Ethylene is involved in the autochemotropism of Phycomyces

The sporangiophore of the fungus Phycomyces blakesleeanus has the property of growing away from a barrier which is few mm from the growing zone of the sporangiophore (avoidance or autochemotropic response). A model has been published (Cohen, R.J., Jan, N.Y., Matricon, J., Delbrück, M.: J. Gen. Physiol. 66, 67–95 (1975)). To explain the avoidance response which postulates that the sporangiophore emits and readsorbs a volatile growth-promoting effector (gas X) and that the barrier modifies the effector distribution by acting as an aerodynamic obstacle, causing a higher concentration of gas X on the side of the sporangiophore closer to the barrier. From this model we deduced three properties of the gas X. Of the several gases tested (N₂, CO₂, CH₄, C₂H₂, C₂H₄, C₂H₆) only ethylene (C₂H₄) had all these three properties, a finding which suggests that it has a role in the avoidance response (autochemotropism).Abbreviation Spph Sporangiophore     

Detection of hydrogen sulphide using cataluminescence sensors based on alkaline-earth metal salts

Detection of hydrogen sulphide (H₂S) was conducted based on cataluminescence (CTL) sensors, using alkaline‐earth metal carbonates as catalysts. Optimal working conditions, analytical characteristics and the response properties of the sensor were investigated. CTL intensity examination showed that sensors fabricated with CaCO₃, SrCO₃ or BaCO₃ could be used to detect H₂S gas sensitively. The optimal sensing temperature was about 320 °C. Under the sensing conditions with temperature at ca. 320 °C and gas flow rate in the range 180–200 mL/min, the linear range of CTL intensity vs H₂S concentration was 25–500 ppm, with a detection limit of 2 ppm. The response and recovery times of the sensor were within 5 and 25 min, respectively. Also, the sensor had the property of high selectivity to H₂S with very weak or no obvious response to 14 other gases, such as NO₂, NH₃, hydrocarbons and alcohol. Copyright © 2011 John Wiley & Sons, Ltd.     

Pyruvate Protects Pathogenic Spirochetes from H2O2 Killing

Pathogenic spirochetes cause clinically relevant diseases in humans and animals, such as Lyme disease and leptospirosis. The causative agent of Lyme disease, Borrelia burgdorferi, and the causative agent of leptospirosis, Leptospria interrogans, encounter reactive oxygen species (ROS) during their enzootic cycles. This report demonstrated that physiologically relevant concentrations of pyruvate, a potent H₂O₂ scavenger, and provided passive protection to B. burgdorferi and L. interrogans against H₂O₂. When extracellular pyruvate was absent, both spirochetes were sensitive to a low dose of H₂O₂ (≈0.6 µM per h) generated by glucose oxidase (GOX). Despite encoding a functional catalase, L. interrogans was more sensitive than B. burgdorferi to H₂O₂ generated by GOX, which may be due to the inherent resistance of B. burgdorferi because of the virtual absence of intracellular iron. In B. burgdorferi, the nucleotide excision repair (NER) and the DNA mismatch repair (MMR) pathways were important for survival during H₂O₂ challenge since deletion of the uvrB or the mutS genes enhanced its sensitivity to H₂O₂ killing; however, the presence of pyruvate fully protected ΔuvrB and ΔmutS from H₂O₂ killing further demonstrating the importance of pyruvate in protection. These findings demonstrated that pyruvate, in addition to its classical role in central carbon metabolism, serves as an important H₂O₂ scavenger for pathogenic spirochetes. Furthermore, pyruvate reduced ROS generated by human neutrophils in response to the Toll-like receptor 2 (TLR2) agonist zymosan. In addition, pyruvate reduced neutrophil-derived ROS in response to B. burgdorferi, which also activates host expression through TLR2 signaling. Thus, pathogenic spirochetes may exploit the metabolite pyruvate, present in blood and tissues, to survive H₂O₂ generated by the host antibacterial response generated during infection.     

Nitric oxide and hydrogen peroxide are important signals mediating the allelopathic response of Arabidopsis to p‐hydroxybenzoic acid

Both nitric oxide (NO) and hydrogen peroxide (H₂O₂) are important signals that mediate plant response to environmental stimulation. Their role in plants' allelopathic interactions has also been reported, but the underlying mechanism remains little understood. p‐Hydroxybenzoic acid (pHBA) has been proposed to be an allelopathic chemical. Here, we found that pHBA at 0.4 mM efficiently suppressed Arabidopsis growth. Meanwhile, pHBA rapidly induced the accumulation of NO and H₂O₂, where such effect could be reversed by NO or H₂O₂ metabolism inhibitors or scavengers. Also, pHBA‐induced NO and H₂O₂ could be compromised in NO synthesis mutants noa1, nia1 and nia2, or H₂O₂ metabolism mutant rbohD/F, but suppressing NO accumulation with a NO synthesis inhibitor or using NO synthesis‐related mutants did not reduce pHBA‐induced H₂O₂ accumulation. Furthermore, we found that the effect of pHBA on allelopathic inhibition of growth was aggravated in NO/H₂O₂ metabolism‐related mutants or reducing NO/H₂O₂ by different inhibitors, whereas the addition of an NO/H₂O₂ donor could partly relieve the inhibitory effect of pHBA on the growth of wild type. However, adding only an NO donor, but not low concentration of H₂O₂ as the donor, could relieve the inhibitory effect of pHBA on root growth in NO metabolism mutants. On the basis of these results, we propose that both NO and H₂O₂ are important signals that mediate Arabidopsis response to the allelopathic chemical pHBA, where during this process H₂O₂ may work upstream of the NO signal.     

Differential responses to oxidative stress and calcium influx on expression of the transforming growth factor‐β family in myoblasts and myotubes

Changes in gene expression of TGF‐β family members and their receptors in response to treatment with H₂O₂ and a calcium ionophore, A23187, were examined in C2C12 myoblasts and myotubes. The expression of Myf5, an initial regulator of myogenesis, was increased by A23187, and H₂O₂ inhibited the up‐regulation of Myf5. Treatment with H₂O₂ decreased the expression of MHC IIb, a protein component of the myofibrils, irrespective of the presence of A23187, suggesting an inhibitory role of oxidative stress for myogenesis. Expression of ligands and receptors for the TGF‐β family was modulated in response to H₂O₂ and A23187. Treatment with H₂O₂ decreased expression of TGF‐β3, BMP‐4, ALK4, ALK5, and ActRIIB, and increased expression of inhibin α and inhibin βA in either the myoblast stage or the myotube stage, or both. A23187 potentiated down‐regulation of BMP‐4 and ALK4 expression, and up‐regulation of TGF‐β1, TGF‐β2, inhibin α, inhibin βA, ALK2, and ALK3 expression. These results indicate that oxidative stress and Ca²⁺ influx affect expression of the TGF‐β family in C2C12 myoblasts and myotubes. Copyright © 2009 John Wiley & Sons, Ltd.     

Hydrogen peroxide produced by NADPH oxidase: a novel downstream signaling pathway in melatonin‐induced stress tolerance in Solanum lycopersicum

The beneficial effects of melatonin on abiotic stress have been demonstrated in several plants. However, little is known about the signal transduction pathway of melatonin involved in the plant stress response. Here, we manipulated the melatonin levels in tomato plants through a chemical approach. The roles of melatonin in stress tolerance were studied by assessing the symptoms, chlorophyll fluorescence and stress‐responsive gene expression. Moreover, both chemical and genetic approaches were used to study the roles of hydrogen peroxide (H₂O₂) in melatonin‐induced signal transduction in tomato plants. We found that melatonin activates NADPH oxidase (RBOH) to enhance H₂O₂ levels by reducing its S‐nitrosylation activity. Furthermore, melatonin‐induced H₂O₂ accumulation was accompanied by obtainable stress tolerance. Inhibition of RBOH or chemical scavenging of H₂O₂ significantly reduced the melatonin‐induced defense response, including reduced expression of several stress‐related genes (CDPK1, MAPK1, TSPMS, ERF4, HSP80 and ERD15) and reduced antioxidative enzyme activity (SOD, CAT and APX), which were responsible for the stress tolerance. Collectively, these results revealed a novel mechanism in which RBOH activity and H₂O₂ signaling are important components of the melatonin‐induced stress tolerance in tomato plants.     

Azolla-Anabaena azollae Relationship: IV. Photosynthetically Driven, Nitrogenase-catalyzed H(2) Production

The water fern, Azolla caroliniana Willd., containing the symbiotic, heterocystous blue-green alga, Anabaena azollae, has been studied under various growth conditions to characterize its light-dependent production of H₂. The response of H₂ production to N₂ and C₂H₂ and the absence of a differential effect of m-chlorocarbonyl cyanide phenylhydrazone on H₂ production and C₂H₂ reduction, coupled with the parallel inhibition of both processes by DCMU imply that the production of H₂ is nitrogenase-catalyzed and ATP-dependent.     

Oxidative stress response of Blakeslea trispora induced by H2O2 during β-carotene biosynthesis

The cellular response of Blakeslea trispora to oxidative stress induced by H₂O₂ in shake flask culture was investigated in this study. A mild oxidative stress was created by adding 40 μm of H₂O₂ into the medium after 3 days of the fermentation. The production of β-carotene increased nearly 38 % after a 6-day culture. Under the oxidative stress induced by H₂O₂, the expressions of hmgr, ipi, carG, carRA, and carB involving the β-carotene biosynthetic pathway all increased in 3 h. The aerobic metabolism of glucose remarkably accelerated within 24 h. In addition, the specific activities of superoxide dismutase and catalase were significantly increased. These changes of B. trispora were responses for reducing cell injury, and the reasons for increasing β-carotene production caused by H₂O₂.     

Mitochondrial H<Subscript>2</Subscript>O<Subscript>2</Subscript> as an enable signal for triggering autophosphorylation of insulin receptor in neurons

Background

Insulin receptors are widely distributed in the brain, where they play roles in synaptic function, memory formation, and neuroprotection. Autophosphorylation of the receptor in response to insulin stimulation is a critical step in receptor activation. In neurons, insulin stimulation leads to a rise in mitochondrial H₂O₂ production, which plays a role in receptor autophosphorylation. However, the kinetic characteristics of the H₂O₂ signal and its functional relationships with the insulin receptor during the autophosphorylation process in neurons remain unexplored to date.

Results

Experiments were carried out in culture of rat cerebellar granule neurons. Kinetic study showed that the insulin-induced H₂O₂ signal precedes receptor autophosphorylation and represents a single spike with a peak at 5–10 s and duration of less than 30 s. Mitochondrial complexes II and, to a lesser extent, I are involved in generation of the H₂O₂ signal. The mechanism by which insulin triggers the H₂O₂ signal involves modulation of succinate dehydrogenase activity. Insulin dose–response for receptor autophosphorylation is well described by hyperbolic function (Hill coefficient, n_H, of 1.1±0.1; R²=0.99). N-acetylcysteine (NAC), a scavenger of H₂O₂, dose-dependently inhibited receptor autophosphorylation. The observed dose response is highly sigmoidal (Hill coefficient, n_H, of 8.0±2.3; R²=0.97), signifying that insulin receptor autophosphorylation is highly ultrasensitive to the H₂O₂ signal. These results suggest that autophosphorylation occurred as a gradual response to increasing insulin concentrations, only if the H₂O₂ signal exceeded a certain threshold. Both insulin-stimulated receptor autophosphorylation and H₂O₂ generation were inhibited by pertussis toxin, suggesting that a pertussis toxin-sensitive G protein may link the insulin receptor to the H₂O₂-generating system in neurons during the autophosphorylation process.

Conclusions

In this study, we demonstrated for the first time that the receptor autophosphorylation occurs only if mitochondrial H₂O₂ signal exceeds a certain threshold. This finding provides novel insights into the mechanisms underlying neuronal response to insulin. The neuronal insulin receptor is activated if two conditions are met: 1) insulin binds to the receptor, and 2) the H₂O₂ signal surpasses a certain threshold, thus, enabling receptor autophosphorylation in all-or-nothing manner. Although the physiological rationale for this control remains to be determined, we propose that malfunction of mitochondrial H₂O₂ signaling may lead to the development of cerebral insulin resistance.

     

H2O2 localization in the green alga Micrasterias after salt and osmotic stress by TEM-coupled electron energy loss spectroscopy

Reactive oxygen species (ROS), including hydrogen peroxide (H₂O₂), are constantly generated as by-products of normal metabolic cellular pathways and can be overproduced in response to stress. In this study, we investigated ROS production and localization of H₂O₂ after salt (200 mM KCl) and osmotic (iso-osmotic sorbitol concentration) stress in the unicellular green alga Micrasterias. By means of the dye H₂DCFDA and confocal laser scanning microscopy, most ROS production could be detected in KCl-treated cells when compared to sorbitol-exposed cells and controls. For ultrastructural detection of H₂O₂, CeCl₃, which reacts with H₂O₂ and produces cerium perhydroxide deposits, has been used. Cerium was identified by transmission electron microscopy (TEM)-coupled electron energy loss spectroscopy (EELS) in organelles of KCl- and sorbitol-treated cells and in controls. Statistical measurements of the presence of the cerium M_4,5 edge were performed in mitochondria, chloroplasts, cell walls, and cytoplasmic sites of five individual cells after each treatment. The most pronounced increase in H₂O₂ production was found in chloroplasts of KCl- and sorbitol-treated cells. This shows that the chloroplast reveals the strongest response in H₂O₂ production after stress induction in Micrasterias. Significant elevation of H₂O₂ production also occurred in mitochondria and cytoplasm, whereas H₂O₂ levels remained unchanged or even slightly decreased in cell walls of treated cells. Additionally, TEM micrographs and EELS analyses provided indirect evidence for an increased H₂O₂ production at the plasma membrane of KCl-treated cells, indicating an involvement of the plasma membrane NADPH oxidase in H₂O₂ generation.     

The involvement of hydrogen peroxide in plant responses to stresses

The role of reactive oxygen species, especially H₂O₂, in plant response to stresses has been the focus of much attention. Hydrogen peroxide has been postulated to play multiple functions in plant defence against pathogens. (1) H₂O₂ may possess direct microbicidal activity at the sites of pathogen invasion. (2) It is used for cell-wall reinforcing processes: lignification and oxidative cross-linking of hydroxyproline-rich proteins and other cell-wall polymers. (3) It was found to be necessary for phytoalexin synthesis. (4) H₂O₂ may trigger programmed plant cell death during the hypersensitive response that restricts the spread of infection. (5) H₂O₂ has been suggested to act as a signal in the induction of systemic acquired resistance and (6) it induces defence genes. Recently H₂O₂ has been proposed to be involved in the signal transduction pathways leading to acclimation and protection from abiotic stresses. The present review discusses new insights into the function of H₂O₂ in plant responses to biotic and abiotic stresses.     

The male antigen. II. Regulation of the primary and secondary responses to H-Y by H-2 associated genes

The primary response of females of ten inbred mouse strains to the male antigen (H-Y) was investigated by transfer of peritoneal exudate cells (PEC). Three distinct classes of reactivity were seen. Early primary response to H-Y was associated with H-2 haplotypes b and s; intermediate response with H-2 haplotypes, k, d, i, and h; and late or absent response with H-2 haplotypes a and f. The failure of A.CA (H-2^f) females to mount a detectable primary response against syngeneic male cells was not due to the lack of the antigen from A.CA male cells. The ability of (A.CA × B10)F₁ hybrid females to respond to the male antigen demonstrated the dominant nature of the B10 (H-2^b) response and excluded the possibility that A.CA females possess a dominant self-antigen cross-reactive with H-Y. The secondary response of eight inbred strains was investigated; at least three distinct levels of reactivity were apparent. The speed of the secondary response was associated with the various H-2 haplotypes in the same way as the primary response. The implications of differential strain reactivity, background effect, and the association of Ir-1 with response to H-Y are discussed.     

Introduction of perfluoroalkyl chain into the esterifying moiety of bacteriochlorophyll c in the green sulfur photosynthetic bacterium Chlorobaculum tepidum by pigment biosynthesis

The green sulfur photosynthetic bacterium Chlorobaculum (Cba.) tepidum was grown in liquid cultures containing perfluoro-1-decanol, 1H,1H,2H,2H-heptadecafluoro-1-decanol [CF₃(CF₂)₇(CH₂)₂OH] or 1H,1H-nonadecafluoro-1-decanol [CF₃(CF₂)₈CH₂OH], to introduce rigid and fluorophilic chains into the esterifying moiety of light-harvesting bacteriochlorophyll (BChl) c. Exogenous 1H,1H,2H,2H-heptadecafluoro-1-decanol was successfully attached to the 17²-carboxy group of bacteriochlorophyllide (BChlide) c in vivo: the relative ratio of the unnatural BChl c esterified with this perfluoroalcohol over the total BChl c was 10.3%. Heat treatment of the liquid medium containing 1H,1H,2H,2H-heptadecafluoro-1-decanol with β-cyclodextrin before inoculation increased the relative ratio of the BChl c derivative esterified with this alcohol in the total BChl c in Cba. tepidum. In a while, 1H,1H-nonadecafluoro-1-decanol was not attached to BChlide c in Cba. tepidum, which was grown by its supplementation. These results suggest that the rigidity close to the hydroxy group of the esterifying alcohol is not suitable for the recognition by the BChl c synthase called BchK in Cba. tepidum. The unnatural BChl c esterified with 1H,1H,2H,2H-heptadecafluoro-1-decanol participated in BChl c self-aggregates in chlorosomes.     

Hydrogen evolution by several algae

Summary Out of 33 strains of unicellular algae examined, H₂ evolution was observed only in species of Chlamydomonas, Chlorella and Scenedesmus. While the photoevolution of H₂ by these algae was generally stimulated both by an organic substrate and by the uncoupler CCCP¹, response to DCMU varied. On the basis of the response to DCMU, it was concluded that the mechanism of photoevolution of H₂ differed from one alga to another. The reaction in some algae appeared to be dependent on either the photooxidation of water or oxidative carbon metabolism for reductant; that in other algae was supported by reductant from both these sources.     

A series of d transition metal coordination complexes: Structures and comparative study of surface electron behaviors (n = 9, 8, 7, 6, 5)

Ten transition metal coordination complexes [Cu₂(phen)(p-tpha)(μ-O)]_n1, [Cu(m-tpha)(imH)₂]_n2, [Ni(5-Haipa)₂(H₂O)₂]_n3, [Ni(phen)₂(H₂O)₂]·btc·[Ni(H₂O)₆]_0.5·9H₂O 4, [Co(2,5-pdc)(H₂O)₂]_n·nH₂O 5, [Co₂(2,5-pdc)₂(H₂O)₆]_n·2nH₂O 6, [Fe(2,5-Hpdc)₂(H₂O)₂]·H₂O 7, [Co(C₆H₄NO₂)₃]·H₂O 8, [Fe₂(μ₂-btec)(μ₂-H₂btec)(bipy)₂(H₂O)₂]_n9, [Mn(phen)(2,5-pdc)(H₂O)₂]·H₂O 10 (H₄btec = 1,2,4,5-benzenetetracarboxylic acid, phen = 1,10-phenanthroline, 2,5-H₂pdc = 2,5-pyridine-dicarboxylic acid, p-tpha = p-phthalic acid, m-tpha = m-phthalic acid, bipy = 2,2′-bipyridine, 5-H₂aipa = 5-aminoisophthalic acid, imH = imidazole, H₃btc = 1,3,5-benzenetricarboxylic acid) were synthesized through hydrothermal method. They were characterized by UV-Vis absorption spectra, single-crystal X-ray diffraction and surface photovoltage spectra (SPS). Structural analysis indicated that the complexes 1, 2, 3, 5, 6 and 9 were linked into infinite structures bridged by organic acid ligands. The other four complexes were molecular complexes and further connected to 2D or 3D structures by the hydrogen bonds. The SPS of complexes 1-10 indicate that there are positive response bands in the range of 300-800 nm showing different levels of photo-electric conversion properties. The intensity, position, shape and the number of the response bands in SPS are obviously different since the structure, species, valence, dⁿ electrons configuration and coordinated environment of the center metals are different. There are good relationships between SPS and UV-Vis spectra.     

Use of response surface methodology to study the effect of media composition on aflatoxin production by Aspergillus flavus

Aflatoxins are one of the most important secondary metabolites. These extrolites are produced by a number of Aspergillus fungi. In this study, we demonstrate the effect of media components and enhanced aflatoxin yield shown by A. flavus using response surface methodology in response to different nutrients. Different components of a chemically defined media that influence the aflatoxin production were monitored using Plackett–Burman experimental design and further optimized by Box–Behnken factorial design of response surface methodology in liquid culture. Interactions were studied with five variables, namely sorbitol, fructose, ammonium sulfate, KH₂PO₄, and MgSO₄.7H₂O. Maximum aflatoxin production was envisaged in medium containing 4.94 g/l sorbitol, 5.56 g/l fructose, 0.62 g/l ammonium sulfate, 1.33 g/l KH₂PO₄, and 0.65 g/l MgSO₄·7H₂O using response surface plots and the point prediction tool of the DESIGN EXPERT 8.1.0 (Stat-Ease, USA) software. However, a production of 5.25 μg/ml aflatoxin production was obtained, which was in agreement with the prediction observed in verification experiment. The other component (MgSO₄.7H₂O) was found to be an insignificant variable.     

LSD1‐, EDS1‐ and PAD4‐dependent conditional correlation among salicylic acid,hydrogen peroxide,water use efficiency and seed yield in Arabidopsis thaliana

In Arabidopsis thaliana, LESION SIMULATING DISEASE 1 (LSD1), ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) and PHYTOALEXIN DEFICIENT 4 (PAD4) proteins are regulators of cell death (CD) in response to abiotic and biotic stresses. Hormones, such as salicylic acid (SA), and reactive oxygen species, such as hydrogen peroxide (H₂O₂), are key signaling molecules involved in plant CD. The proposed mathematical models presented in this study suggest that LSD1, EDS1 and PAD4 together with SA and H₂O₂ are involved in the control of plant water use efficiency (WUE), vegetative growth and generative development. The analysis of Arabidopsis wild‐type and single mutants lsd1, eds1, and pad4, as well as double mutants eds1/lsd1 and pad4/lsd1, demonstrated the strong conditional correlation between SA/H₂O₂ and WUE that is dependent on LSD1, EDS1 and PAD4 proteins. Moreover, we found a strong correlation between the SA/H₂O₂ homeostasis of 4‐week‐old Arabidopsis leaves and a total seed yield of 9‐week‐old plants. Altogether, our results prove that SA and H₂O₂ are conditionally regulated by LSD1/EDS/PAD4 to govern WUE, biomass accumulation and seed yield. Conditional correlation and the proposed models presented in this study can be used as the starting points in the creation of a plant breeding algorithm that would allow to estimate the seed yield at the initial stage of plant growth, based on WUE, SA and H₂O₂ content.     

Differential effects of superoxide,hydrogen peroxide,and hydroxyl radical on intracellular calcium in human endothelial cells

Changes in intracellular Ca²⁺ homeostasis are thought to contribute to cell dysfunction in oxidative stress. The hypoxanthine-xanthine oxidase system (X-XO) mobilizes Ca²⁺ from intracellular stores and induces a marked rise in cytosolic calcium in different cell types. To identify the reactive O₂ species involved in the disruption of calcium homeostasis by X-XO, we studied the effect of X-XO on [Ca²⁺]_i by spectrofluorimetry with fura-2 in human umbilical vein endothelial cells (HUVEC). The [Ca²⁺]_i response to X-XO was essentially diminished by superoxide dismutase (SOD) (200 U/ml) and catalase (CAT) (200 U/ml), which scavenge the superoxide anion, O₂^?, or H₂O₂, respectively. The [Ca²⁺]_i increase stimulated by 10 nmol H₂O₂/ml/min, generated from the glucose-glucose oxidase system, or 10 μM H₂O₂, given as bolus, was about a third of that induced by X-XO (10 nmol O₂^?/ml/min) but was comparable to that induced by X-XO in the presence of SOD. The X-XO—stimulated [Ca²⁺]_i increase was significantly reduced by 100 μM o-phenanthroline, which inhibits the iron-catalysed formation of the hydroxyl radical. On the other hand, the [Ca²⁺]_i response to low dose X-XO (1 nmol O₂^?/ml/min) was markedly enhanced in the presence of 1 μM H₂O₂, which itself had no effect on [Ca²⁺]_i. More than 50% of this synergistic effect was prevented by o-phenanthroline. These results indicate that the effect of X-XO on calcium homeostasis appears to result from an interaction of O₂^? and H₂O₂, which could be explained by the formation of the hydroxyl radical. © 1995 Wiley-Liss, Inc.