Drought-induced senescence is characterized by a loss of antioxidant defences in chloroplasts

The relationship between drought, oxidative stress and leaf senescence was evaluated in field‐grown sage (Salvia officinalis L.), a drought‐susceptible species that shows symptoms of senescence when exposed to stress. Despite the photoprotection conferred by the xanthophyll cycle, drought‐stressed senescing leaves showed enhanced lipid peroxidation, chlorophyll loss, reduced photosynthetic activity and strong reductions of membrane‐bound chloroplastic antioxidant defences (i.e. β‐carotene and α‐tocopherol), which is indicative of oxidative stress in chloroplasts. H₂O₂ accumulated in drought‐stressed senescing leaves. Subcellular localization studies showed that H₂O₂ accumulated first in xylem vessels and the cell wall and later in the plasma membrane of mesophyll cells, but not in chloroplasts, indicating reactive oxygen species other than H₂O₂ as direct responsible for the oxidative stress observed in the chloroplasts of drought‐stressed senescing leaves. The strong degradation of β‐carotene and α‐tocopherol suggests an enhanced formation of singlet oxygen as the putative reactive oxygen species responsible for oxidative stress to senescing chloroplasts. This study demonstrates that oxidative stress in chloroplasts mediates drought‐induced leaf senescence in sage growing in Mediterranean field conditions.     

Cross-talk between salicylic acid and NaCl-generated reactive oxygen species and nitric oxide in tomato during acclimation to high salinity

Hydrogen peroxide (H₂O₂) and nitric oxide (NO) generated by salicylic acid (SA) are considered to be functional links of cross‐tolerance to various stressors. SA‐stimulated pre‐adaptation state was beneficial in the acclimation to subsequent salt stress in tomato (Solanum lycopersicum cv. Rio Fuego). At the whole‐plant level, SA‐induced massive H₂O₂ accumulation only at high concentrations (10^?3–10^?2M), which later caused the death of plants. The excess accumulation of H₂O₂ as compared with plants exposed to 100 mM NaCl was not associated with salt stress response after SA pre‐treatments. In the root tips, 10^?3–10^?2M SA triggered the production of reactive oxygen species (ROS) and NO with a concomitant decline in the cell viability. Sublethal concentrations of SA, however, decreased the effect of salt stress on ROS and NO production in the root apex. The attenuation of oxidative stress because of high salinity occurred not only in pre‐adapted plants but also at cell level. When protoplasts prepared from control leaves were exposed to SA in the presence of 100 mM NaCl, the production of NO and ROS was much lower and the viability of the cells was higher than in salt‐treated samples. This suggests that, the cross‐talk of signalling pathways induced by SA and high salinity may occur at the level of ROS and NO production. Abscisic acid (ABA), polyamines and 1‐aminocyclopropane‐1‐carboxylic acid, the compounds accumulating in pre‐treated plants, enhanced the diphenylene iodonium‐sensitive ROS and NO levels, but, in contrast to others, ABA and putrescine preserved the viability of protoplasts.     

Polyphenols suppress hydrogen peroxide‐induced oxidative stress in human bone‐marrow derived mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) are considered a highly promising candidate cell type for cell‐based tissue engineering and regeneration because of their self‐renewal and multi‐lineage differentiation characteristics. Increased levels of reactive oxygen/nitrogen species (ROS/RNS) are associated with tissue injury and inflammation, impact a number of cellular processes, including cell adhesion, migration, and proliferation, and have been linked to cellular senescence in MSCs, potentially compromising their activities. Naturally occurring polyphenolic compounds (polyphenols), epigallocatechin‐3‐gallate (EGCG), and curcumin, block ROS/RNS and are potent inflammation‐modulating agents. However, their potential protective effects against oxidative stress in hMSCs have not been examined. In this study, we carried out a systematic analysis of the effects of polyphenols on hMSCs in their response to oxidative stress in the form of treatment with H₂O₂ and S‐nitroso‐N‐acetylpenicillamine (SNAP), respectively. Parameters measured included colony forming activity, apoptosis, and the levels of antioxidant enzymes and free reactive species. We found that polyphenols reversed H₂O₂‐induced loss of colony forming activity in hMSCs. In a dose‐dependent manner, polyphenols inhibited increased levels of ROS and NO, produced by H₂O₂ or SNAP, respectively, in MSCs. Notably, polyphenols rapidly and almost completely blocked H₂O₂‐induced ROS in the absence of significant direct effect on H₂O₂ itself. Polyphenols also protected the antioxidant enzymes and reduced apoptotic cell death caused by H₂O₂ exposure. Taken together, these findings demonstrate that EGCG and curcumin are capable of suppressing inducible oxidative stress in hMSCs, and suggest a possible new approach to maintain MSC viability and potency for clinical application. J. Cell. Biochem. 114: 1163–1173, 2013. © 2012 Wiley Periodicals, Inc.     

The detection of hydrogen peroxide involved in plant virus infection by fluorescence spectroscopy

The production of reactive oxygen species (ROS) forms part of the defense reaction of plants against invading pathogens. ROS have multifaceted signaling functions in mediating the establishment of multiple responses. To verify whether hydrogen peroxide (H₂O₂) contributes to plant virus infection and the development of induced symptoms, we used fluorescence to monitor the generation of H₂O₂ and confocal laser scanning microscopy (CLSM) to investigate the subcellular distribution of H₂O₂ in leaves. In this study, the M strain of Cucumber mosaic virus (M‐CMV) induced heavy chlorotic symptoms in Nicotiana tabacum cv. white burley during systemic infection. Compared with mock‐inoculated leaves, H₂O₂ accumulation in inoculated leaves increased after inoculation, then decreased after 4 days. For systemically infected leaves that showed chlorotic symptoms, H₂O₂ accumulation was always higher than in healthy leaves. Subcellular H₂O₂ localization observed using CLSM showed that H₂O₂ in inoculated leaves was generated mainly in the chloroplasts and cell wall, whereas in systemically infected leaves H₂O₂ was generated mainly in the cytosol. The levels of coat protein in inoculated and systemically infected leaves might be associated with changes in the level of H₂O₂ and symptom development. Further research is needed to elucidate the generation mechanism and the relationship between coat protein and oxidative stress during infection and symptom development. Copyright © 2016 John Wiley & Sons, Ltd.     

Efficiency of hydrogen photoproduction by chloroplast-bacterial hydrogenase systems

A comparative study of H₂ photoproduction by chloroplasts and solubilized chlorophyll was performed in the presence of hydrogenase preparations of Clostridium butyricum. The photoproduction of H₂ by chloroplasts in the absence of exogenous electron donors, and with irreversibly oxidized dithiothreitol and cysteine, is thought to be limited by a cyclic transport of electrons wherein methylviologen short-circuits the electron transport in photosystem I. The efficiency of H₂ photoproduction by chloroplasts with ascorbate and NADPH is limited by a back reaction between light-reduced methylviologen and the oxidized electron donors. The use of a combination of electron donors (dithiothreitol and ascorbate), providing anaerobiosis without damage to chloroplasts, makes it possible to avoid consumption of reduced methylviologen for the reduction of oxidized electron donors and to exclude the short-circuiting of electron transfer. Under these conditions, photoproduction of H₂ was observed to occur with a rate of 350 to 400 micromoles H₂ per milligram chlorophyll per hour. In this case, the full electron-transferring capability of photosystem I (measured by irreversible photoreduction of methyl red or O₂) is used to produce H₂.     

Cadmium-induced subcellular accumulation of O2·− and H2O2 in pea leaves

Cadmium is a toxic metal that produces disturbances in plant antioxidant defences giving rise to oxidative stress. The effect of this metal on H₂O₂ and O₂^·? production was studied in leaves from pea plants growth for 2 weeks with 50 µm Cd, by histochemistry with diaminobenzidine (DAB) and nitroblue tetrazolium (NBT), respectively. The subcellular localization of these reactive oxygen species (ROS) was studied by cytochemistry with CeCl₃ and Mn/DAB staining for H₂O₂ and O₂^·?, respectively, followed by electron microscopy observation. In leaves from pea plants grown with 50 µm CdCl₂ a rise of six times in the H₂O₂ content took place in comparison with control plants, and the accumulation of H₂O₂ was observed mainly in the plasma membrane of transfer, mesophyll and epidermal cells, as well as in the tonoplast of bundle sheath cells. In mesophyll cells a small accumulation of H₂O₂ was observed in mitochondria and peroxisomes. Experiments with inhibitors suggested that the main source of H₂O₂ could be a NADPH oxidase. The subcellular localization of O₂^·? production was demonstrated in the tonoplast of bundle sheath cells, and plasma membrane from mesophyll cells. The Cd‐induced production of the ROS, H₂O₂ and O₂^·?, could be attributed to the phytotoxic effect of Cd, but lower levels of ROS could function as signal molecules in the induction of defence genes against Cd toxicity. Treatment of leaves from Cd‐grown plants with different effectors and inhibitors showed that ROS production was regulated by different processes involving protein phosphatases, Ca²⁺ channels, and cGMP.     

The role of insulin against hydrogen peroxide-induced oxidative damages in differentiated SH-SY5Y cells

Abstract

Exogenous hydrogen peroxide (H₂O₂) can easily penetrate into biological membranes and enhance the formation of other reactive oxygen species (ROS). In the present study, we have investigated the neuroprotective effects of insulin on H₂O₂-induced toxicity of retinoic acid (RA)-differentiated SH-SY5Y cells. To measure the changes in the cell viability of SH-SY5Y cells at different concentrations of H₂O₂ for 24?h, a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT)-based assay was used and a 100?µM H₂O₂ was selected to establish a model of H₂O₂-induced oxidative stress. Further assays showed that 24?h of 100?µM H₂O₂-induced significant changes in the levels of lactate dehydrogenase (LDH), nitric oxide (NO), ROS, and calcium ion (Ca²⁺) in neuronal cells, but insulin can effectively diminish the H₂O₂-induced oxidative damages to these cells. Moreover, cells treated with insulin increased H₂O₂-induced suppression of glutathione levels and exerted an apparent suppressive effect on oxidative products. The results of insulin treatment with SH-SY5Y cells increased the Bcl-2 levels and decreased the Akt levels. The treatment of insulin had played a protective effect on H₂O₂-induced oxidative stress related to the Akt/Bcl-2 pathways.     

Low hydrogen peroxide production in mitochondria of the long‐lived Arctica islandica: underlying mechanisms for slow aging

The observation of an inverse relationship between lifespan and mitochondrial H₂O₂ production rate would represent strong evidence for the disputed oxidative stress theory of aging. Studies on this subject using invertebrates are surprisingly lacking, despite their significance in both taxonomic richness and biomass. Bivalve mollusks represent an interesting taxonomic group to challenge this relationship. They are exposed to environmental constraints such as microbial H₂S, anoxia/reoxygenation, and temperature variations known to elicit oxidative stress. Their mitochondrial electron transport system is also connected to an alternative oxidase that might improve their ability to modulate reactive oxygen species (ROS) yield. Here, we compared H₂O₂ production rates in isolated mantle mitochondria between the longest‐living metazoan—the bivalve Arctica islandica—and two taxonomically related species of comparable size. In an attempt to test mechanisms previously proposed to account for a reduction of ROS production in long‐lived species, we compared oxygen consumption of isolated mitochondria and enzymatic activity of different complexes of the electron transport system in the two species with the greatest difference in longevity. We found that A. islandica mitochondria produced significantly less H₂O₂ than those of the two short‐lived species in nearly all conditions of mitochondrial respiration tested, including forward, reverse, and convergent electron flow. Alternative oxidase activity does not seem to explain these differences. However, our data suggest that reduced complex I and III activity can contribute to the lower ROS production of A. islandica mitochondria, in accordance with previous studies. We further propose that a lower complex II activity could also be involved.     

Icariside II,a novel phosphodiesterase 5 inhibitor,protects against H2O2‐induced PC12 cells death by inhibiting mitochondria‐mediated autophagy

Oxidative stress is a major cause of cellular injury in a variety of human diseases including neurodegenerative disorders. Thus, removal of excessive reactive oxygen species (ROS) or suppression of ROS generation may be effective in preventing oxidative stress‐induced cell death. This study was designed to investigate the effect of icariside II (ICS II), a novel phosphodiesterase 5 inhibitor, on hydrogen peroxide (H₂O₂)‐induced death of highly differentiated rat neuronal PC12 cells, and to further examine the underlying mechanisms. We found that ICS II pre‐treatment significantly abrogated H₂O₂‐induced PC12 cell death as demonstrated by the increase of the number of metabolically active cells and decrease of intracellular lactate dehydrogenase (LDH) release. Furthermore, ICS II inhibited H₂O₂‐induced cell death through attenuating intracellular ROS production, mitochondrial impairment, and activating glycogen synthase kinase‐3β (GSK‐3β) as demonstrated by reduced intracellular and mitochondrial ROS levels, restored mitochondrial membrane potential (MMP), decreased p‐tyr216‐GSK‐3β level and increased p‐ser9‐GSK‐3β level respectively. The GSK‐3β inhibitor SB216763 abrogated H₂O₂‐induced cell death. Moreover, ICS II significantly inhibited H₂O₂‐induced autophagy by the reducing autophagosomes number and the LC3‐II/LC3‐I ratio, down‐regulating Beclin‐1 expression, and up‐regulating p62/SQSTM1 and HSP60 expression. The autophagy inhibitor 3‐methyl adenine (3‐MA) blocked H₂O₂‐induced cell death. Altogether, this study demonstrated that ICS II may alleviate oxidative stress‐induced autophagy in PC12 cells, and the underlying mechanisms are related to its antioxidant activity functioning via ROS/GSK‐3β/mitochondrial signalling pathways.     

H2O2-induced Leaf Cell Death and the Crosstalk of Reactive Nitric/Oxygen Species([F])

In plants, the chloroplast is the main reactive oxygen species (ROS) producing site under high light stress. Catalase (CAT), which decomposes hydrogen peroxide (H₂O₂), is one of the controlling enzymes that maintains leaf redox homeostasis. The catalase mutants with reduced leaf catalase activity from different plant species exhibit an H₂O₂‐induced leaf cell death phenotype. This phenotype was differently affected by light intensity or photoperiod, which may be caused by plant species, leaf redox status or growth conditions. In the rice CAT mutant nitric oxide excess 1 (noe1), higher H₂O₂ levels induced the generation of nitric oxide (NO) and higher S‐nitrosothiol (SNO) levels, suggesting that NO acts as an important endogenous mediator in H₂O₂‐induced leaf cell death. As a free radical, NO could also react with other intracellular and extracellular targets and form a series of related molecules, collectively called reactive nitrogen species (RNS). Recent studies have revealed that both RNS and ROS are important partners in plant leaf cell death. Here, we summarize the recent progress on H₂O₂‐induced leaf cell death and the crosstalk of RNS and ROS signals in the plant hypersensitive response (HR), leaf senescence, and other forms of leaf cell death triggered by diverse environmental conditions. [ Chengcai Chu (Corresponding author)]     

Oxidative pathways in response to polyunsaturated aldehydes in the marine diatom Skeletonema marinoi (Bacillariophyceae)

Polyunsaturated aldehydes (PUA) have recently been shown to induce reactive oxygen species (ROS) and possibly reactive nitrogen species (RNS, e.g., peroxynitrite) in the diatom Skeletonema marinoi (S. marinoi), which produces high amounts of PUA. We now are attempting to acquire better understanding of which reactive molecular species are involved in the oxidative response of S. marinoi to PUA. We used flow cytometry, the dye dihydrorhodamine 123 (DHR) as the main indicator of ROS (but which is also known to partially detect RNS), and different scavengers and inhibitors of both nitric oxide (NO) synthesis and superoxide dismutase activity (SOD). Both the scavengers Tempol (for ROS) and uric acid (UA, for peroxynitrite) induced a lower DHR‐derived green fluorescence in S. marinoi cells exposed to the PUA, suggesting that both reactive species were produced. When PUA‐exposed S. marinoi cells were treated with the NO scavenger 2‐4‐carboxyphenyl‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide (cPTIO), an opposite response was observed, with an increase in DHR‐derived green fluorescence. A higher DHR‐derived green fluorescence was also observed in the presence of sodium tungstate (ST), an inhibitor of NO production via nitrate reductase. In addition, two different SOD inhibitors, 2‐methoxyestradiol (2ME) and sodium diethyldithiocarbamate trihydrate (DETC), had an effect, with DETC inducing the strongest inhibition after 20 min. These results indicate the involvement of O₂^? generation and SOD activity in H₂O₂ formation (with downstream ROS generation dependent from H₂O₂) in response to PUA exposure. This is relevant as it refines the biological impact of PUA and identifies the specific molecules involved in the response. It is speculated that in PUA‐exposed S. marinoi cells, beyond a certain threshold of PUA, the intracellular antioxidant system is no longer able to cope with the excess of ROS, thus resulting in the observed accumulation of both O₂^?? and H₂O₂. This might be particularly relevant for population dynamics at sea, during blooms, when cell lysis increases and PUA are released. It can be envisioned that in the final stages of blooms, higher local PUA concentrations accumulate, which in turn induces intracellular ROS generation that ultimately leads to cell death and bloom decay.     

Grape seed extract enhances eNOS expression and NO production through regulating calcium‐mediated AKT phosphorylation in H2O2‐treated endothelium

GSE (grape seed extract) has been shown to exhibit protective effects against cardiovascular events and atherosclerosis, although the underlying molecular mechanisms of action are unknown. Herein, we assessed the ability of GSE to enhance eNOS (endothelial nitric oxide synthase) expression and NO (nitric oxide) production in H₂O₂ (hydrogen peroxide)‐treated HUVECs (human umbilical vein endothelial cells). GSE enhanced eNOS expression and NO release in H₂O₂‐treated cells in a dose‐dependent manner. GSE inhibited intracellular ROS (reactive oxygen species) and reduced intracellular calcium in a dose‐dependent manner in H₂O₂‐treated cells, as shown by confocal microscopy. ROS was inhibited in cells pretreated with 5.0 μM GSE, 2.0 μM TG (thapsigargin) and 20.0 μM 2‐APB (2‐aminoethoxydiphenyl borate) instead of 0.25 μM extracellular calcium. In addition, GSE enhanced eNOS expression and reduced ROS production via increasing p‐AKT (AKT phosphorylation) with high extracellular calcium (13 mM). In conclusion, GSE protected against endothelial injury by up‐regulation of eNOS and NO expression via inhibiting InsP₃Rs (inositol 1,4,5‐trisphosphate receptors)‐mediated intracellular excessive calcium release and by activating p‐AKT in endothelial cells.     

Nitric oxide activates superoxide dismutase and ascorbate peroxidase to repress the cell death induced by wounding

Wounding caused by rain, wind, and pathogen may lead plants to onset defense response. Previous studies indicated that mechanical wounding stimulates plants to generate nitric oxide (NO) and hydrogen peroxide (H₂O₂). In this study, the functions of NO and H₂O₂ after wounding in sweet potato (Ipomoea batatas cv. Tainung 57) was further analyzed. Mechanical wounding damaged cells and resulted in necrosis, but the presence of NO donors or NO scavenger might reduce or enhance the cell death caused by wounding, respectively. The amount of H₂O₂ induced by wounding was also decreased or increased when plants were incubated with NO donors or NO scavenger, individually. These results indicate that NO may regulate H₂O₂ generation to affect cell death. NO-induced proteins isolated from two-dimensional electrophoresis were identified to be Copper/Zinc superoxide dismutases (CuZnSODs). The activities of CuZnSODs and ascorbate peroxidase (APX) could be enhanced by NO. In addition, the expression of CuZnSOD and APX was induced by wounding via NO, and their expression was further stimulated by NO through the generation of cGMP. The influx of calcium ions and the activity of NADPH oxidase were also involved in the NO signal transduction pathway inducing APX expression. Collectively, the generation of H₂O₂ in wounded plants might trigger cell death. Meanwhile, the production of NO induced by wounding stimulated signal transducers including cGMP, calcium ions, and H₂O₂ to activate CuZnSOD and APX, which further decreased H₂O₂ level and reduced the cell death caused by wounding.     

Protective Effects of Anthocyanins from Coreopsis tinctoria against Oxidative Stress Induced by Hydrogen Peroxide in MIN6 Cells

Anthocyanins (AC) from Coreopsis tinctoria possesses strong antioxidant properties, while the effects of AC on cells damage induced by reactive oxygen species (ROS) in diabetes mellitus diseases progression have not been reported. The present study was carried out to evaluate the protective property of AC against cellular oxidative stress with an experimental model, H₂O₂‐exposed MIN6 cells. AC could reverse the decrease of cell viability induced by H₂O₂ and efficiently suppressed cellular ROS production and cell apoptosis. In addition, Real‐time PCR and Western blot analyses indicated that AC could protect MIN6 cells against oxidative injury through increasing the translocation of Nrf2 into nuclear, decreasing the phosphorylation level of p38 and up‐regulating the protein expression of antioxidant enzyme (SOD1, SOD2 and CAT). Thus, this study provides evidence to support the beneficial effect of AC in inhibiting MIN6 cells from H₂O₂‐induced oxidative injury.     

VIRAL INFECTION OF EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE) LEADS TO ELEVATED PRODUCTION OF REACTIVE OXYGEN SPECIES1

The effect of viral infection of Emiliania huxleyi (Lohman) Hay and Mohler on the concentration of intracellular reactive oxygen species (ROS), hydrogen peroxide (H₂O₂) excretion and cell photosynthetic capacity (CPC) was examined. During the crash of an E. huxleyi culture induced by viruses intracellular ROS concentrations were generally elevated and reached levels of approximately double those observed in non‐infected control cultures. H₂O₂ concentrations also increased in the media of the infected cultures from background levels of around 130 nM to approximately 580 nM while levels in the controls decreased. These data suggest that oxidative stress is elevated in infected cells. Although the precise mechanism for ROS production was not identified, a traditional defense related oxidative burst was ruled out, as no evidence of a rapid intracellular accumulation of ROS following addition of the virus was found. CPC declined substantially in the infected culture from a healthy 0.6–0 arbitrary units. Clearly infection disrupted normal photosynthetic processes, which could lead to the production of ROS via interruption of the electron transport chain at the PSII level. Alternatively, ROS may also be a necessary requirement for viral replication in E. huxleyi, possibly due to a link with viral‐induced cell death or associated with general death processes.     

Nitric oxide protects against cellular damage produced by methylviologen herbicides in potato plants.

Methylviologen compounds are normally used in agronomy as herbicides. They cause an overproduction of reactive oxygen species (ROS) within chloroplasts, subjecting the plant to a severe oxidative stress. Since nitric oxide (NO) is a bioactive ROS scavenger, we analyzed its effect over some toxic processes caused by the methylviologens diquat and paraquat in potato leaves (Solanum tuberosum L. cv. Pampeana). Three NO donors, (i) sodium nitroprusside (SNP), (ii) S-nitroso-N-acetylpenicillamine, and (iii) a mixed solution of ascorbic acid and NaNO2, were able to prevent chlorophyll loss. Residual products from NO generation and decomposition failed to prevent chlorophyll decline and a specific NO scavenger, carboxy-PTIO, arrested NO-mediated chlorophyll protection. Dichlorophenyldimethylurea, an inhibitor of chloroplastic electron transport, mimicked NO-mediated chlorophyll protection. During oxidative stress, cell ion leakage to intercellular compartments occurs as an early step, leading to a special kind of programmed cell death. NO proved to specifically decrease the extent of ion leakage originated by diquat, since the protection originated by 100 microM SNP was completely arrested by carboxy-PTIO. These results suggest that NO can strongly protect plants from methylviologen damage and strengthen the evidence in favor of NO as a potent antioxidant in some situations.     

Stress‐triggered redox signalling: what's in pROSpect?

Reactive oxygen species (ROS) have a profound influence on almost every aspect of plant biology. Here, we emphasize the fundamental, intimate relationships between light‐driven reductant formation, ROS, and oxidative stress, together with compartment‐specific differences in redox buffering and the perspectives for their analysis. Calculations of approximate H₂O₂ concentrations in the peroxisomes are provided, and based on the likely values in other locations such as chloroplasts, we conclude that much of the H₂O₂ detected in conventional in vitro assays is likely to be extracellular. Within the context of scant information on ROS perception mechanisms, we consider current knowledge, including possible parallels with emerging information on oxygen sensing. Although ROS can sometimes be signals for cell death, we consider that an equally important role is to transmit information from metabolism to allow appropriate cellular responses to developmental and environmental changes. Our discussion speculates on novel sensing mechanisms by which this could happen and how ROS could be counted by the cell, possibly as a means of monitoring metabolic flux. Throughout, we place emphasis on the positive effects of ROS, predicting that in the coming decades they will increasingly be defined as hallmarks of viability within a changing and challenging environment.