Reactive oxygen signalling: the latest news

Molecular characterization of VvSDIR1 from Vitis vinifera and its functional analysis by heterologous expression in Nicotiana tabacum

The proteins harboring really interesting new gene (RING) finger domains comprise a large family and play key roles in a variety of cellular processes. One among them is the tolerance to biotic and abiotic stresses in plants. In the present study, we characterize Vitis vinifera salt- and drought-induced RING finger 1 (VvSDIR1) a homologue of the Arabidopsis SDIR1 gene obtained from V. vinifera. The VvSDIR1 gene was identified using in silico approaches and encodes a membrane-localized protein. This was evident as expression of VvSDIR1 fused with green fluorescent protein was detected in cell membrane. Southern blot analysis indicates that VvSDIR1 is present in single copy number in grape genome. The expression of VvSDIR1 gene is elevated by multiple abiotic stresses like salt, drought, cold, and heat as well as upon exogenous application of methyl jasmonate, salicylic acid, methyl viologen, abscisic acid, and ethephon. In silico analysis shows that the VvSDIR1 cDNA is 831-bp long and codes for a 276-amino acid-long protein containing a characteristic RING finger domain in its C-terminal end. Overexpression of VvSDIR1 in tobacco leads to enhanced transcript levels of many genes, homologues of which are reported to be important in regulating many stress conditions. The heterologous expression of VvSDIR1 in tobacco was found to enhance the oxidative stress tolerance in tobacco. Tobacco lines transgenic for VvSDIR1 showed enhanced tolerance to treatment with methyl viologen, NaCl, and polyethylene glycol. To the best of our knowledge, this is the first report of the heterologous expression of VvSDIR1 in oxidative stress tolerance in transgenic tobacco.

Hydrogen peroxide functions as a secondary messenger for brassinosteroids-induced CO2 assimilation and carbohydrate metabolism in Cucumis sativus

Brassinosteroids (BRs) are potent regulators of photosynthesis and crop yield in agricultural crops; however, the mechanism by which BRs increase photosynthesis is not fully understood. Here, we show that foliar application of 24-epibrassinolide (EBR) resulted in increases in CO(2) assimilation, hydrogen peroxide (H(2)O(2)) accumulation, and leaf area in cucumber. H(2)O(2) treatment induced increases in CO(2) assimilation whilst inhibition of the H(2)O(2) accumulation by its generation inhibitor or scavenger completely abolished EBR-induced CO(2) assimilation. Increases of light harvesting due to larger leaf areas in EBR- and H(2)O(2)-treated plants were accompanied by increases in the photochemical efficiency of photosystem II (Φ(PSII)) and photochemical quenching coefficient (q(P)). EBR and H(2)O(2) both activated carboxylation efficiency of ribulose-1,5-bisphosphate oxygenase/carboxylase (Rubisco) from analysis of CO(2) response curve and in vitro measurement of Rubisco activities. Moreover, EBR and H(2)O(2) increased contents of total soluble sugar, sucrose, hexose, and starch, followed by enhanced activities of sugar metabolism such as sucrose phosphate synthase, sucrose synthase, and invertase. Interestingly, expression of transcripts of enzymes involved in starch and sugar utilization were inhibited by EBR and H(2)O(2). However, the effects of EBR on carbohydrate metabolisms were reversed by the H(2)O(2) generation inhibitor diphenyleneodonium (DPI) or scavenger dimethylthiourea (DMTU) pretreatment. All of these results indicate that H(2)O(2) functions as a secondary messenger for EBR-induced CO(2) assimilation and carbohydrate metabolism in cucumber plants. Our study confirms that H(2)O(2) mediates the regulation of photosynthesis by BRs and suggests that EBR and H(2)O(2) regulate Calvin cycle and sugar metabolism via redox signaling and thus increase the photosynthetic potential and yield of crops.

The MPK6-ERF6-ROS-responsive cis-acting Element7/GCC box complex modulates oxidative gene transcription and the oxidative response in Arabidopsis

Reactive oxygen species (ROS) have been characterized as both important signaling molecules and universal stressors that mediate many developmental and physiological responses. So far, details of the transcriptional mechanism of ROS-responsive genes are largely unknown. In the study reported here, we identified seven potential ROS-responsive cis-acting elements (ROSEs) from the promoters of genes up-regulated by ROS in Arabidopsis (Arabidopsis thaliana). We also found that the APETALA2/ethylene-responsive element binding factor6 (ERF6) could bind specifically to the ROSE7/GCC box. Coexpression of ERF6 enhanced luciferase activity driven by ROSE7. The deficient mutants of ERF6 showed growth retardation and higher sensitivity to photodamage. ERF6 interacted physically with mitogen-activated protein kinase6 (MPK6) and also served as a substrate of MPK6. MPK6-mediated ERF6 phosphorylation at both serine-266 and serine-269 affected the dynamic alternation of the ERF6 protein, which resulted in changes in ROS-responsive gene transcription. These data might provide new insight into the mechanisms that regulate ROS-responsive gene transcription via a complex of MPK6, ERF6, and the ROSE7/GCC box under oxidative stress or a fluctuating light environment.

Cloning and molecular characterization of a putative bZIP transcription factor VvbZIP23 from Vitis vinifera

The proteins harboring bZIP domains comprise a large family and play key roles in many cellular processes, one of them being tolerance to biotic and abiotic stresses in plants. In the present study, we characterize a putative bZIP transcription factor from Vitis vinifera namely VvbZIP23. Our studies revealed that a GFP fusion of VvbZIP23 is localized in the nucleus showing VvbZIP23 codes for a nuclear localized protein. VvbZIP23 identified by in silico approaches from grapevine DNA databases available in the public domain NCBI is present in a single copy in the grapevine genome as shown by Southern blot analysis. Expression of VvbZIP23 is induced by a wide spectrum of abiotic stresses, including drought, salt, and cold. Exogenous application of signaling chemicals like abscisic acid, methyl viologen, salicylic acid, jasmonic acid, and ethephon also induced expression of VvbZIP23. This shows that VvbZIP23 is involved in regulating a number of stress responses in V. vinifera. The 5' proximal region of VvbZIP23 contains many cis-acting elements, which show induction of VvbZIP23 expression in multiple stress responses. Transcripts of VvbZIP23 were found in many parts of the grapevine plant with the highest expression detected in leaves. Further in silico analysis shows that the open reading frame of VvbZIP23 is 822 bp long and codes for a 273 amino acid long protein having a characteristic bZIP domain in its N-terminal end. Overexpression of VvbZIP23-GFP fusion protein in grapevine callus leads to enhanced transcript levels of genes, homologues of which are reported to be important in regulating many stress conditions.

Nitric oxide (NO) counteracts cadmium induced cytotoxic processes mediated by reactive oxygen species (ROS) in Brassica juncea: cross-talk between ROS, NO and antioxidant responses

Research on NO in plants has achieved huge attention in recent years mainly due to its function in plant growth and development under biotic and abiotic stresses. In the present study, we investigated Cd induced NO generation and its relationship to ROS and antioxidant regulation in Brassica juncea. Cd accumulated rapidly in roots and caused oxidative stress as indicated by increased level of lipid peroxidation and H2O2 thus, inhibiting the overall plant growth. It significantly decreased the root length, leaf water content and photosynthetic pigments. A rapid induction in intracellular NO was observed at initial exposures and low concentrations of Cd. A 2.74-fold increase in intracellular NO was recorded in roots treated with 25 μM Cd than control. NO effects on Malondialdehyde (MDA) content and on antioxidant system was investigated by using sodium nitroprusside (SNP), a NO donor and a scavenger, [2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylinidazoline-1-oxyl-3-oxide] (cPTIO). Roots pretreated with 5 mM SNP for 6 h when exposed to 25 μM Cd for 24 h reduced the level of proline, non-protein thiols, SOD, APX and CAT in comparison to only Cd treatments. However, this effect was almost blocked by 100 μM cPTIO pretreatment to roots for 1 h. This ameliorating effect of NO was specific because cPTIO completely reversed the effect in the presence of Cd. Thus, the present study report that NO strongly counteracts Cd induced ROS mediated cytotoxicity in B. juncea by controlling antioxidant metabolism as the related studies are not well reported in this species.

A laterally acquired galactose oxidase-like gene is required for aerial development during osmotic stress in Streptomyces coelicolor

Phylogenetic reconstruction revealed that most Actinobacterial orthologs of S. coelicolor SCO2837, encoding a metal-dependent galactose oxidase-like protein, are found within Streptomyces and were probably acquired by horizontal gene transfer from fungi. Disruption of SCO2837 (glxA) caused a conditional bld phenotype that could not be reversed by extracellular complementation. Studies aimed at characterising the regulation of expression of glxA showed that it is not a target for other bld genes. We provide evidence that glxA is required for osmotic adaptation, although independently from the known osmotic stress response element SigB. glxA has been predicted to be part of an operon with the transcription unit comprising the upstream cslA gene and glxA. However, both phenotypic and expression studies indicate that it is also expressed from an independent promoter region internal to cslA. GlxA displays an in situ localisation pattern similar to that one observed for CslA at hyphal tips, but localisation of the former is independent of the latter. The functional role of GlxA in relation to CslA is discussed.

Putative role of proteins involved in detoxification of reactive oxygen species in the early response to gravitropic stimulation of poplar stems

Gravity perception and gravitropic response are essential for plant development. In herbaceous species it is widely accepted that one of the primary events in gravity perception involves the displacement of amyloplasts within specialized cells. However the signaling cascade leading to stem reorientation is not fully known especially in woody species in which primary and secondary growth occur. Several different second messengers and proteins have been suggested to be involved in signal transduction of gravitropism. Reactive oxygen species (ROS) have been implicated as second messengers in several plant hormone responses. It has been shown that ROS are asymmetrically generated in roots by gravistimulation to regions of reduced growth. Proteins involved in detoxification of ROS and defense were identified by mass spectrometry: i.e., Thioredoxin h (Trx h), CuZn superoxide dismutase (CuZn SOD), ascorbate peroxidase (APX2), oxygen evolving enhancer 1 (OEE1), oxygen evolving enhancer 2 (OEE2), and ATP synthase. These differentially accumulated proteins that correspond to detoxification of ROS were analyzed at the mRNA level. The mRNA levels showed different expression patterns than those of the corresponding proteins, and revealed that transcription levels were not completely concomitant with translation. Our data showed that these proteins may play a role in the early response to gravitropic stimulation.

Ethylene-induced overproduction of reactive oxygen species is responsible for the development of watersoaking in immature cucumber fruit

Watersoaking is an ethylene-induced disorder observed in some members of the Cucurbitaceae including cucumber (Cucumis sativus L.), watermelon (Citrullus lanatus Thunb. Matsum and Nakai), and tropical pumpkin (Cucurbita moschata Duch.). Previous studies have found that immature beit-alpha cucumber (cv. Manar) exhibit watersoaking after 6d of continuous exposure to 10 μLL(-1) ethylene in air (21 kPa O(2)). The present study was designed to investigate the early dynamics of ethylene responses in immature cucumber fruit in order to provide insight into the watersoaking triggering mechanism. Changes in respiration, epidermal color, firmness, reactive oxygen species (ROS) production and electrolyte leakage were evaluated as a function of time under different ethylene concentrations and exposure duration. Ethylene concentrations exceeding 10 μLL(-1) did not accelerate changes in any of the evaluated responses. The first detectable change was a significant rise in respiration on day 2, followed by a significant rise in ROS on day 4, and significant degreening, mesocap softening, and increased electrolyte leakage on day 6; the latter responses coincident with incipient watersoaking. Varying the duration of exposure to ethylene indicated that the critical exposure time is between 2 and 4d. Notably, all deleterious responses to ethylene were suppressed under a hypoxic atmosphere. A model is proposed in which ethylene induces a sharp increase in respiration with a concomitant sharp rise in ROS, which the immature fruit is incapable of quenching. The resulting production of excess ROS leads to discoloration and membrane deterioration, leading to the release of cytoplasmic content, rapid softening, and the visual symptom of watersoaking.

Regulation of fruit and seed response to heat and drought by sugars as nutrients and signals

A large body of evidence shows that sugars function both as nutrients and signals to regulate fruit and seed set under normal and stress conditions including heat and drought. Inadequate sucrose import to, and its degradation within, reproductive organs cause fruit and seed abortion under heat and drought. As nutrients, sucrose-derived hexoses provide carbon skeletons and energy for growth and development of fruits and seeds. Sugar metabolism can also alleviate the impact of stress on fruit and seed through facilitating biosynthesis of heat shock proteins (Hsps) and non-enzymic antioxidants (e.g., glutathione, ascorbic acid), which collectively maintain the integrity of membranes and prevent programmed cell death (PCD) through protecting proteins and scavenging reactive oxygen species (ROS). In parallel, sugars (sucrose, glucose, and fructose), also exert signaling roles through cross-talk with hormone and ROS signaling pathways and by mediating cell division and PCD. At the same time, emerging data indicate that sugar-derived signaling systems, including trehalose-6 phosphate (T6P), sucrose non-fermenting related kinase-1 (SnRK), and the target of rapamycin (TOR) kinase complex also play important roles in regulating plant development through modulating nutrient and energy signaling and metabolic processes, especially under abiotic stresses where sugar availability is low. This review aims to evaluate recent progress of research on abiotic stress responses of reproductive organs focusing on roles of sugar metabolism and signaling and addressing the possible biochemical and molecular mechanism by which sugars regulate fruit and seed set under heat and drought.

OsDGL1, a homolog of an oligosaccharyltransferase complex subunit, is involved in N-glycosylation and root development in rice

A leaky rice mutant was isolated from an ethylmethane sulfonate (EMS)-mutagenized rice library based on its short root phenotype. The map-based cloning results showed that the mutant was due to a point mutation in the intron of OsDGL1 (LOC_Os07g10830), which encodes the dolichyl-diphosphooligosaccharide-protein glycosyltransferase 48 kDa subunit precursor. The mutation results in premature termination of protein synthesis. OsDGL1 is an ortholog of Arabidopsis DGL1, human OST48 and yeast WBP1, an essential protein subunit of the oligosaccharyltransferase (OST) complex, which is involved in N-glycosylation in eukaryotes. The leaky rice mutant, Osdgl1, displayed a change of matrix polysaccharides in its root cell wall, shorter root cell length, smaller root meristem and cell death in the root. Consistent with the known function of the OST complex in eukaryotes, the Osdgl1 mutation leads to a defect in N-glycosylation in the root. It was also found that reactive oxygen species (ROS) may be involved in this process.

Catalytic Properties and Immobilization Studies of Catalase fromMalva sylvestrisL

Catalase was partially purified fromMalva sylvestrisL. and immobilized onto chitosan. Then, its catalytic properties were investigated. (NH4)2SO4precipitation and dialysis were performed in the extracted enzyme. Further purification was performed with sephadex G-200 column. Kinetic studies of the purified enzyme activity were measured and characterized. The inhibitory effects of KCN, NaN3, CuSO4, and EDTA onM. sylvestrisL. catalase activity were observed except NaCl. Furthermore,M. sylvestrisL. catalase was immobilized covalently with glutaraldehyde onto chitosan particles. The pH and temperature optima as well as the changes in the kinetics (Km, Vmax) of the immobilized and freeM. sylvestrisL. catalase were determined. The Km value for immobilized catalase (23.4 mM) was higher than that of free enzyme (17.6 mM). Optimum temperature was observed higher than that of the free enzyme. The optimum pH was the same for both free and immobilized catalases (pH 7.50). Immobilized catalase showed higher storage and thermal stabilities than free catalases. Free catalase lost all its activity within 60 days whereas immobilized catalase lost 45% of its activity during the same incubation period at 4°C. The remaining immobilized catalase activity was about 70% after 8 cycles of batch operations.

Reactive oxygen species generation and signaling in plants

The introduction of molecular oxygen into the atmosphere was accompanied by the generation of reactive oxygen species (ROS) as side products of many biochemical reactions. ROS are permanently generated in plastids, peroxisomes, mitochiondria, the cytosol and the apoplast. Imbalance between ROS generation and safe detoxification generates oxidative stress and the accumulating ROS are harmful for the plants. On the other hand, specific ROS function as signaling molecules and activate signal transduction processes in response to various stresses. Here, we summarize the generation of ROS in the different cellular compartments and the signaling processes which are induced by ROS.

A novel role for cyanide in the control of cucumber (Cucumis sativus L.) seedlings response to environmental stress

The effects of potassium cyanide (KCN) pretreatment on the response of cucumber (Cucumis sativus L.) plants to salt, polyethylene glycol (PEG) and cold stress were investigated in the present study. Here, we found that KCN pretreatment improved cucumber seedlings tolerance to stress conditions with maximum efficiency at a concentration of 20 µM. The results showed that pretreatment with 20 µM KCN alleviated stress-induced oxidative damage in plant cells and clearly induced the activity of alternative oxidase (AOX) and the ethylene production. Furthermore, the structures of thylakoids and mitochondria in the KCN-pretreated seedlings were less damaged by the stress conditions, which maintained higher total chlorophyll content, photosynthetic rate and photosystem II (PSII) proteins levels than the control. Importantly, the addition of the AOX inhibitor salicylhydroxamic acid (1 mm; SHAM) decreased plant resistance to environmental stress and even compromised the cyanide (CN)-enhanced stress tolerance. Therefore, our findings provide a novel role of CN in plant against environmental stress and indicate that the CN-enhanced AOX might contribute to the reactive oxygen species (ROS) scavenging and the protection of photosystem by maintaining energy charge homoeostasis from chloroplast to mitochondria.

Spatial and temporal nature of reactive oxygen species production and programmed cell death in elm (Ulmus pumila L.) seeds during controlled deterioration

Seed deterioration is poorly understood and remains an active area for research. Seeds of elm (Ulmus pumila L.) were aged at 37 °C above water [controlled deterioration treatment (CDT)] for various lengths of time to assess programmed cell death (PCD) and reactive oxygen species (ROS) product in embryonic tissues during a 5 d period. The hallmarks of PCD were identified in the elm seeds during CDT including TUNEL experiments, DNA laddering, cytochrome c (cyt c) leakage and enzymatic activities. These analyses indicated that PCD occurred systematically and progressively in deteriorated elm seeds. Cyt c release and increase in caspase-3-like/DEVDase activity occurred during CDT, which could be suppressed by ascorbic acid (AsA) and caspase-3 inhibitor Ac-DEVD-CHO, respectively. In situ localization of ROS production indicated that the distinct spatial-temporal signature of ROS during CDT coincided with the changes in PCD hallmark features. Multiple antioxidant elements were activated during the first few days of CDT, but were subsequently depleted as PCD progressed. Taken together, our findings identify PCD as a key mechanism that occurs asymmetrically during elm seeds CDT and suggest an important role for PCD in seeds deterioration.

The PSBP2 protein of Chlamydomonas reinhardtii is required for singlet oxygen-dependent signaling

In the green alga Chlamydomonas reinhardtii, the cytosolic Glutathione Peroxidase 5 gene (GPX5) is known to be transcriptionally up-regulated in response to singlet oxygen ((1)O(2)). As demonstrated by previous studies, fusion of the promoter region of GPX5 to the Arylsulfatase 2 gene (ARS2) creates an effective reporter system that can be used to monitor (1)O(2)-driven GPX5 expression. This system was also used in this study to generate a stably transformed C. reinhardtii strain which expresses ARS2 in a (1)O(2)-dependent manner, resulting in the synthesis of a functional protein with detectable activity. Using the strain of C. reinhardtii harboring a (1)O(2)-sensitive reporter construct, a secondary mutagenic screen was performed. This allowed identification of mutant cell lines that were unable to up-regulate expression of the GPX5-ARS2 fusion in response to (1)O(2). In one of these lines, the mutation was subsequently localized to the first exon of the PSBP-like gene (PSBP2). The PSBP2 gene is part of a small protein family in C. reinhardtii, also present in all angiosperms studied thus far. While each member of the PSBP protein family contains a similar domain to the PSBP1 protein, which is a member of the oxygen evolving complex of photosystem II (PSII), the PSBP2 protein does not appear to be involved in PSII function, but may function as a sensor and/or signal mediating molecule of the (1)O(2) generated in the chloroplast.

Hydrogen peroxide functions as a secondary messenger for brassinosteroids-induced CO2 assimilation and carbohydrate metabolism in Cucumis sativus

Brassinosteroids (BRs) are potent regulators of photosynthesis and crop yield in agricultural crops; however, the mechanism by which BRs increase photosynthesis is not fully understood. Here, we show that foliar application of 24-epibrassinolide (EBR) resulted in increases in CO(2) assimilation, hydrogen peroxide (H(2)O(2)) accumulation, and leaf area in cucumber. H(2)O(2) treatment induced increases in CO(2) assimilation whilst inhibition of the H(2)O(2) accumulation by its generation inhibitor or scavenger completely abolished EBR-induced CO(2) assimilation. Increases of light harvesting due to larger leaf areas in EBR- and H(2)O(2)-treated plants were accompanied by increases in the photochemical efficiency of photosystem II (Φ(PSII)) and photochemical quenching coefficient (q(P)). EBR and H(2)O(2) both activated carboxylation efficiency of ribulose-1,5-bisphosphate oxygenase/carboxylase (Rubisco) from analysis of CO(2) response curve and in vitro measurement of Rubisco activities. Moreover, EBR and H(2)O(2) increased contents of total soluble sugar, sucrose, hexose, and starch, followed by enhanced activities of sugar metabolism such as sucrose phosphate synthase, sucrose synthase, and invertase. Interestingly, expression of transcripts of enzymes involved in starch and sugar utilization were inhibited by EBR and H(2)O(2). However, the effects of EBR on carbohydrate metabolisms were reversed by the H(2)O(2) generation inhibitor diphenyleneodonium (DPI) or scavenger dimethylthiourea (DMTU) pretreatment. All of these results indicate that H(2)O(2) functions as a secondary messenger for EBR-induced CO(2) assimilation and carbohydrate metabolism in cucumber plants. Our study confirms that H(2)O(2) mediates the regulation of photosynthesis by BRs and suggests that EBR and H(2)O(2) regulate Calvin cycle and sugar metabolism via redox signaling and thus increase the photosynthetic potential and yield of crops.

Hydrogen peroxide induced phenylpropanoids pathway eliciting a defensive response in plants micropropagated in Temporary Immersion Bioreactors (TIBs)

The relation between the oxidative burst and phenylpropanoid pathways has been studied using the sugarcane cultivar C86-56, which does not release phenolics in agar-base micropropagation systems. In stationary liquid culture, a significant production of phenolic compounds and plant survival were determined in sugarcane plants treated with 5mM H(2)O(2). The spectrophotometer determinations and the gene expression analysis corroborated that releasing of phenolics and soluble θ-quinones was induced during the first 24h of treatment. In comparison with the control treatments, sugarcane plants treated with H(2)O(2) demonstrated differences in the micropropagation-related variables when multiplied in Temporary Immersion Bioreactors (TIBs) supplemented with polyethyleneglycol (PEG 20%). Expression of selected genes related to photosynthesis, ethylene, auxins, oxidative burst, and defense pathways were confirmed during the entire PEG 20% stress in the plants coming from the 5mM H(2)O(2) treatment; whereas, much more heterogeneous expression patterns were evidenced in plants stressed with PEG but not previously treated with H(2)O(2). RT-PCR expression analysis supports the hypothesis that while H(2)O(2) induces the oxidative burst, the phenylpropanoids pathways elicit and maintain the defensive response mechanism in micropropagated sugarcane plants.

Integration of stress-related and reactive oxygen species-mediated signals by Topoisomerase VI in Arabidopsis thaliana

Environmental stress often leads to an increased production of reactive oxygen species that are involved in plastid-to-nucleus retrograde signaling. Soon after the release of singlet oxygen ((1)O(2)) in chloroplasts of the flu mutant of Arabidopsis, reprogramming of nuclear gene expression reveals a rapid transfer of signals from the plastid to the nucleus. We have identified extraplastidic signaling constituents involved in (1)O(2)-initiated plastid-to-nucleus signaling and nuclear gene activation after mutagenizing a flu line expressing the luciferase reporter gene under the control of the promoter of a (1)O(2)-responsive AAA-ATPase gene (At3g28580) and isolating second-site mutations that lead to a constitutive up-regulation of the reporter gene or abrogate its (1)O(2)-dependent up-regulation. One of these mutants, caa39, turned out to be a weak mutant allele of the Topoisomerase VI (Topo VI) A-subunit gene with a single amino acid substitution. Transcript profile analysis of flu and flu caa39 mutants revealed that Topo VI is necessary for the full activation of AAA-ATPase and a set of (1)O(2)-responsive transcripts in response to (1)O(2). Topo VI binds to the promoter of the AAA-ATPase and other (1)O(2)-responsive genes, and hence could directly regulate their expression. Under photoinhibitory stress conditions, which enhance the production of (1)O(2) and H(2)O(2), Topo VI regulates (1)O(2)-responsive and H(2)O(2)-responsive genes in a distinct manner. These results suggest that Topo VI acts as an integrator of multiple signals generated by reactive oxygen species formed in plants under adverse environmental conditions.

Role of acylamino acid-releasing enzyme/oxidized protein hydrolase in sustaining homeostasis of the cytoplasmic antioxidative system

Acylamino acid-releasing enzyme/oxidized protein hydrolase (AARE/OPH) has been biochemically demonstrated to be a bifunctional protease that has exopeptidase activity against Nα-acylated peptides and endopeptidase activity against oxidized and glycated proteins; however, its physiological role remains unknown. In this study, to determine its physiological significance, we produced AARE/OPH-overexpressing and -suppressed plants and assessed the biological impacts of AARE/OPH. The subcellular localization of Arabidopsis AARE/OPH was found to be cytoplasmic and nuclear by transient expression analysis of tdTomato-fused Arabidopsis AARE/OPH. Overexpression of AARE/OPH exhibited no apparent effect on the level of oxidized proteins because wild types probably have inherently high AARE/OPH activity. Through RNAi gene suppressing, we successfully produced AARE/OPH-suppressed Arabidopsis plants (aare) that exhibited almost no AARE activity. In the aare plant, electrolyte leakage by methyl viologen treatment was enhanced compared to that of non-transformant plants, suggesting that the plasma membranes of aare easily suffered oxidative damage, probably as a result of deterioration of the cytoplasmic antioxidative system. Correspondingly, proteomic analysis revealed that the aare plant accumulated a number of oxidized proteins including cytoplasmic antioxidant enzymes. On the basis of these results, we concluded that AARE/OPH plays a homeostatic role in sustaining the cytoplasmic antioxidative system.

Ectopic expression of VpALDH2B4, a novel aldehyde dehydrogenase gene from Chinese wild grapevine (Vitis pseudoreticulata), enhances resistance to mildew pathogens and salt stress in Arabidopsis

Aldehyde dehydrogenases (ALDHs) catalyze the irreversible oxidation of a broad spectrum of reactive aldehydes to their corresponding carboxylic acids. Although the proteins have been studied from various organisms and at different growth stages in plants, their potential roles in pathogen infection have not been examined. Here we isolated and functionally characterized a pathogen-inducible ALDH gene (VpALDH2B4) from Chinese wild grapevine Vitis pseudoreticulata accession Baihe-35-1. When transiently expressed in Arabidopsis leaves, VpALDH2B4 was found to be localized in mitochondria. Escherichia coli expressed GST-VpALDH2B4 exhibited ALDH activity in vitro and was capable of utilizing malondialdehyde (MDA), acetaldehyde and glyceraldehydes as its substrate. Over-expression of VpALDH2B4 in Arabidopsis resulted in hypersensitive response-like cell death, enhanced resistance to downy mildew and powdery mildew presumably via the SA-signaling pathway. The same Arabidopsis transgenic plants also showed enhanced tolerance to salt stress, which is accompanied by less MDA accumulation and upregulation of the stress-responsive superoxide dismutase activity. Taken together, our results suggest that VpALDH2B4 and perhaps its orthologous genes may be involved in responses of plants to stresses imposed by both biotrophic pathogens and high salinity conditions.

Apoplastic calcium executes a shut-down function on plant peroxidases: a hypothesis

Recently it was demonstrated that PO activity is switched by calcium within the typical range of apoplastic free calcium concentrations (Plieth and Vollbehr, Plant Signal Behav 2012;7: 650-660). The heat stability of POs is also dependent on calcium. Here, a scenario is put forward which assigns calcium a switch-off function under heat: Peroxidases are switched off by heat stress-triggered apoplastic calcium depletion. It is assumed that this initiates apoplastic accumulation of reactive oxygen species (ROS) and eventually triggers a self-amplifying cascade of cellular events involving plasma membrane ion transport. Calcium depletion-initiated ROS accumulation (CaDIRA) may also trigger signal percolation and the formation of systemic responses to many different stress factors in plants. This hypothesis can explain some as yet unexplained observations.

Cardiac response to chronic intermittent hypoxia with a transition from adaptation to maladaptation: the role of hydrogen peroxide

Obstructive sleep apnea (OSA) is a highly prevalent respiratory disorder of sleep, and associated with chronic intermittent hypoxia (CIH). Experimental evidence indicates that CIH is a unique physiological state with potentially “adaptive” and “maladaptive” consequences for cardio-respiratory homeostasis. CIH is also a critical element accounting for most of cardiovascular complications of OSA. Cardiac response to CIH is time-dependent, showing a transition from cardiac compensative (such as hypertrophy) to decompensating changes (such as failure). CIH-provoked mild and transient oxidative stress can induce adaptation, but severe and persistent oxidative stress may provoke maladaptation. Hydrogen peroxide as one of major reactive oxygen species plays an important role in the transition of adaptive to maladaptive response to OSA-associated CIH. This may account for the fact that although oxidative stress has been recognized as a driver of cardiac disease progression, clinical interventions with antioxidants have had little or no impact on heart disease and progression. Here we focus on the role of hydrogen peroxide in CIH and OSA, trying to outline the potential of antioxidative therapy in preventing CIH-induced cardiac damage.

Differential expression of Arabidopsis defense-related genes in response to sulfur dioxide

Sulfur dioxide (SO(2)) is one of the most common and harmful air pollutants. To analyze cellular responses to SO(2), we investigated the transcript alterations, antioxidant enzyme activities and reactive oxygen species (ROS) levels in Arabidopsisthaliana (Col-0) exposed to SO(2). Transcriptional profiling using Affymetrix GeneChip technology identified 494 genes differentially expressed (≥2-fold change) in plants exposed to 30 mg m(-3) SO(2) for 72 h, including up-regulation of some defense-related genes encoding antioxidant enzymes and heat shock proteins. Moreover, numerous genes encoding pathogenesis-related proteins and enzymes required for the phenylpropanoid pathway and for cell wall modification were highly activated upon SO(2) exposure. We selected eight of the significantly differentially expressed defense-related genes for analysis using semi-quantitative RT-PCR and confirmed that their expression was up-regulated under SO(2) stress. In addition, SO(2) exposure caused the enhancement of ROS production, and also increased activities of antioxidant enzymes (superoxide dismutase, peroxidase, glutathione peroxidase and glutathione S-transferase) in Arabidopsis plants. Our results indicated that increased ROS may act as a signal to induce defense responses, which provide enhanced defense capacity to protect plants against SO(2) and other environmental stress. This is the first transcriptional profiling that identifies novel genes and pathways involved in SO(2) stress responses in plant cells. These data will be helpful for better understanding the molecular basis for plant adaptation to SO(2) stress.

Sulfur dioxide induced programmed cell death in Vicia guard cells

Sulfur dioxide (SO(2)) induced nuclear condensation and nuclear fragmentation and rapid loss of guard cell viability in detached epidermis of Vicia leaves at concentrations of 1 mM and higher (3 h exposure). Caspase inhibitors Z-Asp-CH(2)-DCB (0.1 mM) and TLCK (0.1 mM) markedly suppressed SO(2)-induced cell death. The typical nuclear morphological changes and the inhibition effects of caspase inhibitors suggest the activation of a programmed cell death (PCD) pathway. SO(2)-induced cell death can be blocked by either antioxidants (0.1 mM AsA or 200 U/mL CAT) or Ca(2+) antagonists (0.1mM EGTA or LaCl(3)). AsA and CAT also blocked SO(2)-induced ROS production and [Ca(2+)](cyt) increase. However, EGTA and LaCl(3) can inhibit SO(2)-induced [Ca(2+)](cyt) increase, but cannot suppress SO(2)-induced ROS production. Our results indicate that high concentrations of SO(2) induce guard cell death via a PCD pathway through ROS mediating [Ca(2+)](cyt) elevation, which causes harmful effects to plants.

Exogenous hydrogen peroxide reversibly inhibits root gravitropism and induces horizontal curvature of primary root during grass pea germination

During germination in distilled water (dH(2)O) on a horizontally positioned Petri dish, emerging primary roots of grass pea (Lathyrus sativus L.) grew perpendicular to the bottom of the Petri dish, due to gravitropism. However, when germinated in exogenous hydrogen peroxide (H(2)O(2)), the primary roots grew parallel to the bottom of the Petri dish and asymmetrically, forming a horizontal curvature. Time-course experiments showed that the effect was strongest when H(2)O(2) was applied prior to the emergence of the primary root. H(2)O(2) failed to induce root curvature when applied post-germination. Dosage studies revealed that the frequency of primary root curvature was significantly enhanced with increased H(2)O(2) concentrations. This curvature could be directly counteracted by dimethylthiourea (DMTU), a scavenger of H(2)O(2), but not by diphenylene iodonium (DPI) and pyridine, inhibitors of H(2)O(2) production. Exogenous H(2)O(2) treatment caused both an increase in the activities of H(2)O(2)-scavenging enzymes [including ascorbate peroxidase (APX: EC 1.11.1.11), catalase (CAT: EC 1.11.1.6) and peroxidase (POD: EC 1.11.1.7)] and a reduction in endogenous H(2)O(2) levels and root vitality. Although grass pea seeds absorbed exogenous H(2)O(2) during seed germination, DAB staining of paraffin sections revealed that exogenous H(2)O(2) only entered the root epidermis and not inner tissues. These data indicated that exogenously applied H(2)O(2) could lead to a reversible loss of the root gravitropic response and a horizontal curvature in primary roots during radicle emergence of the seedling.

Photosynthetic characteristics and enzymatic antioxidant capacity of leaves from wheat cultivars exposed to drought

Two durum (Triticum durum L.), Barakatli-95 and Garagylchyg-2; and two bread (Triticum aestivum L.) wheat cultivars, Azamatli-95 and Giymatli-2/17 with different sensitivities to drought were grown in the field on a wide area under normal irrigation and severe water deficit. Drought caused a more pronounced inhibition in photosynthetic parameters in the more sensitive cvs Garagylchyg-2 and Giymatli-2/17 compared with the tolerant cvs Barakatli-95 and Azamatli-95. Upon dehydration, a decline in total chlorophyll and relative water content was evident in all cultivars, especially in later periods of ontogenesis. Potential quantum yield of PS II (F(v)/F(m) ratio) in cv Azamatli-95 was maximal during stalk emergency stage at the beginning of drought. This parameter increased in cv Garagylchyg-2, while in tolerant cultivar Barakatli-95 significant changes were not observed. Contrary to other wheat genotypes in Giymatli-2/17 drought caused a decrease in PS II quantum yield. Drought-tolerant cultivars showed a significant increase in CAT activity as compared to control plants. In durum wheat cultivars maximal activity of CAT was observed at the milk ripeness and in bread wheat cultivars at the end of flowering. APX activity also increased in drought-treated leaves: in tolerant wheat genotypes maximal activity occurred at the end of flowering, in sensitive ones at the end of ear formation. GR activity increased in the tolerant cultivars under drought stress at all stages of ontogenesis. SOD activity significantly decreased in sensitive cultivars and remained at the control level or increased in resistant ones. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

Reactive oxygen species from chloroplasts contribute to 3-acetyl-5-isopropyltetramic acid-induced leaf necrosis of Arabidopsis thaliana

3-Acetyl-5-isopropyltetramic acid (3-AIPTA), a derivate of tetramic acid, is responsible for brown leaf-spot disease in many plants and often kills seedlings of both mono- and dicotyledonous plants. To further elucidate the mode of action of 3-AIPTA, during 3-AIPTA-induced cell necrosis, a series of experiments were performed to assess the role of reactive oxygen species (ROS) in this process. When Arabidopsis thaliana leaves were incubated with 3-AIPTA, photosystem II (PSII) electron transport beyond Q(A) (the primary plastoquinone acceptor of PSII) and the reduction of the end acceptors at the PSI acceptor side were inhibited; this was followed by increase in charge recombination and electron leakage to O(2), resulting in chloroplast-derived oxidative burst. Furthermore, the main antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) lost their activity. Excess ROS molecules directly attacked a variety of cellular components and subsequently caused electrolyte leakage, lipid peroxidation and cell membrane disruption. Finally, this led to cell destruction and leaf tissue necrosis. Thus, 3-AIPTA-triggered leaf necrosis of Arabidopsis was found to be a result of direct oxidative injury from the chloroplast-originated ROS burst initiated by the inhibition of normal photosynthetic electron transport.

ROS production during symbiotic infection suppresses pathogenesis-related gene expression

Leguminous plants have exclusive ability to form symbiotic relationship with soil bacteria of the genus Rhizobium. Symbiosis is a complex process that involves multiple molecular signaling activities, such as calcium fluxes, production of reactive oxygen species (ROS) and synthesis of nodulation genes. We analyzed the role of ROS in defense gene expression in Medicago truncatula during symbiosis and pathogenesis. Studies in Arabidopsis thaliana showed that the induction of pathogenesis-related (PR) genes during systemic acquired resistance (SAR) is regulated by NPR1 protein, which resides in the cytoplasm as an oligomer. After oxidative burst and return of reducing conditions, the NPR1 undergoes monomerization and becomes translocated to the nucleus, where it functions in PR genes induction. We show that ROS production is both stronger and longer during symbiotic interactions than during interactions with pathogenic, nonhost or common nonpathogenic soil bacteria. Moreover, root cells inoculated with Sinorhizobium meliloti accumulated ROS in the cytosol but not in vacuoles, as opposed to Pseudomonas putida inoculation or salt stress treatment. Furthermore, increased ROS accumulation by addition of H₂O₂ reduced the PR gene expression, while catalase had an opposite effect, establishing that the PR gene expression is opposite to the level of cytoplasmic ROS. In addition, we show that salicylic acid pretreatment significantly reduced ROS production in root cells during symbiotic interaction.

NO, ROS, and cell death associated with caspase-like activity increase in stress-induced microspore embryogenesis of barley

Under specific stress treatments (cold, starvation), in vitro microspores can be induced to deviate from their gametophytic development and switch to embryogenesis, forming haploid embryos and homozygous breeding lines in a short period of time. The inductive stress produces reactive oxygen species (ROS) and nitric oxide (NO), signalling molecules mediating cellular responses, and cell death, modifying the embryogenic microspore response and therefore, the efficiency of the process. This work analysed cell death, caspase 3-like activity, and ROS and NO production (using fluorescence probes and confocal analysis) after inductive stress in barley microspore cultures and embryogenic suspension cultures, as an in vitro system which permitted easy handling for comparison. There was an increase in caspase 3-like activity and cell death after stress treatment in microspore and suspension cultures, while ROS increased in non-induced microspores and suspension cultures. Treatments of the cultures with a caspase 3 inhibitor, DEVD-CHO, significantly reduced the cell death percentages. Stress-treated embryogenic suspension cultures exhibited high NO signals and cell death, while treatment with S-nitrosoglutathione (NO donor) in control suspension cultures resulted in even higher cell death. In contrast, in microspore cultures, NO production was detected after stress, and, in the case of 4-day microspore cultures, in embryogenic microspores accompanying the initiation of cell divisions. Subsequent treatments of stress-treated microspore cultures with ROS and NO scavengers resulted in a decreasing cell death during the early stages, but later they produced a delay in embryo development as well as a decrease in the percentage of embryogenesis in microspores. Results showed that the ROS increase was involved in the stress-induced programmed cell death occurring at early stages in both non-induced microspores and embryogenic suspension cultures; whereas NO played a dual role after stress in the two in vitro systems, one involved in programmed cell death in embryogenic suspension cultures and the other in the initiation of cell division leading to embryogenesis in reprogrammed microspores.

The control of root growth by reactive oxygen species in Salix nigra Marsh. seedlings

The production of reactive oxygen species (ROS) in specific regions of Salix seedlings roots seems essential for the normal growth of this organ. We examined the role of different ROS in the control of root development in Salix nigra seedlings, and explored possible mechanisms involved in the regulation of ROS generation and action. Root growth was not significantly affected by OH quenchers, while it was either partially or completely inhibited in the presence of H₂O₂ or O₂·⁻ scavengers, respectively. O₂·⁻ production was elevated in the root apex, particularly in the subapical meristem and protodermal zones. Apical O₂·⁻ generation activity was correlated to a high level of either Cu/Zn superoxide dismutase protein as well as carbonylated proteins. While NADPH-oxidase (NOX) was probably the main source of O₂·⁻ generation, the existence of other sources should not be discarded. O₂·⁻ production was also high in root hairs during budding, but it markedly decreased when the hair began to actively elongate. Root hair formation increased in the presence of H₂O₂ scavengers, and was suppressed when H₂O₂ or peroxidase inhibitors were supplied. The negative effect of H₂O₂ was partially counteracted by a MAPKK inhibitor. Possible mechanisms of action of the different ROS in comparison with other plant model systems are discussed.

Reactive oxygen species are involved in pollen tube initiation in kiwifruit

The role of reactive oxygen species (ROS) during pollen tube growth has been well established, but its involvement in the early germination stage is poorly understood. ROS production has been reported in germinating tobacco pollen, but evidence for a clear correlation between ROS and germination success remains elusive. Here, we show that ROS are involved in germination and pollen tube formation in kiwifruit. Using labelling with dihydrofluorescein diacetate (H(2) FDA) and nitroblue tetrazolium (NBT), endogenous ROS were detected immediately following pollen rehydration and during the lag phase preceding pollen tube emergence. Furthermore, extracellular H(2) O(2) was found to accumulate, beginning a few minutes after pollen suspension in liquid medium. ROS production was essential for kiwifruit pollen performance, since in the presence of compounds acting as superoxide dismutase/catalase mimic (Mn-5,10,15,20-tetrakis(1-methyl-4-pyridyl)21H,23H-porphin, Mn-TMPP) or as NADPH oxidase inhibitor (diphenyleneiodonium chloride, DPI), ROS levels were reduced and pollen tube emergence was severely or completely inhibited. Moreover, ROS production was substantially decreased in the absence of calcium, and by chromium and bisphenol A, which inhibit germination in kiwifruit. Peroxidase activity was cytochemically revealed after rehydration and during germination. In parallel, superoxide dismutase enzymes, particularly the Cu/Zn-dependent subtype - which function as superoxide radical scavengers - were detected by immunoblotting and by an in-gel activity assay in kiwifruit pollen, suggesting that ROS levels may be tightly regulated. Timing of ROS appearance, early localisation at the germination aperture and strict requirement for germination clearly suggest an important role for ROS in pollen grain activation and pollen tube initiation.

NADPH oxidase AtrbohD and AtrbohF function in ROS-dependent regulation of Na⁺/K⁺homeostasis in Arabidopsis under salt stress

Maintaining cellular Na(+)/K(+) homeostasis is pivotal for plant survival in saline environments. However, knowledge about the molecular regulatory mechanisms of Na(+)/K(+) homeostasis in plants under salt stress is largely lacking. In this report, the Arabidopsis double mutants atrbohD1/F1 and atrbohD2/F2, in which the AtrbohD and AtrbohF genes are disrupted and generation of reactive oxygen species (ROS) is pronouncedly inhibited, were found to be much more sensitive to NaCl treatments than wild-type (WT) and the single null mutant atrbohD1 and atrbohF1 plants. Furthermore, the two double mutant seedlings had significantly higher Na(+) contents, lower K(+) contents, and resultant greater Na(+)/K(+) ratios than the WT, atrbohD1, and atrbohF1 under salt stress. Exogenous H(2)O(2) can partially reverse the increased effects of NaCl on Na(+)/K(+) ratios in the double mutant plants. Pre-treatments with diphenylene iodonium chloride, a widely used inhibitor of NADPH oxidase, clearly enhanced the Na(+)/K(+) ratios in WT seedlings under salt stress. Moreover, NaCl-inhibited inward K(+) currents were arrested, and NaCl-promoted increases in cytosolic Ca(2+) and plasma membrane Ca(2+) influx currents were markedly attenuated in atrbohD1/F1 plants. No significant differences in the sensitivity to osmotic or oxidative stress among the WT, atrbohD1, atrbohF1, atrbohD1/F1, and atrbohD2/F2 were observed. Taken together, these results strongly suggest that ROS produced by both AtrbohD and AtrbohF function as signal molecules to regulate Na(+)/K(+) homeostasis, thus improving the salt tolerance of Arabidopsis.

Calcium-sensing receptor regulates stomatal closure through hydrogen peroxide and nitric oxide in response to extracellular calcium in Arabidopsis

The Arabidopsis calcium-sensing receptor CAS is a crucial regulator of extracellular calcium-induced stomatal closure. Free cytosolic Ca(2+) (Ca(2+)(i)) increases in response to a high extracellular calcium (Ca(2+)(o)) level through a CAS signalling pathway and finally leads to stomatal closure. Multidisciplinary approaches including histochemical, pharmacological, fluorescent, electrochemical, and molecular biological methods were used to discuss the relationship of hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) signalling in the CAS signalling pathway in guard cells in response to Ca(2+)(o). Here it is shown that Ca(2+)(o) could induce H(2)O(2) and NO production from guard cells but only H(2)O(2) from chloroplasts, leading to stomatal closure. In addition, the CASas mutant, the atrbohD/F double mutant, and the Atnoa1 mutant were all insensitive to Ca(2+)(o)-stimulated stomatal closure, as well as H(2)O(2) and NO elevation in the case of CASas. Furthermore, it was found that the antioxidant system might function as a mediator in Ca(2+)(o) and H(2)O(2) signalling in guard cells. The results suggest a hypothetical model whereby Ca(2+)(o) induces H(2)O(2) and NO accumulation in guard cells through the CAS signalling pathway, which further triggers Ca(2+)(i) transients and finally stomatal closure. The possible cross-talk of Ca(2+)(o) and abscisic acid signalling as well as the antioxidant system are discussed.

Hydrogen peroxide permeability of plasma membrane aquaporins of Arabidopsis thaliana

Although aquaporins have been known to transport hydrogen peroxide (H(2)O(2)) across cell membranes, the H(2)O(2)-regulated expression patterns and the permeability of every family member of the plasma membrane intrinsic protein (PIP) toward H(2)O(2) have not been determined. This study investigates the H(2)O(2)-regulated expression levels of all plasma membrane aquaporins of Arabidopsis thaliana (AtPIPs), and determines the permeability of every AtPIP for H(2)O(2) in yeast. Hydrogen peroxide treatment of Arabidopsis down-regulated the expression of AtPIP2 subfamily in roots but not in leaves, whereas the expression of AtPIP1 subfamily was not affected by H(2)O(2) treatment. The growth and survival of yeast cells that expressed AtPIP2;2, AtPIP2;4, AtPIP2;5, or AtPIP2;7 was reduced in the presence of H(2)O(2), while the growth of yeast cells expressing any other AtPIP family member was not affected by H(2)O(2). These results show that only certain isoforms of AtPIPs whose expression is regulated by H(2)O(2) treatment are permeable for H(2)O(2) in yeast cells, and suggest that the integrated regulation of aquaporin expression by H(2)O(2) and the capacity of individual aquaporin to transport H(2)O(2) are important for plant response to H(2)O(2).

Comparative proteomics and phosphoproteomics analyses of DHEA-induced on hepatic lipid metabolism in broiler chickens

Dehydroepiandrosterone (DHEA) is a precursor of the adrenocorticosteroid hormones that are common to all animals, including poultry. The study described herein was undertaken to investigate the effect of DHEA on lipid metabolism in broiler chickens during embryonic development and to determine the regulatory mechanisms involved in its physiological action. Treatment group eggs were injected with 50mg DHEA diluted in 50 μL dimethyl sulfoxide (DMSO) per kg, while control group eggs (arbor acres [AA] fertilized) were injected with 50 μL DMSO per kg prior to incubation. Liver samples were collected on days 9, 14 and 19 of embryonic development as well as at hatching. Extracted proteins were analyzed by two dimensional gel electrophoresis (2-DE) in combination with western blotting for specific anti-phosphotyrosine. The differential spots were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS) or MALDI-TOF-TOF-MS. Peptide mass fingerprinting (PMF) of the differentially-expressed proteins were performed using the MASCOT, Prospector or proFound server. Thirty-seven proteins and twenty-two tyrosine phosphorylation proteins were successfully identified. All 37 proteins and 22 tyrosine phosphorylation proteins exhibited a significant volume difference from the control group. These results demonstrated that DHEA increased the expression and level of tyrosine phosphorylation and sulfotransferase proteins in broilers (at pI 5.9), therefore promoting the biotransformation of DHEA. The expression of apolipoproteinA-I was increased in the DHEA treatment group, which facilitated the conversion of cholesterol to cholesterol esters. Also, DHEA increased the expression of peroxiredoxin-6 and its tyrosine phosphorylation protein levels, thus enhancing its anti-oxidative activity. Furthermore, pyruvate dehydrogenase expression was decreased and the level of its tyrosine phosphorylation proteins increased in the DHEA treatment group. Take together, those data indicate that DHEA reduces the supply of acetyl-CoA by inhibiting the activity of its target enzyme (i.e., pyruvate dehydrogenase), thus affecting both protein synthesis and phosphorylation level and decreasing fat deposition in broiler chickens during embryonic development, which could reflect a physiologically-relevant DHEA fat-reduction mechanism in the broiler chicken.

Recent advances in electrochemical sensing for hydrogen peroxide: a review

Due to the significance of hydrogen peroxide (H(2)O(2)) in biological systems and its practical applications, the development of efficient electrochemical H(2)O(2) sensors holds a special attraction for researchers. Various materials such as Prussian blue (PB), heme proteins, carbon nanotubes (CNTs) and transition metals have been applied to the construction of H(2)O(2) sensors. In this article, the electrocatalytic H(2)O(2) determinations are mainly focused on because they can provide a superior sensing performance over non-electrocatalytic ones. The synergetic effect between nanotechnology and electrochemical H(2)O(2) determination is also highlighted in various aspects. In addition, some recent progress for in vivo H(2)O(2) measurements is also presented. Finally, the future prospects for more efficient H(2)O(2) sensing are discussed.

Singlet oxygen stress in microorganisms

Singlet oxygen is the primary agent of photooxidative stress in microorganisms. In photosynthetic microorganisms, sensitized generation by pigments of the photosystems is the main source of singlet oxygen and, in nonphotosynthetic microorganisms, cellular cofactors such as flavins, rhodopsins, quinones, and porphyrins serve as photosensitizer. Singlet oxygen rapidly reacts with a wide range of cellular macromolecules including proteins, lipids, DNA, and RNA, and thereby further reactive substances including organic peroxides and sulfoxides are formed. Microorganisms that face high light intensities or exhibit potent photosensitizers have evolved specific mechanisms to prevent photooxidative stress. These mechanisms include the use of quenchers, such as carotenoids, which interact either with excited photosensitizer molecules or singlet oxygen itself to prevent damage of cellular molecules. Scavengers like glutathione react with singlet oxygen. Despite those protection mechanisms, damage by reactions with singlet oxygen on cellular macromolecules disturbs cellular functions. Microorganisms that regularly face photooxidative stress have evolved specific systems to sense singlet oxygen and tightly control the removal of singlet oxygen reaction products. Responses to photooxidative stress have been investigated in a range of photosynthetic and nonphotosynthetic microorganisms. However, detailed knowledge on the regulation of this response has only been obtained for the phototrophic alpha-proteobacterium Rhodobacter sphaeroides. In this organism and in related proteobacteria, the extracytoplasmic function (ECF) sigma factor RpoE is released from the cognate antisigma factor ChrR in the presence of singlet oxygen and triggers the expression of genes providing protection against photooxidative stress. Recent experiments show that singlet oxygen acts as a signal, which is sensed by yet unknown components and leads to proteolysis of ChrR. RpoE induces expression of a second alternative sigma factor, RpoH(II), which controls a large set of genes that partially overlaps with the heat-shock response controlled by RpoH(I). In addition to the transcriptional control of gene regulation by alternative sigma factors, a set of noncoding small RNAs (sRNAs) appear to affect the synthesis of several proteins involved in the response to photooxidative stress. The interaction of mRNA targets with those sRNAs is usually mediated by the RNA chaperone Hfq. Deletion of the gene encoding Hfq leads to a singlet oxygen-sensitive phenotype, which underlines the control of gene regulation on the posttranscriptional level by sRNAs in R. sphaeroides. Hence, a complex network of different regulatory components controls the defense against photooxidative stress in anoxygenic photosynthetic bacteria.

DNA alteration and programmed cell death during ageing of sunflower seed

Sunflower (Helianthus annuus L.) seed viability is affected by moisture content (MC) during ageing and is related to accumulation of hydrogen peroxide and changes in energy metabolism. The aim of the present work was to investigate the effect of ageing on DNA alteration events by RAPD (random amplification of polymorphic DNA) analysis and to determine whether loss of seed viability might correspond to a controlled programmed cell death (PCD). Ageing of sunflower seeds was carried out at 35 °C for 7 d at different MCs. The higher the MC, the lower was the seed viability. RAPD analysis showed that DNA alterations occurred during ageing especially in seeds containing a high MC. In addition, PCD, as revealed by DNA fragmentation and TUNEL (terminal deoxynucleotide transferase-mediated dUTP nick-end labelling) assay, was detected in aged seeds at MCs which resulted in ∼50% seed viability. At the cellular level, TUNEL assay and propidium iodide staining showed that cell death concerns all the cells of the embryonic axis. The quantification of the adenylate pool highlights mitochondrial dysfunction in aged seeds containing a high MC. The involvement of oxidative burst, mitochondria dysfunction, and PCD in seed loss of viability is proposed.

Hydrogen peroxide acts on sensitive mitochondrial proteins to induce death of a fungal pathogen revealed by proteomic analysis

How the host cells of plants and animals protect themselves against fungal invasion is a biologically interesting and economically important problem. Here we investigate the mechanistic process that leads to death of Penicillium expansum, a widespread phytopathogenic fungus, by identifying the cellular compounds affected by hydrogen peroxide (H₂O₂) that is frequently produced as a response of the host cells. We show that plasma membrane damage was not the main reason for H₂O₂-induced death of the fungal pathogen. Proteomic analysis of the changes of total cellular proteins in P. expansum showed that a large proportion of the differentially expressed proteins appeared to be of mitochondrial origin, implying that mitochondria may be involved in this process. We then performed mitochondrial sub-proteomic analysis to seek the H₂O₂-sensitive proteins in P. expansum. A set of mitochondrial proteins were identified, including respiratory chain complexes I and III, F₁F₀ ATP synthase, and mitochondrial phosphate carrier protein. The functions of several proteins were further investigated to determine their effects on the H₂O₂-induced fungal death. Through fluorescent co-localization and the use of specific inhibitor, we provide evidence that complex III of the mitochondrial respiratory chain contributes to ROS generation in fungal mitochondria under H₂O₂ stress. The undesirable accumulation of ROS caused oxidative damage of mitochondrial proteins and led to the collapse of mitochondrial membrane potential. Meanwhile, we demonstrate that ATP synthase is involved in the response of fungal pathogen to oxidative stress, because inhibition of ATP synthase by oligomycin decreases survival. Our data suggest that mitochondrial impairment due to functional alteration of oxidative stress-sensitive proteins is associated with fungal death caused by H₂O₂.

Calmodulin-dependent activation of MAP kinase for ROS homeostasis in Arabidopsis

Rapid recognition and signal transduction of mechanical wounding through various signaling molecules, including calcium (Ca²+), protein phosphorylation, and reactive oxygen species (ROS), are necessary early events leading to stress resistance in plants. Here we report that an Arabidopsis mitogen-activated protein kinase 8 (MPK8) connects protein phosphorylation, Ca²+, and ROS in the wound-signaling pathway. MPK8 is activated through mechanical wounding, and this activation requires direct binding of calmodulins (CaMs) in a Ca²+-dependent manner. MPK8 is also phosphorylated and activated by a MAPKK MKK3 in the prototypic kinase cascade, and full activation of MPK8 needs both CaMs and MKK3 in planta. The MPK8 pathway negatively regulates ROS accumulation through controlling expression of the Rboh D gene. These findings suggest that two major activation modes in eukaryotes, Ca²+/CaMs and the MAP kinase phosphorylation cascade, converge at MPK8 to monitor or maintain an essential part of ROS homeostasis.

Signal transduction during cold, salt, and drought stresses in plants

Abiotic stresses, especially cold, salinity and drought, are the primary causes of crop loss worldwide. Plant adaptation to environmental stresses is dependent upon the activation of cascades of molecular networks involved in stress perception, signal transduction, and the expression of specific stress-related genes and metabolites. Plants have stress-specific adaptive responses as well as responses which protect the plants from more than one environmental stress. There are multiple stress perception and signaling pathways, some of which are specific, but others may cross-talk at various steps. In this review article, we first expound the general stress signal transduction pathways, and then highlight various aspects of biotic stresses signal transduction networks. On the genetic analysis, many cold induced pathways are activated to protect plants from deleterious effects of cold stress, but till date, most studied pathway is ICE-CBF-COR signaling pathway. The Salt-Overly-Sensitive (SOS) pathway, identified through isolation and study of the sos1, sos2, and sos3 mutants, is essential for maintaining favorable ion ratios in the cytoplasm and for tolerance of salt stress. Both ABA-dependent and -independent signaling pathways appear to be involved in osmotic stress tolerance. ROS play a dual role in the response of plants to abiotic stresses functioning as toxic by-products of stress metabolism, as well as important signal transduction molecules and the ROS signaling networks can control growth, development, and stress response. Finally, we talk about the common regulatory system and cross-talk among biotic stresses, with particular emphasis on the MAPK cascades and the cross-talk between ABA signaling and biotic signaling.

Reactive oxygen species and nitric oxide mediate actin reorganization and programmed cell death in the self-incompatibility response of papaver

Pollen-pistil interactions are critical early events regulating pollination and fertilization. Self-incompatibility (SI) is an important mechanism to prevent self-fertilization and inbreeding in higher plants. Although data implicate the involvement of reactive oxygen species (ROS) and nitric oxide (NO) in pollen-pistil interactions and the regulation of pollen tube growth, there has been a lack of studies investigating ROS and NO signaling in pollen tubes in response to defined, physiologically relevant stimuli. We have used live-cell imaging to visualize ROS and NO in growing Papaver rhoeas pollen tubes using chloromethyl-2'7'-dichlorodihydrofluorescein diacetate acetyl ester and 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate and demonstrate that SI induces relatively rapid and transient increases in ROS and NO, with each showing a distinctive "signature" within incompatible pollen tubes. Investigating how these signals integrate with the SI responses, we show that Ca(2+) increases are upstream of ROS and NO. As ROS/NO scavengers alleviated both the formation of SI-induced actin punctate foci and also the activation of a DEVDase/caspase-3-like activity, this demonstrates that ROS and NO act upstream of these key SI markers and suggests that they signal to these SI events. These data represent, to our knowledge, the first steps in understanding ROS/NO signaling triggered by this receptor-ligand interaction in pollen tubes.

ABA controls H₂O₂ accumulation through the induction of OsCATB in rice leaves under water stress

The production of both ABA and H₂O₂ is induced by drought and can act as signals under stress conditions. We investigated the relationships between ABA, H₂O₂ and catalase (CAT) in rice leaves when rice seedlings were treated with polyethylene glycol as water stress treatment. As a key gene in ABA biosynthesis, OsNCED3 was significantly induced in rice by water stress treatment and such induction preceded the rapid increase in ABA. Water stress inhibited the expression of CATA and CATC but substantially enhanced the expression of CATB. Exogenously applied ABA promoted the expression of CATB also and inhibited the expression of CATC in a concentration-dependent manner. When ABA production was inhibited by using ABA biosynthesis inhibitors nordihydroguaiaretic acid and tungstate, expression of CATB was also subdued while CATC was enhanced under the water stress. Accumulation of H₂O₂ was also reduced when endogenous ABA production was inhibited and showed a correlation with the total activity of catalases. Our results suggest that water stress-induced ABA prevents the excessive accumulation of H₂O₂, through the induction of the expression of CATB gene during water stress.

Evidence of Arabidopsis salt acclimation induced by up-regulation of HY1 and the regulatory role of RbohD-derived reactive oxygen species synthesis

In Arabidopsis thaliana, a family of four genes (HY1, HO2, HO3 and HO4) encode haem oxygenase (HO), and play a major role in phytochrome chromophore biosynthesis. To characterize the contribution of the various haem oxygenase isoforms involved in salt acclimation, the effects of NaCl on seed germination and primary root growth in Arabidopsis wild-type and four HO mutants (hy1-100, ho2, ho3 and ho4) were compared. Among the four HO mutants, hy1-100 displayed maximal sensitivity to salinity and showed no acclimation response, whereas plants over-expressing HY1 (35S:HY1) exhibited tolerance characteristics. Mild salt stress stimulated biphasic increases in RbohD transcripts and production of reactive oxygen species (ROS) (peaks I and II) in wild-type. ROS peak I-mediated HY1 induction and subsequent salt acclimation were observed, but only ROS peak I was seen in the hy1-100 mutant. A subsequent test confirmed the causal relationship of salt acclimation with haemin-induced HY1 expression and RbohD-derived ROS peak II formation. In atrbohD mutants, haemin pre-treatment resulted in induction of HY1 expression, but no similar response was seen in hy1-100, and no ROS peak II or subsequent salt acclimatory responses were observed. Together, the above findings suggest that HY1 plays an important role in salt acclimation signalling, and requires participation of RbohD-derived ROS peak II.

Nuclear Argonaute 2 regulates adipose tissue-derived stem cell survival through direct control of miR10b and selenoprotein N1 expression

Argonaute 2 (Ago2) has a leading function in miRNA-induced RNA silencing, a conserved gene regulatory mechanism in cells and organisms. miRNAs are critical for stem cell self-renewal, development, and other functions. Here, we report that nuclear Ago2, by binding to a specific region of functional genes, directly controls adipose tissue-derived stem cell (ATSC) survival in response to a critical dose of reactive oxygen species (ROS)-mediated oxidative cell damage or senescence. The role of nuclear Ago2 has not been previously reported. Here, we show that human ATSCs in which Ago2 was downregulated underwent apoptosis. Silencing of Ago2 in ATSCs significantly induces upregulation of miR10b and miR23b expression. These miRNAs directly interfere with ROS-scavenging gene expression, such as TXNL1 and GPX3. Upregulation of miR10b and miR23b is sufficient to induce ATSC cell apoptosis via p38 MAPK phosphorylation and caspase 3 activation. In addition, Ago2 overexpression or interference by miR10b and miR23b expression in ATSCs partially rescued H(2) O(2) /ROS-mediated apoptotic cell death by upregulating the expression of TXNL2, JUNK, caspase-3, and cytochrome C. Nuclear Ago2-mediated miR10b and miR23b downregulation also allows cells to escape senescence, which results in telomerase reverse transcriptase, stemness overexpression, and improved self-renewal and differentiation through Wnt5a/β-catenin activation. Argonaute 2 expression is critical for stem cells to escape senescence by downregulating miR10b and miR23b. The Ago2-binding gene selenoprotein N1 (SEPN1) was also effectively involved in ATSC survival and self-renewal through ROS-mediated p38 MAPK inactivation.

Catalase in fluvial biofilms: a comparison between different extraction methods and example of application in a metal-polluted river

Antioxidant enzymes are involved in important processes of cell detoxification during oxidative stress and have, therefore, been used as biomarkers in algae. Nevertheless, their limited use in fluvial biofilms may be due to the complexity of such communities. Here, a comparison between different extraction methods was performed to obtain a reliable method for catalase extraction from fluvial biofilms. Homogenization followed by glass bead disruption appeared to be the best compromise for catalase extraction. This method was then applied to a field study in a metal-polluted stream (Riou Mort, France). The most polluted sites were characterized by a catalase activity 4-6 times lower than in the low-polluted site. Results of the comparison process and its application are promising for the use of catalase activity as an early warning biomarker of toxicity using biofilms in the laboratory and in the field.