CHO cell responses to low oxygen: regulation of oxygen consumption and sensitization to oxidative stress

We have investigated the regulation of oxygen consumption and modulation of glutathione levels in CHO-K1 cells under oxygen-limiting conditions. We report here suppression of oxygen consumption and alteration of the supply-dependent relationship as a consequence of prolonged hypoxic or anoxic exposure. The suppression is characterized by an increase in the value of P(o(2)/50) (the oxygen tension at which oxygen consumption is half maximal). Under prolonged anoxia there is also a decrease in the cells' potential to use oxygen. Elevated glucose consumption under low oxygen conditions may contribute to the suppression in respiration. The glutathione concentration remains constant throughout hypoxic exposure but may decrease by as much as 40% under anoxia. The glutathione level in hypoxic and anoxic cells increases by two- and four-fold, respectively, over that of the control cells when exposed to a cytotoxic level of oxygen (93%). This suggests that anoxic and hypoxic exposure sensitizes CHO cells to oxidative stress. (c) 1992 John Wiley & Sons, Inc.     

低温胁迫对嫁接西瓜耐冷性和活性氧清除系统的影响

研究了西瓜实生苗和以黑籽南瓜、超丰F1为砧木的嫁接苗的耐冷性及活性氧清除系统的差异．结果表明,低温胁迫下,嫁接苗的耐冷性明显高于实生苗,表现为以黑籽南瓜为砧木的嫁接苗的耐冷性>以超丰F1为砧木的嫁接苗>实生苗,此外嫁接苗和实生苗均表现为叶片中叶绿素含量下降,丙二醛(MDA)含量上升,非酶促抗氧化剂抗坏血酸(AsA)、谷胱甘肽(GSH)含量和抗氧化酶超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(AsA-POD)、脱氢抗坏血酸还原酶(DR)活性下降,说明低温逆境降低了植物体防御活性氧有关的酶促和非酶促保护系统能力,提高了体内自由基浓度,加剧了膜脂过氧化．嫁接苗的活性氧清除能力均高于自根苗,且嫁接苗中耐冷性越强的活性氧清除能力越高,说明西瓜嫁接后耐冷性的提高是与植物体内活性氧清除系统中抗氧化剂含量和抗氧化酶活性提高有关。     

How plants sense low oxygen

The recent identification of the oxygen-sensing mechanism in plants is a breakthrough in plant physiology. The presence of a conserved N-terminal motif on some ethylene responsive factors (ERFs), targets the protein for post-translational modifications finally leading to degradation under normoxia and thus providing a mechanism for sensing the presence of oxygen. The stabilization of the N-terminus under low oxygen activates these ERFs, which regulate low oxygen core genes that enable plants to tolerate abiotic stress such as flooding. Additional mechanisms that signal low-oxygen probably also exist, and the production of reactive oxygen species (ROS) has been observed under low oxygen, suggesting that ROS might be part of the network involved in plant acclimation. Here, we review the most recent findings related to oxygen sensing.     

Lunar influences in the diet habits and selectivity of larval clingfish Gobiesox marmoratus

The influence of the lunar cycle on the feeding habits, feeding success and selectivity was tested in situ on larval stages of the clingfish Gobiesox marmoratus (Gobiesocidae). Gobiesox marmoratus larvae and their prey were collected in the water column during the lunar cycle in austral spring 2015 and 2016, in shallow waters (<30 m depth) of El Quisco, central Chile. Feeding incidence was high (80–100%) throughout the moon cycle. The diet was composed of 32 prey items, being gastropod larvae and invertebrate eggs the most important. Prey composition varied among lunar phases with the lowest prey richness during new moon. During 2016, G. marmoratus larvae ingested the lowest number, but the largest prey during new moon. In spring 2015, there were no significant changes in the abundance of each prey taxon in the water column among moon phases, but in spring 2016 there were significant differences in the abundance of cypris and copepod nauplii, particularly between full and new moon. Feeding selectivity index showed that gastropod larvae were positively selected throughout the lunar cycle during spring 2015. In spring 2016, invertebrate eggs were selectively ingested in full moon and third quarter, but at a new moon G. marmoratus larvae selected gastropod larvae. Mean temperature of the water column and its vertical gradient and nocturnal cloud cover influences the feeding success of larval G. marmoratus. Lunar illumination favoured only an increase of richness of prey items. Therefore, nocturnal cloud cover precludes a greater influence of lunar illumination in the larval trophic ecology of this crypto-benthic fish.     

茄子嫁接苗根系对低温环境胁迫的响应

以‘济农2000’为对照,研究了低温胁迫下不同抗冷性茄子砧木嫁接苗根系的生理生化变化及其与抗冷性的关系.结果表明,在10 ℃(昼)/3 ℃(夜)低温处理初期,根系对低温最敏感,表现为MDA含量、冷害指数、POD活性、脯氨酸含量、可溶性蛋白含量等迅速增加,而根系呼吸速率、SOD、CAT活性等迅速降低.随着低温胁迫时间的延长,根系呼吸速率持续降低,而冷害指数持续升高,渗透调节物质基本呈增加的趋势.常温恢复3 d后,呼吸速率、渗透调节物质、SOD活性等升高,但均以抗冷性较强的赤茄砧木嫁接苗恢复能力较强,而抗冷性较弱的台茄砧木嫁接苗与自根苗较差.利用抗冷性较强的砧木进行嫁接,可显著增强茄子根系的活性,进而提高其抗冷性.     

A rainbow trout Oncorhynchus mykiss strain with higher aerobic scope in normoxia also has superior tolerance of hypoxia

This study compared parr from three strains of rainbow trout Oncorhynchus mykiss to examine intraspecific variation in metabolic traits, hypoxia tolerance and upper thermal tolerance in this species. At the strain level, variation in absolute aerobic scope (AAS), critical oxygen level (O_2crit), incipient lethal oxygen saturation (ILOS) and critical thermal maximum (CT_max) generally exhibited consistent differences among the strains, suggesting the possibility of functional associations among these traits. This possibility was further supported at the individual level by a positive correlation between ILOS and O_2crit and a negative correlation between O_2crit and AAS. These results indicate that intraspecific differences in hypoxia tolerance among strains of O. mykiss may be primarily determined by differences in the ability to maintain oxygen uptake in hypoxia and that variation in aerobic scope in normoxia probably plays a role in determining the ability of these fish to sustain metabolism aerobically as water oxygen saturation is reduced.     

Salt stress and resistance to hypoxic challenges in the common carp (Cyprinus carpio L.)

Long term exposure to brackish water (171 mm NaCl) affected the capacity of common carp Cyprinus carpio to deal with hypoxic conditions and the critical oxygen concentrations for oxygen consumption increased. In addition, regulation of ammonia excretion was lost. The cytosolic phosphorylation potential (the index of the energy status of a cell in terms of potential transferable phosphate groups) in the lateral muscle on the other hand remained relatively unaffected, indicating that oxygen transport to the tissues was not severely compromised. It appears that exposure to brackish water reduces the capacity of common carp to cope with hypoxic conditions mainly because of the high energetic cost of hyperventilation under conditions where energy stores are depleted, and not because of any impeded oxygen transport mechanisms.     

Tolerance, behaviour and oxygen consumption in the sand goby, Pomatoschistus minutus (Pallas), exposed to hypoxia

Behavioural and metabolic reactions of Pomatoschistus minutus (Pallas) exposed to various degrees of hypoxia were studied. At 15°C and 20‰ mortality was 50% at 15.2% oxygen saturation. Avoidance and oxygen saturation showed a linear inverse relationship. At levels lower than 60% saturation increased activity occurred; avoidance was significant at 30% saturation. Active, routine and standard MO₂ correlated linearly with weight at 6 and 15°C (salinity = 19‰). During hypoxia at 15°C routine MO₂ rose significantly at 60–50% and 40–30% saturation expressed either as MO₂ during longer periods at night or MO₂ at shorter intervals during the day. Standard MO₂ was unaffected by hypoxia at 15°C. Haemoglobin concentration was significantly increased when P. minutus was acclimatized to 35% saturation.     

The in vitro growth of murine high proliferative potential-colony forming cells is not enhanced by growth in a low oxygen atmosphere

The growth of primitive murine hematopoietic progenitors, high proliferative potential colony-forming cells (HPP-CFC), has been reported to be improved in low O2 tension cultures. In this report we investigated the growth of HPP-CFC stimulated by combinations of interleukin (IL)-1, IL-6, kit-ligand (KL), granulocyte (G) colony-stimulating factor (CSF), macrophage-CSF (M-CSF), granulocyte-macrophage-CSF (GM-CSF) and IL-3 in clonal cultures incubated at 7% or 21% O2 tension. Neither the numbers of HPP-CFC colonies nor the number of cells per HPP-CFC colony differed significantly between cultures grown under 7% or 21% O2 tension. The mean number of cells per HPP-CFC colony was found to range from 3.9 x 10(4) to 2.2 x 10(5). The smallest HPP-CFC colonies were stimulated by the cytokine combination IL-1 + IL-6 + KL, whereas the largest colonies were stimulated by a combination of all seven cytokines tested. The growth of erythroid colonies from murine or human bone marrow did, however, show some enhancement when cultured at a lower O2 tension. These results demonstrate that the growth of murine HPP-CFC was not compromised when cultured at ambient O2 concentration.     

Responses of invertebrates to temperature and water stress: A polar perspective

As small bodied poikilothermic ectotherms, invertebrates, more so than any other animal group, are susceptible to extremes of temperature and low water availability. In few places is this more apparent than in the Arctic and Antarctic, where low temperatures predominate and water is unusable during winter and unavailable for parts of summer. Polar terrestrial invertebrates express a suite of physiological, biochemical and genomic features in response to these stressors. However, the situation is not as simple as responding to each stressor in isolation, as they are often faced in combination. We consider how polar terrestrial invertebrates manage this scenario in light of their physiology and ecology. Climate change is also leading to warmer summers in parts of the polar regions, concomitantly increasing the potential for drought. The interaction between high temperature and low water availability, and the invertebrates׳ response to them, are therefore also explored.     

Simultaneous methanogenesis and oxygen reduction by Methanobrevibacter cuticularis at low oxygen fluxes

Methanogenic Archaea are often encountered in habitats that are not entirely anoxic in space or time. Recent biochemical and genomic studies have revealed the capacity of methanogens to reduce molecular oxygen. O(2) reduction by Methanobrevibacter species was investigated. Cell suspensions incubated in agar tubes under a headspace of H(2)-CO(2) and increasing concentrations of O(2) formed a distinct growth band, which coincided with the oxic-anoxic interface and indicated that the influx of O(2) into the band was balanced by its consumption. However, in batch cultures methanogenesis ceased as soon as traces of O(2) were added. Focusing on Methanobrevibacter cuticularis, a species colonizing the microoxic gut epithelium of termites, a diffusion-limited setup was used that allowed the exposure of dense cell suspensions to controlled O(2) fluxes. Here, Methanobrevibacter cuticularis was capable of simultaneous CH(4) production and O(2) consumption. Low O(2) fluxes (10% of the CH(4) production rate) had virtually no influence on methanogenesis [4.5 micromol CH(4) (mg dry wt)(-1) h(-1)], whereas higher O(2) fluxes (up to 30% of the initial CH(4) production rate) caused a reversible decrease in methanogenesis, which was accompanied by a reversible, partial conversion of coenzyme F(420) to factor F(390). The maximum O(2) reduction rate [4.8 micromol O(2) (mg dry wt)(-1) h(-1)] that could be maintained over extended time periods (>30 min) was similar to the CH(4) production rate under anoxic conditions.     

Respiratory responses of Oreochromis niloticus (Pisces, Cichlidae) to environmental hypoxia under different thermal conditions

The oxygen uptake ( V O₂), breathing frequency ( f _R), breath volume ( V _S.R), gill ventilation ( V G) and oxygen extraction (%) from the ventilatory current of four groups of Oreochromis niloticus during graded hypoxia were measured under the following acclimation temperatures: 20. 25. 30 and 35°C. The critical oxygen tensions ( P O₂), determined from V O₂ v. P O₂ of inspired water at each experimental temperature were, respectively. 19±1±3±1. 18±0±4±9, 29±7± 4±1 and 30±2± 0.6 mmHg. The f _R remained nearly constant during the reductions of O₂ at all the temperatures studied. V G increased discretely from normoxic levels until the P O₂ was reached, below which it assumed extremely high values (17-fold higher or more). The increases observed in V G resulted, at all the acclimation temperatures, in an elevation in V _S.R rather than in f _R. The extraction of O₂ decreased gradually from normoxia until the P O₂ was reached, below which an abrupt reduction of extraction was recorded, except at 35°C when fish showed a gradual reduction in extraction just below the tension of 80 mmHg.     

Responses of sub-arctic dwarf shrubs to low oxygen and high carbon dioxide conditions

Arctic plants can experience prolonged periods of ice encasement in winter, leading to hypoxia which may cause damage to plants and reduce subsequent summer growth. Further, high CO₂ concentrations, which can occur when plants respire within ice, may cause additional injury, as has been shown to occur in crops. The tolerance of arctic plants to these within-ice atmospheric conditions has previously remained unknown, yet this knowledge is essential for understanding icing impacts on plant community structure and productivity – especially given that icing events are predicted to increase in frequency as a result of climate change. Using a unique field chamber experiment, this study quantified the responses of three widespread sub-arctic dwarf shrubs, Empetrum nigrum and Vaccinium vitis-idaea (both evergreen) and V. myrtillus (deciduous), to 14 days hypoxia and high CO₂ in winter in a factorial field experiment in northern Sweden. Growth, phenology and mortality responses were used to quantify impacts in the following spring supported by electrolyte leakage and chlorophyll fluorescence to assess leaf damage in the two evergreens. Overall, all species showed high resistance to 14 days of hypoxia with no indications of damage. Increased CO₂ did lead to 33% lower bud dormancy in E. nigrum and 70% greater shoot mortality in V. vitis-idaea indicating that these species might be negatively affected by increased occurrences of ice encasement, through elevated CO₂ levels. Despite these responses, effects of high CO₂ were rare overall. Given that the impacts of hypoxia and high CO₂ were considerably less than reported for species in temperate habitats, this suggests a moderate to high degree of tolerance to short periods of icing among these species. If these results apply to longer periods of ice encasement, increasing frequency of icing may only have some species specific impacts without being a major environmental threat to arctic dwarf shrubs.     

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.     

Physiological ecology of aquatic overwintering in ranid frogs

In cold-temperate climates, overwintering aquatic ranid frogs must survive prolonged periods of low temperature, often accompanied by low levels of dissolved oxygen. They must do so with the energy stores acquired prior to the onset of winter. Overwintering mortality is a significant factor in their life history, occasionally reaching 100% due to freezing and/or anoxia. Many species of northern ranid frogs overwinter in the tadpole stage, which increases survival during hypoxic episodes relative to adults, as well as allowing for larger sizes at metamorphosis. At temperatures below 5 degrees C, submerged ranid frogs are capable of acquiring adequate oxygen via cutaneous gas exchange over a wide range of ambient oxygen partial pressures (PO(2)), and possess numerous physiological and behavioural mechanisms that allow them to maintain normal rates of oxygen uptake across the skin at a relatively low PO(2). At levels of oxygen near and below the critical PO(2) that allows for aerobic metabolism, frogs must adopt biochemical mechanisms that act to minimise oxygen utilisation and assist in maintaining an aerobic state to survive overwintering. These mechanisms include alterations in mitochondrial metabolism and affinity, changes in membrane permeability, alterations in water balance, and reduction in cellular electrochemical gradients, all of which lead to an overall reduction in whole-animal metabolism. Winter energetic requirements are fueled by the energy stores in liver, muscle, and fat depots, which are likely to be sufficient when the water is cold and well oxygenated. However, under hypoxic conditions fat stores cannot be utilised efficiently and glycogen stores are used up rapidly due to recruitment of anaerobiosis. Since ranid frogs have minimal tolerance to anoxia, it is untenable to suggest that they spend a significant portion of the winter buried in anoxic mud, but instead utilise a suite of behavioural and physiological mechanisms geared to optimal survival in cold, hypoxic conditions.     

Hypoxia tolerance decreases with body size in red drum Sciaenops ocellatus

Mass‐specific oxygen consumption rate, i.e. standard metabolic rate (R_s) and critical oxygen tension (P_crit) of red drum Sciaenops ocellatus were measured and scaled over a 2500‐fold range in mass (M_F; 0·26–686 g). R_s conformed to well established models (R_s = 3·73·91 M_F^?0·21; r² = 0·86) while P_crit increased over the size range (P_crit = 3·15 log₁₀M_F + 16·19; r² = 0·44). This relationship may be ecologically advantageous as it would allow smaller S. ocellatus to better utilize hypoxic zones as habitat and refuge from predators.     

高温胁迫下外源褪黑素对黄瓜幼苗活性氧代谢的影响

以黄瓜品种‘津春4号’为试材,用叶面喷施的方法,研究了高温胁迫条件下外源褪黑素(melatonin,MT)对黄瓜幼苗活性氧（ROS）代谢的影响.结果表明：外源MT能显著降低高温胁迫下黄瓜叶片超氧阴离子自由基（O₂^-.）产生速率、过氧化氢（H₂O₂）含量、电解质漏渗率（relative electric conductivity, REC）及丙二醛(MDA)含量,增强黄瓜幼苗叶片中超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)活性,提高抗坏血酸（AsA）、谷胱甘肽（GSH）及可溶性蛋白质含量.说明MT预处理能抑制高温胁迫条件下黄瓜幼苗体内ROS的产生,提高抗氧化酶系的活性及抗氧化物质的含量,降低膜质过氧化水平,保护脂膜的完整性,减少电解质的外渗,减轻高温胁迫对幼苗造成的伤害,提高幼苗抗高温胁迫的能力.