Effect of molecular hydrogen and carbon dioxide on chemo-organotrophic growth of Acetobacterium woodii and Clostridium aceticum

During growth of Acetobacterium woodii on fructose, glucose or lactate in a medium containing less than 0.04% bicarbonate, molecular hydrogen was evolved up to 0.1 mol per mol of substrate. Under an H₂-atmosphere growth of A. woodii with organic substrates was completely inhibited whereas under an H₂/CO₂-atmosphere rapid growth occurred. Under these conditions H₂+CO₂ and the organic substrate were utilized simultaneously indicating that A. woodii was able to grow mixotrophically. Clostridium aceticum differed from A. woodii in that H₂ was only evolved in the stationary phase, that the inhibition by H₂ was observed at pH 8.5 but not at pH 7.5, anf that in the presence of fructose and H₂+CO₂ only fructose was utilized.The hydrogenase activity of fructose-grown cells of C. aceticum amounted to only 12% of that of H₂+CO₂-grown cells. With A. woodii a corresponding decrease of the activity of this enzyme was not observed.     

Effects of CO2 concentrations on the freshwater microalgae, Chlamydomonas reinhardtii, Chlorella pyrenoidosa and Scenedesmus obliquus (Chlorophyta)

In order to investigate the possible impacts of increased atmospheric CO₂ levels on algal growth and photosynthesis, the influence of CO₂ concentration was tested on three planktonic algae (Chlamydomonas reinhardtii, Chlorella pyrenoidosa, and Scenedesmus obliquus). Increased CO₂ concentration enhanced significantly the growth rate of all three species. Specific growth rates reached maximal values at 30, 100, and 60 M CO₂ in C. reinhardtii, C. pyrenoidosa, and S. obliquus, respectively. Such significant enhancement of growth rate with enriched CO₂ was also confirmed at different levels of inorganic N and P, being more profound at limiting levels of N inC. pyrenoidosa and P in S. obliquus. The maximal rates of net photosynthesis, photosynthetic efficiency and light-saturating point increased significantly (p < 0.05) in high-CO₂-grown cells. Elevation of the CO₂ levels in cultures enhanced the photoinhibition of C. reinhardtii, but reduced that of C. pyrenoidosa and S. obliquus when exposed to high photon flux density. The photoinhibited cells recovered to some extent (from 71% to 99%) when placed under dim light or in darkness, with better recovery in high-CO₂-grownC. pyrenoidosa and S. obliquus. Although pH and pCO₂ effects cannot be distinguished from this study, it can be concluded that increased CO₂ concentrations with decreased pH could affect the growth rate and photosynthetic physiology of C. reinhardtii, C. pyrenoidosa, and S. obliquus.     

Growth,14CO2 fixation,activites of photosystems,ribulose 1,5-bisphosphate carboxylase and nitrate reductase in trees as affected by simulated acid rain

In seedlings of the tropical tree speciesErythrina variegata Lam. andHardwickia binata Roxb. exposed to different acidic mist (H₂SO₄, pH 5, 3 and 2) for 5 d significant reduction in seedling growth, biomass accumulation and¹⁴CO₂ fixation were determined. In isolated chloroplasts a decrease in the activities of photosystem 2 and whole electron transport chain was observed only at pH 3 and 2, but no significant change in photosystem 1 activity was observed. SDS-PAGE analysis of crude leaf extracts of ribulose 1,5-bisphosphate carboxylase (RuBPC) indicated a significant loss of 55 and 15 kDa polypeptides at pH 2 inErythrina. The reduction in the RuBPC activity in seedlings grown under acidic mists correlated well with CO₂ fixation.     

Gas Exchange Responses to CO2 Concentration Instantaneously Elevated in Flag Leaves of Winter Wheat Cultivars Released in Different Years

Three winter wheat (Triticum aestivum L.) cultivars, representatives of those widely cultivated in Beijing over the past six decades, were grown in the same environmental conditions. Net photosynthetic rate (P _N) per unit leaf area and instantaneous water use efficiency (WUE) of flag leaves increased with elevated CO₂ concentration. With an increase in CO₂ concentration from 360 to 720 µmol mol^–1, P _N and WUE of Jingdong 8 (released in 1990s and having the highest yield) increased by 173 and 81 %, while those of Nongda 139 (released in 1970s) increased by 88 and 66 %, and Yanda 1817 (released in 1945, with lowest yield) by 76 and 65 %. Jingdong 8 had the highest P _N and WUE values under high CO₂ concentration, but Yanda 1817 showed the lowest P _N. Stomatal conductance (g _s) of Nongda 139 and Yanda 1817 declined with increasing CO₂ concentration, but g _s of Jingdong 8 firstly went down and then up as the CO₂ concentration further increased. Intercellular CO₂ concentration (C _i) of Jingdong 8 and Nongda 139 increased when CO₂ concentration elevated, while that of Yanda 139 increased at the first stage and then declined. Jingdong 8 had the lowest C _i of the three wheat cultivars, and Yanda 1817 had the highest C _i value under lower CO₂ concentrations. However, Jingdong 8 had the highest P _N and lowest C _i at the highest CO₂ concentration which indicates that its photosynthetic potential may be high.     

Stomatal responses to carbon dioxide of isolated epidermis from a C3 plant,the Argenteum mutant of Pisum sativum L., and a crassulacean-acid-metabolism plant Kalanchoë daigremontiana Hamet et Perr

The response of stomata in isolated epidermis to the concentration of CO₂ in the gaseous phase was examined in a C₃ species, the Argenteum mutant of Pisum sativum, and a crassulacean-acid-metabolism (CAM) species, Kalanchoë daigremontiana. Epidermis from leaves of both species was incubated on buffer solutions in the presence of air containing various volume fractions of CO₂ (0 to 10000·10^–6). In both species and in the light and in darkness, the effect of CO₂ was to inhibit stomatal opening, the maximum inhibition of opening occurring in the range 0 to 360·10^–6. The inhibition of opening per unit change in concentration was greatest between volume fractions of 0 and 240·10^–6. There was little further closure above the volume fraction of 360·10^–6, i.e. approximately ambient concentration of CO₂. Thus, although leaves of CAM species may experience much higher internal concentrations of CO₂ in the light than those of C₃ plants, this does not affect the sensitivity of their stomata to CO₂ concentration or the range over which they respond. Stomatal responses to CO₂ were similar in both the light and the dark, indicating that effects of CO₂ on stomata occur via mechanisms which are independent of light. The responses of stomata to CO₂ in the gaseous phase took place without the treatments changing the pH of the buffered solutions. Thus it is unlikely that CO₂ elicited stomatal movement by changing either the pH or the HCO ₃ ^– /CO ₃ ^2- equilibria. It is suggested that the concentration of dissolved unhydrated CO₂ may be the effector of stomatal movement and that its activity is related to its reactivity with amines.     

A CO2-Flux Mechanism Operating via pH-Polarity in Hydrilla Verticillata Leaves With C3 and C4 Photosynthesis

The aquatic angiosperm Hydrilla verticillata lacks Kranz anatomy, but has an inducible, C₄-based, CO₂ concentrating mechanism (CCM) that concentrates CO₂ in the chloroplasts. Both C₃ and C₄ Hydrilla leaves showed light-dependent pH polarity that was suppressed by high dissolved inorganic carbon (DIC). At low DIC (0.25 mol m⁻³), pH values in the unstirred water layer on the abaxial and adaxial sides of the leaf were 4.2 and10.3, respectively. Abaxial apoplastic acidification served as a CO₂ flux mechanism (CFM), making HCO₃ ⁻ available for photosynthesis by conversion to CO₂. DIC at 10 mol m⁻³ completely suppressed acidification and alkalization. The data, along with previous results, indicated that inhibition was specific to DIC, and not a buffer effect. Acidification and alkalization did not necessarily show 1:1 stoichiometry; their kinetics for the apolar induction phase differed, and alkalization was less inhibited by 2.5 mol m⁻³ DIC. At low irradiance (50 μmol photons m⁻² s⁻¹), where CCM activity in C₄ leaves is minimized, both leaf types had similar DIC inhibition of pH polarity. However, as irradiance increased, DIC inhibition of C₃ leaves decreased. In C₄ leaves the CFM and CCM seemed to compete for photosynthetic ATP and/or reducing power. The CFM may require less, as at low irradiance it still operated maximally, if [DIC] was low. Iodoacetamide (IA), which inhibits CO₂ fixation in Hydrilla, also suppressed acidification and alkalization, especially in C₄ leaves. IA does not inhibit the C₄ CCM, which suggests that the CFM and CCM can operate independently. It has been hypothesized that irradiance and DIC regulate pH polarity by altering the chloroplastic [DIC], which effects the chloroplast redox state and subsequently redox regulation of a plasma-membrane H⁺-ATPase. The results lend partial support to a down-regulatory role for high chloroplastic [DIC], but do not exclude other sites of DIC action. IA inhibition of pH polarity seems inconsistent with the chloroplast NADPH/NADP⁺ ratio being the redox transducer. The possibility that malate and oxaloacetate shuttling plays a role in CFM regulation requires further investigation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Methanobacterium thermoalcaliphilum spec. nov., a new moderately alkaliphilic and thermophilic autotrophic methanogen

An autotrophic moderately alkaliphilic and thermophilic nonmotile rod-shaped methanogen was isolated from a biogas plant. The isolate grows only on H₂+CO₂ and requires yeast extract. Growth optimum is at 60°C with a generation time of 4 h. In the absence of substrates complete lysis occurs. The pH range for growth is 7.5–8.5. Growth was also observed at pH values above 9.0. The DNA base composition is 38.8 mol% G+C. According to its physiological properties the nameMethanobacterium thermoalcaliphilum is proposed.Abbreviations G+C Guanine+cytosine     

Variable HCO 3 - affinity of Elodea canadensis Michaux in response to different HCO 3 - and CO2 concentrations during growth

Summary Elodea canadensis grows over a wide range of inorganic carbon, nutrient, and light conditions in lakes and streams. Affinity for HCO ₃ ^- use during photosynthesis ranged from strong to weak in Elodea collected from seven localities with different HCO ₃ ^- and CO₂ concentrations. The response to HCO ₃ ^- was also very plastic in plants grown in the laboratory at high HCO ₃ ^- concentrations and CO₂ concentrations varying from 14.8 to 2,200 M. Bicarbonate affinity was markedly reduced with increasing CO₂ concentrations in the growth medium so that ultimately HCO ₃ ^- use was not detectable. High CO₂ concentrations also decreased CO₂ affinity and induced high CO₂ compensation points (360M CO₂) and tenfold higher half-saturation values (800 M CO₂).The variable HCO ₃ ^- affinity is probably environmentally based. Elodea is a recently introduced species in Denmark, where it reproduces only vegetatively, leaving little opportunity for genetic variation. More important, local populations in the same water system had different HCO ₃ ^- affinities, and a similar variation was created by exposing one plant collection to different laboratory conditions.Bicarbonate use enabled Elodea to photosynthesize rapidly in waters of high alkalinity and enhanced the carbon-extracting capacity by maintaining photosynthesis above pH 10. On the other hand, use of HCO ₃ ^- represents an investment in transport apparatus and energy which is probably not profitable when CO₂ is high and HCO ₃ ^- is low. This explanation is supported by the findings that HCO ₃ ^- affinity was low in field populations where HCO ₃ ^- was low (0.5 and 0.9 m M) or CO₂ was locally high, and that HCO ₃ ^- affinity was suppressed in the laboratory by high CO₂ concentrations.Abbreviations DIC dissolved inorganic carbon (CO₂+ HCO ₃ ^- +CO ₃ ^- ) - CO₂ compensation point - K _1/2 apparent halfsaturation constant - P_{HCO 3} ^– interpolated photosynthesis in pure HCO ₃ ^- and zero CO₂ - P_max photosynthetic rate under carbon and light saturation     

Chlorophyll fluorescence imaging of photosynthetic activity in sun and shade leaves of trees

The differences in pigment levels, photosynthetic activity and the chlorophyll fluorescence decrease ratio R _Fd (as indicator of photosynthetic rates) of green sun and shade leaves of three broadleaf trees (Platanus acerifolia Willd., Populus alba L., Tilia cordata Mill.) were compared. Sun leaves were characterized by higher levels of total chlorophylls a + b and total carotenoids x + c as well as higher values for the weight ratio chlorophyll (Chl) a/b (sun leaves 3.23–3.45; shade leaves: 2.74–2.81), and lower values for the ratio chlorophylls to carotenoids (a + b)/(x + c) (with 4.44–4.70 in sun leaves and 5.04–5.72 in shade leaves). Sun leaves exhibited higher photosynthetic rates P _N on a leaf area basis (mean of 9.1–10.1 μmol CO₂ m⁻² s⁻¹) and Chl basis, which correlated well with the higher values of stomatal conductance G _s (range 105–180 mmol m⁻² s⁻¹), as compared to shade leaves (G _s range 25–77 mmol m⁻² s⁻¹; P _N: 3.2–3.7 μmol CO₂ m⁻² s⁻¹). The higher photosynthetic rates could also be detected via imaging the Chl fluorescence decrease ratio R _Fd, which possessed higher values in sun leaves (2.8–3.0) as compared to shade leaves (1.4–1.8). In addition, via R _Fd images it was shown that the photosynthetic activity of the leaves of all trees exhibits a large heterogeneity across the leaf area, and in general to a higher extent in sun leaves than in shade leaves.     

Inorganic-carbon transport in some marine eukaryotic microalgae

Inorganic-carbon transport was investigated in the eukaryotic marine microalgaeStichococcus minor, Nannochloropsis oculata and aMonallantus sp. Photosynthetic O₂ evolution at constant inorganic-carbon concentration but varying pH showed thatS. minor had a greater capacity for CO₂ rather than HCO ₃ ^– utilization but forN. oculata andMonallantus HCO ₃ ^– was the preferred source of inorganic carbon. All three microalgae had a low affinity for CO₂ as shown by the measurement of inorganic-carbon-dependent photosynthetic O₂ evolution at pH 5.0. At pH 8.3, where HCO ₃ ^– is the predominant form of inorganic carbon, the concentration of inorganic carbon required for half-maximal rate of photosynthetic O₂ evolution [K _0.5 (CO₂)] was 53 M forMonallantus sp. and 125 M forN. oculata, values compatible with HCO ₃ ^– transport. Neither extra- nor intracellular carbonic anhydrase was detected in these three microalgal species. It is concluded that these microalgae lack a specific transport system for CO₂ but that HCO ₃ ^– transport occurs inN. oculata andMonallantus, and in the absence of intracellular carbonic anhydrase the conversion of HCO ₃ ^– to CO₂ may be facilitated by the internal pH of the cell.     

北京典型树种木质组织碳释放速率温度敏感性的时间变化规律和铅锤分异特征

采用红外气体分析法(IRGA)于2014年1—12月原位测定了北京市4个典型树种(国槐Sophora japonica,旱柳Salix matsudana,华北落叶松Larix principis-rupprechtii和侧柏Platycladus orientalis)在不同高度上的木质组织CO_2通量速率(E_(CO_2)),旨在比较不同树种间E_(CO_2)及其温度敏感性(Q_(10))的时间变化规律和铅锤分异特征。研究结果显示:(1)4个树种的E_(CO_2)均表现为单峰型季节变化规律,生长月份内的E_(CO_2)显著高于非生长月份,温度和枝干的径向生长是影响E_(CO_2)季节变化的主要因素;(2)E_(CO_2)对温度的敏感性在夏季月份明显降低,且出现明显的垂直分异:Q_(10)随测量高度的增加而增加,呈现出非连续的阶梯分布;(3)在日间尺度上,阔叶树种E_(CO_2)对温度的感性系数Q_(10)出现昼夜不对称现象,晚上Q_(10)明显升高。准确量化E_(CO_2)的时间变化规律和铅锤分异特征,细化不同时间尺度下E_(CO_2)对温度的响应特征,成为准确估算木质组织碳排放的前提条件。     

Nitrogen and Carbon Concentrations, and Stable Isotope Ratios in Mediterranean Shrubs Growing in the Proximity of a CO2 spring

Seasonal changes in foliage nitrogen (N) and carbon (C) concentrations and δ¹⁵N and δ¹³C ratios were monitored during a year in Erica arborea, Myrtus communis and Juniperus communis co-occurring at a natural CO₂ spring (elevated [CO₂], about 700 μmol mol⁻¹) and at a nearby control site (ambient [CO₂], 360 μmol mol⁻¹) in a Mediterranean environment. Leaf N concentration was lower in elevated [CO₂] than in ambient [CO₂] for M. communis, higher for J. communis, and dependent on the season for E. arborea. Leaf C concentration was negatively affected by atmospheric CO₂ enrichment, regardless of the species. C/N ratio varied concomitantly to N. Leaves in elevated [CO₂] showed lower δ¹³C, and therefore likely lower water use efficiencies than leaves at the control site, regardless of the species, suggesting substantial photosynthetic acclimation under long-term CO₂-enriched atmosphere. Leaves of E. arborea showed lower values of δ¹⁵N under elevated [CO₂], but this was not the case of M. communis and J. communis foliage. The use of the resources and leaf chemical composition are affected by elevated [CO₂], but such an effect varies during the year, and is species-dependent. The seasonal dependency and species specificity suggest that plants are able to exploit different available water and N resources within Mediterranean sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fossil plant evidence for Early and Middle Jurassic paleoenvironmental changes in Lanzhou area, Northwest China

Estimating the paleoclimate changes through CO₂ levels has become a promising area of geological research. This paper focuses on analysis of fossil Ginkgo in continuous sedimentary series in northwestern China using plant anatomy and organic geochemistry approaches. The CO₂ variation curve during Early and Middle Jurassic is reconstructed based on the stomatal ratio method, which is consistent with the estimated results of GEOCARB III. In comparison with the carbon isotopic composition measured from the fossil leaves of Ginkgo, we suggest that the stomata-based CO₂ concentrations for the Jurassic are generally consistent with the predictions of the geochemical model, ranging from 1000 to 1600 ppmv. Measurements of carbon isotope values demonstrate that the water use efficiency of the fossil Ginkgo in a “green house” world is higher than that of the living Ginkgo. Investigations of physiological responses of plants to the increasing CO₂ level at the present and in the future should help demonstrate this effect. The cause of the carbon isotopic shift at the boundary between Aalenian and Bajocian for the Yaojie Basin is unclear and therefore needs further investigation.     

Effects of low and elevated CO2 on C3 and C4 annuals

Abutilon theophrasti (C₃) and Amaranthus retroflexus (C₄), were grown from seed at four partial pressures of CO₂: 15 Pa (below Pleistocene minimum), 27 Pa (pre-industrial), 35 Pa (current), and 70 Pa (future) in the Duke Phytotron under high light, high nutrient, and wellwatered conditions to evaluate their photosynthetic response to historic and future levels of CO₂. Net photosynthesis at growth CO₂ partial pressures increased with increasing CO₂ for C₃ plants, but not C₄ plants. Net photosynthesis of Abutilon at 15 Pa CO₂ was 70% less than that of plants grown at 35 Pa CO₂, due to greater stomatal and biochemical limitations at 15 Pa CO₂. Relative stomatal limitation (RSL) of Abutilon at 15 Pa CO₂ was nearly 3 times greater than at 35 Pa CO₂. A photosynthesis model was used to estimate ribulose-1,5-bisphosphate carboxylase (rubisco) activity (Vc_max), electron transport mediated RuBP regeneration capacity (J _max), and phosphate regeneration capacity (PiRC) in Abutilon from net photosynthesis versus intercellular CO₂ (A–C _i) curves. All three component processes decreased by approximately 25% in Abutilon grown at 15 Pa compared with 35 Pa CO₂. Abutilon grown at 15 Pa CO₂ had significant reductions in total rubisco activity (25%), rubisco content (30%), activation state (29%), chlorophyll content (39%), N content (32%), and starch content (68%) compared with plants grown at 35 Pa CO₂. Greater allocation to rubisco relative to light reaction components and concomitant decreases in J _max and PiRC suggest co-regulation of biochemical processes occurred in Abutilon grown at 15 Pa CO₂. There were no significant differences in photosynthesis or leaf properties in Abutilon grown at 27 Pa CO₂ compared with 35 Pa CO₂, suggesting that the rise in CO₂ since the beginning of the industrial age has had little effect on the photosynthetic performance of Abutilon. For Amaranthus, limitations of photosynthesis were balanced between stomatal and biochemical factors such that net photosynthesis was similar in all CO₂ treatments. Differences in photosynthetic response to growth over a wide range of CO₂ partial pressures suggest changes in the relative performance of C₃ and C₄ annuals as atmospheric CO₂ has fluctuated over geologic time.     

Performance of a generalist grasshopper on a C<Subscript>3</Subscript> and a C<Subscript>4</Subscript> grass: compensation for the effects of elevated CO<Subscript>2</Subscript> on plant nutritional quality

The increasing CO₂ concentration in Earths atmosphere is expected to cause a greater decline in the nutritional quality of C₃ than C₄ plants. As a compensatory response, herbivorous insects may increase their feeding disproportionately on C₃ plants. These hypotheses were tested by growing the grasses Lolium multiflorum C₃) and Bouteloua curtipendula C₄) at ambient (370 ppm) and elevated (740 ppm) CO₂ levels in open top chambers in the field, and comparing the growth and digestive efficiencies of the generalist grasshopper Melanoplus sanguinipes on each of the four plant × CO₂ treatment combinations. As expected, the nutritional quality of the C₃ grass declined to a greater extent than did that of the C₄ grass at elevated CO₂; protein levels declined in the C₃ grass, while levels of carbohydrates (sugar, fructan and starch) increased. However, M. sanguinipes did not significantly increase its consumption rate to compensate for the lower nutritional quality of the C₃ grass grown under elevated CO₂. Instead, these grasshoppers appear to use post-ingestive mechanisms to maintain their growth rates on the C₃ grass under elevated CO₂. Consumption rates of the C₃ and C₄ grasses were also similar, demonstrating a lack of compensatory feeding on the C₄ grass. We also examined the relative efficiencies of nutrient utilization from a C₃ and C₄ grass by M. sanguinipes to test the basis for the C₄ plant avoidance hypothesis. Contrary to this hypothesis, neither protein nor sugar was digested with a lower efficiency from the C₄ grass than from the C₃ grass. A novel finding of this study is that fructan, a potentially large carbohydrate source in C₃ grasses, is utilized by grasshoppers. Based on the higher nutrient levels in the C₃ grass and the better growth performance of M. sanguinipes on this grass at both CO₂ levels, we conclude that C₃ grasses are likely to remain better host plants than C₄ grasses in future CO₂ conditions.     

Influence of enhanced CO2 on growth and photosynthesis of the red algaeGracilaria sp. andG. chilensis

The influence of elevated CO₂ concentrations on growth and photosynthesis ofGracilaria sp. andG. chilensis was investigated in order to procure information on the effective utilization of CO₂. Growth of both was enhanced by CO₂ enrichment (air + 650 ppm CO₂, air + 1250 ppm CO₂, the enhancement being greater inGracilaria sp. Both species increased uptake of NO₃ ^– with CO₂ enrichment. Photosynthetic inorganic carbon uptake was depressed inG. chilensis by pre-culture (15 days) with CO₂ enrichment, but little affected inGracilaria sp. Mass spectrometric analysis showed that O₂ uptake was higher in the light than in the dark for both species and in both cases was higher inGracilaria sp. The higher growth enhancement inGracilaria sp. was attributed to greater depression of photorespiration by the enrichment of CO₂ in culture.     

On the mechanism of autotrophic fixation of CO2 bychloroflexus aurantiacus

The activity of two carboxylating enzymes was studied in the green filamentous bacteriumChloroflexus aurantiacus. The carboxylation reaction involving pyruvate synthase was optimized using¹⁴CO₂ and cell extracts. Pyruvate synthase was shown to be absent from cells ofCfl. aurantiacus OK-70 and present (in a quantity sufficient to account for autotrophic growth) in cells ofCfl. aurantiacus B-3. Differences in the levels of acetyl CoA carboxylase activity were revealed between cells of the strains studied grown under different conditions. The data obtained confirm the operation of different mechanisms of autotrophic CO₂ assimilation inCfl. aurantiacus B-3 andCfl. aurantiacus OK-70: in the former organism, it is the reductive cycle of dicarboxylic acids, and in the latter one, it is the 3-hydroxypropionate cycle.     

Reactivity of glyoxylate with hydrogen perioxide and simulation of the glycolate pathway of C3 plants and Euglena

The nonenzymatic reaction of glyoxylate and H₂O₂ was measured under physiological conditions of the pH and concentrations of reactants. The reaction of glyoxylate and H₂O₂ was secondorder, with a rate constant of 2.27 l mol^-1 s^-1 at pH 8.0 and 25° C. The rate constant increased by 4.4 times in the presence of Zn²⁺ and doubled at 35°C. We propose a mechanism for the reaction between glyoxylate and H₂O₂. From a comparison of the rates of H₂O₂ decomposition by catalase and the reaction with glyoxylate, we conclude that H₂O₂ produced during glycolate oxidation in peroxisomes is decomposed by catalase but not by the reaction with glyoxylate, and that photorespiratory CO₂ originates from glycine, but not from glyoxylate, in C₃ plants. Simulation using the above rate constant and reported kinetic parameters leads to the same conclusion, and also makes it clear that alanine is a satisfactory amino donor in the conversion of glyoxylate to glycine. Some serine might be decomposed to give glycine and methylene-tetrahydrofolate; the latter is ultimately oxidized to CO₂. In the simulation of the glycolate pathway of Euglena, the rate constant was high enough to ensure the decarboxylation of glyoxylate by H₂O₂ to produce photorespiratory CO₂ during the glycolate metabolism of this organism.Abbreviations Chl chlorophyll - GGT glutamate: glyoxylate aminotransferase (EC 2.6.1.4) - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - SGT serine: glyoxylate aminotransferase (EC 2.6.1.45) This is the ninth in a series on the metabolism of glycolate in Euglena gracilis. The eighth is Yokota et al. (1982)     

Incorporation of 14CO2 into C4 acids by leaves of C3-C4 intermediate and C3 species of Moricandia and Panicum at the CO2 compensation concentration

Comparative ¹⁴CO₂ pulse-¹²CO₂ chase studies performed at CO₂ compensation ()-versus air-concentrations of CO₂ demonstrated a four-to eightfold increase in assimilation of ¹⁴CO₂ into the C₄ acids malate and aspartate by leaves of the C₃-C₄ intermediate species Panicum milioides Nees ex Trin., P. decipiens Nees ex Trin., Moricandia arvensis (L.) DC., and M. spinosa Pomel at . Specifically, the distribution of ¹⁴C in malate and aspartate following a 10-s pulse with ¹⁴CO₂ increases from 2% to 17% (P. milioides) and 4% to 16% (M. arvensis) when leaves are illuminated at the CO₂ compensation concentration (20 l CO₂/l, 21% O₂) versus air (340 l CO₂/l, 21% O₂). Chasing recently incorporated ¹⁴C for up to 5 min with ¹²CO₂ failed to show any substantial turnover of label in the C₄ acids or in carbon-4 of malate. The C₄-acid labeling patterns of leaves of the closely related C₃ species, P. laxum Sw. and M. moricandioides (Boiss.) Heywood, were found to be relatively unresponsive to changes in pCO₂ from air to . These data demonstrate that the C₃-C₄ intermediate species of Panicum and Moricandia possess an inherently greater capacity for CO₂ assimilation via phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) at the CO₂ compensation concentration than closely related C₃ species. However, even at , CO₂ fixation by PEP carboxylase is minor compared to that via ribulosebisphosphate carboxylase (EC 4.1.1.39) and the C₃ cycle, and it is, therefore, unlikely to contribute in a major way to the mechanism(s) facilitating reduced photorespiration in the C₃-C₄ intermediate species of Panicum and Moricandia.Abbreviations Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - PEP phosphoenolpyruvate - CO₂ compensation concentration - 3PGA 3-phosphoglycerate - SuP sugar monophosphates - SuP₂ sugar bisphosphates Published as Paper No. 8249, Journal Series, Nebraska Agricultural Research Division