Influence of acetate on the growth of Candida utilis in continuous culture

Candida utilis was grown on acetate in chemostat cultures that were, successively, carbon and ammonia-limited (30° C; pH 5.5). With carbon(acetate)-limited cultures, the specific rate of oxygen consumption (q _{O 2}) was not a linear function of the growth rate but was markedly stimulated at the higher dilution rates, thus effecting a marked decrease in the Y _O value. This increased respiration rate, and decreased yield value, correlated closely with a marked increase in the extracellular acetate concentration. Under ammonia-limiting conditions, very low Y _O values were found, generally comparable with those found with carbon-limited cultures growing at the higher dilution rates, but these varied markedly with the extracellular acetate concentration. Thus, when the unused acetate concentration was raised progressively from about 5 g/l to about 21 g/l, the Y _O value decreased non-linearly from 11.4 to 5.8. When the extracellular acetate concentration was further increased to 25 g/l, growth was inhibited and the culture washed out. This relationship between respiration rate and the extracellular concentration of unused acetate was also markedly influenced by the culture pH value. Thus, with a fixed extracellular acetate concentration (16±2g/l) and dilution rate (0.14 h^–1), lowering the culture pH value progressively from 6.9 to 5.1 effected a marked and progressive increase in the respiration rate. Further lowering of the culture pH to 4.8, however, caused a complete collapse of respiration. In contrast to this situation, progressively lowering the pH value of an acetatelimited culture from 6.9 to 4.5 affected only slightly the culture respiration rate, and growth was possible even at a pH value of 2.5. These results are discussed in the context of the possible mechanisms whereby acetate exerts its toxic effect on the growth of C. utilis.     

Alternative respiration and antibiotic production of Acremonium chrysogenum

The influence of potassium cyanide (KCN), dissolved O₂ concentration and medium composition on alternative respiration (AR) of Acremonium chrysogenum were investigated. The respiration of the fungus was only partially inhibited by KCN, but completely inhibited by the combination of KCN with salicylhydroxamic acid. It has been proved by in-situ measurements of the NADH-dependent fluorescence that the AR is active at low dissolved O₂ concentrations. The influence of the medium composition and the age of the fungus on the specific oxygen uptake rate is considered. Correpondence to: K. Schügerl     

Variability of photosynthesis-irradiance curves and ecosystem respiration in a small river

• 1 We investigated photosynthesis‐irradiance relationships (P‐I curves; P = oxygen production rate due to photosynthesis, I = light irradiance rate at the water surface) and ecosystem respiration in a 9 km long reach of a river that is characterised by light conditions favouring primary production, high ambient nutrient concentrations, a high re‐aeration rate, and frequent spates. We addressed the question of how disturbances (spates) and season influence photosynthesis and ecosystem respiration.
• 2 We used an oxygen mass‐balance model of the river to identify ecosystem respiration rates and the two parameters of a hyperbolic P‐I function (P_max = maximum oxygen production rate due to photosynthesis, α = the initial slope of the P‐I function). The model was fitted to dissolved oxygen concentrations quasi‐continuously recorded at the end of the reach. We estimated parameters for 137 three‐day periods (during the years 1992–97) and subsequently explored the potential influence of season and disturbances (spates) on P_max, α and ecosystem respiration using stepwise regression analysis.
• 3 Photosynthesis‐irradiance relationships and ecosystem respiration were subject to distinct seasonal variation. Only a minor portion of the variability of P‐I curves could be attributed to disturbance (spates), while ecosystem respiration did not correlate with disturbance related parameters. Regular seasonal variation in photosynthesis and ecosystem respiration apparently prevailed due to the absence of severe disturbances (a lack of significant bedload transport during high flow).

     

Light respiration in <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis>

Respiration and photosynthesis are two important processes in microalgal growth that occur simultaneously in the light. To know the rates of both processes, at least one of them has to be measured. To be able to measure the rate of light respiration of Chlorella sorokiniana, the measurement of oxygen uptake must be fast, preferably in the order of minutes. We measured the immediate post-illumination respiratory O₂ uptake rate (OUR) in situ, using fiber-optic oxygen microsensors, and a small and simple extension of the cultivation system. This method enables rapid and frequent measurements without disturbing the cultivation and growth of the microalgae. Two batch experiments were performed with C. sorokiniana in a short light-path photobioreactor, and the OUR was measured at different time points. The net oxygen production rate (net OPR) was measured online. Adding the OUR and net OPR gives the gross oxygen production rate (gross OPR), which is a measure for the oxygen evolution by photosynthesis. The gross OPR was 35–40% higher than the net OPR for both experiments. The respiration rate is known to be related to the growth rate, and it is suggested that faster algal growth leads to a higher energy (ATP) requirement, and as such, respiratory activity increases. This hypothesis is supported by our results, as the specific OUR is highest in the beginning of the batch culture when the specific growth rate is highest. In addition, the specific OUR decreases toward the end of the experiments until it reaches a stable value of around 0.3 mmol O₂ h⁻¹ g⁻¹. This value for the specific OUR is equal to the maintenance requirement of C. sorokiniana as determined in an independent study of (Zijffers et al. 2010 (in press)). This suggests that respiration could fulfill the maintenance requirements of the microalgal cells.     

Photosynthesis, Respiration and Post-illumination Fixation of CO2 by Corn Leaves as Influenced by Light and Oxygen Concentration

The effect of oxygen concentration on the rate of CO₂-uptake in continuous and intermittent light was studied as well as the CO₂-fixation during a short dark period after light was turned off. In addition the dark respiration and the CO₂-compensation point of attached and detached corn leaves were determined. Leaves of 4 to 22-day old plants were used as experimental material. A closed circuit system of an infrared carbon dioxide analyzer was employed to measure the rate of CO₂-exchange. It was found that in an atmosphere consisting of 100 % oxygen, there was about 50 per cent inhibition of the rate of CO₂-uptake in continuous and intermittent light compared to that in an atmosphere consisting of 21% oxygen. The same was true of the rate of CO₂-fixation in darkness during a short period after the light was turned off. Since the response to oxygen concentration of the CO₂-uptake in light and of the CO₂-fixation in darkness after the light was turned off were similar, it is concluded that the fixation of CO₂ in the short dark period represents an over- shoot of photosynthesis. The rate of dark respiration was little affected by the oxygen concentration in the ranges used in the experiments. The carbon dioxide compensation point which has been observed in leaves of 4 to 14-day old plants was not influenced by either oxygen concentration or light intensity. Since the changes in the rate of CO₂-uptake due to changes in the concentration of oxygen and light intensity had no effect on the CO₂-compensation point, it is concluded that a reabsorption of respiratory CO₂ by photosynthesis could not account for the low value of this point. These results are interpreted as a further corroboration of the statement that the leaves of corn lack the process of photorespiration and that dark respiration is inhibited in light. It was observed that the rate of the CO₂-uptake gradually increased in plants which were from 4 to 22-days old. The inhibitory effect of high concentration of oxygen on the rate of CO₂-uptake was relatively higher in old plants than in young ones.     

Respiration of Senecio Shoots: Inhibition during Photosynthesis, Resistance to Cyanide and Relation to Growth and Maintenance

Respiration and dry matter producation were measured in shoots of senecia aquaticus Hill, which is flood tolerant and in shoots of S. jacobaea L., which is flood- sensitive. Both species were grown in culture solutions of high and of low oxygen concentration Growth of food of S. jacobaca was unaffected by a low oxygen supply bur growth of S. jacobaca was severly hampered by a low oxygen concentration in the root medium. Kinetic data about the rate of apparent photosynthesis at low oxygen conetration and different carbon dioxide concentrations indicated that at light saturation respiration was strongly repressed during photosynthesis. Shoot growth respiration, i.e. the amount of carbon dioxide produced for synthesis of shoot dry, matter appeared to be absent on S. jacobaea and to be very low (13.mg CO₂/g dry shoots) in S. aquaticus. In comparison with values prepiration rate was 2.8. 2.0. 1.5 and 1.3mg CO₂/h.g dry shoots in aerobically and anaerobically growth S. jacobaea and in aerobically and anaerobically growth S. aquabaea respectively. These values were also low in comprision with values previously found for roots of the same species. Shoot dark respiration on S. aquaticus was inbihitedd by a com bination on CN and salicylhydroxamic acid (SHAM), but not by application on one of these inhibitors alone. It was therefore concluded that an alternative oxidative pathway was present but not active in shoots of S. aquaticus. In the absence of inhibited of the cylochorome pathway. The low value of growth respiration and maintenance respiration rate in the shoots as compared with those in the roots of the investigated Sencio species are discussed in relation to the activity of the alternative oxidative pathway and to the possibilbity of a direct supply of ATP by photosynthesis intead of respiratory meta bolism.     

Respiration Rate of Stream Insects Measured <Emphasis Type="Italic">in situ</Emphasis> Along a Large Altitude Range

Field studies of respiration in stream insects are few in comparison with laboratory studies. To evaluate the influence of temperature and oxygen along altitudinal gradients we measured the respiration rate of fully acclimatized larval Trichoptera, Plecoptera and Ephemeroptera under similar field conditions in streams from 400 to 3800 m above sea level in tropical Ecuador. Mean active respiration rates of the animals at 3800 m were approximately half of those at 400 m. Trichoptera showed a slightly larger difference in respiration with altitude than Ephemeroptera. Comparative respiration measurements at 100 and 50% oxygen saturation indicated that highland animals reduced their oxygen uptake more than their counterparts in the lowland when oxygen availability decreased. The temperature response of respiration calculated between the insect assemblages at different altitudes showed a mean assemblage Q₁₀−value of 1.50. Trichopteran larvae had a slightly stronger temperature response (Q₁₀ of 1.68) than ephemeropterans (Q₁₀ of 1.30). These community Q₁₀-values are considerably lower than the mean value of 2.36 found in single species in the laboratory. The weak community-wide response of respiration to temperature in tropical streams is probably due to full acclimatization of the component species to stable and narrow temperature ranges. Adaptations to the low oxygen availability at high altitude probably consist of a suite of genetic physiological and behavioural features.     

THE RESPIRATION OF LUMINOUS BACTERIA AND THE EFFECT OF OXYGEN TENSION UPON OXYGEN CONSUMPTION

1. The respiration of luminous bacteria has been studied by colorimetric and manometric methods. 2. Limulus oxyhaemocyanin has been used as a colorimetric indicator of oxygen consumption and indicator dyes were used for colorimetric determination of carbon dioxide production. 3. The Thunberg-Winterstein microrespirometer has been used for the measurement of the rate of oxygen consumption by luminous bacteria at different partial pressures of oxygen. 4. The effect of oxygen concentration upon oxygen consumption has been followed from equilibrium with air to low pressures of oxygen. 5. Luminous bacteria consume oxygen and produce carbon dioxide independent of oxygen pressures from equilibrium with air (152 mm.) to approximately 22.80 mm. oxygen or 0.03 atmosphere. 6. Dimming of a suspension of luminous bacteria occurs when oxygen tension is lowered to approximately 2 mm. Hg (0.0026 atmosphere) and when the rate of respiration becomes diminished one-half. 7. Pure nitrogen stops respiratory activity and pure oxygen irreversibly inhibits oxygen consumption. 8. The curve for rate of oxygen consumption with oxygen concentration is similar to curves for adsorption of gasses at catalytic surfaces, and agrees with the Langmuir equation for the expression of the amount of gas adsorbed in unimolecular layer at catalytic surfaces with gas pressure. 9. A constant and maximum rate of oxygen consumption occurs in small cells when oxygen concentration becomes sufficient to entirely saturate the surface of the oxidative catalyst of the cell.     

Temperature responses of dark respiration in relation to leaf sugar concentration

Changes in leaf sugar concentrations are a possible mechanism of short‐term adaptation to temperature changes, with natural fluctuations in sugar concentrations in the field expected to modify the heat sensitivity of respiration. We studied temperature‐response curves of leaf dark respiration in the temperate tree Populus tremula (L.) in relation to leaf sugar concentration (1) under natural conditions or (2) leaves with artificially enhanced sugar concentration. Temperature‐response curves were obtained by increasing the leaf temperature at a rate of 1°C min^?1. We demonstrate that respiration, similarly to chlorophyll fluorescence, has a break‐point at high temperature, where respiration starts to increase with a faster rate. The average break‐point temperature (T_RD) was 48.6 ± 0.7°C at natural sugar concentration. Pulse‐chase experiments with ¹⁴CO₂ demonstrated that substrates of respiration were derived mainly from the products of starch degradation. Starch degradation exhibited a similar temperature‐response curve as respiration with a break‐point at high temperatures. Acceleration of starch breakdown may be one of the reasons for the observed high‐temperature rise in respiration. We also demonstrate that enhanced leaf sugar concentrations or enhanced osmotic potential may protect leaf cells from heat stress, i.e. higher sugar concentrations significantly modify the temperature‐response curve of respiration, abolishing the fast increase of respiration. Sugars or enhanced osmotic potential may non‐specifically protect respiratory membranes or may block the high‐temperature increase in starch degradation and consumption in respiratory processes, thus eliminating the break‐points in temperature curves of respiration in sugar‐fed leaves.     

Energy coupling for membrane hyperpolarization in Lemna: respiration rate,ATP level and membrane potential at low oxygen concentrations

Respiration rate, ATP content and membrane potential of Lemna have been measured as a function of the concentration of dissolved oxygen. Kinetic analysis showed that within the range from 1 μM to 20 μM O₂, the respiration rate of isolated mitochondria and intact plants was a hyperbolic function of the oxygen concentration. The apparent Michaelis constant (K _m ) for the oxygen of respiration of intact plants (1.15±0.08 μM) is close to that for isolated mitochondria (1.07±0.06 μM), so that diffusion of oxygen within the tissue was obviously not rate-limiting under the applied experimental conditions. The ATP level decreased in parallel with the respiration rate when the oxygen concentration was reduced. In contrast, the hyperpolarization of the membrane potential above the diffusion potential had already decreased at oxygen concentrations where the respiration rate and ATP level remained practically unchanged and was completely abolished at oxygen concentrations above the K _m of respiration. This result is discussed according to the current models for electrogenic pumps. It is concluded that ATP cannot be the fuel for the electrogenic process under investigation.     

Quantification of oxygen production and respiration rates in mixotrophic cultivation of microalgae in nonstirred photobioreactors

Online monitoring and controlling of different cellular parameters are key issues in aerobic bioprocesses. Since mixotrophic cultivation, in which we observe a mixture of cellular respiration and oxygen production has gained more popularity, there is a need for an on‐process quantification of these parameters. The presented and adapted double gassing‐out method applied to a mixotrophic cultivation of Galdieria sulphuraria , will be a tool for monitoring and further optimization of algal fermentation in nonstirred photobioreactors (PBR). We measured the highest net specific oxygen production rate (opr _net) as 5.73 · 10^?3 mol_O2 g^?1 h^?1 at the lowest oxygen uptake rate (OUR) of 1.00 · 10^?4 mol_O2 L^?1 h^?1. Due to higher cell densities, we also demonstrated the increasing shading effect by a decrease of opr _net, reaching the lowest value of 1.25 10^?5 mol_O2 g^?1 h^?1. Nevertheless, with this on process measurement, we can predict the relation between the zone in which oxygen is net produced to the area where cell respiration dominates in a PBR, which has a major impact to optimize cell growth along with the formation of different products of interest such as pigments.     

Inhibition of Cyanide-Insensitive Respiration in <Emphasis Type="Italic">Klebsiella oxytoca</Emphasis> SYSU-011 by 8-Hydroxyquinolone

The inhibition of the cyanide (KCN)-insensitive respiration of Klebsiella oxytoca SYSU-011 by 8-hydroxyquinoline (8-HQ) was determined. Results showed that the profile of the rate of oxygen uptake of normal-grown and 8-HQ–grown K. oxytoca SYSU-011 was biphasic and similar, suggesting that 8-HQ did not inhibit the respiration of normal-grown K. oxytoca SYSU-011. A different biphasic KCN inhibition profile of respiration was observed for KCN-grown cells treated with and without 8-HQ. No decrease in respiration rate of KCN-grown cells and a 40% decrease in respiration rate of KCN-grown cells treated with 8-HQ were observed when KCN concentration was 10^–1 mM. Comparing differences of the profiles of oxygen uptake in KCN-grown cells with and without 8-HQ addition indicated that 8-HQ inhibited expression of the KCN-insensitive pathway carried out by nonheme oxidase. Greater inhibition of NADH oxidase activity by 2-n-heptyl-4-hydroxyquinoline-N-oxide from the cell membrane of the KCN-grown cells treated with 8-HQ, and more H₂O₂ production from these cells with than without 8-HQ, suggest that the function of the cyanide-insensitive pathway can stabilize the respiration of the cyanide-grown cells to prevent the production of H₂O₂.     

Are altitudinal limits of equatorial stream insects reflected in their respiratory performance?

1. We measured respiration of the larvae of aquatic insects from streams in the Ecuadorian Andes in relation to oxygen saturation at 5, 8, 11, 14 and 17 °C. Polycentropus (Polycentropodidae), Lachlania (Oligoneuriidae), Anchytarsus (Ptilodactylidae) and Anacroneuria (Perlidae) represented genera absent from the highest altitudes, reaching 2720, 2930, 3120, 3450 m a.s.l., respectively, while Claudioperla (Gripopterygidae) and Anomalocosmoecus (Limnephilidae) occurred only above 2900 m a.s.l. Our purpose was to determine whether natural altitudinal limits were reflected in physiological critical points on respiration versus oxygen curves and by the effect of temperature on the ability to oxy‐regulate. 2. For all six genera, respiration was affected by oxygen saturation and temperature. Respiration (mg O₂ g⁻¹ AFDM h⁻¹) at 70% oxygen saturation (Michaelis–Menten fitted) varied from 2.6 to 7.6 between genera at 17 °C, and from 1.3 to 2.5 at 5 °C. Q₁₀ values for this temperature interval ranged 1.5–2.9 (mean 2.3). The two “high‐altitude” genera had higher respiration rates at low temperature and oxygen saturation, and their respiration rate saturated at lower temperatures, than three of the four “low‐altitude” genera. 3. The oxy‐regulatory capacity (critical points and initial decrease in respiration versus oxygen regressions) varied among genera and was affected by temperature. Lachlania, Claudioperla and Anomalocosmoecus had a higher ability to oxy‐regulate at low than at high temperatures, Anacroneuria was not clearly affected by temperature, while Polycentropus and Anchytarsus had a greater oxy‐regulatory capacity at high than at low temperature. These results indicate that the ability to oxy‐regulate is related to the temperature (altitude) at which species naturally occur. 4. Upper altitudinal limits of the six genera were not reflected in their respiratory performance, because all genera had critical minima of temperature and oxygen saturation much lower than those occurring at the limits of their natural distribution. So, the altitudinal limit could not be attributed to absolute short‐term physiological tolerance of low temperature and oxygen concentration. 5. Multiple regressions (based on respiration experiments and previously obtained relationships between water temperature, oxygen saturation and altitude) were used to predict how respiration rates should vary with altitude. At the upper limit of the four “low‐altitude” genera, respiration rates were 50–68% of those predicted at the centre of the range. With an arbitrary increase of 400 m above the actual limit, the effect of temperature would be a 13% decrease, and that of oxygen a 2% decrease, in respiration rate of Polycentropus, Lachlania and Anacroneuria, while respiration in Anchytarsus would be reduced by 5% by both factors. 6. It seems that, while the immediate decrease in respiration with increased altitude is caused mainly by a decrease in temperature, the long‐term survival of a species at given altitudes might be more affected by oxygen saturation. Further quantitative and long‐term studies on survival and recruitment in populations and communities are needed to determine the importance of temperature and oxygen for altitudinal limits of aquatic insects.     

Simulation of the dynamics in the Baker's yeast process

Simulation of the dynamics in a fed batch process for production of Baker's yeast is discussed and applied. Experimental evidences are presented for a model of the energy metabolism. The model involves the concept of a maximum respiratory capacity of the cell. If the sugar concentration is increased above a critical value, corresponding to a critical rate of glycolysis and a maximum rate of respiration, then all additional sugar consumed at higher sugar concentrations is converted into ethanol.In a fed batch process with constant sugar feed the sugar concentration declines slowly. If ethanol is present when the sugar concentration declines below the critical value of 110 mg/dm³ fructose +glucose the metabolism switches rapidly into combined oxidation of sugar and ethanol. Thus, no diauxic growth is involved under process conditions. The rate of ethanol consumption is determined by the free capacity of respiration under these conditions. The invertase activity of the cells was found to be so high that mainly fructose and glucose were present in the medium, typically in the concentration range around 100 mg/dm³. These components are consumed at the same rate but with fructose at a higher concentration, indicating a higher K _s for fructose consumption.The model was used in simulation experiments to demonstrate the dynamics of the Baker's yeast process and the influence of different process conditions.List of Symbols DOT % air sat dissolved oxygen tension - F dm³/h rate of inlet medium flow - H kg/(dm³ % air sat.) oxygen solubility - K kg/m³ saturation constant specified by index - K _L a 1/h volumetric oxygen transfer coefficient - m g/(g · h) maintenance coefficient specified by index - P kg/(m³ · h) mean productivity of biomass in the process - q g/(g · h) specific consumption or production rate - S kg/m³ concentration of sugar in reactor - S ₀ kg/m³ concentration of inlet medium sugar medium t h process time - V dm³ medium volume - X kg/m³ concentration of biomass - Y g/g yield coefficient specified by index - 1/h specific growth rate Index aa anaerobic condition - c critical value - e ethanol - ec ethanol consumption - ep ethanol production - max maximum value - o oxygen - oe oxygen for growth on ethanol - os oxygen for growth on sugar - s sugar - x biomass     

Midday depression of tree root respiration in relation to leaf transpiration

The root respiration rate often shows an exponential or a linear relationship with temperature under laboratory conditions. However, under intact conditions in the field, the root respiration rates of some tree species decreased around midday despite an increment of the root temperature (Bekku et al. 2009). To clarify the cause of midday depression, we examined the relationships between the intact root respiration and parameters of leaf gas exchange through the simultaneous field measurement of the gas exchange in the leaf and root of Quercus crispula and Chamaecyparis obtusa, which are canopy trees. There were no significant relationships between the root respiration rates (R _r) and the parameters of leaf gas exchange in the field. However, in C. obtusa, the relationships between R _r and the transpiration rates (E) at 1 h before the measurement of R _r were fitted by logarithmic function with a determination coefficient of 0.60–0.89. In the light-manipulation experiments using saplings, R _r had significant positive correlations with E at 20 min before the measurement of R _r, root temperature (T _r), and the photosynthesis (P _n) at 20 min before the measurement of R _r. We examined which factor, P _n or E, affects the root respiration rate through a manipulation experiment using a growth chamber regulating the ambient CO₂ concentration and relative humidity independently under constant air temperature and photosynthetic photon flux density. As a result, the root respiration rates changed corresponding to E and not P _n. These results suggest that the root respiration rate of trees changes significantly in the daytime and is affected by the leaf transpiration rate as well as the temperature.     

Effect of PO2 on growth and physiological characteristics of Candida utilis in a multistage tower fermentor

The effect of increasing the partial pressure of oxygen in the aeration gas on growth and physiological activity of the yeast Candida utilis in a multistage tower fermentor was studied. The measurements were made at steady states of continuous culture for single values of dilution rate, temperature, and pH in all stages of the fermentor and with one given ethanol concentration in the growth medium feed. The partial pressure of oxygen in the gas phase was changed in the range from 165 to 310 torr. The results revealed the existence of the upper critical value of the partial oxygen pressure in the gas phase. It was demonstrated that the upper critical value of PO ₂ influences not only the growth rate, biomass yield, and productivity but also the cell physiology resulting in changes of respiration activity and activity of alcohol and aldehyde dehydrogenases.     

Light control of the respiration of exogenous glycerol in the red macroalga Grateloupia doryphora

Heterotrophic activity in macroalgae has been little studied, but the red macroalga Grateloupia doryphora is known to grow in light at a higher rate in a glycerol-containing medium than in seawater. The effects of 0·1 M exogenous glycerol in seawater (SW90-gly) on the respiration rate of G. doryphora and the role played by light were investigated. The algae pretreated for 2 h in the light and in SW90-gly evolved oxygen and fixed carbon dioxide (H¹⁴CO₃ ^?), but also evolved radioactive ¹⁴CO₂ from [¹⁴C]glycerol. The rate of oxygen evolution was lower than that of samples in seawater, due to a high respiration rate and/or a partial inhibition of photosynthesis induced by glycerol. In contrast, the rate of inorganic carbon fixation was higher in SW90-gly than in control samples in seawater, suggesting that non-photosynthetic patterns were operating. In darkness, after pretreatment in the light in SW90-gly, samples showed a high oxygen uptake rate just after the light was turned off. Twenty minutes of darkness were enough to decrease this high respiration rate to that of samples in seawater. The oxygen uptake observed in all experiments with glycerol was mitochondrial as it was inhibited by potassium cyanide and salicylhydroxamic acid (SHAM). Pretreatment of samples in the light in SW90-gly with the photosynthetic inhibitor DCMU did not inhibit ensuing dark respiration, thus providing evidence for a non-photosynthetic effect of the light. The highest dark respiration rate was observed after the samples were pretreated in monochromatic blue light in glycerol-containing media.     

毛白杨树干呼吸及其温度敏感性季节变化特征

树干呼吸(E_s)是森林生态系统碳循环过程的重要组成部分,深入理解树干呼吸过程对未来气候变暖的响应及反馈机制有助于更加精确地估算森林生态系统碳储量。为揭示毛白杨树干呼吸及其温度敏感性的昼夜变化和季节动态规律,利用Li-Cor6400便携式光合作用测定系统及其配套使用的土壤呼吸测量气室(LI-6400-09)对冀南平原区毛白杨的树干呼吸和树干温度实施为期1年的连续监测。结果表明:(1)在生长季,毛白杨树干呼吸与树干温度之间在晚上呈现正相关的关系(R~2=0.88);相反,两者在白天为负相关的关系(R~2=0.96)。(2)整个观测期内,毛白杨树干呼吸和树干温度均呈现"钟形"的变化曲线,树干呼吸与树干温度之间存在着较好的指数函数关系(R~2=0.93),且树干呼吸的温度敏感性系数(Q_(10))为2.62;不同季节毛白杨树干呼吸的Q_(10)存在差异,生长季的Q_(10)(1.95)明显低于非生长季(3.00),表明生长呼吸和维持呼吸对温度的响应也并不相同。(3)温度矫正后的毛白杨树干呼吸(R_(15))在昼夜和季节尺度上均存在明显的变异,即夜晚的R_(15)显著高于白天(P0.01),生长季的R_(15)明显高于非生长季(P0.05);树干可溶性糖含量与生长季的R_(15)存在较好的相关性(R~2=0.52),而非生长季的R_(15)却主要受到树干淀粉含量的影响。研究结果表明,在生长季,毛白杨树干呼吸的在日变化主要受到温度的影响,而在季节尺度上Q_(10)的变异则与树干呼吸中维持呼吸所占比例及树干中非结构性碳水化合物(可溶性糖和淀粉)的含量及类型紧密相关。     

Detection of wood boring insects by measurement of oxygen consumption

A possible method for detection of wood-boring insects in wood is the measurement of oxygen consumption. In order to develop such a method, several parameters have to be determined first. The most important one is to determine the respiration rate of possible pest species. To obtain the data for establishing the method mentioned above, the respiration rates of the following species were determined: the old house borer, Hylotrupes bajulus, common furniture beetle, Anobium punctatum and subterranean termite, Reticulitermes lucifugus. We compared the O₂ consumption between different species as well as between adults and larvae of one species in different environmental conditions (temperature, day/night and light/dark regime). The most intensive respiration rates were found for the larvae of Hylotrupes bajulus (4.0 ml/g h O₂) and Anobium punctatum (3.9 ml/g h O₂). Less intensive breathing was measured by Reticulitermes lucifugus (workers 2.9 ml/g h, nymphs 2.6 ml/g.h and soldiers 2.0 ml/g h O₂). These results indicate that it is possible to detect the presence of wood-boring insects respirometrically. To detect the presence of an individual insect in the wood by means of respirometry, the sensitivity of the instrument for oxygen measurement at the optimal conditions must be around 0.2 ml/h.     

Response of the adenosine phosphate pool level to changes in the catabolic pattern of Saccharomyces cerevisiae

Changes in the catabolic pattern of Saccharomyces cerevisiae, growing in continuous culture, were effected by altering the glucose feed rate or the dissolved oxygen concentration. The cytochrome concentrations and the adenosine phosphate pool level of the yeast in a series of steady states and during three transitions were measured and compared with the glucose uptake rate (Q_G), the respiration rate (QO₂), and the rate of ethanolic fermentation (Q_E). Respiration was decreased at high glucose feed rates only if oxygen was low but cytochromes were glucose repressible at both high and low oxygen concentrations. In the main, Q_E and the levels of ATP, ADP, and AMP were decreased and cytochrome concentration were elevated at low Q_G values. No consistent relationship between any of the adenosine phosphate parameters and QO₂ was discernible. Evidence is presented for the concept that the Q_G directly controls the adenosine phosphate pool level and that a relationship between the concentration of adenosine phosphate anhydride bonds and the adenosine phosphate level is constantly maintained.