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PubMed1974

Respiration and Gas Exchange in Stem Tissue of Opuntia basilaris.

Respiration and gas exchange in the light were studied manometrically with tissue slices from stem material of Opuntia basilaris Engelm. and Bigel. Dark respiration rates were greater in young stems than in mature stems. The timing of the experiment in the day/night cycle influences the magnitude and pattern of respiration and gas exchange in the light. Net dark respiration has a temperature optimum between 35 and 40 C, and is maintained at 60% of the control rate in tissue equilibrated with experimental osmotic potentials of -25 bars. Net gas exchange in the light is regulated by the titratable acidity of the tissue and by the tissue temperature. Increased rates of net CO(2) evolution and net O(2) consumption occur in the light with high levels of titratable acidity and high temperatures. An efflux of CO(2) and influx of O(2) occur following light/dark transitions. These patterns are reversed following dark/light transitions. Similar results were demonstrated at 15, 25, and 35 C, and are interpreted as a mechanism of adaptation to desert environments.

Journal Article↗
PubMed1977

Activation of endogenous respiration and anion transport in corn mitochondria by acidification of the medium.

Acidification of the suspending medium of corn mitochondria (Zea mays L., WF9 x Mo17) from pH 7.5 to pH 6.8 to 6.4 initiates osmotic swelling with the transportable anions citrate, sulfate, and phosphate. Swelling becomes pronounced with a combination of citrate plus sulfate or phosphate. Acidification proves to activate endogenous respiration, which is essentially zero at pH 7.5. The endogenous respiration transports citrate (in the presence of sulfate or phosphate) which then contributes to respiration and the accelerated osmotic swelling. Mersalyl will inhibit the swelling and antimycin inhibits the endogenous respiration. Magnesium appears to reduce the permeability of the membranes under the acid conditions.

Journal Article↗
PubMed1978

Antimycin-insensitive Cytochrome-mediated Respiration in Fresh and Aged Potato Slices.

The effect of antimycin A on the respiration of fresh potato (Solanum tuberosum var. Russet Burbank) slices has been determined in the presence and absence of m-chlorobenzhydroxamic acid (CLAM). Two antimycin-binding sites are indicated. At low concentrations antimycin alone inhibits respiration only slightly. When CLAM and low antimycin are added together, respiration is sharply inhibited, as in response to cyanide. High antimycin alone is as inhibitory as cyanide. The branch point to the alternate path is intact in fresh slices, as is the hydroxamate-sensitive component. The full alternate path is inoperative, however, as indicated by the sensitivity to cyanide. The data suggest an alternate path loop which bypasses the high affinity antimycin site and returns electrons to the cytochrome path. Antimycin at high concentrations prevents articulation of the loop with the cytochrome path.The respiration of aged slices is not only markedly resistant to antimycin at high concentrations, but quite insensitive to CLAM in the presence of antimycin. A model is proposed which involves parallel paths within complex III of the cytochrome path, with one path bearing the high affinity, and the other the low affinity antimycin site. With slice aging the antimycin affinity of the latter site is even further reduced, providing a relatively antimycin-insensitive bypass to both the high affinity antimycin-sensitive cytochrome path, and the CLAM-sensitive alternate path. The alternate path loop in fresh slices is presumed to feed into the low affinity antimycin-sensitive arm of the cytochrome path.

Journal Article↗
PubMed1979

Postharvest Variation in Cellulase, Polygalacturonase, and Pectinmethylesterase in Avocado (Persea americana Mill, cv. Fuerte) Fruits in Relation to Respiration and Ethylene Production.

Cellulase, polygalacturonase (PG), pectinmethylesterase (PME), respiration, and ethylene production were determined in single "Fuerte" avocado fruits from the day of harvest through the start of fruit breakdown. PME declined from its maximum value at the time of picking to a low level early in the climacteric. PG activity was not detectable in the preclimacteric stage, increased during the climacteric, and continued to increase during the postclimacteric phase to a level three times greater than when the fruit reached the edible soft stage. Cellulase activity was low in the preclimacteric fruit, started to increase just as respiration increased, and reached a level two times greater than at the edible soft stage. Cellulase activity started to increase 3 days before PG activity could be detected. Increased production of ethylene followed the increase in respiration and cellulase activity by about 1.5 days. These results indicate that a close relation exists between the rapid increase in the cell wall-depolymerizing enzymes and the rise in respiration and ethylene production and refocused attention on the role of the cell wall and the associated plasma membrane in the early events of fruit ripening.

Journal Article↗
PubMed1979

Cyanide-insensitive Respiration in Pea Cotyledons.

Mitochondria isolated by a zonal procedure from the cotyledons of germinating peas possessed a cyanide-resistant respiration. This respiration was virtually absent in mitochondria isolated during the first 24 hours of germination but thereafter increased gradually until the 6th or 7th day of seedling development. At this time between 15 and 20% of the succinate oxidation was not inhibited by cyanide. The activity of the cyanide-resistant respiration was also determined in the absence of cyanide. Relationships among mitochondrial structure, cyanide-resistant respiration, and seedling development are discussed.

Journal Article↗
PubMed1981

An Analysis of the Relationship between Respiration and the Transmembrane Potential in Corn Roots.

The effects of cyanide, anoxia, and temperatures varying from 2 to 42 C on the cell membrane electropotential difference (PD) of washed and freshly excised corn roots have been determined. Respiration rates of freshly excised root segments in response to cyanide and to varying temperatures were also measured. The cell membrane PD of roots which had been washed for 12 to 15 hours was almost insensitive to cyanide and anoxia but sensitive to low temperature. In contrast, the cell membrane PD of freshly excised roots was reversibly depolarized by all three treatments, cyanide depolarized from -117 to -86 millivolts and the sequential imposition of anoxia further lowered the PD to -69 millivolts. Anoxia applied first depolarized maximally and the PD was not further lowered by sequential cyanide treatment. Arrhenius plot analysis of the temperature response of respiration showed an apparent transition at 13 C with an activation energy of 20.0 kilocalories per mole below and 8.8 kilocalories per mole above the transition temperatures. The energy of activation for repolarization of PD is much higher; 53.4 kilocalories per mole below 7 to 8 C and 25.4 kilocalories per mole above this apparent transition. The energy requirement for polarization of the cell membrane PD was calculated based on the temperature responses of the cell membrane PD and respiration. It was estimated that 3.5% of the energy output from respiration at 22 C is required for cell polarization. It is unlikely that ion transport is limited by energy availability below the 8 C transition in this chill sensitive species.

Journal Article↗
PubMed1982

Cyanide-insensitive respiration in relation to growth of a low-temperature basidiomycete.

The cyanogenic low-temperature basidiomycete (Coprinus psychromorbidus Redhead and Traquair), unlike other cyanide-tolerant fungi, does not detoxify cyanide via formamide hydro-lyase. Instead, tolerance apparently depends on cyanide-insensitive respiration involving activity of the mitochondrial alternative oxidase. Respiration and growth of young mycelium that lacks alternative oxidase activity are blocked both by cyanide and 1 mum antimycin. When activity of the alternative oxidase is elicited in young mycelium by 0.05 mm cyanide, subsequent treatment with antimycin stimulates respiration and fails to halt growth. Older mycelium becomes tolerant coincidentally with the release of cyanide by the mycelium. Tolerant older mycelium in medium containing 0.05 to 1.0 mum antimycin grows at 30 to 45% of the control rate. Cyanide- and antimycin-tolerant growth and respiration are blocked by salicyl hydroxamic acid, an inhibitor of the alternative oxidase, and by rotenone, which inhibits ATP synthesis at site I.

Journal Article↗
PubMed1983

Role of o(2) and mitochondrial respiration in a photosynthetic stimulation of oat protoplast acidification of a surrounding medium.

Some photosynthetically stimulated acidification of the medium by oat (Avena sativa L. cv Garry) leaf protoplasts required respiration. The requisite respiration (a) had a low apparent affinity for O(2), (b) was blocked by cyanide plus salicylhydroxamic acid, (c) characterized protoplasts and mitochondria isolated from protoplasts, (d) could be induced in leaf segments, and (e) appeared to result from an inhibition of mitochondrial respiration that included the cytochrome pathway.Carbon monoxide and cyanide prevented acidification of weakly photosynthesizing suspensions. Salicylhydroxamic acid had no effect on acidification, indicating a specific dependence upon cyanide-sensitive respiration. Photosynthesis stimulated acidification through stable products, and exogenously supplied O(2) stimulated acidification. The acidification response to O(2) was additive to the response to photosynthesis at subsaturating levels of light, indicating a common mode of action. Oligomycin prevented stimulation of acidification by low levels of photosynthetic activity; this stimulation appeared to be due to O(2)-induced increases in mitochondrial energy production. Oligomycin only partially inhibited stimulation of acidification by higher levels of light; this stimulation appeared to be partially dependent upon photophosphorylation. Therefore, oligomycin-sensitive acidification of the medium appeared to reflect changes in mitochondrial energy production in photosynthesizing protoplasts.

Journal Article↗
PubMed1983

Effect of supra-ambient oxygen on nitrogenase activity (c(2)h(2)) and root respiration of soybeans and isolated soybean bacteroids.

Isolated soybean (Glycine max [L.] Merr. cv Wilkin) bacteroids have O(2)-dependent nitrogenase activity which is strongly inhibited by supraoptimal O(2) concentrations. Oxygen-inhibited nitrogenase activity is recovered by addition of 10 millimolar sodium succinate or by lowering the O(2) concentration.Brief treatment of roots of intact soybean plants with 1.0 atmosphere O(2) reduces nitrogenase activity (C(2)H(2)). There is a rapid partial recovery of activity within 2 to 3 hours, and a slower return to near normal levels by 36 hours. The drop and recovery of nitrogenase activity is accompanied by a parallel drop and increase in root respiration. There is a direct relationship between the change in respiration and the change in acetylene reduction following O(2) treatment. The O(2)-mediated changes in nitrogenase activity and root respiration are not affected by the planting medium. The ratio of the change in respiration to the change in nitrogenase activity was the same in 13 soybean cultivars.

Journal Article↗
PubMed1986

Root Respiration in White Spruce (Picea glauca [Moench] Voss) Seedlings in Relation to Morphology and Environment.

Roots of white spruce seedlings (Picea glauca [Moench] Voss) undergo respiratory changes during the year that are related to changing metabolic requirements. An alternative pathway is always present, functions during most of the year, and operates maximally during periods of root and shoot growth. Although some differences in respiration and the apportioning of respiration can be correlated to root morphology, the environment and the stage of shoot development are also important controls. Differences in respiration related to root morphology are not manifest in mitochondrial structure, but overall rates were found to correlate with the number of mitochondria present. Root respiration in seedlings grown under root growth capacity conditions reflects root and shoot growth at that time rather than root growth capacity.

Journal Article↗
PubMed1986

Root respiration associated with nitrate assimilation by cowpea.

Nitrate uptake by roots of cowpea (Vigna unguiculata) was measured using (15)NO(3) (-), and the energy cost to the root was estimated by respirometry. Roots of 8-day-old cowpea seedlings respired 0.6 to 0.8 milligram CO(2) per plant per hour for growth and maintenance. Adding 10 millimolar NO(3) (-) to the root medium increased respiration by 20 to 30% during the following 6 hours. This increase was not observed if the shoots were in the dark. Removal of NO(3) (-) from the root medium slowed the increase of root respiration. The ratios of additional respiration to the total nitrogen uptake and reduced nitrogen content in roots were 0.4 gram C per gram N and 2.3 grams C per gram N, respectively. The latter value is close to theoretical estimates of nitrate assimilation, and is similar to estimates of 1 to 4 grams C per gram N for the respiratory cost of symbiotic N(2) fixation.

Journal Article↗
PubMed1987

Regulation of soybean nitrogen fixation in response to rhizosphere oxygen: I. Role of nodule respiration.

Nitrogen fixation (acetylene reduction) rates of nodules on intact field-grown soybean (Glycine max) subjected to altered oxygen concentration (0.06-0.4 cubic millimeter per cubic millimeter) returned to initial rates during an 8-hour transitory period. Hydroponically grown soybean plants also displayed a transitory (1-4 hours) response to changes in the rhizosphere oxygen concentration after which the fixation rates returned to those observed under ambient oxygen concentrations. It was hypothesized that soybean nodules contain a regulatory mechanism which maintains a stable oxygen concentration inside nodules at a sufficiently low concentration to allow nitrogenase to function. A possible physiological mechanism which could account for this regulation is adjustment in nodule respiration activity such that nodule oxygen concentration and nitrogen fixation are maintained at stable levels. Experiments designed to characterize the non-steady-state oxygen response and to test for the presence of nodule respiratory control are presented. Non-steady-state acetylene reduction and nodule respiration (oxygen uptake) rates measured after alterations in the external oxygen concentration indicated that the regulatory mechanism required 1 to 4 hours to completely adjust to changes in the external oxygen concentration. Steady-state nodule respiration, however, did not respond to alterations in the rhizosphere oxygen concentration. It was concluded that soybean nodules can adjust to a wide range of rhizosphere oxygen concentrations, but the mechanism which controls nitrogen fixation rates does not involve changes in the nodule respiration rate.

Journal Article↗
PubMed1988

Growth and mitochondrial respiration of mungbeans (Phaseolus aureus Roxb.) germinated at low pressure.

Mungbean (Phaseolus aureus Roxb.) seedlings were grown hypobarically to assess the effects of low pressure (21-24 kilopascals) on growth and mitochondrial respiration. Control seedlings grown at ambient pressure (101 kilopascals) were provided amounts of O2 equivalent to those provided experimental seedlings at reduced pressure to factor out responses to O2 concentration and to total pressure. Respiration was assayed using washed mitochondria, and was found to respond only to O2 concentration. Regardless of total pressure, seedlings grown at 2 millimoles O2 per liter had higher state 3 respiration rates and decreased percentages of alternative respiration compared to ambient (8.4 millimoles O2 per liter) controls. In contrast, seedling growth responded to total pressure but not to O2 concentration. Seedlings were significantly larger when grown under low pressure. While low O2 (2 millimoles O2 per liter) diminished growth at ambient pressure, growth at low pressure in the same oxygen concentration was enhanced. Respiratory development and growth of mungbean seedlings under low pressure is unimpaired whether oxygen or air is used as the chamber gas, and further, low pressure can improve growth under conditions of poor aeration.

Atmosphere Exposure Chambers↗
PubMed1990

Control of Seed Respiration and Growth in Vicia faba by Oxygen and Temperature: No Evidence for an Oxygen Diffusion Barrier.

The rate of dry matter accumulation by seeds of Vicia faba L. cv. Minica increases with temperature in the range of 16 to 26 degrees C. The duration of dry matter accumulation decreases with temperature, resulting in a decrease of final seed dry weight. In this study we test the hypothesis that a diffusion barrier for O(2), located in the seed coat, inhibits seed respiration and growth. The rate of O(2) uptake of intact seeds and of excised embryos and seed coats (separated seeds) was measured in air and buffer at 16, 20, and/or 26 degrees C at various O(2) concentrations and developmental stages. Oxygen uptake rates of intact seeds in buffer were only 9 to 15% of those in air. In buffer, the respiration rate of intact seeds decreased at a pO(2) below air saturation (21 kilopascals), whereas separated seeds showed a decline of O(2) uptake only below 80% of air saturation. In air, embryo excision had no effect on the sensitivity of seed respiration to pO(2), at both 20 and 26 degrees C. In air at 20 degrees C, separated and intact seeds showed similar rates of O(2) uptake. Oxygen uptake by intact seeds, both halfway and beyond the linear growth phase, showed a temperature coefficient Q(10) of 2.3 and was insensitive to pO(2) in the range of 80 to 100% of ambient. These results indicate that V. faba seed respiration in air is not limited by the diffusion of O(2) into the seed.

Journal Article↗
PubMed1991

Measurement of legume nodule respiration and o(2) permeability by noninvasive spectrophotometry of leghemoglobin.

Physiological regulation of nodule gas permeability has a central role in the response of legumes to such diverse factors as drought, defoliation, and soil nitrate. A new method for quantifying nodule respiration and O(2) permeability, based on noninvasive spectrophotometry of leghemoglobin, was evaluated using intact, attached nodules of Lotus corniculatus. First, the relationship between nodule respiration (O(2) consumption) rate and internal O(2) concentration was determined from the rate of decrease in fractional oxygenation of leghemoglobin (FOL) under N(2). The rate of increase of FOL under 100% O(2) was then used to calculate nodule O(2) permeability, after correcting for respiration. Inactivation of nitrogenase by exposure to 100% O(2) for 15 minutes led to decreases in both permeability and O(2)-saturated respiration (V(max)), but the brief (<15 seconds) exposures to 100% O(2) required by the assay itself had little effect on either parameter. A gradual increase in external O(2) concentration from 20 to 40% resulted in a reversible decrease in permeability, but no change in V(max). The new method is likely to be useful for research on nodule physiology and might also be applicable to agronomic research and crop improvement programs.

Journal Article↗
PubMed1992

Leaf Photosynthesis and Respiration of High CO(2)-Grown Tobacco Plants Selected for Survival under CO(2) Compensation Point Conditions.

Four self-pollinated, doubled-haploid tobacco, (Nicotiana tabacum L.) lines (SP422, SP432, SP435, and SP451), selected as haploids by survival in a low CO(2) atmosphere, and the parental cv Wisconsin-38 were grown from seed in a growth room kept at high CO(2) levels (600-700 parts per million). The selected plants were much larger (especially SP422, SP432, and SP451) than Wisconsin-38 nine weeks after planting. The specific leaf dry weight and the carbon (but not nitrogen and sulfur) content per unit area were also higher in the selected plants. However, the chlorophyll, carotenoid, and alkaloid contents and the chlorophyll a/b ratio varied little. The net CO(2) assimilation rate per unit area measured in the growth room at high CO(2) was not higher in the selected plants. The CO(2) assimilation rate versus intercellular CO(2) curve and the CO(2) compensation point showed no substantial differences among the different lines, even though these plants were selected for survival under CO(2) compensation point conditions. Adult leaf respiration rates were similar when expressed per unit area but were lower in the selected lines when expressed per unit dry weight. Leaf respiration rates were negatively correlated with specific leaf dry weight and with the carbon content per unit area and were positively correlated with nitrogen and sulfur content of the dry matter. The alternative pathway was not involved in respiration in the dark in these leaves. The better carbon economy of tobacco lines selected for low CO(2) survival was not apparently related to an improvement of photosynthesis rate but could be related, at least partially, to a significantly reduced respiration (mainly cytochrome pathway) rate per unit carbon.

Journal Article↗
PubMed2002

A novel method for the detection of apnea and hypopnea events in respiration signals.

The monitoring of breathing dynamics is an essential diagnostic tool in various clinical environments, such as sleep diagnostics, intensive care and neonatal monitoring. This paper introduces an innovative signal classification method that is capable of on-line detection of the presence or absence of normal breathing. Four different artificial neural networks are presented for the recognition of three different patterns in the respiration signals (normal breathing, hypopnea, and apnea). Two networks process the normalized respiration signals directly, while another two use sophisticatedly preprocessed signals. The development of the networks was based on training sets from the polysomnographic records of nine different patients. The detection performance of the networks was tested and compared by using up to 8000 untrained breathing patterns from 16 different patients. The networks which classified the preprocessed respiration signals produced an average detection performance of over 90%. In the light of the moderate computational power used, the presented method is not only viable in clinical polysomnographs and respiration monitors, but also in portable devices.

Algorithms↗
PubMed1985

The relationship between glycolysis, mitochondrial respiration, protein-carboxyl methylation and motility in hamster epididymal spermatozoa.

Endogenous protein-carboxyl methylase activity can be measured in intact motile spermatozoa by using [3H]methionine as a precursor of the methyl donor, S-adenosylmethionine (SAM). Since the conversion of methionine to SAM requires ATP, the relationship between the energy metabolism of spermatozoa and methylation was investigated using inhibitors of glycolysis and mitochondrial respiration. When hamster spermatozoa from cauda epididymides were incubated in 12.2 mM glucose, glycolysis was progressively inhibited as concentrations of 2-deoxyglucose (2-DOG) increased. On the other hand, endogenous protein-carboxyl methylation showed a biphasic response being stimulated at low concentrations of 2-DOG and inhibited at higher concentrations. Sperm movement was also altered by 2-Dog. Increasing concentrations of 2-DOG in the incubation medium resulted in an increase in beat amplitude and a corresponding decrease in beat frequency. When the glucose concentration of the medium was reduced to 5 mM, protein methylation was inhibited at all concentrations of 2-DOG. The biphasic effect of 2-DOG on methylation at 12.2 mM and its monophasic effect at 5 mM suggested that this reaction was related to the effective glucose concentration. To investigate this possibility, endogenous protein-carboxyl methylation was measured after incubation of sperm in glucose concentrations ranging from 0-48.8 mM. Low glucose concentrations stimulated protein methylation (up to 6.1 mM for maximal effect), but further increases in the glucose concentration (10-48.8 mM) suppressed the rate of protein methylation to that observed in the absence of glucose. 2-Deoxyglucose decreased conversion of pyruvate to CO2 consistent with diminished mitochondrial respiration. The inhibition of mitochondrial respiration by antimycin A also inhibited endogenous methylation and motility. The results of these studies suggest that maximal endogenous protein-carboxyl methylation in intact spermatozoa from hamster epididymides depends upon active glycolysis as well as mitochondrial respiration.

Animals↗