Adaptation of the Cyanobacterium Anabaena variabilis to Low CO(2) Concentration in Their Environment

The rate of adaptation of high CO₂ (5% v/v CO₂ in air)-grown Anabaena to a low level of CO₂ (0.05% v/v in air) was determined as a function of O₂ concentration. Exposure of cells to low (2.6%) O₂ concentration resulted in an extended lag in the adaptation to low CO₂ concentration. The rate of adaptation following the lag was not affected by the concentration of O₂. The length of the lag period is markedly affected by the O₂/CO₂ concentration ratio, indicating that the signal for adaptation to low CO₂ may be related to the relative rate of ribulose-1,5-bisphosphate carboxylase/oxygenase activities, rather than to CO₂ concentration proper. This suggestion is supported by the observed accumulation of phosphoglycolate following transfer of cells from high to low CO₂ concentration.     

Inhibition of photosynthesis by intracellular carbonic anhydrase in microalgae under excess concentrations of CO2

When cells of Chlorococcum littorale that had been grown in air (air-grown cells) were transferred to extremely high CO₂ concentrations (>20%), active photosynthesis resumed after a lag period which lasted for 1–4 days. In contrast, C. littorale cells which had been grown in 5% CO₂ (5% CO₂-grown cells) could grow in 40% CO₂ without any lag period. When air-grown cells were transferred to 40% CO₂, the quantum efficiency of PS II (Φ_II) decreased greatly, while no decrease in Φ_II was apparent when the 5% CO₂-grown cells were transferred to 40% CO₂. In contrast to air-grown cells, 5% CO₂-grown cells showed neither extracellular nor intracellular carbonic anhydrase (CA) activity. Upon the acclimation of 5% CO₂-grown cells to air, photosynthetic susceptibility to 40% CO₂ was induced. This change was associated with the induction of CA. In addition, neither suppression of photosynthesis nor arrest of growth was apparent when ethoxyzolamide (EZA), a membrane-permeable inhibitor of CA, had been added before transferring air-grown cells of C. littorale to 40% CO₂. The intracellular pH value (pH_i) decreased from 7.0 to 6.4 when air-grown C. littorale cells were exposed to 40% CO₂ for 1–2 h, but no such decrease in pH_i was apparent in the presence of EZA. Both air- and 5% CO₂-grown cells of Chlorella sp. UK001, which was also resistant to extremely high CO₂ concentrations, grew in 40% CO₂ without any lag period. The activity of CA was much lower in air-grown cells of this alga than those in air-grown C. littorale cells. These results prompt us to conclude that intracellular CA caused intracellular acidification and hence inhibition of photosynthetic carbon fixation when air-grown C. littorale cells were exposed to excess concentrations of CO₂. No such harmful effect of intracellular CA was observed in Chlorella sp. UK001 cells. This revised version was published online in June 2006 with corrections to the Cover Date.     

Relationship between the Level of Adenine Nucleotides and the Carboxylation Activity of Illuminated Isolated Spinach Chloroplasts: A Study with Antimycin A

The changes in the levels of intact spinach (Spinacia oleracea L.) chloroplast adenine nucleotides during the time course of light-dependent CO₂ fixation were determined with respect to the effect of antimycin A. This study demonstrated that antimycin A lowered the rate of ATP formation during the induction period of carboxylation. While the steady state levels of ATP and the energy-charge value also decreased in the presence of antimycin, the concomitant increase of the CO₂ fixation activities insured higher ATP turnover rates. Changes in the labeling of CO₂ fixation products during the lag phase suggested a stepwise activation of the Calvin cycle, with fructose 1,6-diphosphate, and ribulose 5-phosphate kinase being activated before ribulose 1,5-diphosphate carboxylase. The possible mechanisms of the enhancement of CO₂ fixation activity by antimycin A in relation to its action on photophosphorylation during the lag phase are discussed.     

Influence of CO2 on Reduction of Nitrate in Corn Seedlings

The influence of CO₂ on the assimilation of nitrate in intact corn seedlings was measured with ¹⁵N labelled nitrate, 24 and 48 h after the dark-grown seedlings were transferred to the light, either in normal air or in CO₂-free air. During the first 24 h CO₂ had no influence on nitrate reduction in intact seedlings. Experiments with detopped seedlings showed that during this period the roots were the only site of nitrate reduction. After 48 h seedlings grown in normal air had reduced more nitrate than detopped seedlings, and seedlings grown in CO₂-free air had reduced the same amount of nitrate as detopped seedlings. During the whole 48 h period CO₂ had no influence on the level of nitrate reductase of the leaves. It was concluded that in normal air corn leaves started to reduce nitrate after a lag period of 24 h and that in CO₂-free air they were incapable of nitrate reduction.     

Enhancement of CO2 tolerance of Chlorella vulgaris by gradual increase of CO2 concentration

Summary Chlorella vulgaris UTEX259 was cultivated using two different methods of gas supply. In one method the CO₂ concentration in bubbled gas was held constant and in the other method it was increased gradually. Algal growth was almost linear after a short period of lag phase in both methods. With the constant CO₂ concentration, the CO₂ fixation rate in the linear growth phase decreased over 10%(v/v) CO₂, while the rate increased up to 6% CO₂. However, the rate was enhanced by using the latter incremental increase method, especially under a higher concentration of CO₂. The maximum rate of CO₂ fixation was 52 mg CO₂/l·h at 20% CO₂ during the gradual increase of CO₂ concentration.     

A Synergistic Stimulation of Avena sativa Coleoptile Elongation by Indoleacetic Acid and Carbon Dioxide

The ability of 0.03% CO₂ to stimulate growth has been investigated using etiolated Avena coleoptile sections maintained in buffered solution. This concentration of CO₂-stimulated growth after a lag period of 12 to 15 minutes, and a synergistic relationship between indoleacetic acid and CO₂ in stimulating growth has been demonstrated. The response to CO₂ is inhibited by cycloheximide and is lost approximately 10 minutes after exposure to CO₂-free air. Malate can replace CO₂ in stimulating growth. In the light of these data and recent literature on a growth response of coleoptile sections to CO₂-saturated solutions, the existence of two mechanisms of CO₂-simulated growth is proposed. In addition, it is suggested that growth promotion by 0.03% CO₂ is mediated by a process involving dark CO₂ fixation.     

REVIEW: Time lag between photosynthesis and carbon dioxide efflux from soil: a review of mechanisms and controls

CO₂ efflux from soil depends on the availability of organic substances respired by roots and microorganisms. Therefore, photosynthetic activity supplying carbohydrates from leaves to roots and rhizosphere is a key driver of soil CO₂. This fact has been overlooked in most soil CO₂ studies because temperature variations are highly correlated with solar radiation and mask the direct effect of photosynthesis on substrate availability in soil. This review highlights the importance of photosynthesis for rhizosphere processes and evaluates the time lag between carbon (C) assimilation and CO₂ release from soil. Mechanisms and processes contributing to the lag were evaluated. We compared the advantages and shortcomings of four main approaches used to estimate this time lag: (1) interruption of assimilate flow from leaves into the roots and rhizosphere, and analysis of the decrease of CO₂ efflux from soil, (2) time series analysis (TSA) of CO₂ fluxes from soil and photosynthesis proxies, (3) analysis of natural δ¹³C variation in CO₂ with photosynthesis‐related parameters or δ¹³C in the phloem and leaves, and (4) pulse labeling of plants in artificial ¹⁴CO₂ or ¹³CO₂ atmosphere with subsequent tracing of ¹⁴C or ¹³C in CO₂ efflux from soil. We concluded that pulse labeling is the most advantageous approach. It allows clear evaluation not only of the time lag, but also of the label dynamics in soil CO₂, and helps estimate the mean residence time of recently assimilated C in various above‐ and belowground C pools. The impossibility of tracing the phloem pressure–concentration waves by labeling approach may be overcome by its combination with approaches based on TSA of CO₂ fluxes and its δ¹³C with photosynthesis proxies. Numerous studies showed that the time lag for grasses is about 12.5±7.5 (SD) h. The time lag for mature trees was much longer (～4–5 days). Tree height slightly affected the lag, with increasing delay of 0.1 day m^?1. By evaluating bottle‐neck processes responsible for the time lag, we conclude that, for trees, the transport of assimilates in phloem is the rate‐limiting step. However, it was not possible to predict the lag based on the phloem transport rates reported in the literature. We conclude that studies of CO₂ fluxes from soil, especially in ecosystems with a high contribution of root‐derived CO₂, should consider photosynthesis as one of the main drivers of C fluxes. This calls for incorporating photosynthesis in soil C turnover models.     

Use of glucose and carbon isotope fractionation by microbial cells immobilized on solid-phase surface

By the example of glucose uptake by the soil bacteria Pseudomonas aureofaciens BS1393(pBS216) and Rhodococcus sp. 3–30 immobilized on a solid-phase surface (quartz sand), their growth parameters were determined: growth rate (doubling time), total CO₂ production, CO₂ production per cell, lag period with respect to substrate uptake, respiratory quotient. The growth of P. aureofaciens and Rhodococcus sp. on glucose revealed (1) differences of the lag period with respect to substrate (lag time of ～4 h for P. aureofaciens and ～26 h for Rhodococcus sp.); (2) differences between the maximal rates of CO₂ production (～50 μg C-CO₂ g^?1 sand h^?1 for P. aureofaciens and ～8.5 μg C-CO₂ g^?1 sand h^?1 for Rhodococcus sp.); (3) differences in CO₂ production per cell (～1.94 × 10^?9 μM CO₂/CFU for P. aureofaciens and more than ～3.4 × 10^?9 μM CO₂/CFU for Rhodococcus sp.). The kinetics of the metabolic CO₂ isotopic composition was shown to be determined by the difference in the carbon isotopic characteristics of products in the cell. Upon introduction of glucose into the medium (the preparatory stage of the metabolism), the uptake of intracellular ¹³C-depleted products (lipids) is noted; at the stage of the maximal cell growth rate, introduced glucose is mainly metabolized; and at the final stage, upon exhaustion of substrate, the “stored” products—the lipid fraction—get involved in the metabolism. At the maximal rate of glucose uptake, the CO₂ carbon isotopic fractionation coefficient relative to organic products of microbial biosynthesis was determined to be α = 1.009 ± 0.002.     

Effect of pH on Inorganic Carbon Uptake in Algal Cultures

Biomass production by the green algae Scenedesmus obliquus and Chlorella vulgaris in intensive laboratory continuous cultures was considerably affected by the pH at which the cultures were maintained. Carbon photoassimilation experiments revealed that pH values in the range of 8 to 9 were important for determining the free CO₂ concentrations in the medium. With higher pH values, additional pH effects were observed involving a decrease in the relative high affinity of low CO₂-adapted algae to free CO₂. The carbon uptake rate by high CO₂-adapted algae after transfer to low free CO₂ medium was characterized by a lag period of about 30 min, after which the affinity of the algae to CO₂ increased considerably. Both continuous growth and carbon uptake experiments indicated that artificially maintained high free CO₂ concentrations are recommended for maximal production in intensive outdoor algal cultures.     

Formation of CO2 from the carboxyl group of S-adenosylmethionine by liver membrane-associated enzymes involves the demethylation-transsulphuration pathway

The activity released from membrane fragments into the supernatant fraction of rat liver homogenate by Triton X-100 and forming ¹⁴CO₂ from carboxyl-labeled S-adenosylmethionine (1) is not a true S-adenosylmethionine decarboxylase. It did not produce decarboxylated S-adenosylmethionine but was also able to use S-adenosylhomocysteine as a substrate. The formation of CO₂ from these two substrates was absolutely dependent on the presence of cytosol proteins and low-molecular weight compounds and it accounted for 5 to 10% of the total S-adenosylmethionine degrading activity of the supernatant fraction. The reaction showed abn initial lag period and was inhibited by every intermediate of the transsulphuration pathway. It is concluded that the formation of CO₂ from S-adenosylmethionine involves the demethylation-transsulphuration route from S-adenosylmethionine to α-ketobutyric acid which is finally decarboxylated.     

Photosynthesis in Isolated Chloroplasts of the Crassulacean Acid Metabolism Plant Sedum praealtum

Intact chloroplasts were isolated from protoplasts of the Crassulacean acid metabolism plant Sedum praealtum D.C. Typical rates of CO₂ fixation or CO₂-dependent O₂ evolution ranged from 20 to 30 micromoles per milligram chlorophyll per hour and could be stimulated 30 to 50% by several Calvin cycle intermediates. The pH optimum for CO₂ fixation was 7.0 to 7.6 with considerable activity as low as pH 6.4. Low concentrations of orthophosphate (Pi) (optimum 0.4 millimolar) stimulated photosynthesis while high concentrations (5 millimolar) caused some inhibition. Both CO₂ fixation and CO₂-dependent O₂ evolution exhibited a relatively long lag phase (4 to 6 minutes) which remained constant between 0.4 to 5 millimolar Pi. The lag phase could be decreased by addition of dihydroxyacetone-phosphate or ribose 5-phosphate. Further results are presented which suggest these chloroplasts have a functional phosphate translocator.     

Inhibition of oxygen release by anoxia in a C3-plant (Nicotiana tabacum cv. Wisconsin 38). Comparison with C4-plants

Tobacco leaves (Nicotiana tabacum var. Wisconsin 38) submitted to anaerobic conditions behave in a manner similar to that of maize, sugarcane, or sorghum leaves (C₄-plants); more precisely, a lag time in O₂ release is exhibited when the leaves are exposed to light after treatment in the dark under pure nitrogen. Although the conditions for the appearance of this phenomenon in tobacco are somewhat different, the main features are identical to those observed with maize: abolition of the lag time upon immediate exposure to light, release of CO₂ under light (illumination burst of CO₂), photochemical nature of the reactions involved in the abolition of the lag time, activation of oxygen release by far-red light, and the antagonistic effect of red and far-red light on the lag time. The high CO₂ compensation point of tobacco leaves permits the classification of this plant among the C₃ group. A comparison of these experimental results with others from the literature suggests than the distinguishing features between C₃- and C₄-plants are not as sharp as generally thought.     

Reductive Dehalogenations of Halobenzoates by Anaerobic Lake Sediment Microorganisms

Methane-producing freshwater lake sediment was found to dehalogenate chloro-, bromo-, and iodobenzoates by a reductive reaction in which the halogen was replaced by a hydrogen atom. The identity of the dehalogenated products was confirmed by mass spectrometry, nuclear magnetic resonance, or cochromatography. Removal of the halogens to produce benzoate was necessary before mineralization to CH₄ + CO₂ could occur. The dehalogenation occurred after a lag period which lasted from 1 week to more than 6 months, depending on the chemical. Dehalogenation was not observed in the absence of CH₄ production, and it was inhibited by the addition of 20% O₂. Once sediment was acclimated to halobenzoate dehalogenation, new additions of the halobenzoate were degraded without lag. Acclimation was observed regardless of whether the parent substrates were eventually mineralized to CH₄ + CO₂. Sediment acclimated to bromo- and chlorobenzoate degradation generally metabolized bromo- and chlorobenzoates, but sediment acclimated to iodobenzoate degradation only metabolized iodobenzoate. Prior acclimation of sediment to benzoate decomposition did not alter the pattern of dehalogenation, and sediment acclimated to dehalogenation was not concurrently acclimated to benzoate degradation. The presence of this apparent specificity, the lag period, and subsequent acclimation, together with our findings of the absence of dehalogenation in sterile sediments and by sediments previously incubated at ≥39°C, suggests that this reaction was biologically catalyzed. Apparently, a pathway for the reductive dehalogenation of aryl halides is present in anaerobic microorganisms of this methanogenic sediment.     

Glycolate excretion by air-grown Euglena graeilis z

In contrast to reported fact, the air-grown cells of Euglena gracilis z were found to excrete glycolate into the surrounding medium, when placed in an atmosphere of 100% O₂ under illumination at 20000 lux at the same rate of the 5% CO₂-grown cells, but with a lag phase of about 30 min. The lag was eliminated by lowering intracellular CO₂ concentration in the air-grown cells.This paper is the eighth in a series on the metabolism of glycolate in Euglena gracilis.     

Changing Kinetic Properties of Fructose-1,6-bisphosphatase from Pea Chloroplasts during Photosynthetic Induction

After dark-light transitions, there is a delay in photosynthetic CO₂ fixation by isolated pea chloroplasts in the range of some minutes. In order to assess the physiological significance of light modulation of enzyme activity in the control of induction, we made estimates of the kinetic parameters of fructose-1,6-bisphosphatase immediately upon release from pea chloroplasts in the dark and after illumination for various time periods. The Michaelis constant for fructose-1,6-bisphosphate decreased and maximal velocities increased during induction. It seems likely that light activation of this enzyme is one of the factors contributing to the overcoming of the lag period in photosynthetic CO₂ fixation.     

Saturation Kinetics of the Velocity of Stomatal Closing in Response to CO(2)

Stomatal closing movements in response to changes from CO₂-free to CO₂-containing air were recorded in leaf sections of Zea mays using air flow porometers. The response to CO₂ was fast; the shortest lag between the application of 300 microliters CO₂ per liter of air and the beginning of a stomatal response was 3 seconds. The velocity of stomatal closing increased with CO₂ concentration and approached its maximal value between 10³ and 10⁴ microliters CO₂ per liter of air. The CO₂ concentration at which the closing velocity reached half its maximal value was approximately 200 microliters CO₂ per liter of air, both in the light and in darkness. This indicates that the mechanism of stomatal responses to CO₂ is the same in both light regimes and that the range of stomatal sensitivity to changes in CO₂ concentration coincides with the range of CO₂ concentrations known to occur in the intercellular spaces of illuminated leaves.     

Modeling of carbon dioxide mass transfer behavior in attached cultivation photobioreactor using the analysis of the pH profiles

The CO₂ mass transfer model associated with growth kinetics of microalgal biofilm in attached cultivation photobioreactor was developed and verified by using the analysis of pH profiles which were in equilibrium with inorganic carbon components concentrations (CO₂, H₂CO₃, HCO₃ ⁻ and CO₃ ²⁻) in medium. Model simulation results showed that the model well presented the biofilm growth process. The overall volumetric mass transfer coefficient of CO₂ was more influenced by CO₂ concentration in aerated gas but less by gas aeration rate and medium circulation rate. Other bio-kinetic parameters related with the microalgal biofilm such as CO₂ diffusion coefficient in biofilm, Monod maximum utilization rate of CO₂, lag phase duration of biofilm and half-saturation CO₂ concentration in the biofilm were independent on operational conditions. The pH profiles provided a way to monitor the variations of inorganic carbon concentrations of medium and to regulate the cultivation of attached microalgal biofilm by CO₂ supplement.

     

Rapidly Induced Wound Ethylene from Excised Segments of Etiolated Pisum sativum L., cv. Alaska: II. Oxygen and Temperature Dependency

Wound-induced ethylene synthesis by subapical stem sections of etiolated Pisum sativum L., cv. Alaska seedlings, as described by Saltveit and Dilley (Plant Physiol 1978 61: 447-450), was half-saturated at 3.6% (v/v) O₂ and saturated at about 10% O₂. Corresponding values for CO₂ production during the same period were 1.1% and 10% O₂, respectively. Anaerobiosis stopped all ethylene evolution and delayed the characteristic pattern of wound ethylene synthesis. Exposing tissue to 3.5% CO₂ in air in a flow-through system reduced wound ethylene synthesis by 30%. Enhancing gas diffusivity by reducing the total pressure to 130 mm Hg almost doubled the rate of wound ethylene synthesis and this effect was negated by exposure to 250 μl liter⁻¹ propylene. Applied ethylene or propylene stopped wound ethylene synthesis during the period of application, but unlike N₂, no lag period was observed upon flushing with air. It is concluded that the characteristic pattern of wound-induced ethylene synthesis resulted from negative feedback control by endogenous ethylene.

No wound ethylene was produced for 2 hours after excision at 10 or 38 C. Low temperatures prolonged the lag period, but did not prevent induction of the wound response, since tissue held for 2 hours at 10 C produced wound ethylene immediately when warmed to 30 C. In contrast, temperatures above 36 C prevented induction of wound ethylene synthesis, since tissue cooled to 30 C after 1 hour at 40 C required 2 hours before ethylene production returned to normal levels. The activation energy between 15 and 36 C was 12.1 mole kilocalories degree⁻¹.

     

Photosynthetic Capacities and Growth Characteristics of Nicotiana tabacum (cv. Xanthi) Cell Suspension Cultures

Photoheterotrophic growth of cell suspensions of Nicotiana tabacum L. (cv. Xanthi) in organic culture medium enriched in sucrose (30 g per liter) showed a classical sigmoid growth curve. The cells developed functional chloroplast structures during the exponential growth phase, when their chlorophyll content increased steadily. A limited drop (30%) in the chlorophyll amount and structural changes of the plastids (starch accumulation) were observed during the lag phase. The measurements of photosynthetic capacities (O₂ evolution and CO₂ fixation) during the growth cycle revealed changes in the photosynthetic ratio (O₂/CO₂), which was near 1 during the lag and stationary phases and near 2 during exponential growth. During exponential growth there was also a rapid NO₃^? uptake. Analysis of label distribution among the products of ¹⁴CO₂ fixation showed that both CO₂ assimilation pathways, linked to the ribulose-biphosphate carboxylase (the autotrophic pathway) and to phosphoenolpyruvate carboxylase (the non-autotrophic pathway) were operative with an important increase of the capacity of the latter during the exponential growth phase. Maximum rate of oxygen evolution, either endogenous or with p-benzoquinone as Hill reagent, as well as the increased CO₂ Fixation capacity via the non-autotrophic pathway during the exponential phase were concomitant with a high cyanide inhibited O₂ uptake.     

Photosynthesis of Lipids from CO(2) in Spinacia oleracea

Young expanding spinach leaves exposed to ¹⁴CO₂ under physiological conditions for up to 20 minutes assimilated CO₂ into lipids at a mean rate of 7.6 micromoles per milligram chlorophyll per hour following a lag period of 5 minutes. Label entered into all parts of the lipid molecule and only 28% of the ¹⁴C fixed into lipids was found in the fatty acid moieties, i.e. fatty acids were synthesized from CO₂in vivo at a mean rate of 2.1 micromoles per milligram chlorophyll per hour. Intact spinach chloroplasts isolated from these leaves incorporated H¹⁴CO₃ into fatty acids at a maximal rate of 0.6 micromole per milligram chlorophyll per hour, but were unable to synthesize either the polar moieties of their lipids or polyunsaturated fatty acids. Since isolated chloroplasts will only synthesize fatty acids at rates similar to the one obtained with intact leaves in vivo if acetate is used as a precursor, it is suggested that acetate derived from leaf mitochondria is the physiological fatty acid precursor.