Oxygen Supply Rate Research Articles

Assessment of singlet oxygen dosimetry concepts in photodynamic therapy through computational modeling.

In photodynamic therapy (PDT) oxygen plays a vital role in killing tumor cells. Therefore oxygen dosimetry is being thoroughly studied. Light distribution into tissue is modelled for radiation-induced fibrosarcoma (RIF) and nodular basal cell carcinoma (nBCC), in order to study the influence of blood flow on singlet oxygen concentration effectively leading to cell death ([1O2]rx) from PDT, within this light distribution. This is achieved through initial oxygen supply rate (g0) and initial molecular oxygen concentration ([3O2]0) calculations. Monte Carlo simulations and mathematical models are used for spatial and temporal distributions of [1O2]rx. Hypoxia conditions are simulated by minimizing [3O2]0 and g0. Furthermore, an optimization algorithm is developed to calculate minimum initial molecular oxygen concentration needed ([3O2]0,min) for constant [1O2]rx, when blood flow changes. Our results validate that in initially well-oxygenated scenarios with normal blood flow maximum [1O2]rx values are significantly higher than corresponding values of hypoxic scenarios both for RIF and nBCC models, with maximum oxygen supply rate percentage variations being independent from g0. Moreover, [1O2]rx appears to be more affected by an increase of g0 than of [3O2]0 values. For low blood flow there is a linear relationship between [3O2]0,min and g0, while for better oxygenated areas high blood flow reduces [3O2]0,min needed in exponential manner. Blood flow appears to be able to compensate for oxygen consumption. The developed optimization protocol on oxygen dosimetry offers a suitable combination of [3O2]0,min and g0 to achieve constant [1O2]rx, despite possible blood flow variations.

Enhancement of l-phenylalanine production in Escherichia coli by heterologous expression of Vitreoscilla hemoglobin.

l-Phenylalanine is an important amino acid that is widely used in the production of food flavors and pharmaceuticals. Generally, l-phenylalanine production by engineered Escherichia coli requires a high rate of oxygen supply. However, the coexpression of Vitreoscilla hemoglobin gene (vgb), driven bya tac promoter, with the genes encoding 3-deoxy-d-arabinoheptulosonate-7-phosphate synthetase (aroF) and feedback-resistant chorismate mutase/prephenate dehydratase (pheAfbr ), led to increased productivity and decreased demand for aeration by E. coli CICC10245. Shake-flask studies showed that vgb-expressing strains displayed higher rates of oxygen uptake, and l-phenylalanine production under standard aeration conditions was increased. In the aerobicfermentation process, cell growth, l-phenylalanine production, and glucose consumption by the recombinant E. coli strain PAPV, which harbored aroF, pheAfbr , and tac-vgb genes, were increased compared to that in the strain harboring only aroF and pheAfbr (E. coli strain PAP), especially under oxygen-limited conditions. The vgb-expressing strain PAPV produced 21.9% more biomass and 16.6% more l-phenylalanine, while consuming only approximately 5% more glucose after 48 H of fermentation. This study demonstrates a method to enhance the l-phenylalanine production by E. coli using less intensive and thus more economical aeration conditions.

Study into the influence of concentration of ions of chlorine and temperature of circulating water on the corrosion stability of carbon steel and cast iron

The impact of the chloride ions concentration and the temperature of the circulating water on the process of corrosion destruction of carbon steel and cast iron has been investigated. It has been shown that an increase in the concentration of chloride ions causes a shift in the values of the stationary potentials of steel and cast iron to the region of negative values and reduces the passive state of these alloys. This leads to an increase in the corrosion rate of St.3 steel and CI 18-36 cast iron. The results of electrochemical studies have shown that the more reliable protective films are formed on steel than on cast iron. The limiting concentration of NaCl, at which reliable operation of equipment made from these alloys is possible, depends on the pH of the solution. At pH=7, it is about 1.2 g l -1 , which is about an order of magnitude less than at pH=12. When the circulating water temperature rises, the corrosion rate of steel and cast iron increases. The stationary potentials of steel and cast iron are shifted to the negative range, and the polarization of the anode process decreases. Corrosion process is limited by the rate of oxygen supply to the cathode areas

A Three-electrode Electro-Fenton System Supplied by Self-generated Oxygen with Automatic pH-regulation for Groundwater Remediation

The applications of electro-Fenton (E-Fenton) systems for groundwater remediation require effective O2 supply and pH adjustment in the aquifer. To avoid air sparging and achieve automatic pH regulation, we proposed a three-electrode E-Fenton system which utilized the electrochemically produced O2 from anodic oxygen evolution reaction (OER) and localized pH conditions near electrodes. In order to address the external demand of O2 for oxygen reduction reaction (ORR, two-electron transfer) compared to the O2 supply from OER (four-electron transfer) in the two-electrode system, an additional cathode (primary reaction as hydrogen evolution reaction, HER) was introduced to increase OER current for enhanced O2 production. With set current of −5mA for the additional cathode, the equivalent oxygen supply rate at the anode was 1.9mLh−1, resulting in a maximum H2O2 concentration of 20.9mgL−1 and Rhodamine B removal of 97.4% within 120min. The contaminant removal was much higher than that of 5.0% for two-electrode E-Fenton systems without aeration. Proton generation from the anode gradually developed the acidic environment (pH 2.9-3.1) in the treatment zone, which was beneficial for OH formation and contaminant removal. The aqueous pH was eventually neutralized by OH− produced from the cathodes, and the final pH was 6.1. Our system represents a promising approach for groundwater electrochemical remediation with efficient contaminant removal and pH regulations.

Determinants of hypoxia-inducible factor activity in the intestinal mucosa.

The intestinal mucosa is exposed to fluctuations in oxygen levels due to constantly changing rates of oxygen demand and supply and its juxtaposition with the anoxic environment of the intestinal lumen. This frequently results in a state of hypoxia in the healthy mucosa even in the physiologic state. Furthermore, pathophysiologic hypoxia (which is more severe and extensive) is associated with chronic inflammatory diseases including inflammatory bowel disease (IBD). The hypoxia-inducible factor (HIF), a ubiquitously expressed regulator of cellular adaptation to hypoxia, is central to both the adaptive and the inflammatory responses of cells of the intestinal mucosa in IBD patients. In this review, we discuss the microenvironmental factors which influence the level of HIF activity in healthy and inflamed intestinal mucosae and the consequences that increased HIF activity has for tissue function and disease progression.

Mechanism of Iron Oxide Scale Reduction in 5%H2–N2 Gas at 650–900 °C

The reduction behaviour of the oxide scale on hot-rolled, low-carbon steel strip in 5%H2–N2 gas at 650–900 °C was studied. In general, the reduction rate of the oxide scale at the centre location was more rapid than that at the near-edge location. In both cases, the reduction rates at 650 °C were extremely low and the rates increased with increased temperature, reaching their maxima at 850 °C. Arrhenius plot of the rate constant derived from the early parabolic stage revealed that the reduction mechanism at 650–750 °C differed from that at 750–850 °C, with the former being oxygen diffusion in α-Fe and the latter most likely iron diffusion in wustite. In all cases, a thin iron layer formed on the scale surface within a very short time and then the thickness of this layer remained essentially unchanged, while the scale layer was gradually reduced via outward migration of the inner wustite–steel interface, as a result of inward iron diffusion through the wustite layer to that interface. More rapid oxygen diffusion through the thin surface iron layer than the oxygen supply rate through interface reaction was believed to result in a lower oxygen potential at the outer iron–wustite interface, thus providing a driving force for iron to diffuse through the wustite layer. The inner wustite–iron interface became undulating initially; then with the rapid advance of some protruding sections, some parts of the wustite layer were reduced through first, and finally the remaining wustite islands were reduced to complete the reduction process. Porosities were generated when wustite islands were reduced due to localized volume shrinkage. Higher oxygen concentrations in the scales of the near-edge samples were believed to be responsible for their slower reduction rates than those of the centre location samples.

Rates of oxygen uptake increase independently of changes in heart rate in late stages of development and at hatching in the green iguana, Iguana iguana

Oxygen consumption (VO2), heart rate (fH), heart mass (Mh) and body mass (Mb) were measured during embryonic incubation and in hatchlings of green iguana (Iguana iguana). Mean fH and VO2 were unvarying in early stage embryos. VO2 increased exponentially during the later stages of embryonic development, doubling by the end of incubation, while fH was constant, resulting in a 2.7-fold increase in oxygen pulse. Compared to late stage embryos, the mean inactive level of VO2 in hatchlings was 1.7 fold higher, while fH was reduced by half resulting in a further 3.6 fold increase in oxygen pulse. There was an overall negative correlation between mean fH and VO2 when data from hatchlings was included. Thus, predicting metabolic rate as VO2 from measurements of fH is not possible in embryonic reptiles. Convective transport of oxygen to supply metabolism during embryonic incubation was more reliably indicated as an index of cardiac output (COi) derived from the product of fH and Mh. However, a thorough analysis of factors determining rates of oxygen supply during development and eclosion in reptiles will require cannulation of blood vessels that proved impossible in the present study, to determine oxygen carrying capacity by the blood and arteriovenous oxygen content difference (A-V diff), plus patterns of blood flow.

Explicit macroscopic singlet oxygen modeling for benzoporphyrin derivative monoacid ring A (BPD)-mediated photodynamic therapy

Photodynamic therapy (PDT) is an effective non-ionizing treatment modality that is currently being used for various malignant and non-malignant diseases. In type II PDT with photosensitizers such as benzoporphyrin monoacid ring A (BPD), cell death is based on the creation of singlet oxygen (1O2). With a previously proposed empirical five-parameter macroscopic model, the threshold dose of singlet oxygen ([1O2]rx,sh]) to cause tissue necrosis in tumors treated with PDT was determined along with a range of the magnitude of the relevant photochemical parameters: the photochemical oxygen consumption rate per light fluence rate and photosensitizer concentration (ξ), the probability ratio of 1O2 to react with ground state photosensitizer compared to a cellular target (σ), the ratio of the monomolecular decay rate of the triplet state photosensitizer (β), the low photosensitizer concentration correction factor (δ), and the macroscopic maximum oxygen supply rate (g). Mice bearing radiation-induced fibrosarcoma (RIF) tumors were treated interstitially with a linear light source at 690nm with total energy released per unit length of 22.5–135J/cm and source power per unit length of 12–150mW/cm to induce different radii of necrosis. A fitting algorithm was developed to determine the photochemical parameters by minimizing the error function involving the range between the calculated reacted singlet oxygen ([1O2]rx) at necrosis radius and the [1O2]rx,sh. [1O2]rx was calculated based on explicit dosimetry of the light fluence distribution, the tissue optical properties, and the BPD concentration. The initial ground state oxygen concentration ([3O2]0) was set to be 40μM in this study. The photochemical parameters were found to be ξ=(55±40)×10−3cm2mW−1s−1, σ=(1.8±3)×10−5μM−1, and g=1.7±0.7μMs−1. We have taken the literature values for δ=33μM, and β=11.9μM. [1O2]rx has shown promise to be a more effective dosimetry quantity for predicting necrosis than either light dose or PDT dose, where the latter is simplistically a temporal integral of the products of the photosensitizer concentration and light fluence rate.

On the effect of operating conditions in liquid-feed direct methanol fuel cells: A multiphysics modeling approach

A multiphysics model for liquid-feed Direct Methanol Fuel Cells is presented. The model accounts for two-dimensional (2D) across-the-channel anisotropic mass and charge transport in the anode and cathode Gas Diffusion Layers (GDLs), including the effect of GDL assembly compression and electrical contact resistances at the Bipolar Plate (BPP) and membrane interfaces. A one-dimensional (1D) across-the-membrane model is used to describe local species diffusion through the microporous layers, methanol/water crossover, proton transport, and electrochemical reactions, thereby coupling both GDL sub-models. The 2D/1D model is extended to the third dimension and supplemented with 1D descriptions of the flow channels to yield a 3D/1D + 1D model that is successfully validated. A parametric study is then conducted on the 2D/1D model to examine the effect of operating conditions on cell performance. The results show that an optimum methanol concentration exists that maximizes power output due to the trade-off between anode polarization and cathode mixed overpotential. For fixed methanol concentration, cell performance is largely affected by the oxygen supply rate, cell temperature, and liquid/gas saturation levels. There is also an optimal GDL compression due to the trade-off between ohmic and concentration losses, which strongly depends on BPP material and, more weakly, on the actual operating conditions.

SU‐F‐J‐01: Measurement of Blood Flow During PDT Using Diffuse Correlation Spectroscopy

Purpose:To investigate the variation in blood flow during PDT and to determine the oxygen supplying rate, g, to refine the empirical macroscopic model.Methods:RIF tumors were propagated in female C3H mice by injecting cell suspension at a concentration of 1×106 cells/ml on the shoulder region. Photosensitizer(e.g., HPPH) was injected into the mice through tail vein at a concentration of 0.25 mg/kg when the tumors grew to ∼6 mm in diameter and depth. Temporal changes of tissue oxygen concentration were recorded prior, during and post PDT treatment using OxyLite single‐channel tissue pO2 monitor(OXFORD OPTRONIX). [3O2] was approximated by multiplying the measured pO2 with 3O2 solubility in tissue(1.295 µM/mmHg). The experimental [3O2] profile were compared with those simulated with the macroscopic model with and without considering the blood flow changes. The dynamical change of blood flow during PDT was simulated by making parameter g to be time dependent, in which the g function was obtained from Photofrin‐mediated PDT in RIF tumors. The relative blood flow changes in the tumors prior, during and post PDT treatment were measured using diffuse correlation spectroscopy (DCS) in a non‐contact configuration.Results:Both macroscopic models, with and without blood flow changes, show reasonably good agreement with the experimental [3O2] measurements. However, a rapid increase in the measured [3O2] between 700–1200s during PDT treatment could not be simulated with our empirical models. As blood flow is the direct measure of tissue oxygen supply and different photosensitizers might impact the blood flow differently, detailed studies are essential to investigate the variation in blood flow changes and the impact on the [3O2] consumption using different photosensitizers.Conclusion:DCS can be used to monitor relative blood flow noninvasively. The continuous input of oxygen supply rate is essential to refine our empirical macroscopic model to better predict PDT treatment outcome.

Study of tissue oxygen supply rate in a macroscopic photodynamic therapy singlet oxygen model

An appropriate expression for the oxygen supply rate (Γ(s)) is required for the macroscopic modeling of the complex mechanisms of photodynamic therapy (PDT). It is unrealistic to model the actual heterogeneous tumor microvascular networks coupled with the PDT processes because of the large computational requirement. In this study, a theoretical microscopic model based on uniformly distributed Krogh cylinders is used to calculate Γ(s) = g (1 - [³O₂]/[³O₂]₀) that can replace the complex modeling of blood vasculature while maintaining a reasonable resemblance to reality; g is the maximum oxygen supply rate and [³O₂]/[³O₂]₀ is the volume-average tissue oxygen concentration normalized to its value prior to PDT. The model incorporates kinetic equations of oxygen diffusion and convection within capillaries and oxygen saturation from oxyhemoglobin. Oxygen supply to the tissue is via diffusion from the uniformly distributed blood vessels. Oxygen can also diffuse along the radius and the longitudinal axis of the cylinder within tissue. The relations of Γ(s) to [³O₂]/[³O₂]₀ are examined for a biologically reasonable range of the physiological parameters for the microvasculature and several light fluence rates (ϕ). The results show a linear relationship between Γ(s) and [³O₂]/[³O₂]₀, independent of ϕ and photochemical parameters; the obtained g ranges from 0.4 to 1390 μM/s.

Consequences of artificial deepwater ventilation in the Bornholm Basin for oxygen conditions, cod reproduction and benthic biomass – a model study

Abstract. We develop and use a circulation model to estimate hydrographical and ecological changes in the isolated basin water of the Bornholm Basin. By pumping well-oxygenated so-called winter water to the greatest depth, where it is forced to mix with the resident water, the rate of deepwater density reduction increases as well as the frequency of intrusions of new oxygen-rich deepwater. We show that pumping 1000 m3 s−1 should increase the rates of water exchange and oxygen supply by 2.5 and 3 times, respectively. The CRV (cod reproduction volume), the volume of water in the isolated basin meeting the requirements for successful cod reproduction (S > 11, O2 > 2 mL L−1), should every year be greater than 54 km3, which is an immense improvement, since it has been much less in certain years. Anoxic bottoms should no longer occur in the basin, and hypoxic events will become rare. This should permit extensive colonization of fauna on the earlier periodically anoxic bottoms. Increased biomass of benthic fauna should also mean increased food supply to economically valuable demersal fish like cod and flatfish. In addition, re-oxygenation of the sediments should lead to increased phosphorus retention by the sediments.

Association between swimming performance, cardiorespiratory morphometry, and thermal tolerance in Atlantic salmon (Salmo salar L.)

This experiment tested the hypothesis that swimming performance in Atlantic salmon (Salmo salar) parr is connected to cardiorespiratory performance and morphology, as well as maximum heart rate (fHmax) related measures of thermal tolerance. Moreover, it was hypothesized that the cardiorespiratory differences between poor and strong swimmers will be retained in a later life stage, i.e., 15 weeks post-smoltification and seawater transfer. This experiment screened a population of 3,200 parr (11.2 ± 0.25 g) for their swimming performance, classifying them as poor and good swimmers based on their critical swimming speeds (4.4±0.1 body length s-1 and >6.8±0.1 body length s-1, respectively). Compared with poor performing parr, good swimmers had a significantly thicker compact myocardium (by 23.7%) and taller gill secondary lamellae (by 16.2%). In contrast, there was no significant difference in maximum oxygen consumption between the two groups as assessed using a ‘chase’ protocol, and the relationship between heart rate specific measures of thermal tolerance and swim performance was variable. For example, three measures did not differ between the two groups, whereas the Arrhenius breakpoint temperature for fHmax and fHmax were higher and lower, respectively, in the poor swimmers. Importantly, the identified morphological and fHmax differences at the parr stage persisted after 15 weeks of common garden rearing in seawater, and they were associated with an increase in relative ventricular mass and a small, but significant, improvement in growth rate. Therefore, it seems that an early assessment of swimming performance can effectively screen for morphological capacities related to oxygen supply and growth rate, but less so for heart rate related measures of thermal tolerance.

α-Acetolactate overexpression from glucose in the diacetyl producer Lactococcus lactis ssp. lactis bv. diacetylactis B2103, a natural mutant lacking α-acetolactate decarboxylase

We investigated the effects of the oxygen supply rate on the activity of pyruvate metabolic pathways and their end products, the lactatedehydrogenase (LDH), pyruvateformiatelyase (PFL), pyruvatedehydrogenase (PDH) and acetolactatesynthase (ALS) pathways, in the Lactococcus lactis ssp. lactis bv. diacetylactis strain B2103/74. We found that this culture, apart from inactivated α-acetyldecarboxylase, also possesses a unique natural capacity to overexpress α-acetolactate (AL) up to 25–28 mM. Our search for similar properties among the diacetilicus bv. strains showed that this ability is quite rare. We identified a single additional strain, 7590 from the National Russian Collection of Industrial Microorganisms (NRCIM-7590), which displayed a similar capacity. However, unlike B2103/74, NRCIM-7590 has an active α-acetolactate decarboxylase and therefore can only produce acetoin. AL overexpression took place under conditions of intense aeration (KLa ≥ 90–120 h−1), and the composition of the medium played a decisive role in AL productivity. We found that AL overproduction is determined by a diversion of a portion of pyruvate flow from the LDH to the PDH and ALS pathways. We further found that all additional pyruvate, supplied from LDH, is utilized exclusively by the ALS pathway because of the restricted capacity of the PDH pathway. This shift in pyruvate metabolism in the B2103/74 strain, from LDH to PDH and ALS pathways, is associated with the initiation of an oxidation reaction that reduces oxygen to H2O and sequesters NADH from the LDH pathway in the process. A specific manifestation of this reaction in B2103/74 and NRCIM-7590 cultures, which results in a profound shift of the pyruvate metabolism towards the production of α-acetolactate, is due to the function of a potent oxidative system that shifts 75–80% of NADH flow from LDH to the oxidative pathway, resulting in the regeneration of NAD+. The nature of this oxidative system is not known. Based on our studies, we propose that the structure of the newly discovered oxidative system is similar to a simple transmembrane electron transport chain.

Design Criteria for Generating Physiologically Relevant In Vitro Models in Bioreactors

In this paper, we discuss the basic design requirements for the development of physiologically meaningful in vitro systems comprising cells, scaffolds and bioreactors, through a bottom up approach. Very simple micro- and milli-fluidic geometries are first used to illustrate the concepts, followed by a real device case-study. At each step, the fluidic and mass transport parameters in biological tissue design are considered, starting from basic questions such as the minimum number of cells and cell density required to represent a physiological system and the conditions necessary to ensure an adequate nutrient supply to tissues. At the next level, we consider the use of three-dimensional scaffolds, which are employed both for regenerative medicine applications and for the study of cells in environments which better recapitulate the physiological milieu. Here, the driving need is the rate of oxygen supply which must be maintained at an appropriate level to ensure cell viability throughout the thickness of a scaffold. Scaffold and bioreactor design are both critical in defining the oxygen profile in a cell construct and are considered together. We also discuss the oxygen-shear stress trade-off by considering the levels of mechanical stress required for hepatocytes, which are the limiting cell type in a multi-organ model. Similar considerations are also made for glucose consumption in cell constructs. Finally, the allometric approach for generating multi-tissue systemic models using bioreactors is described.

Evaluation of pH and redox conditions in subsurface disposal system for assessing influence of metal corrosion

The properties of metal corrosion, such as the corrosion rate and corrosion expansion rate, are key factors for assessing the long term performance of the subsurface disposal system. In this study, transient changes in pH were first simulated using a finite difference computer code. In the second step, the consumption times of the residual oxygen in the facility after the backfill were calculated. Finally, the supply of dissolved oxygen in the groundwater to the engineered barrier and the corrosion amount resulting from it were estimated. A high pH of around 12·5 would persist at least for 105 years inside the low permeability layer (LPL). In addition, the results suggest that the rate of oxygen supply in the form of dissolved oxygen in the groundwater was very small due to the restriction of mass transport by the LPL and the low diffusivity layer. Thus, the environment in which aerobic corrosion extremely limited was found to be of long duration. This strongly suggests that, for assessing the long term performance of the engineered barrier system, anaerobic corrosion will have to be evaluated carefully.

Comparison of PDT parameters for RIF and H460 tumor models during HPPH-mediated PDT.

Singlet oxygen (1O2) is the major cytotoxic species producing PDT effects, but it is difficult to monitor in vivo due to its short life time in real biological environments. Mathematical models are then useful to calculate 1O2 concentrations for PDT dosimetry. Our previously introduced macroscopic model has four PDT parameters: ξ, σ, β and g describing initial oxygen consumption rate, ratio of photobleaching to reaction between 1O2 and cellular targets, ratio of triplet state (T) phosphorescence to reaction between T and oxygen (3O2), and oxygen supply rate to tissue, respectively. In addition, the model calculates a fifth parameter, threshold 1O2 dose ([1O2]rx,sd). These PDT parameters have been investigated for HPPH using radiation-induced fibrosarcoma (RIF) tumors in an in-vivo C3H mouse model. In recent studies, we additionally investigated these parameters in human non-small cell lung carcinoma (H460) tumor xenografts, also using HPPH-mediated PDT. In-vivo studies are performed with nude female mice with H460 tumors grown intradermally on their right shoulders. HPPH (0.25 mg/kg) is injected i.v. at 24 hours prior to light delivery. Initial in vivo HPPH concentration is quantified via interstitial HPPH fluorescence measurements after correction for tissue optical properties. Light is delivered by a linear source at various light doses (12-50 J/cm) with powers ranging from 12 to 150 mW per cm length. The necrosis radius is quantified using ScanScope after tumor sectioning and hematoxylin and eosin (H&E) staining. The macroscopic optimization model is used to fit the results and generate four PDT parameters. Initial results of the parameters for H460 tumors will be reported and compared with those for the RIF tumor.

ROOT OXYGEN USE DURING PROPAGATION OF CUCUMBER ON ROCKWOOL CUBES

Cucumbers were propagated in rockwool cubes in a climate cell for four weeks. The complete root system of each cucumber was enclosed in an airtight box. Each box was connected to an air bag, which acted as an air reservoir. A peristaltic pump ensured air circulation in the system. Treatments included maintenance of oxygen levels at 21%, 7% and 2% in specific box-bag systems. The goal of this experiment was to measure the critical oxygen supply rate for normal production. An additional goal was to characterize plant and root growth affected by sub optimal oxygen avail¬ability. With a fiber optic oxygen meter it proved possible to measure and monitor the oxygen level in the box-bag system in time at various points. A critical oxygen maintenance level between 8 and 12% was found for this system. A maximum oxygen use of 5.8 mg.h-1.plant-1 was reached by plants with a growth equal to the reference plants. The above ground growth reaction to mild but prolonged sub-optimal oxygen supply rates included a 20-50% reduction in leaf area, fresh and dry above ground and below ground mass production and, less pronounced, a reduction in plant length. The dry mass root/shoot ratio remained constant despite widely different oxygen supply. The root oxygen use rate during the light period was 5-10 times higher than during the dark period. It is argued that the growth reduction is not so much related to a critical oxygen level in the air but to local oxygen depletion in the substrate. Local oxygen depletion might be the result of the interaction of oxygen supply rate and substrate diffusivity or the accumulation of gasses as carbon dioxide and ethylene to phytotoxic concentrations.

A paradigm shift for local blood flow regulation

a remarkable example of physiological regulation is the coordination between metabolic rate and local blood flow in microscopic volumes of an organ. In skeletal muscle an increase in oxygen consumption (Vo2) over a wide range evokes a proportional (∼5 to 6 × Vo2) increase in blood flow ([29][

Kinase Activity of ArcB from Escherichia coli Is Subject to Regulation by Both Ubiquinone and Demethylmenaquinone

Expression of the catabolic network in Escherichia coli is predominantly regulated, via oxygen availability, by the two-component system ArcBA. It has been shown that the kinase activity of ArcB is controlled by the redox state of two critical pairs of cysteines in dimers of the ArcB sensory kinase. Among the cellular components that control the redox state of these cysteines of ArcB are the quinones from the cytoplasmic membrane of the cell, which function in ‘respiratory’ electron transfer. This study is an effort to understand how the redox state of the quinone pool(s) is sensed by the cell via the ArcB kinase. We report the relationship between growth, quinone content, ubiquinone redox state, the level of ArcA phosphorylation, and the level of ArcA-dependent gene expression, in a number of mutants of E. coli with specific alterations in their set of quinones, under a range of physiological conditions. Our results provide experimental evidence for a previously formulated hypothesis that not only ubiquinone, but also demethylmenaquinone, can inactivate kinase activity of ArcB. Also, in a mutant strain that only contains demethylmenaquinone, the extent of ArcA phosphorylation can be modulated by the oxygen supply rate, which shows that demethylmenaquinone can also inactivate ArcB in its oxidized form. Furthermore, in batch cultures of a strain that contains ubiquinone as its only quinone species, we observed that the ArcA phosphorylation level closely followed the redox state of the ubiquinone/ubiquinol pool, much more strictly than it does in the wild type strain. Therefore, at low rates of oxygen supply in the wild type strain, the activity of ArcB may be inhibited by demethylmenaquinone, in spite of the fact that the ubiquinones are present in the ubiquinol form.