Spatio-Temporal Patterns in Rhizosphere Oxygen Profiles in the Emergent Plant Species Acorus calamus

Rhizosphere oxygen profiles are the key to understanding the role of wetland plants in ecological remediation. Though in situ determination of the rhizosphere oxygen profiles has been performed occasionally at certain growing stages within days, comprehensive study on individual roots during weeks is still missing. Seedlings of Acorus calamus, a wetland monocot, were cultivated in silty sediment and the rhizosphere oxygen profiles were characterized at regular intervals, using micro-optodes to examine the same root at four positions along the root axis. The rhizosphere oxygen saturation culminated at 42.9% around the middle part of the root and was at its lowest level, 3.3%, at the basal part of the root near the aboveground portion. As the plant grew, the oxygen saturation at the four positions remained nearly constant until shoot height reached 15 cm. When shoot height reached 60 cm, oxygen saturation was greatest at the point halfway along the root, followed by the point three-quarters of the way down the root, the tip of the root, and the point one-quarter of the way down. Both the internal and rhizosphere oxygen saturation steadily increased, as did the thickness of stably oxidized microzones, which ranged from 20 µm in younger seedlings to a maximum of 320 µm in older seedlings. The spatial patterns of rhizosphere oxygen profiles in sediment contrast with those from previous studies on radial oxygen loss in A. calamus that used conventional approaches. Rhizosphere oxygen saturation peaked around the middle part of roots and the thickness of stably oxidized zones increased as the roots grew.     

光照和生长阶段对菖蒲根系泌氧的影响

以自然湖泊沉积物为研究基质,利用微型电机控制溶氧微电极实现纵向精确微位移,在照光与遮光条件下,对典型湿地植物菖蒲幼苗、成株根系根基部起总根长1/4处(根1/4)、根系中部(根1/2)、从根基部起总根长3/4处(根3/4)及根尖(根1)处根系微界面径向溶氧浓度变化进行原位精确测定。结果表明:无论有无光照,菖蒲幼苗、成株根系不同部位均存在从根表面至沉积物氧饱和度由高到低的氧扩散层,其厚度0.18—0.68 mm;根1/2、3/4、1处氧扩散能力菖蒲成株较幼苗显著增强(P<0.01),根1/4处二者则无显著差异(P>0.05);光照对菖蒲幼苗、成株根系不同部位氧扩散能力的影响存在差异,光照对菖蒲幼苗根1/2及菖蒲成株根1/2、根3/4处影响显著(照光组显著高于遮光组,P<0.01),而对菖蒲幼苗根1/4、根3/4、根1及菖蒲成株根1/4、根1处无显著影响(P>0.05);从根系泌氧空间差异上看,照光条件下菖蒲幼苗、成株分别表现为根1/2>根3/4≈根1≈根1/4(P<0.01,P>0.05)和根1/2>根3/4>根1>根1/4(P<0.01),遮光条件下菖蒲幼苗、成株分别表现为根1/2≈根3/4≈根1≈根1/4(P>0.05)和根1/2>根3/4≈根1>根1/4(P<0.01,P>0.05)。     

Unique Flexibility in Energy Metabolism Allows Mycobacteria to Combat Starvation and Hypoxia

Mycobacteria are a group of obligate aerobes that require oxygen for growth, but paradoxically have the ability to survive and metabolize under hypoxia. The mechanisms responsible for this metabolic plasticity are unknown. Here, we report on the adaptation of Mycobacterium smegmatis to slow growth rate and hypoxia using carbon-limited continuous culture. When M. smegmatis is switched from a 4.6 h to a 69 h doubling time at a constant oxygen saturation of 50%, the cells respond through the down regulation of respiratory chain components and the F₁F_o-ATP synthase, consistent with the cells lower demand for energy at a reduced growth rate. This was paralleled by an up regulation of molecular machinery that allowed more efficient energy generation (i.e. Complex I) and the use of alternative electron donors (e.g. hydrogenases and primary dehydrogenases) to maintain the flow of reducing equivalents to the electron transport chain during conditions of severe energy limitation. A hydrogenase mutant showed a 40% reduction in growth yield highlighting the importance of this enzyme in adaptation to low energy supply. Slow growing cells at 50% oxygen saturation subjected to hypoxia (0.6% oxygen saturation) responded by switching on oxygen scavenging cytochrome bd, proton-translocating cytochrome bc₁-aa₃ supercomplex, another putative hydrogenase, and by substituting NAD⁺-dependent enzymes with ferredoxin-dependent enzymes thus highlighting a new pattern of mycobacterial adaptation to hypoxia. The expression of ferredoxins and a hydrogenase provides a potential conduit for disposing of and transferring electrons in the absence of exogenous electron acceptors. The use of ferredoxin-dependent enzymes would allow the cell to maintain a high carbon flux through its central carbon metabolism independent of the NAD⁺/NADH ratio. These data demonstrate the remarkable metabolic plasticity of the mycobacterial cell and provide a new framework for understanding their ability to survive under low energy conditions and hypoxia.     

PHOTOXIDATION PROCESSES IN PLANTS

1. Photoxidation in leaves is measured by exposing them to light in an atmosphere free from carbon dioxide but containing varied percentages of oxygen. 2. Photoxidation is observed in living leaves as well as in dead ones and in plant juices. Its rate is only slightly enhanced by feeding the leaves with sugar, but the respiration (autoxidation) becomes considerably enlarged during the exposure and the following dark period. 3. The rate of photoxidation rises slower than linearly with light intensity; its dependence upon oxygen pressure has the character of a saturation curve. Oxygen saturation occurs at about 6/10 of an atmosphere of oxygen. A similar dependence on oxygen pressure has been observed by Gaffron for photoxidation in vitro sensitized by chlorophyll adsorbed on proteins and by Warburg for the depression of the saturation rate of photosynthesis. 4. The influence of photoxidation on photosynthesis and the chemical kinetics of photoxidation are discussed.     

Studies of oxygen binding energy to hemoglobin molecule.

The fractional oxygen saturation of hemoglobin and of its isolated α-chains have been determined by the application of the technique of Mossbauer effect while the oxygen equilibrium pressure was measured directly. By comparing the experimental data so obtained with theoretically derived oxygen saturation curves for hemoglobin and isolated α-chains the values of the oxygen pairing energy and oxygen binding energy to hemoglobin molecule have been found to be 0.043 ± 0.004 and 0.60 ± 0.06 eV respectively.     

Flow velocity affects internal oxygen conditions in the seagrass Cymodocea nodosa

The internal oxygen status of seagrass tissues, which is believed to play an important role in events of seagrass die-off, is partly determined by the rates of gas exchange between leaves and water column. In this study, we examined whether water column flow velocity has an effect on gas exchange, and hence on internal oxygen partial pressures (pO₂) in the Mediterranean seagrass, Cymodocea nodosa. We measured the internal pO₂ in the horizontal rhizomes of C. nodosa in darkness at different mainstream flow velocities, combined with different levels of water column oxygen pO₂ using an experimental flume in the laboratory. Flow velocity clearly had an effect on the internal oxygen status. In stagnant, but fully aerated water the mean internal pO₂ was 6.9 kPa, corresponding to about 30% of air saturation. The internal pO₂ increased with increasing flow velocity reaching saturation of around 12.2 kPa (60% of air saturation) at flow velocities ≥7 cm s⁻¹. Flow had a relatively larger influence on internal pO₂ at lower water column oxygen concentrations. By extrapolating linear relationships between internal and water column pO₂ in this experimental setup, rhizomes would become anoxic at a water column oxygen pO₂ of 4–4.5 kPa (∼20% of air saturation) in flowing water, but already at 6.4 kPa (∼30% of air saturation) in stagnant water. Water flow may play an important role for seagrass performance and survival in areas with poor water column oxygen conditions and may, in general, be of importance for the distribution of submerged rooted plants.     

Oxygen and Heterotrophy Affect Calcification of the Scleractinian Coral Galaxea fascicularis

Heterotrophy is known to stimulate calcification of scleractinian corals, possibly through enhanced organic matrix synthesis and photosynthesis, and increased supply of metabolic DIC. In contrast to the positive long-term effects of heterotrophy, inhibition of calcification has been observed during feeding, which may be explained by a temporal oxygen limitation in coral tissue. To test this hypothesis, we measured the short-term effects of zooplankton feeding on light and dark calcification rates of the scleractinian coral Galaxea fascicularis (n = 4) at oxygen saturation levels ranging from 13 to 280%. Significant main and interactive effects of oxygen, heterotrophy and light on calcification rates were found (three-way factorial repeated measures ANOVA, p<0.05). Light and dark calcification rates of unfed corals were severely affected by hypoxia and hyperoxia, with optimal rates at 110% saturation. Light calcification rates of fed corals exhibited a similar trend, with highest rates at 150% saturation. In contrast, dark calcification rates of fed corals were close to zero under all oxygen saturations. We conclude that oxygen exerts a strong control over light and dark calcification rates of corals, and propose that in situ calcification rates are highly dynamic. Nevertheless, the inhibitory effect of heterotrophy on dark calcification appears to be oxygen-independent. We hypothesize that dark calcification is impaired during zooplankton feeding by a temporal decrease of the pH and aragonite saturation state of the calcifying medium, caused by increased respiration rates. This may invoke a transient reallocation of metabolic energy to soft tissue growth and organic matrix synthesis. These insights enhance our understanding of how oxygen and heterotrophy affect coral calcification, both in situ as well as in aquaculture.     

Cerebral Oxygen Saturation: Graded Response to Carbon Dioxide with Isoxia and Graded Response to Oxygen with Isocapnia

Background

Monitoring cerebral saturation is increasingly seen as an aid to management of patients in the operating room and in neurocritical care. How best to manipulate cerebral saturation is not fully known. We examined cerebral saturation with graded changes in carbon dioxide tension while isoxic and with graded changes in oxygen tension while isocapnic.

Methodology/Principal Findings

The study was approved by the Research Ethics Board of the University Health Network at the University of Toronto. Thirteen studies were undertaken in healthy adults with cerebral oximetry by near infrared spectroscopy. End-tidal gas concentrations were manipulated using a model-based prospective end-tidal targeting device. End-tidal carbon dioxide was altered ±15 mmHg from baseline in 5 mmHg increments with isoxia (clamped at 110±4 mmHg). End-tidal oxygen was changed to 300, 400, 500, 80, 60 and 50 mmHg under isocapnia (37±2 mmHg). Twelve studies were completed. The end-tidal carbon dioxide versus cerebral saturation fit a linear relationship (R² = 0.92±0.06). The end-tidal oxygen versus cerebral saturation followed log-linear behaviour and best fit a hyperbolic relationship (R² = 0.85±0.10). Cerebral saturation was maximized in isoxia at end-tidal carbon dioxide of baseline +15 mmHg (77±3 percent). Cerebral saturation was minimal in isocapnia at an end-tidal oxygen tension of 50 mmHg (61±3 percent). The cerebral saturation during normoxic hypocapnia was equivalent to normocapnic hypoxia of 60 mmHg.

Conclusions/Significance

Hypocapnia reduces cerebral saturation to an extent equivalent to moderate hypoxia.     

Lambda phage cro repressor. DNA sequence-dependent interactions seen by tyrosine fluorescence

The thermodynamics of sickle cell hemoglobin gelation in the presence of oxygen has been investigated by measuring the fractional saturation of the solution and polymer phases, and the solubility. The fractional saturation of the solution phase with oxygen and the solubility were measured by near infrared spectrophotometry after sedimentation of the polymers, while the fractional saturation of the polymer phase was determined from linear dichroism measurements on gels formed by nucleation with an argon ion laser. Using the solution binding data of Gill et al. (1979) to calculate the oxygen pressure corresponding to the solution phase saturation, the initial portion of the polymer binding curve was determined. The self-consistency of the data analysis in terms of the two-phase model for the gel was tested by comparing measured and calculated gel (i.e. solution plus polymer) binding curves, and by comparing the observed solubilities with those calculated from the solution and polymer binding curves using Gibbs-Duhem relations.Oxygen binding to the polymer was found to be non-co-operative up to the maximum measured fractional saturation of 0.14. The binding constant was 0.0059 ± 0.0015 torr^?1 (p₅₀ = 170 ± 40 torr), which is about three times smaller than that of hemoglobin in the low-affinity T quaternary structure. Both the non-co-operative binding and the low affinity could be qualitatively explained in terms of an allosteric model and the current information on the polymer structure.     

Effect of 30% Oxygen Administration on Verbal Cognitive Performance, Blood Oxygen Saturation and Heart Rate

This study investigated the effect of 30% oxygen administration on verbal cognitive performance, blood oxygen saturation, and heart rate. Five male (24.6(±0.9) years) and five female (22.2(±1.9) years) college students were selected as the subjects for this study. Two psychological tests were developed to measure the performance level of verbal cognition. The experiment consisted of two runs: one was a verbal cognition task, with normal air (21% oxygen) administered and the other was with hyperoxic air (30% oxygen) administered. The experimental sequence in each run consisted of Rest 1 (1 min), Control (1 min), Task (4 min), and Rest 2 (4 min). Blood oxygen saturation and heart rate were measured throughout the four phases. The results of the verbal behavioural analysis reveal that accuracy rates were enhanced with 30% oxygen administration compared to 21% oxygen. When 30% oxygen was supplied, blood oxygen saturation was increased significantly compared to that with 21% oxygen administration, whereas heart rate showed no significant difference. Significant positive correlations were found between changes in oxygen saturation and cognitive performance. This result supports the hypothesis that 30% oxygen administration would lead to increases in verbal cognitive performance.     

Respiration and avoidance reaction of a cyprinid fishPseudogobio esocinus under hypoxia

A cyprinid fish,Pseudogobio esocinus showed gradual bradycardia at oxygen saturation (%) of less than 29.7±4.6 (1.89±0.29 ml/l of oxygen concentration), surfacing at 14.7±1.3 (0.94±0.09ml/l), drastic decrease of oxygen consumption at less than 14.2±0.8 (0.91 ±0.06ml/l) and asphyxia at 9.7±1.4 (0.62±0.09ml/l). The fish avoided water having low oxygen saturation of less than 54.0± 5.4 (3.38±0.30ml/l), and markedly at less than 26.2±3.4 (1.62±0.16 ml/l).     

Depolarization Laplace Transform Analysis of Exchangeable Hyperpolarized Xe for Detecting Ordering Phases and Cholesterol Content of Biomembrane Models

We present a highly sensitive nuclear-magnetic resonance technique to study membrane dynamics that combines the temporary encapsulation of spin-hyperpolarized xenon (¹²⁹Xe) atoms in cryptophane-A-monoacid (CrA_ma) and their indirect detection through chemical exchange saturation transfer. Radiofrequency-labeled Xe@CrA_ma complexes exhibit characteristic differences in chemical exchange saturation transfer-driven depolarization when interacting with binary membrane models composed of different molecular ratios of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine). The method is also applied to mixtures of cholesterol and POPC. The existence of domains that fluctuate in cluster size in DPPC/POPC models at a high (75–98%) DPPC content induces up to a fivefold increase in spin depolarization time τ at 297 K. In POPC/cholesterol model membranes, the parameter τ depends linearly on the cholesterol content at 310 K and allows us to determine the cholesterol content with an accuracy of at least 5%.     

Effect of temazepam on oxygen saturation and sleep quality at high altitude: randomised placebo controlled crossover trial

Objective: To determine the effects of temazepam on the quality of sleep and on oxygen saturation during sleep in subjects at high altitude. Design: Randomised, blinded, crossover, placebo controlled trial. Setting: Base camp at Mount Everest (altitude 5300 m). Subjects: 11 members of British Mount Everest Medical Expedition recently arrived at base camp. Intervention: Participants were randomly allocated to receive either temazepam 10 mg or placebo on their first night at base camp and the other treatment on the second night. Main outcome measures: Quality of sleep (assessed subjectively), mean arterial oxygen saturation value, and changes in saturation values (as measure of periodic breathing) while participants taking temazepam or placebo. Results: All participants noted subjective improvements in sleep. Mean saturation value remained unchanged when temazepam was compared with placebo (74.65% v 75.70%, P=0.5437). There were fewer changes in oxygen saturation when participants took temazepam and when measured as decreases >4% below the mean value of saturation each hour (P=0.0036, paired Student’s t test (two tailed)). Conclusions: Participants taking temazepam at 5300 m showed no significant drop in mean oxygen saturation values during sleep. Both the number and severity of changes in saturation during sleep decreased and the quality of sleep improved. This may be a result of a reduction in the number of awakenings and might lead to greater respiratory stability and fewer episodes of periodic breathing. This has the effect of improving the quality of sleep and reducing the number of periods of desaturation during sleep

Key messages

• Poor sleep at high altitude is common and may be due to a combination of physiological and physical factors
• Frequent arousals, periodic breathing, and episodes of oxygen desaturation lead to poor sleep and daytime symptoms of drowsiness and reduced performance
• In this study 10 mg temazepam improved subjective reports of the quality of sleep and reduced episodes of arterial desaturation, with no significant effect on mean oxygen saturation during sleep

     

Depolarization Laplace Transform Analysis of Exchangeable Hyperpolarized 129Xe for Detecting Ordering Phases and Cholesterol Content of Biomembrane Models

We present a highly sensitive nuclear-magnetic resonance technique to study membrane dynamics that combines the temporary encapsulation of spin-hyperpolarized xenon (¹²⁹Xe) atoms in cryptophane-A-monoacid (CrA_ma) and their indirect detection through chemical exchange saturation transfer. Radiofrequency-labeled Xe@CrA_ma complexes exhibit characteristic differences in chemical exchange saturation transfer-driven depolarization when interacting with binary membrane models composed of different molecular ratios of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine). The method is also applied to mixtures of cholesterol and POPC. The existence of domains that fluctuate in cluster size in DPPC/POPC models at a high (75–98%) DPPC content induces up to a fivefold increase in spin depolarization time τ at 297 K. In POPC/cholesterol model membranes, the parameter τ depends linearly on the cholesterol content at 310 K and allows us to determine the cholesterol content with an accuracy of at least 5%.     

The effects of oxygen on cutaneous propionibacteria grown in continuous culture

Propionibacterium acnes, Propionibacterium avidum and Propionibacterium granulosum were grown in continuous culture at 0–100% air saturation using a semi-synthetic medium. All 3 species utilised oxygen and showed increased growth at 10% air saturation. Oxygen depressed the levels of the fermentation end products propionic and acetic acids. The 3 species differed in the production of ‘oxygen-detoxifying’ enzymes. P. acnes produced catalase, P. avidum produced superoxide dismutase and P. granulosum produced catalase anaerobically and cytochrome c reductase aerobically. The results suggest that under aerobic conditions these bacteria may obtain energy without increased substrate-level phosphorylation and that they may employ different strategies to overcome the toxic effects of oxygen.     

Noninvasive estimation of human tissue respiration with wavelet-analysis of oxygen saturation and blood flow oscillations in skin microvessels

Laser Doppler flowmetry, laser spectrophotometry of oxygen saturation, and the fluorescence determination of the NADH/FAD ratio were carried out in 30 subjects in the upper limb skin zones with and without arteriolovenular anastomoses (AVAs). It was demonstrated that the wavelet-analysis of oxygen saturation and blood flow oscillations in microvessels was an efficient approach to noninvasive estimation of the skin oxygen extraction (OE) and oxygen consumption (OC) rates. OE = (SaO₂ ? SvO₂)/SaO₂, where SaO₂ (%) and SvO₂ (%) are the oxygen saturations of arterial and venular blood, respectively. If the cardiac (A_c, perfusion units, p.u.) to respiratory rhythm amplitude (A_r, p.u.) ratio A_c/A_r ?? 1, SvO₂ = SO₂. If A_c/A_r > 1, SvO₂ = SO₂/(A_c/A_r). OC = M _nutr (SaO₂ ?? SvO₂) in p.u. · %O₂, where M _nutr is the nutritive blood flow value in p.u. M _nutr = M/SI, where SI is the shunting index of blood flow in microvessels. The perfusion, OE, and OC values were higher in the skin with AVAs than in the skin without AVAs. The perfusion and oxygen saturation values were more variable in the skin with AVAs. The oxygen diffusing from the tiniest arterioles and capillaries is the most important for tissue metabolism. The contribution of the total perfusion and the oxygen diffusion from arterioles to tissue metabolism increased under the tissue ischemia conditions.     

Oxygen dissociation of whole blood studied polarographically

The polarographic current of whole blood is in excess of that given by plasma at the same oxygen tension. The magnitude of this difference depends on (a) the oxygen content of the sample and thus is determined by the red blood cell content and by the state of oxygen saturation of hemoglobin, and (b) on the rate of dissociation of oxyhemoglobin and therefore is influenced by changes in pH, pCO₂, and temperature. The total current at 37°C. is proportional to the oxygen content of the sample and can be used to determine the latter. The theoretical basis of the studied phenomena is discussed in detail.     

A new method to measure the haemoglobin oxygen saturation by the oxygen electrode

We describe a new polarographic method to measure the haemoglobin oxygen saturation in whole blood, employing up to 10 μl of sample in a standard case. The measurement is done in an anaerobic staineless-steel cuvette (1 ml) recording three oxygen tension values: (1) that of an air-equilibrated buffer before the addition of the sample; (ii) that after the addition of the sample; and (iii) that after the addition of an oxidant. The haemoglobin oxygen saturation is then calculated from the three oxygen tension values, the volume of the reagents, and solubility coefficient of oxygen. This method is simple, inexpensive and accurate, and correlates well with other standard methods.     

Wireless Monitoring of Liver Hemodynamics In Vivo

Liver transplants have their highest technical failure rate in the first two weeks following surgery. Currently, there are limited devices for continuous, real-time monitoring of the graft. In this work, a three wavelengths system is presented that combines near-infrared spectroscopy and photoplethysmography with a processing method that can uniquely measure and separate the venous and arterial oxygen contributions. This strategy allows for the quantification of tissue oxygen consumption used to study hepatic metabolic activity and to relate it to tissue stress. The sensor is battery operated and communicates wirelessly with a data acquisition computer which provides the possibility of implantation provided sufficient miniaturization. In two in vivo porcine studies, the sensor tracked perfusion changes in hepatic tissue during vascular occlusions with a root mean square error (RMSE) of 0.135 mL/min/g of tissue. We show the possibility of using the pulsatile wave to measure the arterial oxygen saturation similar to pulse oximetry. The signal is also used to extract the venous oxygen saturation from the direct current (DC) levels. Arterial and venous oxygen saturation changes were measured with an RMSE of 2.19% and 1.39% respectively when no vascular occlusions were induced. This error increased to 2.82% and 3.83% when vascular occlusions were induced during hypoxia. These errors are similar to the resolution of a commercial oximetry catheter used as a reference. This work is the first realization of a wireless optical sensor for continuous monitoring of hepatic hemodynamics.     

Reverse temperature dependence of tuna hemoglobin oxygenation

At a pH around 7.5 with 0.05 M NaP_i, the shape of the oxygen equilibrium curve of hemoglobin from the bluefin tuna (Thunnus thynnus) is temperature dependent. The affinity at low saturation increases, and that at high saturation decreases on cooling from 20°C to 10°C. The equilibrium curves at the two temperatures therefore cross over. This behavior is physiologically advantageous to a warm-bodied fish. It may be explained in terms of the two-state model by supposing that the allosteric constant L increases markedly on cooling the solutions.