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PubMed2006

Powered, air-purifying particulate respirator filter penetration by a DOP aerosol.

In 1995, new certification requirements for all nonpowered, air-purifying particulate filter respirators were put in place when 42 CFR 84 replaced 30 CFR 11. However, the certification requirements for all other classes of respirators, including powered air-purifying respirators (PAPRs), were transferred to 42 CFR 84 from 30 CFR 11 without major changes. Since the inception of 42 CFR 84, researchers have learned that the efficiency of electrostatic filter media, in contrast with mechanical filter media, can be rapidly degraded by oil aerosols. Further, confusion may exist among respirator users, since electrostatic PAPR filters have the same magenta color assigned to high-efficiency filters for nonpowered particulate respirators that have been tested and certified for use against oil aerosols (i.e., P100 filters). Users may expect that the magenta color of certified PAPR filters indicates suitability for use against oil aerosols. This may not be the case. To illustrate the potential degradation of electrostatic PAPR filters, new filters certified under 42 CFR 84 were tested using a TSI model 8122 Automated Respirator Tester against charged and neutralized DOP aerosols with intermittent loading schedules. The performance of a magenta-colored electrostatic PAPR filter--one for which the manufacturer's user instructions appropriately indicates is not suitable for use in oily environments--was compared with the performance of several mechanical PAPR filters. In tests against both DOP aerosols, the electrostatic PAPR filter showed a significant decrease in performance at DOP loadings exceeding 400 mg, whereas mechanical filters showed no significant change in the performance except at extremely high loadings. The decreased performance of the electrostatic PAPR filter was found to be significantly greater when tested against a neutralized DOP aerosol when compared with a charged DOP aerosol. While laboratory tests show that the filtration efficiency of this electrostatic PAPR filter degrades with exposure to DOP aerosol, the observed laboratory degradation may or may not affect workplace performance, as similar degradation has not been verified in workplace studies. Based on these laboratory results, a proposed method for evaluating high-efficiency PAPR filters is presented. This proposed method would ensure that high-efficiency PAPR filters (> or = 99.97% efficient and magenta in color) meet critical performance criteria when loaded.

Aerosols↗
PubMed1969

Effects of division-synchronizing hypoxic and hyperthermic shocks upon Tetrahymena, a respiration and intracellular ATP concentration.

The division of Tetrahymena pyriformis GL cells was synchronized with either seven hypoxic or five hyperthermic (heat) shocks. Hyperthermic shocks of 34 degrees C produced no reduction in respiration rate and only a 19% decline in intracellular ATP concentration. Hypoxic shocks of 0.15% ambient oxygen concentration depressed intracellular ATP concentration 50%. It therefore appears that hypoxic shock, but not hyperthermic shock, reverses progress of Tetrahymena toward fission by reducing ATP concentration through a reduction of the rate of oxidative phosphorylation. After the first synchronized division, whether synchronized by intermittent hypoxia or hyperthermia, total respiration rate increased exponentially at the same rate of increase as total respiration rate in an exponentially growing (log phase) Tetrahymena cell culture. Before the first synchronized division, the total respiration rate increased exponentially but more slowly than after completion of the first synchronized division. The pattern of increase of total respiration during division synchronized by either procedure was different than the pattern of increase of total respiration of synchronous cells observed by Zeuthen.

Adenosine Triphosphate↗
PubMed1955

Silicon metabolism in diatoms. III. Respiration and silicon uptake in Navicula pelliculosa.

1. Evidence is presented that silicon uptake in the diatom Navicula pelliculosa is linked with aerobic respiration. 2. Cyanide, fluoride, iodoacetate, arsenite, azide, and fluoroacetate, at concentrations inhibitory to respiration, were also inhibitory to silicon uptake. 3. 2,4-Dinitrophenol (1 to 2 x 10(-5)M) stimulated respiration by 100 per cent, but almost completely inhibited silicon uptake. 4. The respiratory quotient of non-Si-deficient cells decreased from 0.93 to 0.75 after 4 days of starvation in darkness. Glucose (1 per cent) raised the respiratory quotient of such starved cells to 1.05. 5. Silicate (20 mg. Si/liter) stimulated respiration of unstarved Si-deficient cells by about 40 per cent. The effect of silicate on the respiration of Si-deficient cells which had been starved in darkness for 4 days was less marked. 6. The respiratory quotient of Si-deficient cells decreased from 0.8-0.9 to 0.3 after 4 days of starvation in darkness. The addition of silicate to starved cells raised the quotient to 0.5. This represented a 25 per cent stimulation of oxygen uptake concomitant with a 90 per cent stimulation of carbon dioxide evolution. 7. Glucose (1 per cent) caused an increase of respiratory quotient in starved cells from 0.3 to 0.7-0.8. The addition of silicate had no effect on the R.Q. during the oxidation of exogenous glucose. 8. Substrates (glucose, fructose, galactose, lactate, succinate, citrate, glycerol), which caused a stimulation of respiration in starved cells, also stimulated silicon uptake by those cells. However, the stimulation of silicon uptake (50 to 100 per cent) was not proportional to the respiratory stimulation by these substrates (30 to 300 per cent).

Diatoms↗
PubMed1996

The effect of respirator training on the ability of healthcare workers to pass a qualitative fit test.

OBJECTIVES: To determine the effect of different methods of training on the ability of hospital workers to wear respirators and pass a qualitative fit test, and to compare the direct cost of the training. DESIGN: 179 hospital employees were recruited for study and were stratified into three groups based on the type of training they received in the use of respirators. Employees in Group A received one-on-one training by the hospital's industrial hygienist and were fit tested as part of this training. Employees in Group B received classroom instruction and demonstration by infection control nurses in the proper use of respirators, but were not fit tested as part of training. Employees in Group C received no formal training. Each participant in our study underwent a subsequent qualitative fit test using irritant smoke to check for the employee's ability to adjust correctly the fit and seal of the respirator. The direct cost of each method of training was determined by accounting for the cost of trainers and the cost of employee-hours lost during training. SETTING: 775-bed Veterans' Affairs hospital. RESULTS: 94% of Group A participants (49 of 52) passed the qualitative fit test, compared to 91% of Group B participants (58 of 64) and 79% of Group C participants (50 of 63; P = .036, 2 x 3 chi-square). Group A had a significantly higher pass rate than Group C (P = .043), but Group B did not differ significantly from Group A or Group C. Location or professional status did not affect pass rate, but prior experience wearing respirators did. When the study groups were compared after stratifying for prior experience, we found no difference in pass rates, except when Groups A and B (those with any training) were combined and compared with Group C (107 of 116 versus 50 of 63, P = .05, Mantel-Haenszel chi-square). We estimate that the method of training involving individual instruction followed by fit testing took 20 minutes per employee to complete, compared to 10 minutes per six employee class for the method of classroom demonstration. The difference in direct cost between the two methods, applied to the training of 1,200 employees at our hospital, would be approximately $19,000 per year. CONCLUSION: Our study indicates that training in the proper use of respirators is important, but the method of training may not be, as the two methods we evaluated were nearly equivalent in their pass rates on fit testing (94% versus 91%). Fit testing as part of training may have enhanced the performance of our participants marginally, but was more time consuming and accounted for most of the excess cost.

Chi-Square Distribution↗
PubMed2002

Examining the role of mitochondrial respiration in vanilloid-induced apoptosis.

BACKGROUND: The vanilloids capsaicin and resiniferatoxin are natural products that contain a vanillyl moiety (4-hydroxy-3-methoxybenzyl). Both vanilloids can induce apoptosis in certain cell types by a mechanism that has not been fully elucidated but may involve plasma membrane or mitochondrial targets. We investigated the role of mitochondrial respiration in vanilloid-induced apoptosis. METHODS: Cytofluorometric analysis was used to evaluate the effects of vanilloids on apoptosis, Ca(2+) mobilization, hydroperoxide generation, and DNA content in cells from two human cutaneous squamous cell carcinoma (SCC) cell lines (parental cells) and in their respiration-deficient clones. Oxygen consumption by the cells was determined polarographically. RESULTS: The majority of the parental SCC cells underwent apoptosis after a 12-hour exposure to 100 micro M capsaicin or 10 micro M resiniferatoxin. The induction of apoptosis was associated with the mitochondrial permeability transition (i.e., an increase in the permeability of the inner mitochondrial membrane associated with the opening of a nonspecific pore). Exposure of parental cells to either vanilloid was not associated with an increase in intracellular free Ca(2+) levels but was associated with a rapid increase in hydroperoxide generation and a decrease in oxygen consumption. After vanilloid treatment, the respiration-deficient clones generated less hydroperoxide and were resistant to the mitochondrial permeability transition and the induction of apoptosis. Moreover, vanilloid treatment inhibited cell proliferation in the respiration-deficient clones by promoting G(1) arrest. CONCLUSIONS: Vanilloid-induced apoptosis in the parental SCC cells appears to involve the inhibition of mitochondrial respiration. The apoptogenic effects promoted by vanilloid treatment in parental SCC cells, as well as the antiproliferative effects observed in their respiration-deficient clones, suggest that vanilloids may be useful for preventing or treating skin cancers or other hyperproliferative skin disorders.

Apoptosis↗
PubMed1994

Carbohydrate requirements for dark respiration by peach vegetative organs.

The specific respiration rate at 20 degrees C (R(20)) of peach leaves and stems declined rapidly from a high value in the early spring (22.5 nmol CO(2) g(dw) (-1) s(-1)) to relatively constant rates by July (3.1 nmol CO(2) g(dw) (-1) s(-1)). Leaf R(20) declined more rapidly than current-year stem R(20), but leaf and current-year stem R(20)s were similar by July. The R(20) of current-year stems in July was approximately 2.5 times greater than that of one-year-old stems (1.3 nmol CO(2) g(dw) (-1) s(-1)), and about 30 times greater than that of the trunk R(20) (0.1 nmol CO(2) g(dw) (-1) s(-1)). The Q(10)s of leaves and stems were approximately 2 for a temperature increase between 20 and 30. The Q(10)s above 30 were 2.03 for leaves but only 1.61 for stems. Leaves and current-year stems accounted for 2 and 17% of the aboveground vegetative biomass in April and August, respectively, but accounted for 59-80% of total daily (24 h) respiration. Although trunk biomass accounted for 91 and 77% of aboveground vegetative biomass, in April and August, respectively, trunk respiration accounted for only 8-15% of daily aboveground respiration. Before harvest, during a period when fruit growth was source-limited, daily fruit respiration exceeded respiration by all aboveground vegetative organs.

Journal Article↗
PubMed1999

Fine root respiration in mature eastern white pine (Pinus strobus) in situ: the importance of CO(2) in controlled environments.

We measured seasonal fine root respiration rate in situ while controlling chamber temperature and [CO(2)]. Atmospheric [CO(2)] ([CO(2)](a)) and measured soil [CO(2)] ([CO(2)](s)) were alternately delivered to a cuvette containing intact fine roots of eastern white pine (Pinus strobus L.). Respiration rates were consistently higher in [CO(2)](a) than in [CO(2)](s) and were almost three times higher during midsummer. Respiration rates were immediately reversed after returning to the alternate [CO(2)] (i.e., [CO(2)](a) --> [CO(2)](s) --> [CO(2)](a), and vice versa) suggesting a direct effect of elevated [CO(2)] on apparent respiration. Soil-[CO(2)]-based respiration rates decreased with increasing [CO(2)] on a dry mass and tissue [N] basis. We conclude that estimates of soil CO(2) flux and soil carbon budgets may be improved by more completely accounting for the rhizosphere microclimate (i.e., soil temperature and [CO(2)](s)) during measurement of fine root respiration.

Journal Article↗
PubMed2000

Direct effect of elevated CO(2) on nocturnal in situ leaf respiration in nine temperate deciduous tree species is small.

Direct (i.e., short-term) effects of elevated CO(2) on nocturnal in situ leaf respiration rate were measured in nine deciduous tree species (seven genera) in 20 3.5-4.0-h experiments. During the experiments, CO(2) concentration was alternated between 400 and 800 ppm (approximately 40 and 80 Pa of CO(2)). Data analysis accounted for effects on respiration rate of the normal decline in temperature with time after sunset. The median response to a 40-Pa increase in CO(2) was a 1.5% decrease in respiration rate, with responses ranging from a 5.6% inhibition to a 0.4% stimulation. Direct effects of elevated CO(2) on respiration were similar among the species. Thus, the response of nocturnal leaf respiration rate to a short-term CO(2) increase was small, and of little practical importance to the accuracy of measurements of respiration involving similar changes in CO(2) concentration during measurement. These direct respiratory responses of leaves to elevated CO(2) would translate into only slight, if any, effects on the carbon balance of temperate deciduous forests in a future atmosphere containing as much as 80 Pa CO(2).

Journal Article↗
PubMed2006

Influences of canopy photosynthesis and summer rain pulses on root dynamics and soil respiration in a young ponderosa pine forest.

Our first objective was to link the seasonality of fine root dynamics with soil respiration in a ponderosa pine (Pinus ponderosa P. & C. Lawson) plantation located in the Sierra Nevada of California. The second objective was to examine how canopy photosynthesis influences fine root initiation, growth and mortality in this ecosystem. We compared CO2 flux measurements with aboveground and belowground root dynamics. Initiation of fine root growth coincided with tree stem thickening and shoot elongation, preceding new needle growth. In the spring, root, shoot and stem growth occurred simultaneously with the increase in canopy photosynthesis. Compared with the other tree components, initial growth rate of fine roots was the highest and their growing period was the shortest. Both above and belowground components completed 90% of their growth by the end of July and the growing season lasted approximately 80 days. The period for optimal growth is short at the study site because of low soil temperatures during winter and low soil water content during summer. High photosynthetic rates were observed following unusual late-summer rains, but tree growth did not resume. The autotrophic contribution to soil respiration was 49% over the whole season, with daily contributions ranging between 18 and 87%. Increases in soil and ecosystem respiration were observed during spring growth; however, the largest variation in soil respiration occurred during summer rain events when no growth was observed. Both the magnitude and persistence of the soil respiration pulses were positively correlated with the amount of rain. These pulses accounted for 16.5% of soil respiration between Days 130 and 329.

Carbon Dioxide↗
PubMed1995

Acinar cell respiration in experimental acute pancreatitis.

The early pathogenetic steps that finally lead to acinar cell necrosis in acute pancreatitis have been characterized only scarcely as yet. Among a lot of hypotheses, one concept favors disturbances of cellular energy metabolism as a major factor that contributes to preterm cell decline. To investigate, whether an experimental acute pancreatitis alters cell respiration, the respiratory capacities of acinar cells isolated from rats with acute pancreatitis were measured. Acute pancreatitis was induced using Popper's model, i.e., a combination of duct obstruction, secretory stimulation, and mesenteric short-term ischemia with subsequent reperfusion. Acinar cells were isolated using a collagenase digestion technique. The respiratory rates of the isolated cells in suspension were measured at 37 degrees C in 100% oxygen-saturated N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid-buffered Eagle's-minimal essential medium. Resting respiration of the acinar cells uniformly amounted to about 60 pmol of O2/s x 10(6) cells in both the control and the pancreatitis group. Cellular respiration could significantly be stimulated by stepwise uncoupling of oxidative phosphorylation by means of 2,4-dinitrophenol in all cell suspensions investigated. The maximum rate of stimulated respiration was diminished in the cells isolated from rats with acute pancreatitis as compared with the controls (79.3 +/- 5.0 vs. 160.2 +/- 15.5 pmol of O2/s x 10(6) cells, p < .05), however. This reduced respiratory load capacity of the acinar cells in acute pancreatitis reflects the restricted ability of the cells to increase respiration on enhanced cellular demand. Since mitochondrial respiration is coupled to oxidative phosphorylation, an altered energy-transforming potential of the acinar cells in acute pancreatitis becomes evident.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed2000

Risk-based selection of respirators against infectious aerosols: application to anthrax spores.

This article presents two methods for estimating infection risk among individuals wearing air-purifying respirators against airborne pathogens, with the overall aim of selecting appropriate respiratory protection. Necessary data inputs are the parameters for the ambient pathogen concentration distribution, the respirator penetration distribution, and the infectious dose distribution, along with the breathing rate, duration of a respirator use period, and the number of use periods. The first method assumes that the pathogen does not exhibit a cumulative dose effect, whereas the second accounts for a cumulative dose effect. The methods are illustrated with hypothetical scenarios involving Bacillus anthracis (anthrax) spores. Available data suggest that anthrax spores would exhibit a cumulative dose effect for multiple exposures occurring close in time, as would likely affect personnel responding to a bioterrorist release. The analysis shows that failure to account for a cumulative dose effect when present leads to underestimating infection risk. Three types of air-purifying respirators are compared for their predicted efficacy in reducing the risk of inhalation anthrax. Although uncertainty analyses are not performed, a general conclusion is that a full-facepiece powered air-purifying respirator would be the best air-purifying device for responding to an anthrax spore release. Because such respirators would not prevent all personnel from inhaling an infectious dose, it would be advisable for users not previously vaccinated against anthrax to receive post-exposure prophylactic therapy.

Adult↗
PubMed2002

Respirable antisense oligonucleotides: a new, third drug class targeting respiratory disease.

PURPOSE OF REVIEW: To describe the potential of a new class of respiratory drugs, respirable antisense oligonucleotides. RECENT FINDINGS: The first respirable antisense oligonucleotide, EPI-2010, has now reached clinical trials. It has shown intriguing initial indications of efficacy and the potential to be the first once-per-week asthma preventative. Respirable antisense oligonucleotides are capable of addressing targets that have proven to be intractable to traditional 'small molecule' approaches, and against which newer monoclonal antibody strategies may also not be optimal. Respirable antisense oligonucleotides functionally, but not genetically, ablate gene expression by blocking the template function of target respiratory messenger RNAs by as yet incompletely defined mechanisms. They do so with an avidity and specificity which can be several orders of magnitude greater than those shown by small molecule antagonists for their protein targets. The target properties of respiratory messenger RNAs are strikingly different from those of respiratory proteins, enabling respirable antisense oligonucleotides to offer the potential of longer duration of effect, increased specificity of effect, and lack of systemic side effects compared with either traditional small molecule protein antagonists or monoclonal antibodies. SUMMARY: Respirable antisense oligonucleotides represent a new, third class of respiratory drugs with the potential to extend the range of therapeutic responses to otherwise intractable respiratory targets, and to address precedented targets with the possibility of improving on such features as safety and durability of response.

Administration, Inhalation↗
PubMed1992

A Comparison of Dark Respiration between C(3) and C(4) Plants.

Lower respiratory costs were hypothesized as providing an additional benefit in C(4) plants compared to C(3) plants due to less investment in proteins in C(4) leaves. Therefore, photosynthesis and dark respiration of mature leaves were compared between a number of C(4) and C(3) species. Although photosynthetic rates were generally greater in C(4) when compared to C(3) species, no differences were found in dark respiration rates of individual leaves at either the beginning or after 16 h of the dark period. The effects of nitrogen on photosynthesis and respiration of individual leaves and whole plants were also investigated in two species that occupy similar habitats, Amaranthus retroflexus (C(4)) and Chenopodium album (C(3)). For mature leaves of both species, there was no relationship between leaf nitrogen and leaf respiration, with leaves of both species exhibiting a similar rate of decline after 16 h of darkness. In contrast, leaf photosynthesis increased with increasing leaf nitrogen in both species, with the C(4) species displaying a greater photosynthetic response to leaf nitrogen. For whole plants of both species grown at different nitrogen levels, there was a clear linear relationship between net CO(2) uptake and CO(2) efflux in the dark. The dependence of nightly CO(2) efflux on CO(2) uptake was similar for both species, although the response of CO(2) uptake to leaf nitrogen was much steeper in the C(4) species, Amaranthus retroflexus. Rates of growth and maintenance respiration by whole plants of both species were similar, with both species displaying higher rates at higher leaf nitrogen. There were no significant differences in leaf or whole plant maintenance respiration between species at any temperature between 18 and 42 degrees C. The data suggest no obvious differences in respiratory costs in C(4) and C(3) plants.

Journal Article↗
PubMed1994

Comparison of Methods to Estimate Dark Respiration in the Light in Leaves of Two Woody Species.

Dark respiration in the light was estimated in leaves of two woody species (Heteromeles arbutifolia Ait. and Lepechinia fragans Greene) using two different approaches based on gas-exchange techniques: the Kok method and the Laisk method. In all cases, dark respiration in the light was lower (P < 0.05) than respiration in darkness, indicating that dark respiration was inhibited in the light. Rates of dark respiration in the light estimated by the Laisk method were 52% higher (P < 0.05) than those estimated by the Kok method. Differences between the methods could be explained by the low ambient CO2 concentrations required by the Laisk approach. The mean value of the inhibition of respiration by light for the two species, corrected for the ambient CO2 concentration effect, was 55%. Despite the differences in leaf characteristics between the species, values of the CO2 photocompensation point, at which the rate of photosynthetic CO2 uptake equaled that of photorespiratory CO2 evolution, were very constant, suggesting an excellent consistency in the results obtained with the Laisk approach.

Journal Article↗
PubMed1970

Effect of adenine nucleotides on the respiration of carrot root slices.

Sodium pyruvate and dinitrophenol stimulated O(2) uptake of freshly cut phloem parenchyma from carrot roots by 63 and 120% at optimal concentrations, indicating that production of pyruvate by glycolysis regulates over-all respiratory rate. Adding 0.5 to 6.7 mm Na(3)ADP and Na(3)ATP to slices rapidly stimulates respiration rate by 20 to 85%. The effect is greater at the lower end of this concentration range and is not due to change in pH or active cation uptake. It is suggested that treating tissue with both nucleotides stimulates pyruvate kinase, the rate-limiting step in respiration of freshly cut slices, by increasing the concentration of endogenous ADP. Adenosine diphosphate continued to stimulate O(2) uptake until the peak of induced respiration, but ATP inhibited respiration during development and decline of this peak. Absence of respiratory stimulation by NaH(2)PO(4) and of respiratory inhibition by added nucleosides confirms that inorganic phosphate is not a limiting factor of respiration in freshly cut slices. The stimulation of respiration rate of these slices by dinitrophenol is consistent with results from experiments in which ADP and ATP were applied to the tissue.

Adenine Nucleotides↗
PubMed1971

The Rate of Photorespiration during Photosynthesis and the Relationship of the Substrate of Light Respiration to the Products of Photosynthesis in Sunflower Leaves.

Single attached leaves of sunflower (Helianthus annus L. "Mennonite") were supplied (14)CO(2) of constant specific radioactivity in gas mixtures containing various CO(2) and O(2) concentrations. The (14)CO(2) and CO(2) fluxes were measured concurrently in an open system using an ionization chamber and infrared gas analyzer.The rate of photorespiration (5.7 +/- 0.3 mg CO(2).dm(-2).(-1)) during photosynthesis in 21% O(2) at 25 C and 3,500 footcandles was over three times the rate of dark respiration and was independent of CO(2) concentrations from 0 to 300 mul/l. The steady rate of CO(2) evolution into CO(2)-free air was about 30% lower. Low oxygen (1%) inhibited both (14)CO(2) and CO(2) evolution, both during photosynthesis and in CO(2)-free air in the light.At 300 mul/l CO(2) apparent photosynthesis was inhibited 41% by 21% O(2). Two-thirds of the inhibition was due to the inhibition of true photosynthesis by oxygen and one-third due to the stimulation of photorespiration. At 50 mul/l CO(2), where the percentage inhibition of apparent photosynthesis by 21% oxygen was 92%, photorespiration accounted for two-thirds of the total inhibition.The rate of (14)CO(2) uptake by the leaf decreased about 30 seconds after the introduction of (14)CO(2), indicating that (14)CO(2) was rapidly evolved from the leaf. The rate of (14)CO(2) evolution increased rapidly with time, the kinetics depending on the CO(2) concentration. The high specific radioactivity of the (14)CO(2) evolved during photosynthesis or in the early period of flushing in CO(2)-free air showed that the substrate for light respiration was an early product of photosynthesis. From the measurement of (14)CO(2) and CO(2) evolution into CO(2)-free air over a longer time period it was apparent that at least three compounds, each of decreased (14)C content, could supply the substrate for light respiration.Based on a consideration of the specific radioactivity of (14)CO(2) evolved under a variety of conditions, it is suggested that total CO(2) evolution in the light or photorespiration is composed of two processes, dark respiration and light respiration. Light respiration is a process that only occurs in the light, persists for some time on darkening, and metabolizes substrates that are quite different from those of dark respiration.

Journal Article↗
PubMed1972

Postillumination respiration of maize in relation to oxygen concentration and glycolic Acid metabolism.

Prior illumination in CO(2)-free air enhances a respiration from maize (Zea mays L.) leaves different in onset and duration from the postillumination burst of photorespiration. The course of respiration after brief illumination of attached leaves was measured as CO(2) efflux in darkness into CO(2)-free atmospheres with four O(2) concentrations. The peak of CO(2) efflux following illumination was suppressed by 2.23% O(2), was completely eliminated by 0.04% O(2), and was not stimulated by 40% O(2) compared with air. Compared with air, steady dark respiration was suppressed by 0.04% O(2) but was not affected by 2.23% nor 40% O(2). Excision and subsequent uptake of distilled water through the vascular system nearly eliminated the enhanced respiration.Several metabolites fed to excised leaves through the vascular system during illumination doubled or tripled the respiration of maize in darkness. The sensitivity to 2.23% O(2) of the respiration of glycolic acid in the dark imitated the sensitivity to O(2) of attached leaves.The respiration of glycolic acid was inhibited by alpha-hydroxy-2-pyridinemethanesulfonate.While attached leaves and leaves fed glycolic acid both released little CO(2) into CO(2)-free air in bright light, declining illuminance caused a larger and prompter CO(2) efflux from leaves fed glycolic acid than from attached leaves. Leaves fed glycolic acid plus 3-(p-chlorophenyl)-1, 1-dimethyl urea released more CO(2) into CO(2)-free air in bright light than did controls fed glycolic acid.

Journal Article↗
PubMed1976

Effects of Cyanide and Ethylene on the Respiration of Cyanide-sensitive and Cyanide-resistant Plant Tissues.

The effects of cyanide and ethylene, respectively, were studied on the respiration of a fully cyanide-sensitive tissue-the fresh pea, a slightly cyanide-sensitive tissue-the germinating pea seedling, and a cyanide-insensitive tissue-the cherimoya fruit. Cyanide inhibition of both fresh pea and pea seedling respiration was attended by a conventional Pasteur effect where fermentation was enhanced with an accumulation of lactate and ethanol and a change in the level of glycolytic intermediates indicative of the activation of phosphofructokinase and pyruvate kinase accompanied by a sharp decline in ATP level. In these tissues, ethylene had little or no effect on the respiration rate, or on the level of glycolytic intermediates or ATP. By contrast, ethylene as well as cyanide enhanced both respiration and aerobic glycolysis in cherimoya fruits with no buildup of lactate and ethanol and with an increase in the level of ATP. The data support the proposition that for ethylene to stimulate respiration the capacity for cyanide-resistant respiration must be present.

Journal Article↗