Action de quelques phytohormones sur la respiration et ľabsorption du phosphate par des disques de tubercules de pomme de terre en survie

Action of some phytohormones on the respiration and on the absorption of phosphate by aging potato tuber discs. Discs of potato tuber incubated in aerated medium show an increase of the rates of respiration and phosphate absorption with aging time; the rates increase by two and nine respectively during the time period between 5 and 24 h of aging. Adenine or some N-6 substituted adenines [benzylaminopurine (BAP), furfurylaminopurine (FAP), methylaminopurine (MAP)], which present variable degrees of cytokinin activity, partially inhibit the increase of the rate of phosphate absorption and, to a lesser extent, the increase of the rate of respiration. Also abscisic acid (ABA), indole 3-acetic acid (IAA), and gibberellic acid (GA₃) produce inhibition of the increase of the rate of phosphate absorption with varied effects on the respiration. With regard to phosphate uptake, the effects of ABA, 1AA and GA₃ were additive to those of BAP. The effects on respiration were different from the effects on phosphate uptake, so that there is no direct relationship between inhibition of respiration and inhibition of phosphate uptake.     

Continuous cultivation of Saccharomyces cerevisiae. II. Growth on ethanol under transient-state conditions

Growth of Saccharomyces cerevisiae LBG H 1022 on ethanol under transient-state conditions was studied. As a cultivation device, an aerated Chemap fermentor combined with continuously working gas analyzers for oxygen and carbon dioxide was used. Yeast cell dry matter, substrate concentration, specific oxygen uptake, specific carbon dioxide release, and respiration quotient were measured during the different transient states. Depending on which range of the dilution rate the initial steady state was found, we obtain different responses to the shift experiment. For the lower range, up to D = 0.07, we deal with damped oscillations ranging above and below the steady-state values. For the higher specific growth rates, the rate of damping is strongly enhanced and the shape of the curves becomes an asymptotic approach to the final steady states.     

Diurnal variation of root respiration rates and nitrate uptake as influenced by nitrogen supply

Root respiration rates of Lolium multiflorum supplied with nitrate or ammonium were measured continuously during several days (Exp. A). Net uptake rate of nitrate was similarly measured by an ion selective nitrate electrode in a system of flowing nutrient solution (Exp. B). Diurnal variation of in vitro nitrate reductase activity and nitrate content of tops and roots were determined (Exp. C). Two levels of irradiance were applied throughout, with day:night of 16:8 h. Root respiration rates showed diurnal patterns, most pronounced in the nitrate treatment, with two peaks appearing about 6 and 16 h after commencement of the photoperiod. Respiration rates were highest in the nitrate treatment and at high irradiance. Respiration rates fell after removal of nitrogen, particularly in the nitrate supplied plant and at high irradiance. Net uptake rate of nitrate exhibited diurnal patterns, often with two peaks occurring at the same times as those of respiration rates. In vitro nitrate reductase activity of tops increased steeply 16 h after commencement of the photoperiod and remained at the high level during the following 8 h of darkness. Nitrate content of tops was highest during the 8 h dark period and fell at the start of the photoperiod. Possible controlling systems of the apparent coincidences of diurnal variation rates, net nitrate uptake and nitrate reduction are discussed.     

The physiological basis of seed dormancy in Avena fatua VI. Respiration and the stimulation of germination by ethanol

Ethanol induced germination in several partly after-ripened dormant lines of Avena fatua L. The dose-response curves for the stimulation of germination and for oxygen uptake were similar, indicating that ethanol may stimulate germination by promoting oxygen uptake. A time-sequence study showed that ethanol stimulated oxygen uptake by as much as 70% prior to the first visible signs of germination. A similar methanol treatment failed to induce germination or significantly elevate oxygen uptake, indicating that the promotive effects of ethanol are not common to all alcohols. The stimulation of both germination and oxygen uptake by ethanol was not inhibited significantly by salicylhydroxamic acid, an inhibitor of alternative respiration. Thus, stimulation of germination and oxygen uptake by ethanol does not require the operation of the alternative pathway of respiration. Similarly, the stimulation of germination and oxygen uptake by ethanol were not inhibited by sodium azide, an inhibitor of cytochrome-mediated respiration. However, both germination and oxygen uptake were prevented when salicylhydroxamic acid and sodium azide were administered together. Thus, stimulation of these events by ethanol requires only the operation of one or other of these pathways of respiration; a specific requirement for the operation of the alternative pathway of respiration does not exist. The function of ethanol as a promoter of respiration is discussed with reference to dormancy and involvement of the Krebs cycle.     

Restricted oxygen supply and excretion of metabolites

Summary The effect of oxygen supply on the formation of metabolites by Escherichia coli K12, Enterobacter aerogenes and Brevibacterium lactofermentum was studied. The relative respiration rate (i.e. the ratio, in percent, of the respiration rate during the production phase to that at the end of exponential growth phase) was taken as a measure of cell response to oxygen supply to which the production of metabolites was also correlated. Several metabolites were excreted at distinct relative respiration rates: ethanol, hydrogen gas, acetate, butanoate, capronate, malate, succinate, acetoin, 2,3-butanediol, 2-methylpropanoate, 3-methylbutanoate, formate, cis-aconitate and 2-oxoglutarate. At relative respiration rates above 80% the excretion of metabolites ceased and the substrate was completely oxidized.The effects of oxygen and of NADH, respectively, on synthesis and activity of several enzymes involved in the formation of these metabolites are discussed. The efficiency of aeration in a fermentation process can be controlled by means of analysis of excreted metabolites.     

Respiratory energy costs for the maintenance of biomass, for growth and for ion uptake in roots of Carex diandra and Carex acudformis

van der Werf, A., Kooijman, A., Welschen, R. and Lambers, H. 1988. Respiratory energy costs for the maintenance of biomass, for growth and for ion uptake in roots of Carex diandra and Carex acutiformis. - Physiol. Plant. 72: 483–491. The respiratory characteristics of the roots of Carex diandra Schrank and Carex acutiformis Ehrh. were investigated. The aims were, firstly to determine the respiratory energy costs for the maintenance of root biomass, for root growth and for ion uptake, and secondly to explain the higher rate of root respiration and ATP production in C. diandra. The three respiratory energy components were derived from a multiple regression analysis, using the relative growth rate and the net rate of nitrate uptake as independent variables and the rate of ATP production as a dependent variable. Although the rate of root respiration and ATP production was significantly higher in C. diandra than in C. acutiformis, the two species showed no significant difference in their rate of ATP production for the maintenance of biomass, in the respiratory energy coefficient for growth (the amount of ATP production per unit of biomass produced) and the respiratory energy coefficient for ion uptake (amount of ATP production per unit of ions absorbed). It is concluded that the higher rate of root respiration of C. diandra is caused by a higher rate of nitrate uptake. At relatively high rates of growth and nitrate uptake, the contribution of the rate of ATP production for ion uptake to the total rate of ATP production amounted to 38 and 25% for C. diandra and C. acutiformis, respectively. At this growth rate, the respiratory energy production for growth contributed 37 and 50%, respectively, to the total rate of ATP production. The relative contribution of the rate of ATP production for the maintenance of biomass increased from 25 to 70% with increasing plant age for both species. The results suggest that ion uptake is one of the major sinks for respiratory energy in roots. These experimentally derived values for the rate of ATP production for the maintenance of biomass, the respiratory energy coefficient for growth and the respiratory energy coefficient for ion uptake are discussed in relation to other experimentally and theoretically derived values.     

Why do fast- and slow-growing grass species differ so little in their rate of root respiration,considering the large differences in rate of growth and ion uptake?

Herbaceous plants grown with free access to nutrients exhibit inherent differences in maximum relative growth rate (RGR) and rate of nutrient uptake. Measured rates of root respiration are higher in fast-growing species than in slow-growing ones. Fast-growing herbaceous species, however, exhibit lower rates of respiration than would be expected from their high rates of growth and nitrate uptake. We investigated why the difference in root O₂ uptake between fast- and slow-growing species is relatively small. Inhibition of respiration by the build-up of CO₂ in closed cuvettes, diurnal variation in respiration rates or an increasing ratio of respiratory CO₂ release to O₂ uptake (RQ) with increasing RGR failed to explain the relatively low root respiration rates in fast-growing grasses. Furthermore, differences in alternative pathway activity can at most only partly explain why the difference in root respiration between fast- and slow-growing grasses is relatively small. Although specific respiratory costs for maintenance of biomass are slightly higher in the fast-growing Dactylis glomerata L. than those in the slow-growing Festuca ovina L., they account for 50% of total root respiration in both species. The specific respiratory costs for ion uptake in the fast-growing grass are one-third of those in the slow-growing grass [0·41 versus 1·22 mol O₂ mol (NO₃^–)^–1]. We conclude that this is the major cause of the relatively low rates of root respiration in fast-growing grasses.     

Role of Hexose Transport in Control of Glycolytic Flux in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae predominantly ferments glucose to ethanol at high external glucose concentrations, irrespective of the presence of oxygen. In contrast, at low external glucose concentrations and in the presence of oxygen, as in a glucose-limited chemostat, no ethanol is produced. The importance of the external glucose concentration suggests a central role for the affinity and maximal transport rates of yeast's glucose transporters in the control of ethanol production. Here we present a series of strains producing functional chimeras between the hexose transporters Hxt1 and Hxt7, each of which has distinct glucose transport characteristics. The strains display a range of decreasing glycolytic rates resulting in a proportional decrease in ethanol production. Using these strains, we show for the first time that at high glucose levels, the glucose uptake capacity of wild-type S. cerevisiae does not control glycolytic flux during exponential batch growth. In contrast, our chimeric Hxt transporters control the rate of glycolysis to a high degree. Strains whose glucose uptake is mediated by these chimeric transporters will undoubtedly provide a powerful tool with which to examine in detail the mechanism underlying the switch between fermentation and respiration in S. cerevisiae and will provide new tools for the control of industrial fermentations.     

Kinetics of phenol oxidation by Candida tropicalis: effects of oxygen supply rate and nutrients on phenol inhibition

The kinetics of phenol degradation was estimated in a fed-batch reactor system. Effects of oxygen and nutrient excess or limitation as well as the presence of several essential ions on the phenol- and oxygen-specific uptake rates achieved simultaneously in a bioreactor were shown.Candida tropicalis was grown on phenol as the only carbon and energy source. Applying the best fit of polynomial function, the maximum specific uptake rates of phenol and oxygen, the critical concentrations of phenol, the half-saturation constants and inhibition constants were determined. Linear relationship between specific phenol uptake rate and the exogenous respiration rate was found regardless of the kind and presence of essential nutrients. At oxygen limitation both the phenol uptake rate and the cell affinity to phenol decreased more strongly compared with those under nutrient limitation. Oxygen in excess resulted in a significant increase of cell tolerance toward phenol. The presence of essential nutrients increased the specific phenol degradation rate and led to complete phenol oxidation.     

STUDIES OF CARBON AND NITROGEN METABOLISM BY THREE MARINE PHYTOPLANKTON SPECIES IN NITRATE-LIMITED CONTINUOUS CULTURE1,2

Characteristics of carbon production, excretion and dark respiration, and nitrate uptake kinetics were studied using continuous culture techniques for Thalassiosira allenii Takano, Monorhrysis lutheri Droop and Dunaliella tertiolccta Butcher. Fur T. allenii. the ratio of dark C loss to daytime net C production varied between 0.1 and 0.2 over a growth rate range from ca. 0.005 to 0.06 h^-1. For M. lutheri and D. tertiolecta. this same ratio varied belween 0.2 and 0.3 between growth rates of ca. 0.005 and 0.025 h^-1, but declined at higher growth rates when the dark nitrate uptake capacity of the cells was exceeded by the pumping rate. Carbon excretion rates averaged less than 1.5% of daytime net C production rates. Productivity indices showed little correlation with growth rate, due to the significant poisitive correlation between chl a:C ratios and growth rate. Chlorophyll a:C ratios for T. allenii were less than 0.01 al growth rates less than 0.03 h^-1, and appoached zero at zero growth rate. Dark nitrate maximum uptake rates for M. lutheri, D. tertiolecta and T. allenii averaged 23, 64 and 120%, respectively, of light nitrate maximum uptake rates. Excretion of nitrite was observed during most nitrate uptake experiments. This excretion reduced net uptake of nitrate spikes in the dark for M. lutheri and D. tertiolecta by 79 and 23%, respectively.     

Does excess dietary carbon affect respiration of <Emphasis Type="Italic">Daphnia</Emphasis>?

Like many invertebrate herbivores, Daphnia frequently face diets with excess carbon (C) relative to elements like phosphorus (P), and with limited ability to store C-rich compounds. To cope with this relative surplus of C they may either regulate the net uptake of C or dispose of excess assimilated C via increased release of dissolved organic carbon or CO₂. Here we investigate whether juvenile Daphnia magna use respiration as a means of stoichiometrically regulating excess C. Growth rate and respiration were measured under different algal food qualities (P-replete and P-depleted algae). Growth rate was strongly reduced by P-depleted food, implying a stoichiometric disposal of excess ingested C. Respiration rates of feeding animals were measured after short- (0.5 h), medium- (12 h) and long- (five days) term acclimation to P-limited food. The respiration rates of animals during active feeding were not affected by the acclimation period per se, whereas food quality had a significant effect; respiration rates of feeding animals increased slightly in individuals receiving low-P food under all acclimation regimes. Respiration was also measured on nonfeeding and fasting animals that had been acclimated for five days to P-limited food. Respiration rates of these animals were strongly affected by feeding conditions but not by food quality; feeding individuals had higher respiration rates than those deprived of food, which again had higher respiration than fasting animals. Although animals grown on low-P food had strongly reduced growth and thus were expected to have decreased respiration rates due to reduced growth-related costs, this seems to be canceled out by increased stoichiometric respiration under P-deficiency. These results indicate that D. magna partly releases excess C as CO₂, but other means of stoichiometric regulation most likely add to this.     

Rates of oxygen uptake by the planktonic community of a shallow equatorial lake (Lake George,Uganda)

Summary Community respiration rates of the plankton in the upper meter of a shallow equatorial lake (Lake George, Uganda) show diurnal fluctuations within the range 1 to 4.5 mg O₂/mg chlorophyll a · h. In the deeper water, below the euphotic zone, rates show less variation and approximate to a value of 1 mg O₂/mg chl a · h. Comparative field and laboratory measurements of the relationship between community respiration and temperature indicate that the diurnal variation observed is not a simple function of temperature variation. Field measurements suggest that the rate of community respiration tends to increase, in a non-linear manner, as the daily cumulative photosynthesis per unit population increases.A series of laboratory experiments are described which attempt to fractionate, by chemical means, the oxygen uptake due to phytoplankton, bacteria and zooplankton. Although the results were very variable they indicate that somewhere between 10 and 50% of the total oxygen uptake is due non-algal material. The influence of these findings on calculations of net daily photosynthesis is discussed.     

Acclimation of respiration to temperature and CO2 in seedlings of boreal tree species in relation to plant size and relative growth rate

The role of acclimation of dark respiration to temperature and CO₂ concentration and its relationship to growth are critical in determining plant response to predicted global change. We explored temperature acclimation of respiration in seedlings of tree species of the North American boreal forest. Populus tremuloides, Betula papyrifera, Larix laricina, Pinus banksiana, and Picea mariana plants were grown from seed in controlled-environments at current and elevated concentrations of CO₂ (370 and 580 μmol mol^–1) in combination with three temperature treatments of 18/12, 24/18, and 30/24 °C (light/dark period). Specific respiration rates of roots and shoots acclimated to temperature, damping increases in rates across growth-temperature environments compared to short-term temperature responses. Compared at a standard temperature, root and shoot respiration rates were, on average, 40% lower in plants grown at the highest compared to lowest growth temperature. Broad-leaved species had a lower degree of temperature acclimation of respiration than did the conifers. Among species and treatment combinations, rates of respiration were linearly related to size and relative growth rate, and relationships were comparable among growth environments. Specific respiration rates and whole-plant respiratory CO₂ efflux as a proportion of daily net CO₂ uptake increased at higher growth temperatures, but were minimally affected by CO₂ concentration. Whole-plant specific respiration rates were two to three times higher in broad-leaved than coniferous species. However, compared to faster-growing broad-leaved species, slower-growing conifers lost a larger proportion of net daily CO₂ uptake as respiratory CO₂ efflux, especially in roots. Interspecific variation in acclimation responses of dark respiration to temperature is more important than acclimation of respiration to CO₂ enrichment in modifying tree seedling growth responses to projected increases in CO₂ concentration and temperature.     

Restricted oxygen supply and excretion of metabolites

Summary The effect of restricted oxygen supply on the excretion of metabolites was studied in Pseudomonas acidovorans (DSM 39), P. delafieldii (DSM 64) and a mutant strain of Paracoccus denitrificans unable to accumulate poly-3-hydroxybutanoic acid. Different metabolites were produced at distinct submaximum respiration rates by these strains. These metabolites were, in order of decreasing respiration rates; 2-oxoglutarate, 2-oxo-3-methylbutanoate, cisaconitate, 3-hydroxybutanoate, succinate, hydrogen gas, formate, acetate, butanoate, acetoin, meso- and D,L-2,3-butanediol, and ethanol. Poly-3-hydroxy-butanoic acid (PHB) accumulated intracellularly at almost the same respiration rates at which the excretion of 3-hydroxybutanoate occurred.The production of ethanol, 2,3-butanediol, butanoate, formate, and hydrogen gas indicate the function of enzymes such as ethanol and butanediol dehydrogenases, pyruvate formate lyase, formate hydrogen lyase, and butanoyl-CoA dehydrogenase. These enzymes are not expected to be present in strict aerobes at different degrees of restricted oxygen supply.Excreted metabolites are indicators of the degree to which the oxygen demand of cells is met. On the other hand, a fermentation process designed for the production of a distinct metabolite can be controlled by maintaining the appropriate oxygen supply.     

Oxygen uptake of microorganisms entrapped in Ca-alginate

Summary The oxygen uptake rates of Pseudomonas putida, Saccharomyces cerevisiae and Aspergillus niger, immobilized in Ca-alginate gel, were determined in comparison with the respiration of free cells. The specific oxygen uptake rate of immobilized microorganisms decreased with increasing cell content of the gel beads and increasing alginate concentration.Abbreviations ATCC American Type Culture Collection - DFA Deutsche Forschungsanstalt für Lebensmittelchemie - DSM Deutsche Stammsammlung von Mikroorganismen - DW dry weight - rpm rounds per minute     

EFFECTS OF O2 ON AMMONIUM UPTAKE AND ROOT RESPIRATION BY SPARTINA ALTERNIFLORA

Previously the growth of Spartina alterniflora has been found to be limited by nitrogen and correlated with sediment redox potential. In this study we have investigated a possible connection between these two factors. We have found that internal O₂ transport is insufficient to saturate NH₄⁺ uptake in short S. alterniflora in hydroponic culture. Rates of NH₄⁺ uptake and root respiration were very sensitive to O₂ concentration in the rhizosphere, saturating at about 5% O₂. Ammonium uptake continued at a reduced rate for at least 4 hr under anaerobic conditions. Plant to plant variations in anaerobic rates of NH₄⁺ uptake and root respiration were significantly correlated to the diffusion rate of CH₄ tracer gas from the leaves to the roots of individual plants.     

Experimental bioenergetics ofSaccharomyces cerevisiae in respiration and fermentation

Aerobic growth of Saccharomyces cerevisiae on glucose was investigated, focusing on the heat evolution as it relates to biomass and ethanol synthesis. “Aerobic fermentation” and “aerobic respiration” were established respectively in the experimental system by performing batch and fed-batch experiments. “Balanced growth” batch cultivations were carried out with initial sugar concentrations ranging from 10 to 70 g/L, resulting in different degrees of catabolite repression. The fermentative heat generation was continuously monitored in addition to the key culture parameters such as ethanol production rate, CO₂ evolution rate, O₂ uptake rate, specific growth rate, and sugar consumption rate. The respective variations of the above quantities reflecting the variations in the catabolic activity of the culture were studied. This was done in order to evaluate the microbial regulatory system, the energetics of microbial growth including the rate of heat evolution and the distribution of organic substrate between respiration and fermentation. This study was supported by closing C, energy, and electron balances on the system. The comparison of the fractions of substrate energy evolved as heat (δ_h) with the fraction of available electrons transferred to oxygen (?_O2) indicated equal values of the two (0.46) in the aerobic respiration (fed-batch cultivation). However, the glucose effect in batch cultivations resulted in smaller ?_O2 than δ_h, while both values decreased in their absolute values. The evaluation of the heat energetic yield coefficients, together with the fraction of the available electrons transferred to O, contributed to the estimation of the extent of heat production through oxidative phosphorylation.     

Cultivation of Saccharomyces cerevisiae in continuous culture

Summary Growth of Saccharomyces cerevisiae was investigated under aerobic conditions in a glucose limited chemostat. The steady state concentrations of cells, glucose and ethanol were measured in dependence of the dilution rate. The growth rate showed a biphasic dependence from the glucose concentration. A shift from respiratory to fermentative metabolism (Crabtree-effect) altering heavily the cell yield and the ethanol yield took place in the range of dilution rates between 0.3 h^-1 and 0.5 h^-1. Therefore the classical theory of continuous cultures is not applicable on aerobic growth of Saccharomyces cerevisiae under glucose limitation without introducing further premises. On the other hand the steady state cell concentration as a function of the dilution rate fits well the theoretically calculated curves, if cells are cultivated under conditions where only fermentation or respiration is possible.     

Mitochondrial alternative oxidase acts to dampen the generation of active oxygen species during a period of rapid respiration induced to support a high rate of nutrient uptake

When wild type (wt) tobacco ( Nicotiana tabacum L. cv. Petit Havana SR1) suspension cells were grown under phosphate (P) limitation, they contained large amounts of mitochondrial alternative oxidase (AOX). When these cells were resupplied with P, there was a large, immediate and sustained stimulation of respiration to support a period of rapid P uptake. Two lines of evidence suggest that the abundant level of AOX present in wt cells contributed to this stimulated rate of respiration. First, when P-limited transgenic antisense tobacco cells (AS8) lacking AOX were resupplied with P, the stimulation of respiration was much less dramatic even though these cells displayed similar rates of P uptake. Second, while the stimulated rate of respiration in AS8 cells was insensitive (as expected) to the AOX inhibitor n -propyl gallate (nPG), much of the stimulated rate of respiration in wt cells could be inhibited by nPG. Given the non-phosphorylating nature of AOX respiration, wt cells required higher rates of electron transport to O₂ than AS8 cells to support similar rates of P uptake. The utilization of AOX by wt cells during P uptake was apparently not occurring because the cytochrome (Cyt) pathway alone could not fully support the rate of P uptake, as the respiration of cells lacking AOX (either untreated AS8 cells or wt cells treated with nPG) supported similar rates of P uptake as wt cells with abundant AOX. Rather, we provide in vivo evidence that the utilization of AOX during the period of high respiration supporting P uptake was to dampen the mitochondrial generation of active oxygen species (AOS).     

Acclimation of leaf respiratory properties in Alocasia odora following reciprocal transfers of plants between high- and low-light environments

Acclimation of respiration to the light environments is important for a plant’s carbon balance. Respiratory rates of mature leaves of Alocasia odora, a typical shade‐tolerant species, were measured during the night for 14 d after reciprocal transfers between high‐ (330 µ mol m^?2 s^?1) and low‐light (20 µ mol m^?2 s^?1) environments. Following the transfer, both the rate of CO₂ efflux and that of O₂ uptake of A. odora leaves adjusted to the new light environments. The O₂‐uptake rates changed more slowly than the CO₂‐efflux rates under the new environments. Leaf mass per area also changed after the transfer. We analysed whether substrate availability or ATP‐consumption rates influence the respiratory acclimation. Since the addition of sucrose to leaf segments did not influence the O₂‐uptake rates, the change of respiratory substrate availability was not responsible for the respiratory acclimation. The addition of an uncoupler induced increases in the O₂‐uptake rates, and the degree of enhancement significantly decreased after the transfer from low to high irradiance. Thus, the change in ATP‐consumption rates was responsible for the changes in respiratory rates in the plants transferred from low to high light. Potential rates of O₂ uptake, as measured in the presence of both the substrate and the uncoupler, changed after the transfer, and strongly correlated with the O₂‐uptake rates, irrespective of the directions of transfer (r = 0·961). There was a strong correlation between maximal activities of NAD‐isocitrate dehydrogenase and the potential rates of O₂ uptake (r = 0·933), but a weaker correlation between those of cytochrome c oxidase and the potential rates (r = 0·689). These data indicate that the changes of light environments altered the respiratory rates via the change of the respiratory ATP demand, and that the altered rates of respiration will induce the changes of the respiratory capacities.