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PubMed1991

Short-term effects of dehydroepiandrosterone treatment in rats on mitochondrial respiration.

Administration of dehydroepiandrosterone (DHEA) to rats results in alterations in liver and serum factors. This study was undertaken to determine the earliest metabolic change(s) associated with DHEA treatment. Serum cholesterol, triacylglycerol, glucose, insulin, glucagon, thyroid hormones and hepatic glucose-6-phosphate dehydrogenase activity were, in general, unaltered in obese Zucker rats after 7 d and 24, 12 and 3 h of DHEA treatment. Malic enzyme, long-chain fatty acyl-coenzyme A hydrolase and catalase activities and peroxisomal beta-oxidation rates were elevated after 7 d and 24 h in DHEA treatment, but not after 12 h. Mitochondrial beta-oxidation was not altered. Hepatic mitochondrial state 3 respiration per g liver with glutamate-malate was elevated after 7 d and 24, 12 and 3 h in DHEA-treated rats and was elevated per mg protein except after 7 d. Succinate-supported state 3 respiration per g liver was also elevated after 7 d and 24 and 12 h of DHEA treatment. Mitochondria from rats treated for 7 d had lower levels of cardiolipin and phosphatidylethanolamine and an increase in phosphatidylcholine. Changes in fatty acid composition of these phospholipids occurred after 7 d and 24 h of DHEA treatment. In an additional study, rats were treated with DHEA or DHEA plus ethidium bromide for 3 d. Ethidium bromide inhibited the increase in mitochondrial protein and respiration associated with DHEA treatment. These findings indicate that mitochondrial respiration is the earliest factor affected by DHEA and may be associated with protein synthesis.

Acyl Coenzyme A↗
PubMed2004

Ethanol synthesis and aerobic respiration in the laboratory by leader segments of Douglas-fir seedlings from winter and spring.

Stem segments from terminal leaders of Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, seedlings were sampled in mid-December when cambial cells were dormant. The residual, debudded leaders were resampled again in early May when the cambium was metabolically active. May stems had higher constitutive ethanol concentrations than December stems. This was not the result of cambial hypoxia generated by rapid spring respiration rates, because when aerobic respiration was stimulated by incubating the stems in air at 30 degrees C ethanol production was induced in December, but not in May. Rapid respiration rates at 30 degrees C may have depleted O(2) supplies and induced ethanol production in December stems because dormant, thick-walled cambial cells may be less permeable to CO(2) and O(2), compared with metabolically active, thin-walled cambial cells in May. December stem segments incubated in a N(2) atmosphere at 30 degrees C synthesized 1.8 times more ethanol than segments from May, most likely because spring growth had reduced the soluble sugars available for fermentation. CO(2) efflux from May stems (after 5.5 h of incubation at 30 degrees C) was equal to December stems per unit volume, but greater than December stems per unit surface area. N(2)-induced ethanol concentrations were positively related with CO(2) efflux per unit volume, indicating that rapidly respiring leaders can maintain rapid fermentation rates, provided soluble sugars are readily available. N(2)-induced ethanol and CO(2) efflux per unit volume declined with increasing leader diameter in both seasons, whereas there were no relationships between CO(2) efflux per unit surface area and diameter. Cambium physiology and phenology influence the induction of fermentation and concentrations of ethanol produced in terminal leaders of Douglas-fir, and probably other conifers as well. This needs to be considered when comparing fermentation among species, or comparing individuals from different seasons, or disparate ages within a species.

Aerobiosis↗
PubMedDate not supplied

Direct and indirect effects of elevated CO(2) on whole-shoot respiration in ponderosa pine seedlings.

We determined the short-term direct and long-term indirect effects of CO(2) on apparent dark respiration (CO(2) efflux in the dark) in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings grown in 35 or 70 Pa CO(2) partial pressure for 163 days in naturally lit, controlled-environment chambers. Two soil N treatments (7 and 107 ppm total N, low-N and high-N treatments, respectively) were imposed by watering half the plants every 2 weeks with 15/15/18 fertilizer (N,P,K) and the other half with demineralized water. Direct effects of ambient CO(2) partial pressure on apparent dark respiration were measured during short-term manipulations (from minutes to hours) of the CO(2) environment surrounding the aboveground portion of individual seedlings. Short-term increases in the ambient CO(2) partial pressure consistently resulted in significant decreases in CO(2) efflux of seedling in all treatments. Efflux of CO(2) decreased by 3 to 13% when measurement CO(2) partial pressure was increased from 35 to 70 Pa, and by 8 to 46% over the entire measurement range from 0 to 100 Pa. No significant interactions between the indirect effects of growth CO(2) partial pressure and the direct effects of the measurement CO(2) partial pressure were found. Seedlings grown in the high-N treatment were significantly less sensitive to short-term changes in CO(2) partial pressures than seedlings grown in the low-N treatment. Apparent respiration tended to decrease in seedlings grown in elevated CO(2), but the decrease was not significant. Nitrogen had a large effect on CO(2) efflux, increasing apparent respiration more than twofold on both a leaf area and a leaf or shoot mass basis. Both the direct and indirect effects of elevated CO(2) were correlated with changes in the C/N ratio. A model of cumulative CO(2) efflux for a 160-day period demonstrated that, despite a 49% increase in total plant biomass, seedlings grown in the high-N + high-CO(2) treatment lost only 2% more carbon than seedlings grown in the high-N + low-CO(2) treatment, suggesting increased carbon use efficiency in plants grown in elevated CO(2). We conclude that small changes in instantaneous CO(2) efflux, such as those observed in ponderosa pine seedlings, could scale to large changes in carbon sequestration.

Journal Article↗
PubMedDate not supplied

Growth and maintenance respiration rates of aspen, black spruce and jack pine stems at northern and southern BOREAS sites.

We measured stem respiration rates during and after the 1994 growing season of three common boreal tree species at sites near the northern and southern boundaries of the closed-canopy boreal forest in central Canada. The growth respiration coefficient (r(g); carbon efflux per micro mole of carbon incorporated in structural matter) varied between 0.25 and 0.76, and was greatest for black spruce (Picea mariana (Mill.) B.S.P.), least for jack pine (Pinus banksiana Lamb.) and intermediate for trembling aspen (Populus tremuloides Michx.). There was a consistent trend for higher r(g) at northern sites than at southern sites. Maintenance respiration rates at 15 degrees C (r(m)) varied from 0.5 to 2.7 nmol C mol(-1) C(sapwood) s(-1). Values of r(m) were high at sapling-stage jack pine sites and mature black spruce sites, and low at mature trembling aspen and mature jack pine sites. We found significant relationships between annual maintenance respiration and sapwood relative growth rate and sapwood volume per unit of stem surface area that explained much of the within-stand and between-stand variability. Because of the large differences in parameter values among sites, we conclude that the use of stand-specific respiratory parameters may improve model predictions of ecosystem process models over the use of generic parameter values.

Journal Article↗
PubMed1989

Carbohydrate requirements of peach fruit growth and respiration.

Data on the seasonal patterns of fruit growth and dark respiration of two peach (Prunus persica (L.) Batsch) cultivars were combined with temperature data to calculate the carbohydrate requirements of an "average" peach fruit from bloom to harvest. The two peach cultivars used were June Lady (an early maturing (mid-June) cultivar) and O'Henry (a late maturing (early-August) cultivar). At harvest, the mean dry weight of the June Lady fruit was 17.8 g (139.7 g fresh weight) and of O'Henry fruits was 30.9 g (213.9 g fresh weight), and the times from full bloom to harvest were 107 and 154 days, respectively. The total calculated fruit respiration requirements were 132 and 300 mmol CO(2) fruit(-1) season(-1) for June Lady and O'Henry fruits, respectively. Total calculated carbohydrate requirements for fruit growth and respiration are 23.9 and 43.8 g CH(2)O fruit(-1) season(-1) for June Lady and O'Henry fruits, respectively. Fruit respiration accounted for 16.3% of the total carbohydrate requirements of June Lady fruits and 0.5% of the total carbohydrate requirements of O'Henry fruits.

Journal Article↗
PubMed1989

Assessment of patients' experience of discomforts during respirator therapy.

Patients (n = 158) who had been respirator-treated and who could remember the treatment were retrospectively (after greater than 2 months) interviewed about their experiences. Of all patients, 47% had felt anxiety and/or fear during the treatment. These feelings were intimately related to the experience of agony/panic (p less than .001) and insecurity (p less than .001). Inability to talk and communicate was found to be the dominating reason (p less than .001) for evoking such feelings and also made it difficult for the patients to sleep and rest (p less than .05); no correlation to pain was found. Difficulties to synchronize with the respirator in connection with suctioning also caused feelings of anxiety/fear (p less than .01), agony/panic (p less than .01), and insecurity (p less than .001). Even as long as 4 yr after respirator treatment, most patients (90%) who remember the treatment still recall the situation as unpleasant and stress-evoking. The isolation due to communication difficulties was a greater problem than direct airway-related nursing care activities. This relationship between communication difficulties and severe emotional reactions should be considered in the nursing care of respirator-treated patients.

Adult↗
PubMed1989

Relationship of subjective tolerance of respirator loads to physiologic effects and psychophysical load sensitivity.

The degree to which subjective tolerance of respirator loads is related to physiologic effects and to psychophysical load sensitivity was investigated in this study. Fifty-two normal volunteers walked on a treadmill while breathing through a variety of respirator-type resistance and dead-space loads. Visual analog scales measuring perceived time limit of exercise and discomfort were both related to the ventilatory work imposed by the loads. Respiratory timing was related to discomfort but not to time limit. Psychophysical sensitivity to added resistive loads (LSS) was measured by the magnitude estimation method. Persons with higher objectively measured LSS had greater subjective intolerance induced by respirator use than persons of lower LSS. These findings suggest that subjective respirator tolerance is related to a person's psychophysical characteristics and to the actual physiologic effects. Furthermore, discomfort may be dissociated from actual exercise limitation.

Efficiency↗
PubMed1992

Measurements of the Engagement of Cyanide-Resistant Respiration in the Crassulacean Acid Metabolism Plant Kalanchoë daigremontiana with the Use of On-Line Oxygen Isotope Discrimination.

Discrimination against (18)O during dark respiration in tissues of Kalanchoë daigremontiana, Medicago sativa, and Glycine max was measured using an on-line system that enabled direct measurements of the oxygen fractionation of samples in a gas-phase leaf disk electrode unit. Discrimination factors for cytochrome pathway respiration were 18.6 to 19.8%(o) for all tissues. However, discrimination in cyanide-resistant respiration was significantly higher in green tissues (30.4-31.2%(o)) compared with nongreen tissues (25.3-25.9%(o)). Using these discrimination factors, the partitioning of electron transport to these pathways was calculated from measurements of discrimination in the absence of inhibitors. Changes in flux through the alternative pathway were measured during the light and dark phases of Crassulacean acid metabolism in leaf disks of K. daigremontiana. The flux of electrons through the alternative pathway was higher during deacidification than during the other phases of Crassulacean acid metabolism. The increase in alternative pathway electron flux accounted for all of the increased respiration in the light phase. Despite this increase, simultaneous measurements of malate concentration and respiratory flux confirm that only a small proportion of the total malate decarboxylation occurs in the mitochondria.

Journal Article↗
PubMed1994

Molecular Genetic Alteration of Plant Respiration (Silencing and Overexpression of Alternative Oxidase in Transgenic Tobacco).

The alternative oxidase (AOX) of plant mitochondria is encoded by the nuclear gene Aox1. Sense and antisense DNA constructs of Nicotiana tabacum Aox1 were introduced into tobacco, and transgenic plants with both increased and decreased levels of mitochondrial AOX protein were identified. Suspension cells derived from wild-type and transgenic plants were grown in heterotrophic batch culture. Transgenic cells with increased AOX protein had an increased capacity for cyanide-resistant, salicylhydroxamic acid-sensitive respiration compared to wild-type cells, whereas transgenic cells with decreased AOX protein had a decreased capacity for such respiration. Thus, genetic alteration of the level of AOX protein was sufficient to alter the capacity for electron transport through the alternative pathway. Under our standard growth conditions, "antisense" cells with dramatically reduced levels of AOX protein had growth and respiration rates similar to the wild type. However, whereas wild-type cells were able to grow under conditions that severely suppressed cytochrome pathway activity, antisense cells could not survive this treatment. This suggests that a critical function of AOX may be to support respiration when the cytochrome pathway is impaired. The much higher level of AOX protein in "sense" cells compared to the wild type did not appreciably alter the steady-state partitioning of electrons between the cytochrome path and the alternative pathway in vivo, suggesting that this partitioning may be subject to additional regulatory factors.

Journal Article↗
PubMed1997

Leaf Respiration in Light and Darkness (A Comparison of Slow- and Fast-Growing Poa Species).

We investigated whether leaf dark respiration (nonphotorespiratory mitochondrial CO2 release) is inhibited by light in several Poa species, and whether differences in light inhibition between the species are related to differences in the rate of leaf net photosynthesis. Four lowland (Poa annua L., Poa compressa L., Poa pratensis L., and Poa trivialis L.), one subalpine (Poa alpina L.), and two alpine (Poa costiniana Vick. and Poa fawcettiae Vick.) Poa species differing in whole plant relative growth rates were grown under identical controlled conditions. Nonphotorespiratory mitochondrial CO2 release in the light (Rd) was estimated according to the Laisk method. Photosynthesis was measured at ambient CO2 partial pressure (35 Pa) and 500 [mu]mol photons m-2 s-1. The rate of photosynthesis per unit leaf mass was positively correlated with the relative growth rate, with the slow-growing alpine Poa species exhibiting the lowest photosynthetic rates. Rates of both Rd and respiration in darkness were also substantially lower in the alpine species. Nonphotorespiratory CO2 release in darkness was higher than Rd in all species. However, despite some variation between the species in the level of light inhibition of respiration, no relationship was observed between the level of inhibition and the rate of photosynthesis. Similarly, the level of inhibition was not correlated with the relative growth rate. Our results support the suggestion that rates of leaf respiration in the light are closely associated with rates in darkness.

Journal Article↗
PubMed1967

Oxygen tension a determining factor in the respiration of potato disks of varying thickness.

The effect of temperature on the respiration rate of potato tuber slices has been analyzed in terms of the Arrhenius equation. Freshly cut disks, irrespective of thickness, show a linear response to increasing temperature up to 30 degrees with an activation energy (E) of approximately 12.0 Kcal. Aged disks less than 1.0 mm thick also give a linear response with E similar to that of fresh disks. With aged disks above 1.0 mm thick there is a loss of linearity above 20 degrees and E falls to about 4.0 Kcal indicating that respiration becomes rate-limited by a diffusion process. This departure from linearity can be corrected by raising the oxygen tension or by subdivision of thick disks to give thin slices. It is concluded that the respiration of aged disks is rate-limited by oxygen deficiency and that the inverse relationship between respiration rate and disk thickness is in large part attributable to this factor.

Journal Article↗
PubMed1967

Tissue Respiration and Mitochondrial Oxidative Phosphorylation of NaCl-Treated Pea Seedlings.

The effect of sodium chloride added to root medium of pea seedlings on respiratory activity of tissue segments and on isolated mitochondria was studied. Salinization enhances the respiration of leaves about one-third on a fresh weight, dry weight or protein basis. Roots and stems show only 10 to 15% respiratory stimulation. The onset of respiratory increase in leaves roughly parallels the increase in NaCl content and the decrease in growth rate. At a later stage the elevated respiration is apparent in treated plants even though the concentration of NaCl reaches a plateau and osmotic adjustment is being reached. Stimulation of respiration was found in both etiolated and green plants. Experiments with DNP show that simple uncoupling by salt is not involved; the respiratory increase in control and treated tissue is proportionally the same.In accordance with increased respiration rates observed in vivo, mitochondria from salt-treated plants show higher rates of oxygen uptake on several substrates. The effect of NaCl added during growth is long term and is distinct from the effect of NaCl added to mitochondria isolated from control plants. Since P/O ratios are not affected by NaCl, the potential for oxidative phosphorylation in salt-affected tissue appears to increase. It is postulated that this increase may lead to changes in ADP and ATP content, and in turn, affect regulation of metabolic pathways.

Journal Article↗
PubMed1968

Further evidence of oxygen diffusion as the determining factor in the relation between disk thickness and respiration of potato tissue.

The effect of oxygen tension above atmospheric pO(2) on the development of respiratory capacity in potato disks has been examined. Raising the oxygen tension of the aqueous environment to 40% during the aging of 2.0 mm or 3.0 mm thick disks at 25 degrees progressively increased the respiration rate of the tissue as shown by subsequent assay in 100% oxygen. Disks 3.0 mm thick showed a greater response to increased pO(2) than did 2.0 mm disks. A comparison of center 1.0 mm sections excised from 3.0 mm disks after aging, showed that the respiration rate of internal tissue from disks aged in high pO(2) was approximately 40% greater than such tissue aged with atmospheric pO(2). The characteristic inverse relationship between respiration rate and thickness in aged disks can be modified from a concave-downwards curve to a convex-downwards curve by pretreating the tissue with increased pO(2), thus indicating that raising the pO(2) during aging can increase the thickness threshold at which the transition from tissue manifesting the respiratory characteristics of thin disks to that manifesting the characteristics of thick disks, occurs. Similarly increased pO(2) during aging can modify the hyperbolic relationship obtaining between pretreatment temperature in the range 10 degrees to 25 degrees and respiratory capacity of aged 3.0 mm disks, to approximate to the linear relationship observed with 0.75 mm disks. It is concluded that the development of respiratory capacity in disks between 0.75 mm and 3.0 mm thick is restricted by oxygen dificiency and that the characteristic inverse relationship between respiration rate and thickness in aged disks is largely attributable to this factor, the influence of which is discernible both on the development of respiratory capacity and on its subsequent assay.

Journal Article↗
PubMed1970

Prior illumination and the respiration of maize leaves in the dark.

The course of respiration of attached maize (Zea mays L.) leaves was measured by infrared gas analysis of CO(2) efflux in the dark following illumination in atmospheres of 300 microliters of CO(2) per liter of air, CO(2)-free air, and CO(2)-free N(2) containing 400 microliters of O(2) per liter. CO(2) efflux from control leaves started 3 to 4 minutes after darkening, increased to a maximum after about 20 minutes, and returned to a steady minimum after 2 to 3 hours. Respiration was quantitatively related to prior illumination, independent of net CO(2) fixation in the light, and depressed by N(2). Light, but not air, was required to produce a substrate for respiration in the subsequent dark period; air was required for oxidation of the substrate to CO(2). The stimulation of respiration by prior illumination in maize leaves differs in its slower onset and greater duration from the postillumination burst of photorespiration.

Journal Article↗
PubMed1972

Phosphate-induced Stimulation of Acceptorless Respiration in Corn Mitochondria.

By use of the organic mercurial mersalyl to block phosphate transport, it has been shown that only a small fraction of the respiratory increase of corn mitochondria in response to additions of inorganic phosphate is due to energy expended in phosphate accumulation. Most of the respiratory release occurs from accelerated turnover of the coupling mechanism with internal phosphate in an oligomycin-sensitive reaction. Addition of ADP to mersalyl-blocked mitochondria depletes internal phosphate in ATP formation and respiration declines. Arsenate produces the same responses as phosphate but is more effective in respiratory release.Inhibition of the ADP-ATP antiporter with atractyloside shows that the increased respiration with internal phosphate is not due to turnover of ADP acceptor through exogenous ATPase.Use of valinomycin to facilitate movement of K(+) greatly accelerates the rate of phosphate swelling, but there is no consistent correlation between respiration and swelling. In the absence of phosphate, valinomycin dramatically releases respiration with only trivial swelling.The data indicate that loose coupling in due only fractionally to energy expenditure in ion transport. An explanation consistent with the observations can be derived by assuming that both a high energy intermediate (I approximately X) and a proton motive force-or its electrochemical equivalent-arise at coupling sites.

Journal Article↗
PubMed1973

The Stoichiometry of Respiration-driven Potassium Transport in Corn Mitochondria.

Determinations were made for corn (Zea mays L., WF9-Tms x M14) mitochondria of the stoichiometric relationship between K(+) transport and bond energy produced in respiration (K(+)/ approximately ratio). With inward pumping of potassium acetate activated by NADH oxidation, the initial rate of K(+) transported into the sucrose inaccessible space varied between 0.58 and 0.97 K(+)/ approximately , assuming 2 high energy bond equivalents per NADH oxidized. Only small amounts of H(+) were ejected. Valinomycin did not alter the ratio.Efflux pumping of K(+) in KCl media gave a K(+)/ approximately of 0.92. Substituting sucrose for KCl caused a drop in respiration and H(+) ejection, indicating a requirement for cation efflux pumping in acceptorless respiration. Valinomycin added to the KCl medium accelerated passive swelling but did not impair subsequent efflux pumping, although respiration was partially uncoupled.

Journal Article↗
PubMed1973

The interaction of respiration and photosynthesis in induction of nitrate reductase activity.

The respiration and photosynthesis requirement for induction and maintenance of nitrate reductase activity was determined on leaves of Hordeum vulgare L. In this induction, glucose substituted for light in both dark-grown and carbohydrate-depleted green leaves. Oxygen appeared to be required for induction in all cases studied. In light and under N(2), 3-(3,4-dichlorophenyl)-1,1-dimethylurea completely inhibited induction, presumably by inhibiting the production of O(2), Hence, under N(2) the leaves appeared to utilize both the O(2) produced by photosynthesis and the CO(2) produced by respiration. CO(2) fixation can then produce both photosynthate to drive the induction and terminal electron acceptors to allow photosynthetic electron flow. This possibility was further suggested by the observation that CO(2) was an absolute requirement for induction in carbohydrate-depleted barley leaves. Results obtained with respiratory inhibitors also indicated that respiration drove the induction of nitrate reductase.Exogenously supplied glucose also substantially slowed the loss of nitrate reductase that occurred when barley leaves were placed in darkness. It is presumed that glucose allowed the synthetic or activation phase of the induction to proceed more rapidly. Our results support the hypothesis that one of the main effects of light may be to supply photosynthate to support respiration, which then drives the induction process.

Journal Article↗
PubMed1974

The Metabolism of Oat Leaves during Senescence: I. Respiration, Carbohydrate Metabolism, and the Action of Cytokinins.

When the detached first leaves of green or etiolated oat (Avena sativa cv. Victory) seedlings senesce in the dark, their oxygen consumption shows a large increase, beginning after 24 hours and reaching a peak of up to 2.5 times the initial rate by the 3rd day. This effect takes place while the chlorophyll of green leaves, or the carotenoid of etiolated leaves, is steadily decreasing. Kinetin, at a concentration which inhibits the decrease in pigment, completely prevents the respiratory rise; instead, the oxygen consumption drifts downwards. Lower kinetin concentrations have a proportional effect, 50% reduction of respiration being given by about 0.1 mg/l. About one-fifth of the respiratory rise may be attributed to the free amino acids which are liberated during senescence; several amino acids are shown to cause increases of almost 50% in the oxygen consumption when supplied at the concentrations of total amino acid present during senescence. A smaller part of the rise may also be due to soluble sugars liberated during senescence, largely coming from the hydrolysis of a presumptive fructosan. The remainder, and the largest part, of the increase is ascribed to a natural uncoupling of respiration from phosphorylation. This is deduced from the fact that dinitrophenol causes a similar large rise in the oxygen consumption of the fresh leaves or of leaf segments kept green with kinetin, but causes only a very small rise when the oxygen consumption is near its peak in senescent controls. The respiration of these leaves is resistant to cyanide, and 10 mm KCN even increases it by some 30%; in contrast, etiolated leaves of the same age, which undergo a similar rise in oxygen consumption over the same time period, show normal sensitivity to cyanide. The respiratory quotient during senescence goes down as low as 0.7, both with and without kinetin, though it is somewhat increased by supplying sugars or amino acids; glucose or alanine at 0.3 m bring it up to 1.0 and 0.87, respectively.N(6)-Benzylaminopurine and Delta-2-isopentenylaminopurine act similarly to kinetin in repressing the respiratory rise, the former being five times as active as kinetin, while the latter has only 1% of the activity of kinetin. Zeatin also powerfully prevents senescence. Because the repression of the respiratory rise is shown by each cytokinin at the concentration at which it inhibits senescence, the action is ascribed in both cases to the maintenance of a tight coupling between respiration and phosphorylation. It is pointed out that such an effect would explain many features of cytokinin action.A change in the methodology of the senescence experiments is described and compared with the method previously used, and the influence of temperature and age of the plants on the course of leaf senescence are presented in detail.

Journal Article↗