Proline antioxidant role in the common ice plant subjected to salinity and paraquat treatment inducing oxidative stress

Leaves of 4-week-old (juvenile) and 9-week-old (adult) plants of the halophyte Mesembryanthemum crystallinum L. (the common ice plant), cultured under controlled conditions in the phytotron, were treated with paraquat (0.1 μM), which produces superoxide radical, and (or) paraquat combined with introduction of NaCl (100 mM) or proline (5 mM) into nutrient medium. After a 20-h dark period (23°C), plants were transferred into light (4 h at 54.1 W/m² of photosynthetically active radiation) for stimulation of O°₂⁻ formation in plastids. Activities of antioxidant enzymes, the contents of MDA, H₂O₂, chlorophyll, and free proline were measured in leaves. Plant responses in two age groups, which differed in the type of photosynthesis (juvenile plants had C₃ type of photosynthesis, whereas adult plants were at the transition stage to Crassulacean Acid Metabolism (CAM) photosynthesis), differed in the levels of constitutive proline and proline, induced by NaCl and paraquat, as well as in activities of superoxide dismutase (SOD) and catalase. Changes in SOD activity and proline accumulation in response to paraquat treatment combined with NaCl revealed opposite dependence to accumulation of proline: the more proline accumulated in leaves, the lower activity of the enzyme. In response to paraquat treatment, the content of chlorophylls a and b most drastically declined in juvenile plants. Negative effect of salinity on the content of chlorophylls was lower than that of paraquat and was almost the same in plants of both age groups. Protective effect of exogenous proline was most profound in the case of paraquat treatment. Exogenous proline decreased the rate of lipid peroxidation, the content of superoxide radical and, consequently, SOD activity (almost fivefold), and increased the content of chlorophylls (a and b) in leaves of adult plants. The obtained data suggest that stress-induced accumulation of proline in the common ice plant has both osmoprotectory and antioxidant functions.     

Proline induces calcium-mediated oxidative burst and salicylic acid signaling

Although free proline accumulation is a well-documented phenomenon in many plants in response to a variety of environmental stresses, and is proposed to play protective roles, high intracellular proline content, by either exogenous application or endogenous over-production, in the absence of stresses, is found to be inhibitory to plant growth. We have shown here that exogenous application of proline significantly induced intracellular Ca²⁺ accumulation in tobacco and calcium-dependent ROS production in Arabidopsis seedlings, which subsequently enhanced salicylic acid (SA) synthesis and PR genes expression. This suggested that proline can promote a reaction similar to hypersensitive response during pathogen infection. Other amino acids, such as glutamate, but not arginine and phenylalanine, were also found to be capable of inducing PR gene expression. In addition, proline at concentration as low as 0.5 mM could induce PR gene expression. However, proline could not induce the expression of PDF1.2 gene, the marker gene for jasmonic acid signaling pathway. Furthermore, proline-induced SA production is mediated by NDR1-dependent signaling pathway, but not that mediated by PAD4. Our data provide evidences that exogenous proline, and probably some other amino acids can specifically induce SA signaling and defense response.     

Exogenous auxin affects the oxidative burst in barley roots colonized by Piriformospora indica

Beside a cardinal role in coordination of many developmental processes in the plant, the phytohormone auxin has been recognized as a regulator of plant defense. The molecular mechanisms involved are still largely unknown. Using a sensitive chemiluminescence assay, which measures the oxidation of luminol in the presence of H₂O₂ by horseradish peroxidase (HRP), we report here on the ability of exogenously added indole-3-acetic acid (IAA) to enhance the suppressive effect of the root endophyte Piriformospora indica on the chitin-elicited oxidative burst in barley roots. Thus, the potential of P. indica to produce free IAA during the early colonization phase in barley might provide the symbiont with a means to interfere with the microbe-associated molecular patterns (MAMP)-triggered immunity.     

The oxidative burst in plant defense: Function and signal transduction

The rapid production and accumulation of active oxygen species (AOS), the oxidative burst, has been shown to occur in a variety of plant/pathogen systems. In particular, two species, hydrogen peroxide (H₂O₂) and the superoxide radical anion O₂^? have received considerable attention. H₂O₂ and O₂^?, while acting directly as antimicrobial agents, may also serve as second messengers or catalysts in plants to activate a more diverse set of defense responses. Some of the better studied downstream responses promoted by AOS are (1) the cross-linking of cell wall proteins, (2) the induction of defense-related genes, (3) the stimulation of phytoalexin biosynthesis and (4) promotion of the hypersensitive response (HR). A useful model for studying the oxidative burst in plants is the neutrophil NADPH ox-idase complex, the primary source of AOS production in mammals. Several of the subunits of the neutrophil NADPH oxidase complex have been immunologically identified in plants. Furthermore, many of the components known to be involved in the signal transduction pathway in neutrophils have also been found to play a role in the oxidative burst in plants. Just as various ligands activate the oxidase complex in neutrophils, several ligands (elicitors or pathogens) also lead to induction of the oxidative burst in plant cells. The similarities between the neutrophil and plant oxidative bursts will be elaborated in this review. Following stimulation with elicitors, different signal transduction pathways are activated in plants, depending on the source of elicitor used. While the identities and chronologies of the major intermediates in these pathways remain largely unknown, there is strong evidence at least for participation of phospholipases, H⁺/K⁺ exchange, Ca²⁺ influxes, protein kinases and phosphatases, and GTP binding proteins. In an effort to integrate these various signaling events into a single scheme, we have constructed a hypothetical model that proposes how different elicitors might induce the oxidative burst in the same cell by different pathways.     

Expression of the PIP aquaporin promoter-MipA from the common ice plant in tobacco

The reasons for the presence of a multitude of plasma membrane-localized water channels (PIP aquaporins) in plants may be functional differences in water (or other solute) transport, or in developmental, environmental or tissue-specific regulation of expression. We compared tissue- and cell-specific expression of McMipA, an abundantly expressed PIP from the common ice plant (Mesembryanthemum crystallinum), with that of the previously characterized McMipB [Yamada et al. (1997) Plant Cell Physiol. 38: 1326]. The activity of a 2.2 kb DNA fragment containing the promoter region of McMipA in a fusion with the GUS coding region was studied in transgenic tobacco. The McMipA promoter was active in pericycle and cortex cells in roots and in phloem-associated cells and cells surrounding the pericycle in shoots. In green leaves, mesophyll cells and the minor veins showed GUS activity, but the major veins did not. In floral tissues, GUS activity was observed in the pistil and anthers of immature buds and the tip of the mature pistil and pollen. Neither the apical meristem nor root tip showed any GUS activity. The differences in tissue specificity between the McMipA and McMipB promoters indicated that the two PIPs, MC-MIPA and MC-MIPB, serve different functions in plants.     

Bereavement reduces neutrophil oxidative burst only in older adults: role of the HPA axis and immunesenescence

Background

The effect of the chronic stress of bereavement on immunity is poorly understood. Previous studies have demonstrated negative effects on immunity in older adults, and those who report higher depressive symptoms. The aim of the present study was to compare the effect of bereavement on neutrophil function in healthy young and old adults, also assessing serum levels of the stress hormones, cortisol and dehydroepiandrosterone sulphate (DHEAS). 41 young (mean age 32 years) and 52 older adults (mean age 72 years), bereaved and non-bereaved, took part in the study. They completed questionnaires on socio-demographic and health behaviour characteristics, as well as psychosocial variables, and provided a blood sample for analysis of neutrophil function (phagocytosis and reactive oxygen species (ROS) production) and stress hormone analysis.

Results

Bereaved participants in both age groups reported more symptoms of depression and anxiety than controls and scored moderately highly on bereavement-specific questionnaires for these symptoms. Despite this, young bereaved participants showed robust neutrophil function when compared to age-matched non-bereaved controls, and comparable stress hormone levels, while reduced neutrophil ROS production and raised stress hormone levels (cortisol:DHEAS ratio) were seen in the older bereaved group compared to their age-matched controls.

Conclusions

Reduced neutrophil function among older bereaved participants may be the result of the inability to maintain stress hormone balance, specifically the cortisol:DHEAS ratio.

     

High-fat diet induces metabolic changes and reduces oxidative stress in female mouse hearts

After an acute myocardial infarction, obese patients generally have a better prognosis than their leaner counterparts, known as the “obesity paradox”. In addition, female sex is associated with a lower risk of cardiac ischemic events and smaller infarct size compared to males. The objective of the present work was to study the metabolic phenotype and mitochondrial function associated to female sex and short-term high-fat diet. ¹H NMR spectra of mice heart extracts were analysed by mRMR variable selection and linear discriminant analysis was used to evaluate metabolic changes. In separate experiments, O₂ consumption and H₂O₂ production were measured from isolated mitochondria as well as serum oxidation susceptibility. Fingerprinting showed that male hearts contained more myo-inositol, taurine and glutamate than female hearts. HFD reduced the levels of creatine, taurine citrate and acetate. Profiling showed increased alanine and fumarate in HFD suggesting altered glycolitic and Krebs cycle pathways. Female mice contained less glucose than males. Female sex nor HFD altered mitochondria oxygen consumption but both conditions reduced the amount of H₂O₂ produced in an additive manner. Serum of females had lower oxidation susceptibility than serum from males but there were no differences associated with HFD. In conclusion, female sex and short-term HFD have an effect on the myocardial metabolic pattern and reduce the amount of H₂O₂ produced by mitochondria in an additive manner suggesting different mechanisms of action. This could explain, at least in part, the protection afforded by female sex and the “obesity paradox”.     

6-Substituted indanoyl isoleucine conjugate induces tobacco plant responses in secondary metabolites

To characterize the role of the phytotoxin mimic 6-substituted indanoyl isoleucine conjugate 1 in plant secondary metabolism, tobacco (Nicotiana tabacum L. K326) was treated with compound 1. The volatile compounds of tobacco leaves were analyzed by GC-MS. In contrast to the control, three compounds, farnesene (2), santalol (3) and tetradecanal (4), were induced by treatment with 1 mM of compound 1. Concurrently other volatile compounds were also regulated.     

Isolation and characterization of mutants of common ice plant deficient in crassulacean acid metabolism

Crassulacean acid metabolism (CAM) is a specialized mode of photosynthesis that improves water use efficiency by shifting part or all of net atmospheric CO2 uptake to the night. Genetic dissection of regulatory and metabolic attributes of CAM has been limited by the difficulty of identifying a reliable phenotype for mutant screening. We developed a novel and simple colorimetric assay to measure leaf pH to screen fast neutron-mutagenized populations of common ice plant (Mesembryanthemum crystallinum), a facultative CAM species, to detect CAM-deficient mutants with limited nocturnal acidification. The isolated CAM-deficient mutants showed negligible net dark CO2 uptake compared with wild-type plants following the imposition of salinity stress. The mutants and wild-type plants accumulated nearly comparable levels of sodium in leaves, but the mutants grew more slowly than the wild-type plants. The mutants also had substantially reduced seed set and seed weight relative to wild type under salinity stress. Carbon-isotope ratios of seed collected from 4-month-old plants indicated that C3 photosynthesis made a greater contribution to seed production in mutants compared to wild type. The CAM-deficient mutants were deficient in leaf starch and lacked plastidic phosphoglucomutase, an enzyme critical for gluconeogenesis and starch formation, resulting in substrate limitation of nocturnal C4 acid formation. The restoration of nocturnal acidification by feeding detached leaves of salt-stressed mutants with glucose or sucrose supported this defect and served to illustrate the flexibility of CAM. The CAM-deficient mutants described here constitute important models for exploring regulatory features and metabolic consequences of CAM.     

Zymosan but not phorbol myristate acetate induces an oxidative burst in rat bone marrow-derived macrophages

We found that rat bone marrow-derived macrophages responded to opsonized zymosan by releasing superoxide anion. However, these cells were defective in the response to the potent oxidative burst activator phorbol myristate acetate (PMA). This result was observed whatever the concentration of agonist used and with different concentrations of cells. Since it is strongly suspected that protein kinase C (PKC) is involved in the transductional pathway induced by PMA in numerous cell types, and particularly in phagocytes, we studied PKC and we observed that it was functional in rat bone marrow-derived macrophages, but only present at a low level. Thus, we suggest that our results are consistent with the possibility that zymosan-induced respiratory burst may be independent of PKC and that these cells may not possess the minimal level of PKC required for responding to PMA.     

Effects of various iron supply on oxidative stress development and ferritin formation in the common ice plants

Mesembryanthemum crystallinum L. plants were grown from seeds in perlite. At the age of 4 weeks (juvenile plants) or 6 weeks (adult plants), they were transferred on nutrient media with different Fe³⁺ content brought in as Fe₂(SO₄)₃—EDTA complex (pH 6.0): control, iron deficit, and iron “excess”. Adult plants grown in media differing in iron content were subjected to salinity (300 mM NaCl) during the last 8 days of growth. Biochemical analyses were performed after plant fixation in liquid nitrogen; simultaneously, the samples for electron microscopy were taken. Different content of available Fe³⁺ in medium, especially under salinity conditions, changed sharply the content of chlorophyll and proline, the rate of lipid peroxidation, the level of H₂O₂, the activities of antioxidant enzymes in the leaves and roots, the number and sizes of plastoglobules, and ferritin formation in plastids. Joint action of salinity and iron deficit enhanced oxidative stress development, whereas iron excess hampered oxidative reaction development, reduced the rate of lipid peroxidation, and increased the chlorophyll content. At iron excess, plastoglobule lysis in plastids did not occur, their number and sizes increased, and ferritin deposits appeared, whereas the latter were absent at iron deficit.     

Fucoxanthinol attenuates oxidative stress-induced atrophy and loss in myotubes and reduces the triacylglycerol content in mature adipocytes

Molecular Biology Reports - The combination of sarcopenia and obesity (i.e., sarcopenic obesity) is more strongly associated with disability and metabolic/cardiovascular diseases than obesity or...     

Repeated freezing induces oxidative stress and reduces survival in the freeze-tolerant goldenrod gall fly,Eurosta solidaginis

Freeze tolerant insects must not only survive extracellular ice formation but also the generation of reactive oxygen species (ROS) during oxygen reperfusion upon thawing. Furthermore, diurnal fluctuations in temperature place temperate insects at risk of being exposed to multiple freeze–thaw cycles, yet few studies have examined metrics of survival and oxidative stress in freeze-tolerant insects subjected to successive freezing events. To address this, we assessed survival in larvae of the goldenrod gall fly Eurosta solidaginis, after being subjected to 0, 5, 10, 20, or 30 diurnally repeated cold exposures (RCE) to −18 °C or a single freeze to −18 °C for 20 days. In addition, we measured indicators of oxidative stress, levels of cryoprotectants, and total aqueous antioxidant capacity in animals exposed to the above treatments at 8, 32, or 80 h after their final thaw. Repeated freezing and thawing, rather than time spent frozen, reduced survival as only 30% of larvae subjected to 20 or 30 RCE successfully pupated, compared to those subjected to fewer RCE or a single 20 d freeze, of which 82% pupated. RCE had little effect on the concentration of the cryoprotectant glycerol (4.26 ± 0.66 μg glycerol·ng protein⁻¹ for all treatments and time points) or sorbitol (18.8 ± 2.9 μg sorbitol·mg protein⁻¹ for all treatments and time points); however, sorbitol concentrations were more than twofold higher than controls (16.3 ± 2.2 μg sorbitol·mg protein⁻¹) initially after a thaw in larvae subjected to a single extended freeze, but levels returned to values similar to controls at 80 h after thaw. Thawing likely produced ROS as total aqueous antioxidant capacities peaked at 1.8-fold higher than controls (14.7 ± 1.6 mmol trolox·ng protein⁻¹) in animals exposed to 5, 10, or 20 RCE. By contrast, aqueous antioxidant capacities were similar to controls in larvae subjected to 30 RCE or the single 20 d freeze regardless of time post final thaw, indicating these animals may have had an impaired ability to produce primary antioxidants. Larvae lacking an antioxidant response also had elevated levels of oxidized proteins, nearly twice that of controls (21.8 ± 3.2 mmol chloramine-T·mg protein⁻¹). Repeated freezing also lead to substantial oxidative damage to lipids that was independent of aqueous antioxidant capacity; peroxides were, on average, 5.6-fold higher in larvae subjected to 10, 20 or 30 RCE compared to controls (29.1 ± 7.3 mmol TMOP·μg protein⁻¹). These data suggest that oxidative stress due to repeated freeze–thaw cycles reduces the capacity of E. solidaginis larvae to survive freezing.     

Traffic noise induces oxidative stress and phytohormone imbalance in two urban plant species

Traffic noise pollution is one of the major environmental concerns in crowded cities worldwide. The objective of the present study was to investigate the effects of traffic noise on growth, hormonal balance, oxidative damage, and activity of antioxidant systems in two urban plant species, Tagetes patula and Salvia splendens. Each of the plant species were equally divided into 2 groups (control and traffic noise treatment) and each group was grown under identical controlled conditions in two separate growth chambers for two months. Traffic noise was recorded during peak traffic hours in a highly congested area of the city. Frequency analysis of traffic noise was conducted on the samples during the recording process. Plants in the traffic noise treatment group were exposed to 16 h of road traffic noise each day for a total of 15 days, while the control group was kept under complete silence. Traffic noise exposure led to significant decrease in growth indices of both plant species. The content of H₂O₂ and malondialdehyde (MDA) significantly increased upon traffic noise treatment in both species, followed by an increase in DPPH (2,2-diphenyl-1-picrylhydrazyl) anti-oxidant activity and the activity of antioxidant enzymes including catalase, peroxidase, and ascorbate peroxidase. Road traffic noise significantly reduced the content of phytohormones including zeatin, salicylic acid, indole-3-acetic acid, and gibberellic acid. On the other hand, the content of stress-related hormones including abscisic acid and jasmonic acid significantly increased in response to road traffic noise in both species. Based on our results, daily traffic noise can negatively affect growth and physiology of plants by inducing of oxidative damage and interfering with hormonal balance.     

Continuous production of extracellular antioxidants in suspension cells attenuates the oxidative burst detected in plant microbe interactions

Suspension cells of Solanacearum tuberosum and Nicotiana tabacum placed in fresh buffer rapidly produce and maintain significant pools of extracellular antioxidants. The extracellular antioxidant was detected by first adding a known amount of exogenous H₂O₂ to samples and then immediately measuring the remaining H₂O₂. The difference between the amount added and amount remaining was used to determine the antioxidant capacity of the sample. This extracellular antioxidant pool attenuates levels of hydrogen peroxide produced during plant–bacterial interactions. When tobacco cells were inoculated with an isolate Pseudomonas syringae pv. syringae that causes a hypersensitive response much of the antioxidant capacity had been expended neutralizing the oxidative burst characteristic of such plant–microbe interactions. After a brief delay, the levels of extracellular phenolics increased commensurate to antioxidative capacity in freshly transferred cells within 2–4 h. The strong UV absorbance of these extracellular phenolics within 250 and 350 nm was used to follow oxidation upon reaction with H₂O₂. This extracellular antioxidant pool is an important consideration in cell suspension studies of the plant–microbe oxidative burst. This study demonstrates that the true magnitude and timing of the oxidative burst in cell suspensions is masked by extracellular antioxidants.     

Cytosolic Ca2+ pulses and protein kinase activation in the signal transduction pathways leading to the plant oxidative burst

The oxidative burst, the rapid production of O₂- and H₂O₂ by plant cells in response to pathogens and Stressors, is a critical step in plant disease resistance and is controlled by several different elicitor-initiated signaling pathways. While different defense elicitors appear to activate disparate initial steps in signaling the oxidative burst, all of the elicitors tested thus far appear to stimulate pathways that converge on the same three core signaling intermediates: 1) the Ca₂₊-independent activation of a mitogen-activated protein kinase (MAPK) family member, 2) the influx of Ca₂₊ into the cytosol, deriving most critically from an internal compartment, and 3) the Ca²⁺-dependent activation of additional protein kinases including a second MAPK homologue and possibly calcium dependent protein kinases (CDPKs). Data from several recent reports are summarized to place these signaling events into a complete and updated model of signaling to the plant oxidative burst.