species to the other.

Dissipation of Light Energy Absorbed in Excess: The Molecular Mechanisms

Light is essential for photosynthesis. Nevertheless, its intensity widely changes depending on time of day, weather, season, and localization of individual leaves within canopies. This variability means that light collected by the light-harvesting system is often in excess with respect to photon fluence or spectral quality in the context of the capacity of photosynthetic metabolism to use ATP and reductants produced from the light reactions. Absorption of excess light can lead to increased production of excited, highly reactive intermediates, which expose photosynthetic organisms to serious risks of oxidative damage. Prevention and management of such stress are performed by photoprotective mechanisms, which operate by cutting down light absorption, limiting the generation of redox-active molecules, or scavenging reactive oxygen species that are released despite the operation of preventive mechanisms. Here, we describe the major physiological and molecular mechanisms of photoprotection involved in the harmless removal of the excess light energy absorbed by green algae and land plants. In vivo analyses of mutants targeting photosynthetic components and the enhanced resolution of spectroscopic techniques have highlighted specific mechanisms protecting the photosynthetic apparatus from overexcitation. Recent findings unveil a network of multiple interacting elements, the reaction times of which vary from a millisecond to weeks, that continuously maintain photosynthetic organisms within the narrow safety range between efficient light harvesting and photoprotection.

Fenton-based technologies as efficient advanced oxidation processes for microcystin-LR degradation

In recent years, the safety and ecology threat of cyanobacterial burst has drawn wide concern, especially the release of toxic microcystin-LR (MC-LR). To break through the bottleneck of uncomplete MC-LR degradation by conventional physical-chemistry methods, Fenton-based advanced oxidation processes (AOPs) developed rapidly due to striking degradation efficiency through the potent hydroxyl radicals (HO·) oxidation. Herein, a comprehensive overview is presented on the recent achievements of the various Fenton-based technologies (including conventional Fenton, photo-Fenton, electro-Fenton, ozone-Fenton and sono-Fenton) for MC-LR degradation. In particular, the comparisons between various Fenton-based technologies about advantages and drawbacks are discussed. Based on analyzing the degradation intermediates and pathways, the destruction of Adda chain via hydroxylation was confirmed to be essential for detoxification of MC-LR. Roles of influencing factors such as MC-LR initial concentration, dosages of the catalyst and oxidant, environment alkalinity, natural organic matters (NOMs) as well as other inorganic ions are specifically summarized. This Review also gave special emphasis on technique optimization trends for Fenton application of MC-LR degradation, as well as key challenges and future opportunities in this fast developing field.

Molecular plant responses to combined abiotic stresses put a spotlight on unknown and abundant genes

Environmental stresses such as drought, heat, and salinity limit plant development and agricultural productivity. While individual stresses have been studied extensively, much less is known about the molecular interaction of responses to multiple stresses. To address this problem, we investigated molecular responses of Arabidopsis to single, double, and triple combinations of salt, osmotic, and heat stresses. A metabolite profiling analysis indicated the production of specific compatible solutes depending on the nature of the stress applied. We found that in combination with other stresses, heat has a dominant effect on global gene expression and metabolite level patterns. Treatments that include heat stress lead to strongly reduced transcription of genes coding for abundant photosynthetic proteins and proteins regulating the cell life cycle, while genes involved in protein degradation are up-regulated. Under combined stress conditions, the plants shifted their metabolism to a survival state characterized by low productivity. Our work provides molecular evidence for the dangers for plant productivity and future world food security posed by heat waves resulting from global warming. We highlight candidate genes, many of which are functionally uncharacterized, for engineering plant abiotic stress tolerance.

Quenching of Singlet Oxygen by Carotenoids via Ultrafast Superexchange Dynamics

We analyze the quenching mechanism of singlet molecular oxygen (¹O₂) by carotenoids, namely lycopene, β-carotene, astaxanthin, and lutein, by means of quantum dynamics calculations and ab initio calculations. The singlet carotenoid (¹Car) and ¹O₂ molecules can form a weakly bound complex via donation of electron density from the highest occupied molecular orbital (HOMO) of the carotenoid to the π_g* orbitals of ¹O₂. The Dexter-type superexchange via charge transfer states (Car^•+/O₂^•-) governs the ¹O₂ quenching. The Car^•+/O₂^•- states are substantially higher in energy (2-4 eV) than the initial ¹Car/¹O₂ states. The quantum dynamics calculations indicate an ultrafast ¹O₂ quenching on a timescale of subpicosecond owing to the strong electronic couplings in the carotenoid/O₂ complexes. The superexchange mechanism via the Car^•+/O₂^•- states dominates the ¹O₂ quenching, although the direct two-electron coupling can also play a certain role.

Revealing the Photodynamic Stress In Situ with a Dual-Mode Two-Photon 1O2 Fluorescent Probe

Singlet oxygen (¹O₂) plays significant physiological and pathological functions, especially in causing photodynamic stress in vivo. However, specific ¹O₂ monitoring is an immense challenge, owing to its short half-lives and high oxidizing ability. To address this, we engineered three photostable two-photon fluorescence probe NBs for highly efficient ¹O₂ monitoring based on bioinspired novel tryptophan derivatives, among which NB-MOT was the best one comprehensively. Upon being cracked with ¹O₂, NB-MOT rapidly (within 5 s) demonstrated a remarkable enhancement in fluorescence intensity (∼180 fold) and lifetime (∼18 fold). Taking these advantages into account, NB-MOT was applied to evaluate exogenous and endogenous ¹O₂ in diverse biosystems. We successfully tracked the intracellular ¹O₂ level during photodynamic therapy, and for the first time achieved ¹O₂ mapping in live cells with dual-mode imaging as well as revealed ciprofloxacin-induced photodynamic stress in mice. NB-MOT was thus believed to be of instructive significance for studying the ¹O₂-mediated stress in wider biological milieus.

You Want it Sweeter: How Glycosylation Affects Plant Response to Oxidative Stress

Oxidative stress is a cellular threat which puts at risk the productivity of most of crops valorized by humankind in terms of food, feed, biomaterial, or bioenergy. It is therefore of crucial importance to understand the mechanisms by which plants mitigate the deleterious effects of oxidizing agents. Glycosylation of antioxidant molecules and phytohormones modifies their chemical properties as well as their cellular and histological repartition. This review emphasizes the mechanisms and the outcomes of this conjugation reaction on plant ability to face growing conditions favoring oxidative stress, in mirror with the activity of deglycosylating enzymes. Pioneer evidence bridging flavonoid, glycosylation, and redox homeostasis paved the way for numerous functional analyses of UDP-glycosyltransferases (UGTs), such as the identification of their substrates and their role to circumvent oxidative stress resulting from various environmental challenges. (De)glycosylation appears as a simple chemical reaction regulating the biosynthesis and/or the activity of a myriad of specialized metabolites partaking in response to pathogen and abiotic stresses. This outcome underlies the possibility to valorize UGTs potential to upgrade plant adaptation and fitness in a rising context of sub-optimal growing conditions subsequent to climate change.

The Apocarotenoid β-Cyclocitric Acid Elicits Drought Tolerance in Plants

β-Cyclocitral (β-CC) is a volatile compound deriving from 1O2 oxidation of β-carotene in plant leaves. β-CC elicits a retrograde signal, modulating 1O2-responsive genes and enhancing tolerance to photooxidative stress. Here, we show that β-CC is converted into water-soluble β-cyclocitric acid (β-CCA) in leaves. This metabolite is a signal that enhances plant tolerance to drought by a mechanism different from known responses such as stomatal closure, osmotic potential adjustment, and jasmonate signaling. This action of β-CCA is a conserved mechanism, being observed in various plant species, and it does not fully overlap with the β-CC-dependent signaling, indicating that β-CCA induces only a branch of β-CC signaling. Overexpressing SCARECROW-LIKE14 (SCL14, a regulator of xenobiotic detoxification) increased drought tolerance and potentiated the protective effect of β-CCA, showing the involvement of the SCL14-dependent detoxification in the phenomenon. β-CCA is a bioactive apocarotenoid that could potentially be used to protect crop plants against drought.

Lethal heat stress-dependent volatile emissions from tobacco leaves: what happens beyond the thermal edge?

Natural vegetation is predicted to suffer from extreme heat events as a result of global warming. In this study, we focused on the immediate response to heat stress. Photosynthesis and volatile emissions were measured in the leaves of tobacco (Nicotiana tabacum cv. Wisconsin 38) after exposure to heat shock treatments between 46 °C and 55 °C. Exposure to 46 °C decreased photosynthetic carbon assimilation rates (A) by >3-fold. Complete inhibition of A was observed at 49 °C, together with a simultaneous decrease in the maximum quantum efficiency of PSII, measured as the Fv/Fm ratio. A large increase in volatile emissions was observed at 52 °C. Heat stress resulted in only minor effects on the emission of monoterpenes, but volatiles associated with membrane damage such as propanal and (E)-2-hexenal+(Z)-3-hexenol were greatly increased. Heat induced changes in the levels of methanol and 2-ethylfuran that are indicative of modification of cell walls. In addition, the oxidation of metabolites in the volatile profiles was strongly enhanced, suggesting the acceleration of oxidative processes at high temperatures that are beyond the thermal tolerance limit.

Changes in the photosynthesis properties and photoprotection capacity in rice (Oryza sativa) grown under red, blue, or white light

Non-photochemical quenching (NPQ) of the excited state of chlorophyll a is a major photoprotective mechanism plants utilize to survive under high light. Here, we report the impact of long-term light quality treatment on photosynthetic properties, especially NPQ in rice. We used three LED-based light regimes, i.e., red (648-672 nm), blue (438-460 nm), and "warm" white light (529-624 nm), with the incident photon flux density of 300 µmol photons m^-2 s^-1, the difference in the absorbed photon flux densities by leaves grown under different light quality being less than 7%. Our results show that blue light, as compared to white light, induced a significant decrease in F_v/F_m, a decreased rate of reduction of P₇₀₀⁺ after P₇₀₀ was completely oxidized; furthermore, blue light also induced higher NPQ with an increased initial speed of NPQ induction, which corresponds to the qE component of NPQ, and a lower maximum quantum yield of PSII, i.e., Y(II). In contrast, rice grown under long-term red light showed decreased Y(II) and increased NPQ, but with no change in F_v/F_m. Furthermore, we found that rice grown under either blue or red light showed decreased transcript abundance of both catalase and ascorbate peroxidase, together with an increased H₂O₂ content, as compared to rice grown under white light. All these data suggest that even under a moderate incident light level, rice grown under blue or red light led to compromised antioxidant system, which contributed to decreased quantum yield of photosystem II and increased NPQ.

Stability of metallo-porphyrin networks under oxygen reduction and evolution conditions in alkaline media

Transition metal atoms stabilised by organic ligands or as oxides exhibit promising catalytic activity for the electrocatalytic reduction and evolution of oxygen. Built-up from earth-abundant elements, they offer affordable alternatives to precious-metal based catalysts for application in fuel cells and electrolysers. For the understanding of a catalyst's activity, insight into its structure on the atomic scale is of highest importance, yet commonly challenging to experimentally access. Here, the structural integrity of a bimetallic iron tetrapyridylporphyrin with co-adsorbed cobalt electrocatalyst on Au(111) is investigated using scanning tunneling microscopy and X-ray absorption spectroscopy. Topographic and spectroscopic characterization reveals structural changes of the molecular coordination network after oxygen reduction, and its decomposition and transformation into catalytically active Co/Fe (oxyhydr)oxide during oxygen evolution. The data establishes a structure-property relationship for the catalyst as a function of electrochemical potential and, in addition, highlights how the reaction direction of electrochemical interconversion between molecular oxygen and hydroxyl anions can have very different effects on the catalyst's structure.

Singlet oxygen imaging using fluorescent probe Singlet Oxygen Sensor Green in photosynthetic organisms

Formation of singlet oxygen (¹O₂) was reported to accompany light stress in plants, contributing to cell signaling or oxidative damage. So far, Singlet Oxygen Sensor Green (SOSG) has been the only commercialized fluorescent probe for ¹O₂ imaging though it suffers from several limitations (unequal penetration and photosensitization) that need to be carefully considered to avoid misinterpretation of the analysed data. Herein, we present results of a comprehensive study focused on the appropriateness of SOSG for ¹O₂ imaging in three model photosynthetic organisms, unicellular cyanobacteria Synechocystis sp. PCC 6803, unicellular green alga Chlamydomonas reinhardtii and higher plant Arabidopsis thaliana. Penetration of SOSG differs in both unicellular organisms; while it is rather convenient for Chlamydomonas it is restricted by the presence of mucoid sheath of Synechocystis, which penetrability might be improved by mild heating. In Arabidopsis, SOSG penetration is limited due to tissue complexity which can be increased by pressure infiltration using a shut syringe. Photosensitization of SOSG and SOSG endoperoxide formed by its interaction with ¹O₂ might be prevented by illumination of samples by a red light. When measured under controlled conditions given above, SOSG might serve as specific probe for detection of intracellular ¹O₂ formation in photosynthetic organisms.

Reactive oxygen species initiate a protective response in plant roots to stress induced by environmental bisphenol A

Bisphenol A (BPA), a contaminant of emerging concern, can affect plant growth and development at high concentrations. Reactive oxygen species (ROS) production is a general primary response in plants to stress. Here, the aim is to investigate whether ROS in plants play protective roles for stress induced by BPA exposure at environmental concentrations. In this study, soybean roots (seedling, flowering and podding stages) were exposed to 1.5 and 3.0 mg L-1 BPA, and ROS response was measured. The relationship between ROS levels and residual BPA content in soybean roots was evaluated. The results showed that exposure (9 h) to 1.5 mg L-1 BPA elicited changes in ROS production. ROS then gradually accumulated in soybean roots (seedling stage). Exposure to 3.0 mg L-1 BPA elicited a stronger and earlier ROS responses at the flowering and podding stage, but did not lead to membrane lipid peroxidation. Residual BPA content in soybean roots reached peak concentrations after 9 h of exposure, and then gradually decreased at the flowering and podding stage. These results indicate that ROS in soybean roots might be involved in the oxidative metabolism of BPA, which could prevent BPA from damaging exposed plants. In conclusion, the observed ROS metabolic effects may be self-protection responses of plants to stress induced by BPA exposure.

Chemical quenching of singlet oxygen by plastoquinols and their oxidation products in Arabidopsis

Prenylquinols (tocochromanols and plastoquinols) serve as efficient physical and chemical quenchers of singlet oxygen (1 O2 ) formed during high light stress in higher plants. Although quenching of 1 O2 by prenylquinols has been previously studied, direct evidence for chemical quenching of 1 O2 by plastoquinols and their oxidation products is limited in vivo. In the present study, the role of plastoquinol-9 (PQH2 -9) in chemical quenching of 1 O2 was studied in Arabidopsis thaliana lines overexpressing the SOLANESYL DIPHOSPHATE SYNTHASE 1 gene (SPS1oex) involved in PQH2 -9 and plastochromanol-8 biosynthesis. In this work, direct evidence for chemical quenching of 1 O2 by plastoquinols and their oxidation products is presented, which is obtained by microscopic techniques in vivo. Chemical quenching of 1 O2 was associated with consumption of PQH2 -9 and formation of its various oxidized forms. Oxidation of PQH2 -9 by 1 O2 leads to plastoquinone-9 (PQ-9), which is subsequently oxidized to hydroxyplastoquinone-9 [PQ(OH)-9]. We provide here evidence that oxidation of PQ(OH)-9 by 1 O2 results in the formation of trihydroxyplastoquinone-9 [PQ(OH)3 -9]. It is concluded here that PQH2 -9 serves as an efficient 1 O2 chemical quencher in Arabidopsis, and PQ(OH)3 -9 can be considered as a natural product of 1 O2 reaction with PQ(OH)-9. The understanding of the mechanisms underlying 1 O2 chemical quenching provides information on the role of plastoquinols and their oxidation products in the response of plants to photooxidative stress.

Molecular mechanisms involved in plant photoprotection

Photosynthesis uses sunlight to convert water and carbon dioxide into biomass and oxygen. When in excess, light can be dangerous for the photosynthetic apparatus because it can cause photo-oxidative damage and decreases the efficiency of photosynthesis because of photoinhibition. Plants have evolved many photoprotective mechanisms in order to face reactive oxygen species production and thus avoid photoinhibition. These mechanisms include quenching of singlet and triplet excited states of chlorophyll, synthesis of antioxidant molecules and enzymes and repair processes for damaged photosystem II and photosystem I reaction centers. This review focuses on the mechanisms involved in photoprotection of chloroplasts through dissipation of energy absorbed in excess.

Metabolic Reprogramming in Chloroplasts under Heat Stress in Plants

Increases in ambient temperatures have been a severe threat to crop production in many countries around the world under climate change. Chloroplasts serve as metabolic centers and play a key role in physiological adaptive processes to heat stress. In addition to expressing heat shock proteins that protect proteins from heat-induced damage, metabolic reprogramming occurs during adaptive physiological processes in chloroplasts. Heat stress leads to inhibition of plant photosynthetic activity by damaging key components functioning in a variety of metabolic processes, with concomitant reductions in biomass production and crop yield. In this review article, we will focus on events through extensive and transient metabolic reprogramming in response to heat stress, which included chlorophyll breakdown, generation of reactive oxygen species (ROS), antioxidant defense, protein turnover, and metabolic alterations with carbon assimilation. Such diverse metabolic reprogramming in chloroplasts is required for systemic acquired acclimation to heat stress in plants.

An Overview of Biomembrane Functions in Plant Responses to High-Temperature Stress

Biological membranes are highly ordered structures consisting of mosaics of lipids and proteins. Elevated temperatures can directly and effectively change the properties of these membranes, including their fluidity and permeability, through a holistic effect that involves changes in the lipid composition and/or interactions between lipids and specific membrane proteins. Ultimately, high temperatures can alter microdomain remodeling and instantaneously relay ambient cues to downstream signaling pathways. Thus, dynamic membrane regulation not only helps cells perceive temperature changes but also participates in intracellular responses and determines a cell's fate. Moreover, due to the specific distribution of extra- and endomembrane elements, the plasma membrane (PM) and membranous organelles are individually responsible for distinct developmental events during plant adaptation to heat stress. This review describes recent studies that focused on the roles of various components that can alter the physical state of the plasma and thylakoid membranes as well as the crucial signaling pathways initiated through the membrane system, encompassing both endomembranes and membranous organelles in the context of heat stress responses.

Does the photo-Fenton reaction work for microalgae control? A case study with Desmodesmus subspicatus

This paper presents the first report of photo-Fenton process application aiming microalgae inactivation, using Desmodesmus subspicatus as model species.

Nitric Oxide (NO) in Plant Heat Stress Tolerance: Current Knowledge and Perspectives

High temperature is one of the biggest abiotic stress challenges for agriculture. While, Nitric oxide (NO) is gaining increasing attention from plant science community due to its involvement in resistance to various plant stress conditions, its implications on heat stress tolerance is still unclear. Several lines of evidence indicate NO as a key signaling molecule in mediating various plant responses such as photosynthesis, oxidative defense, osmolyte accumulation, gene expression, and protein modifications under heat stress. Furthermore, the interactions of NO with other signaling molecules and phytohormones to attain heat tolerance have also been building up in recent years. Nevertheless, deep insights into the functional intermediaries or signal transduction components associated with NO-mediated heat stress signaling are imperative to uncover their involvement in plant hormone induced feed-back regulations, ROS/NO balance, and stress induced gene transcription. Although, progress is underway, much work remains to define the functional relevance of this molecule in plant heat tolerance. This review provides an overview on current status and discuss knowledge gaps in exploiting NO, thereby enhancing our understanding of the role of NO in plant heat tolerance.

Formation of singlet oxygen by decomposition of protein hydroperoxide in photosystem II

Singlet oxygen (1O2) is formed by triplet-triplet energy transfer from triplet chlorophyll to O2 via Type II photosensitization reaction in photosystem II (PSII). Formation of triplet chlorophyll is associated with the change in spin state of the excited electron and recombination of triplet radical pair in the PSII antenna complex and reaction center, respectively. Here, we have provided evidence for the formation of 1O2 by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex. Protein hydroperoxide is formed by protein oxidation initiated by highly oxidizing chlorophyll cation radical and hydroxyl radical formed by Type I photosensitization reaction. Under highly oxidizing conditions, protein hydroperoxide is oxidized to protein peroxyl radical which either cyclizes to dioxetane or recombines with another protein peroxyl radical to tetroxide. These highly unstable intermediates decompose to triplet carbonyls which transfer energy to O2 forming 1O2. Data presented in this study show for the first time that 1O2 is formed by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex.

Ultra-weak photon emission in healthy subjects and patients with type 2 diabetes: evidence for a non-invasive diagnostic tool

BACKGROUND

Spontaneous ultra-weak photon emission (UPE) is a common phenomenon in biological systems and has been linked to pathological states. Researchers have always considered ultra-weak photon emission a potential non-invasive diagnostic tool, but its application in the medical field is stagnant due to the lack of relevant data for pathological states.

METHODS

Ultra-weak photon signals from five body sites (forehead, neck, heart, stomach, and navel) in fifty patients with type 2 diabetes and sixty age-matched healthy subjects were measured using a moveable whole-body biophoton detection system. Photon signal is measured for 10 min and detected in bins of 50 ms by a photomultiplier with a range of 290-630 nm. Each signal is a time series of 12 000 elements. Various parameters including photon intensity, Q value, squeezed state parameters (|α|, θ, ø, r) and SSI were analyzed.

RESULTS AND CONCLUSION

we found significant differences in the abovementioned parameters between groups, and all subjects could be clustered into two groups according to the results obtained by principal component analysis. Methods and results from this study could be useful for constructing a UPE database for a range of diseases, which would promote the application of UPE in clinical diagnosis in the future.

Effects of exogenous β-carotene, a chemical scavenger of singlet oxygen, on the millisecond rise of chlorophyll a fluorescence of cyanobacterium Synechococcus sp. PCC 7942

Singlet-excited oxygen (¹O ₂^* ) has been recognized as the most destructive member of the reactive oxygen species (ROS) which are formed during oxygenic photosynthesis by plants, algae, and cyanobacteria. ROS and ¹O ₂^* are known to damage protein and phospholipid structures and to impair photosynthetic electron transport and de novo protein synthesis. Partial protection is afforded to photosynthetic organism by the β-carotene (β-Car) molecules which accompany chlorophyll (Chl) a in the pigment-protein complexes of Photosystem II (PS II). In this paper, we studied the effects of exogenously added β-Car on the initial kinetic rise of Chl a fluorescence (10-1000 μs, the OJ segment) from the unicellular cyanobacterium Synechococcus sp. PCC7942. We show that the added β-Car enhances Chl a fluorescence when it is excited at an intensity of 3000 μmol photons m^-2 s^-1 but not when excited at 1000 μmol photons m^-2 s^-1. Since β-Car is an efficient scavenger of ¹O ₂^* , as well as a quencher of ³Chl a ^* (precursor of ¹O ₂^* ), both of which are more abundant at higher excitations, we assume that the higher Chl a fluorescence in its presence signifies a protective effect against photo-oxidative damages of Chl proteins. The protective effect of added β-Car is not observed in O₂-depleted cell suspensions. Lastly, in contrast to β-Car, a water-insoluble molecule, a water-soluble scavenger of ¹O ₂^* , histidine, provides no protection to Chl proteins during the same time period (10-1000 μs).

Molecular Dynamics of Photosystem II Embedded in the Thylakoid Membrane

Photosystem II (PSII) is one of the key protein complexes in photosynthesis. We introduce a coarse grained model of PSII and present the analysis of 60 μs molecular dynamics simulations of PSII in both monomeric and dimeric form, embedded in a thylakoid membrane model that reflects its native lipid composition. We describe in detail the setup of the protein complex and the many natural cofactors and characterize their mobility. Overall we find that the protein subunits and cofactors are more flexible toward the periphery of the complex as well as near the PLQ exchange cavity and at the dimer interface. Of all cofactors, β-carotenes show the highest mobility. Some of the β-carotenes diffuse in and out of the protein complex via the thylakoid membrane. In contrast with the PSII dimer, the monomeric form adopts a tilted conformation in the membrane, with strong interactions between the soluble PsbO subunit and the glycolipid headgroups. Interestingly, the tilted conformation causes buckling of the membrane. Together, our results provide an unprecedented view of PSII dynamics on a microsecond time scale. Our data may be used as basis for the interpretation of experimental data as well as for theoretical models describing exciton energy transfer.

Titanium dioxide nanoparticles (100-1000 mg/l) can affect vitamin E response in Arabidopsis thaliana

In the present study we analyze the effect of seed treatment by a range of nano-TiO2 concentrations on the growth of Arabidopsis thaliana plants, on the vitamin E content and the expression of its biosynthetic genes, as well as activity of antioxidant enzymes and lipid peroxidation. To conduct the mechanistic analysis of nano-TiO2 on plants growth and antioxidant status we applied nanoparticles concentrations that are much higher than those reported in the environment. We find that as the concentration of nano-TiO2 increases, the biomass, and chlorophyll content in 5-week-old Arabidopsis thaliana plants decrease in a concentration dependent manner. In opposite, higher nano-TiO2 concentration enhanced root growth. Our results indicate that a high concentration of nano-TiO2 induces symptoms of toxicity and elevates the antioxidant level. We also find that the expression levels of tocopherol biosynthetic genes were either down- or upregulated in response to nano-TiO2. Thermoluminescence analysis shows that higher nano-TiO2 concentrations cause lipid peroxidation. To the best of our knowledge, this is the first report concerning the effect of nano-TiO2 on vitamin E status in plants. We conclude that nano-TiO2 affects the antioxidant response in Arabidopsis thaliana plants. This could be an effect of a changes in vitamin E gene expression that is diminished under lower tested nano-TiO2 concentrations and elevated under 1000 μg/ml.

Membranes as Structural Antioxidants: RECYCLING OF MALONDIALDEHYDE TO ITS SOURCE IN OXIDATION-SENSITIVE CHLOROPLAST FATTY ACIDS

Genetic evidence suggests that membranes rich in polyunsaturated fatty acids (PUFAs) act as supramolecular antioxidants that capture reactive oxygen species, thereby limiting damage to proteins. This process generates lipid fragmentation products including malondialdehyde (MDA), an archetypal marker of PUFA oxidation. We observed transient increases in levels of endogenous MDA in wounded Arabidopsis thaliana leaves, raising the possibility that MDA is metabolized. We developed a rigorous ion exchange method to purify enzymatically generated (13)C- and (14)C-MDA. Delivered as a volatile to intact plants, MDA was efficiently incorporated into lipids. Mass spectral and genetic analyses identified the major chloroplast galactolipid: α-linolenic acid (18:3)-7Z,10Z,13Z-hexadecatrienoic acid (16:3)-monogalactosyldiacylglycerol (18:3-16:3-MGDG) as an end-product of MDA incorporation. Consistent with this, the fad3-2 fad7-2 fad8 mutant that lacks tri-unsaturated fatty acids incorporated (14)C-MDA into 18:2-16:2-MGDG. Saponification of (14)C-labeled 18:3-16:3-MGDG revealed 84% of (14)C-label in the acyl groups with the remaining 16% in the head group. 18:3-16:3-MGDG is enriched proximal to photosystem II and is likely a major in vivo source of MDA in photosynthetic tissues. We propose that nonenzymatically generated lipid fragments such as MDA are recycled back into plastidic galactolipids that, in their role as cell protectants, can again be fragmented into MDA.

Chloroplast Retrograde Regulation of Heat Stress Responses in Plants

It is well known that intracellular signaling from chloroplast to nucleus plays a vital role in stress responses to survive environmental perturbations. The chloroplasts were proposed as sensors to heat stress since components of the photosynthetic apparatus housed in the chloroplast are the major targets of thermal damage in plants. Thus, communicating subcellular perturbations to the nucleus is critical during exposure to extreme environmental conditions such as heat stress. By coordinating expression of stress specific nuclear genes essential for adaptive responses to hostile environment, plants optimize different cell functions and activate acclimation responses through retrograde signaling pathways. The efficient communication between plastids and the nucleus is highly required for such diverse metabolic and biosynthetic functions during adaptation processes to environmental stresses. In recent years, several putative retrograde signals released from plastids that regulate nuclear genes have been identified and signaling pathways have been proposed. In this review, we provide an update on retrograde signals derived from tetrapyrroles, carotenoids, reactive oxygen species (ROS) and organellar gene expression (OGE) in the context of heat stress responses and address their roles in retrograde regulation of heat-responsive gene expression, systemic acquired acclimation, and cellular coordination in plants.

Chloroplast Retrograde Regulation of Heat Stress Responses in Plants

It is well known that intracellular signaling from chloroplast to nucleus plays a vital role in stress responses to survive environmental perturbations. The chloroplasts were proposed as sensors to heat stress since components of the photosynthetic apparatus housed in the chloroplast are the major targets of thermal damage in plants. Thus, communicating subcellular perturbations to the nucleus is critical during exposure to extreme environmental conditions such as heat stress. By coordinating expression of stress specific nuclear genes essential for adaptive responses to hostile environment, plants optimize different cell functions and activate acclimation responses through retrograde signaling pathways. The efficient communication between plastids and the nucleus is highly required for such diverse metabolic and biosynthetic functions during adaptation processes to environmental stresses. In recent years, several putative retrograde signals released from plastids that regulate nuclear genes have been identified and signaling pathways have been proposed. In this review, we provide an update on retrograde signals derived from tetrapyrroles, carotenoids, reactive oxygen species (ROS) and organellar gene expression (OGE) in the context of heat stress responses and address their roles in retrograde regulation of heat-responsive gene expression, systemic acquired acclimation, and cellular coordination in plants.

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.

Improving the robustness of cobalt porphyrin water oxidation catalysts by chlorination of aryl groups

A chlorinated cobalt porphyrin (CoClPS) shows extremely high resistance against singlet oxygen and activity for photochemical water oxidation.

Isoprenoid Alcohols are Susceptible to Oxidation with Singlet Oxygen and Hydroxyl Radicals

Isoprenoids, as common constituents of all living cells, are exposed to oxidative agents—reactive oxygen species, for example, singlet oxygen or hydroxyl radicals. Despite this fact, products of oxidation of polyisoprenoids have never been characterized. In this study, chemical oxidation of isoprenoid alcohols (Prenol-2 and -10) was performed using singlet oxygen (generated in the presence of hydrogen peroxide/molybdate or upon photochemical reaction in the presence of porphyrin), oxygen (formed upon hydrogen peroxide dismutation) or hydroxyl radical (generated by the hydrogen peroxide/sonication, UV/titanium dioxide or UV/hydrogen peroxide) systems. The structure of the obtained products, hydroxy-, peroxy- and heterocyclic derivatives, was studied with the aid of mass spectrometry (MS) and nuclear magnetic resonance (NMR) methods. Furthermore, mass spectrometry with electrospray ionization appeared to be a useful analytical tool to detect the products of oxidation of isoprenoids (ESI–MS analysis), as well as to establish their structure on the basis of the fragmentation spectra of selected ions (ESI–MS/MS analysis). Taken together, susceptibility of polyisoprenoid alcohols to various oxidizing agents was shown for the first time.

Reactive oxygen species: Reactions and detection from photosynthetic tissues

Reactive oxygen species (ROS) have long been recognized as compounds with dual roles. They cause cellular damage by reacting with biomolecules but they also function as agents of cellular signaling. Several different oxygen-containing compounds are classified as ROS because they react, at least with certain partners, more rapidly than ground-state molecular oxygen or because they are known to have biological effects. The present review describes the typical reactions of the most important ROS. The reactions are the basis for both the detection methods and for prediction of reactions between ROS and biomolecules. Chemical and physical methods used for detection, visualization and quantification of ROS from plants, algae and cyanobacteria will be reviewed. The main focus will be on photosynthetic tissues, and limitations of the methods will be discussed.