Salicylic acid,hydrogen peroxide and calcium-induced saline tolerance associated with endogenous hydrogen peroxide homeostasis in naked oat seedlings

This study investigates the role of salicylic acid (SA), hydrogen peroxide (H₂O₂) and calcium chloride (CaCl₂) singly or in combination, in inducing naked oat plant tolerance to sodium chloride (NaCl). Two-week-old naked oat plants were pretreated with both single and double of 0.5 mM SA, 0.5 mM H₂O₂ and 5 mM CaCl₂ by adding them to the culture solution for 24 h. At the end of the pretreatment, the plants were subjected to 200 mM NaCl exposure for 7 days. Data were collected on plant biomass, H₂O₂ level, antioxidant enzyme activity, non-enzymatic antioxidant content and malondialdehyde (MDA) content. Results showed that exposure to salt significantly inhibited plant growth, and the shoot and root dry weights were reduced 47.5% and 63.4%, and the H₂O₂ levels elevated 5.8 and 2.4 times in comparison with those in the control, respectively. Under the saline stress, the activities of superoxide dismutase (SOD) and catalase (CAT) were induced, but the contents of ascorbic acid (AA) and glutathione (GSH) decreased, and MDA largely accumulated. The various pretreatments efficiently counteracted the salt-caused growth inhibition, especially with H₂O₂ + CaCl₂ the shoot and root dry weights reduced only 9.4% and 24.4% of the non salt-stressed plants. The determination of endogenous H₂O₂ level demonstrated that the pretreatments induced H₂O₂ accumulation, with H₂O₂ + CaCl₂ being most efficient, but the effect was transient. After 7 days of saline stress, the H₂O₂ contents in the pretreated shoots and roots accounted for 23.7–41.8% and 31.7–57.3% of the non-pretreated plants, varying according to the different pretreatments. Under saline stress, SOD and CAT further increased, AA and GSH maintained higher levels and MDA decreased in the pretreated plants compared to the untreated plants. With application of diphenylene iodonium (DPI) during the pretreatment, which inhibited the accumulation of H₂O₂, the ameliorative effect of the pretreatment on salt-caused plant growth inhibition was reduced. However, applied DPI at the immediate end of the pretreatment did not alter its favorable role, indicating a H₂O₂ peak formed at the early time of saline stress might play an important role in regulating plant tolerance to saline stress.     

损伤条件下油菜黄单胞菜豆致病变种内源过氧化氢与间体形成的联系

【目的】本实验通过透射电子显微镜观察黄单胞菌在细胞损伤条件下的亚细胞结构和过氧化氢积累定位的变化。【方法】采用氯化铈对过氧化氢特异染色的组织化学法。【结果】细菌细胞受损伤后,出现了一个细胞壁之外的过氧化氢大量积累的额外位点。并且这个额外位点出现的频率和过氧化氢积累量都与细胞损伤的程度密切相关。另一方面,亚细胞结构的常规染色结果也显示,受到损伤的细胞中也出现一个额外的亚显微结构,即间体。间体出现的频率和大小也随着细胞损伤程度的增加而显著上升。【结论】多元线性回归分析的结果证明细胞损伤条件下细菌中出现的额外过氧化氢大量积累的位点就是间体。细胞损伤后间体中的过氧化氢积累对受损细胞应是一种主动调控机制。     

Proteins associated with mitochondrial DNA protect it against X-rays and hydrogen peroxide

The high susceptibility of mitochondrial DNA to reactive oxygen species and other damaging agents has been supposed to result from the absence of histones. Here we show that DNA-binding proteins of mitochondrial nucleoids can shield mtDNA from X-ray radiation and hydrogen peroxide just as nuclear histones do. Mitochondria, mitochondrial nucleoid proteins, and histones were isolated from mouse liver and assessed for mtDNA protection by the yield of PCR products. In vitro, mtDNA in complex either with nucleoid proteins or with nuclear histones proved to be much less damaged than naked mtDNA, with little difference in protective efficacy. Most probably, in mitochondria the nucleoid proteins also protect mtDNA against reactive oxygen species and thus attenuate the oxidative damage.     

In-situ Cr(VI) reduction with electrogenerated hydrogen peroxide driven by iron-reducing bacteria

Cr(VI) was reduced in-situ at a carbon felt cathode in an air-cathode dual-chamber microbial fuel cell (MFC). The reduction of Cr(VI) was proven to be strongly associated with the electrogenerated H₂O₂ at the cathode driven by iron-reducing bacteria. At pH 2.0, only 42.5% of Cr(VI) was reduced after 12 h in the nitrogen-bubbling-cathode MFC, while complete reduction of Cr(VI) was achieved in 4 h in the air-bubbling-cathode MFC in which the reduction of oxygen to H₂O₂ was confirmed. Conditions that affected the efficiency of the reduction of Cr(VI) were evaluated experimentally, including the cathodic electrolyte pH, the type of iron-reducing species, and the addition of redox mediators. The results showed that the efficient reduction of Cr(VI) could be achieved with an air-bubbling-cathode MFC.     

Susceptibility to hydrogen peroxide and catalase activity of root nodule bacteria

The root nodule bacteria (free-living cells) tested had higher susceptibility to hydrogen peroxide (H2O2) than the other genera of aerobic or facultative anaerobic bacteria tested. The catalase activities tended to have a positive correlation with H2O2 resistance among all bacteria tested. Addition of a catalase inhibitor such as 3-amino-1, 2, 4-triazole increased the susceptibility to H2O2. These results suggest that the lower catalase activity brings about the higher susceptibility of root nodule bacteria to H2O2. Root nodule bacteria seemed to have two or three catalase isozymes during growth and their catalase activities were higher in log phase than in stationary phase, contrary to other genera of bacteria tested.     

Cell death mediated by MAPK is associated with hydrogen peroxide production in Arabidopsis.

Rapid and localized programmed cell death, known as the hypersensitive response (HR) is frequently associated with plant disease resistance. In contrast to our knowledge about the regulation and execution of apoptosis in animal system, information about plant HR is limited. Recent studies implicated the mitogen-activated protein kinase (MAPK) cascade in regulating plant HR cell death as well as several other defense responses during incompatible interactions between plants and pathogens. Here, we report the generation of transgenic Arabidopsis plants that express the active mutants of AtMEK4 and AtMEK5, two closely related MAPK kinases under the control of a steroid-inducible promoter. Induction of the transgene expression by the application of dexamethasone, a steroid, leads to HR-like cell death, which is preceded by the activation of endogenous MAPKs and the generation of hydrogen peroxide. Both prolonged MAPK activation and reactive oxygen species generation have been implicated in the regulation of HR cell death induced by incompatible pathogens. As a result, we speculate that the prolonged activation of the MAPK pathway in cells could disrupt the redox balance, which leads to the generation of reactive oxygen species and eventually HR cell death.     

Mesosomes in Pseudomonas aeruginosa

The use of a combination fixative-staining procedure has allowed a detailed observation of mesosomes in thin sections of Pseudomonas aeruginosa.     

Vanadium catalyzed oxidation with hydrogen peroxide

Vanadium peroxides are known as very effective oxidants of different organic and inorganic substrates. In this short account reactivity, structural and mechanistic studies concerning the behaviour of peroxovanadates toward a number of different substrates are collected. Homogeneous and two-phase systems are presented, in addition, interesting synthetic results obtained with the use of ionic liquids as reaction media are also presented.     

Enhanced antioxidant enzymes are associated with reduced hydrogen peroxide in barley roots under saline stress

Antioxidant enzymes are related to the resistance to various abiotic stresses including salinity. Barley is relatively tolerant to saline stress among crop plants, but little information is available on barley antioxidant enzymes under salinity stress. We investigated temporal and spatial responses of activities and isoform profiles of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), non-specific peroxidase (POX), and glutathione reductase (GR) to saline stress in barley seedlings treated with 200 mM NaCl for 0, 1, 2, 5 days, respectively. In the control plant, hydrogen peroxide content was about 2-fold higher in the root than in the shoot. Under saline stress, hydrogen peroxide content was decreased drastically by 70% at 2 d after NaCl treatment (DAT) in the root. In the leaf, however, the content was remained unchanged by 2 DAT and increased about 14 % at 5 DAT. In general, the activities of antioxidant enzymes were increased in the root and shoot under saline stress. But the increase was more significant and consistent in the root. The activities of SOD, CAT, APX, POX, and GR were increased significantly in the root within 1 DAT, and various elevated levels were maintained by 5 DAT. Among the antioxidant enzymes, CAT activity was increased the most drastically. The significant increase in the activities of SOD, CAT, APX, POX, and GR in the NaCl-stressed barley root was highly correlated with the increased expression of the constitutive isoforms as well as the induced ones. The hydrogen peroxide content in the root.     

Mesosome formation is accompanied by hydrogen peroxide accumulation in bacteria during the rifampicin effect

Ultrastructural alteration and hydrogen peroxide localization were examined in Xanthomonas campestris pv. phaseoli during rifampicin effect using transmission electron microscopy. Bacterial cells were treated with rifampicin and then were examined by electron microscopy to observe the changes of ultrastructure or hydrogen peroxide accumulation in living cells that took place before lysis. Intriguingly, rifampicin treatment led to presence of an additional location of hydrogen peroxide accumulation within the cells. There was an association between the frequency and size of the additional location of hydrogen peroxide accumulation and the concentration of rifampicin. Furthermore, an additional ultrastructure, mesosomes, was also present in cells during rifampicin effect. The frequency and size of mesosome increased with the increasing concentration of rifampicin. Result of multiple linear regression showed that the size of mesosome plays as a key factor in the quantity of excess hydrogen peroxide accumulation in cells during rifampicin effect. Linear correlation was confirmed between quantity of excess hydrogen peroxide accumulation and the size of mesosome in cells during rifampicin effect. This finding intensely indicated that mesosomes are just the additional location of hydrogen peroxide accumulation in cells under cellular injury caused by rifampicin treatment. The mesosome formation is always accompanied by excess hydrogen peroxide accumulation in X. campestris pv. phaseoli during rifampicin effect.     

The effect of melanin on iron associated decomposition of hydrogen peroxide

The effects of melanin on the iron-catalyzed decomposition of hydrogen peroxide to hydroxyl radicals and hydroxyl ions have been studied using electron spin resonance, spin trapping and visible light spectrophotometry. Melanin altered these reactions by several different mechanisms and consequently, depending on conditions, can significantly increase or decrease the yield of reactive products, including hydroxyl radicals. For low concentrations of ferrous ions, melanin decreased the yield of hydroxyl radicals due to binding of ferrous ions by melanin; ferrous ions bound to melanin did not decompose H2O2 efficiently. Melanins increased the rate of hydroxyl radical production if the predominant form of iron was ferric, due to the ability of melanin to reduce ferric to ferrous iron. Hydroxyl radical production in the presence of a strong chelator (e.g. EDTA) and melanin was greater than in the presence of a weak chelator (e.g. ADP) and melanin. Melanin also increased the rate of destruction of the DMPO-OH adduct.     

Mesosomes in Escherichia coli

When Escherichia coli was grown in a synthetic medium and fixed with osmium, sections of the cells revealed clearly defined mesosomes. These mesosomes appeared to develop, in dividing cells, as coiled infoldings of the cytoplasmic membrane. Mature mesosomes formed a link between the cytoplasmic membrane and the nucleus of the cell. The arrangement of the mesosomes in dividing cells led to the hypothesis that division of the nucleus in these cells is accomplished by two separate polar mesosomes. One mesosome is derived from the parent cell and is present at one pole of the daughter cell. The other is freshly synthesized at or near the newly forming pole of the daughter cell. While the old mesosome remains attached to the chromosome received from the parent cell, the newly synthesized mesosome becomes attached to and initiates replication of the new chromosome. As the cell grows and elongates, the two mesosomes, attached to their respective chromosomes move apart, thus effecting nuclear division.     

Mesosomes in blue-green algae

Summary Mesosome-like, unit-membrane structures are clearly defined in the blue-green algae, Spirulina and three strains of Synechococcus, after osmium or potassium permanganate fixation and observation with the electron microscope. The membranous structures are distinct from the photosynthetic membranes and, in the case of Spirulina, are frequently observed in cells and can occur in large volume within the cell.