Dormancy and impotency of cocklebur seeds I. CO2, C2H4 O2 and high temperature

High O₂ tensions, CO₄, C₂H₄ and high temperatures were effectivenot only in breaking the dormancy of cocklebur (Xanthium pennsylvanicumWallr.) seeds but also in increasing the germination potentialof the nondormant but small seeds. There were few qualitativedifferences in response to these factors between the dormantand impotent seeds. Unlike CO₂, however, enriched O₂ and C₂H₄were stimulative even at the low temperature of 13°C. Germination induced by CO₂, C₂H₄ and high temperature treatmentswas lowered when endogenously evolved C₂H₄ or CO₂ was removed,whereas the effect of O₂ enrichment was not affected by theirremoval. CO₂ and high temperatures remarkably stimulated C₂H₄production, whereas O₂ enrichment had no such effect. C₂H₄ productivity was lower in the dormant than non-dormantseeds, suggesting that the after-ripening is characterized byincreasing C₂H₄ production. (Received August 20, 1974; )     

Synthesis and characterisation of the carboxylate linked osmium clusters [{Os3H(CO)10}2(CO2CH2CO2)], [{Os3H(CO)10}2(CO2C2H4CO2)], [{Os3H(CO)10}2(C4O4)] and [{Os3H(CO)10}2(C4O4){Co2(CO)6}]

Reactions between the activated cluster [Os₃(CO)₁₀(NCMe)₂] and malonic acid, succinic acid and dicarboxylic acetylene, respectively, lead to the formation of the linked cluster complexes [{Os₃H(CO)₁₀}₂(CO₂CH₂CO₂)] (1), [{Os₃H(CO)₁₀}₂(CO₂C₂H₄CO₂)] (2), and [{Os₃H(CO)₁₀}₂(C₄O₄)] (3) in good yield. Cluster 3 was subsequently treated with [Co₂(CO)₈] and this results in the addition of a “Co₂(CO)₆” group giving [{Os₃H(CO)₁₀}₂(C₂O₄){Co₂(CO)₆}] (4). The X-ray crystal structures are reported for 2–4. In each structure the two triangular triosmium units are linked by the carboxylate groups and within each complex the carboxylate groups are chelating and bridge two osmium atoms.     

Effect of Elevated CO2 on the Photosynthesis, Respiration and Growth of Perennial Ryegrass

Single, seed-grown plants of ryegrass (Lolium perenne L. cv.Melle) were grown for 49 d from the early seedling stage ingrowth cabinets at a day/night temperature of 20/15 C, witha 12 h photoperiod, and a CO₂ concentration of either 340 or680µI 1^–1 CO₂. Following complete acclimation tothe environmental regimes, leaf and whole plant CO₂ effluxesand influxes were measured using infra-red gas analysis techniques.Elevated CO₂ increased rates of photosynthesis of young, fullyexpanded leaves by 35–46% and of whole plants by morethan 50%. For both leaves and whole plants acclimation to 680µI^–1 CO₂ reduced rates of photosynthesis in bothCO₂ regimes, compared with plants acclimated to 340µll^–1. There was no significant effect of CO₂ regime onrespiration rates of either leaves or whole plants, althoughleaves developed in elevated CO₂ exhibited generally lower ratesthan those developed in 340µI I^–1 CO₂. Initially the seedling plants in elevated CO₂ grew faster thantheir counterparts in 340µI I^–1 CO₂, but this effectquickly petered out and final plant weights differed by onlyc. 10%. Since the total area of expanded and unexpanded laminaewas unaffected by CO₂ regime, specific leaf area was persistently13–40% lower in elevated CO₂ while, similarly, root/shootratio was also reduced throughout the experiment. Elevated CO₂reduced tissue nitrogen contents of expanded leaves, but hadno effect on the nitrogen contents of unexpanded leaves, sheathsor roots. The lack of a pronounced effect of elevated CO₂ on plant growthwas primarily due to the fact that CO₂ concentration did notinfluence tiller (branch) numbers. In the absence of an effecton tiller numbers, any possible weight increment was restrictedto the c. 2.5 leaves of each tiller. The reason for the lackof an effect on tillering is not known. Key words: Lolium perenne, ryegrass, elevated CO₂, photosynthesis, respiration, growth, development     

Growth, denitrification and nitrate ammonification of the rhizobial strain TNAU 14 in presence and absence of C2H4 and C2H2

Soil-N (NO₃ ^?) initiates as far as a threshold concentration is surpassed manifold physiological reactions on N₂-fixation. Organic N and ammonium oxidised to NO₃ ^? means oxygen depletion. Plants suffering under O₂ or infection stress start to excrete ethylene (C₂H₄). C₂H₄ widens the root intercellulars that O₂-respiration will continue. Now microbes may more easily enter the plant interior by transforming the reached methionine into C₂H₄. Surplus nitrate and C₂H₄ inhibit nodulation of leguminous plants. Excess NO₃ ^? in the nodulesphere could be diminished by N₂-fixing bacteria which in addition can denitrify or ammonify nitrate. Consequently, it was asked whether C₂H₄ interferes with the potential of N₂-fixing bacteria to reduce nitrate. The groundnut-nodule isolate TNAU 14, from which it was known that it denitrifies and ammonifies nitrate, served as inoculum of a KNO₃-mannitol-medium that was incubated under N₂-, 1% (v/v) N₂?C₂H₄-, and 1% (v/v) N₂?C₂H₂-atmosphere in the laboratory. C₂H₂ was included into the experiments because it is frequently used to quantify N₂-fixing potentials (acetylene reduction array, ARA). Gene-16S rDNA-sequencing and physiological tests revealed a high affiliation of strain TNAU 14 toRhizobium radiobacter andRhizobium tumefaciens. Strain TNAU 14 released N₂O into the bottle headspace in all treatments, surprisingly significantly less in presence of C₂H₂. Nitrate-ammonification was even completely blocked by C₂H₂. C₂H₄, in contrast rather stimulated growth, denitrification, and nitrate-ammonification of strain TNAU 14 which consumed the released NH₄ ⁺ during continuing incubation.     

Reduction of Respiration by High Ambient CO2 and the Resulting Error in Measurements of Respiration Made with O2 Electrodes

Respiration rates of Lemna gibba fronds and Orobanche aegyptiacaand Lactuca sativa seedlings, were measured with a Clark typeoxygen electrode in the presence or absence of a carbon-dioxideabsorber (KOH) in the gas phase. Measured respiration ratesin the presence of KOH were 17-34% higher than in its absence.The suppression of respiration by high CO₂ concentrations, [CO₂],was confirmed by parallel studies of CO₂ efflux, made by infraredgas spectrometry. These results are consistent with other reportsof reduced rates of respiration at high [CO₂]. Measurements of respiration quotients of Lemna and Lactuca weremade at 0 and 100 Pa [CO₂]. Results did not support the possibilityof induced dark fixation of CO₂ at the ambient atmospheric [CO₂]predicted for the next century (35-100 Pa). It is concluded that the numerous reports of respiration measurementsmade with O₂ electrodes, in the absence of a CO₂ absorber, maycontain a significant errorCopyright 1993, 1999 Academic Press Lemna gibba, Lactuca sativa, Orobanche aegyptiaca, CO₂ accumulation, O₂ electrode, respiration, dark CO₂ fixation, respiration quotient, atmospheric CO₂     

C4 photosynthesis, atmospheric CO2, and climate

The objectives of this synthesis are (1) to review the factors that influence the ecological, geographical, and palaeoecological distributions of plants possessing C₄ photosynthesis and (2) to propose a hypothesis/model to explain both the distribution of C₄ plants with respect to temperature and CO₂ and why C₄ photosynthesis is relatively uncommon in dicotyledonous plants (hereafter dicots), especially in comparison with its widespread distribution in monocotyledonous species (hereafter monocots). Our goal is to stimulate discussion of the factors controlling distributions of C₄ plants today, historically, and under future elevated CO₂ environments. Understanding the distributions of C₃/C₄ plants impacts not only primary productivity, but also the distribution, evolution, and migration of both invertebrates and vertebrates that graze on these plants. Sixteen separate studies all indicate that the current distributions of C₄ monocots are tightly correlated with temperature: elevated temperatures during the growing season favor C₄ monocots. In contrast, the seven studies on C₄ dicot distributions suggest that a different environmental parameter, such as aridity (combination of temperature and evaporative potential), more closely describes their distributions. Differences in the temperature dependence of the quantum yield for CO₂ uptake (light-use efficiency) of C₃ and C₄ species relate well to observed plant distributions and light-use efficiency is the only mechanism that has been proposed to explain distributional differences in C₃/C₄ monocots. Modeling of C₃ and C₄ light-use efficiencies under different combinations of atmospheric CO₂ and temperature predicts that C₄-dominated ecosystems should not have expanded until atmospheric CO₂ concentrations reached the lower levels that are thought to have existed beginning near the end of the Miocene. At that time, palaeocarbonate and fossil data indicate a simultaneous, global expansion of C₄-dominated grasslands. The C₄ monocots generally have a higher quantum yield than C₄ dicots and it is proposed that leaf venation patterns play a role in increasing the light-use efficiency of most C₄ monocots. The reduced quantum yield of most C₄ dicots is consistent with their rarity, and it is suggested that C₄ dicots may not have been selected until CO₂ concentrations reached their lowest levels during glacial maxima in the Quaternary. Given the intrinsic light-use efficiency advantage of C₄ monocots, C₄ dicots may have been limited in their distributions to the warmest ecosystems, saline ecosystems, and/or to highly disturbed ecosystems. All C₄ plants have a significant advantage over C₃ plants under low atmospheric CO₂ conditions and are predicted to have expanded significantly on a global scale during full-glacial periods, especially in tropical regions. Bog and lake sediment cores as well as pedogenic carbonates support the hypothesis that C₄ ecosystems were more extensive during the last glacial maximum and then decreased in abundance following deglaciation as atmospheric CO₂ levels increased. Received: 12 February 1997 / Accepted: 20 June 1997     

Maximum Quantum Yields of O2 Evolution in C4 Plants under High CO2

The quantum yields of photosynthetic O₂ evolution were measuredin 15 species of C₄ plants belonging to three different decarboxylationtypes (NADP-ME type, NAD-ME type and PEP-CK type) and 5 speciesof C₃ plants and evaluated relative to the maximum theoreticalvalue of 0.125 mol oxygen quanta^-1. At 25°C and 1% CO₂,the quantum yield in C₄ plants averaged 0.079 (differences betweensubgroups not significant) which was significantly lower thanthe quantum yield in C₃ plants (average of 0.105 for 5 species).This lower quantum yield in C₄ plants is thought to reflectthe requirement of energy in the C₄ cycle. For the C₄ NADP-MEtype plant Z. mays and NAD-ME type plant P. miliaceum, quantumyields were also measured over a range of CO₂ levels between1 and 20%. In both species maximum quantum yields were obtainedunder 10% CO₂ (0.105 O₂ quanta_-1 in Z. mays and 0.097 O₂ quanta_-1in P. miliaceum) indicating that at this CO₂ concentration thequantum yields are similar to those obtained in C₃ plants underCO₂ saturation. The high quantum yield values in C₄ plants undervery high CO₂ may be accomplished by direct diffusion of atmosphericCO₂ to bundle sheath cells, its fixation in the C₃ pathway,and feedback inhibition of the C₄ cycle by inorganic carbon. (Received June 6, 1995; Accepted August 15, 1995)     

H2 oxidation,O2 uptake and CO2 fixation in hydrogen treated soils

In many legume nodules, the H₂ produced as a byproduct of N₂ fixation diffuses out of the nodule and is consumed by the soil. To study the fate of this H₂ in soil, a H₂ treatment system was developed that provided a 300 cm³ sample of a soil:silica sand (2:1) mixture with a H₂ exposure rate (147 nmol H₂ cm^–3hr^–1) similar to that calculated exist in soils located within 1–4 cm of nodules (30–254 nmol H₂ cm^–3hr^–1). After 3 weeks of H₂ pretreatment, the treated soils had a K_m and V_max for H₂ uptake (1028 ppm and 836 nmol cm^–3 hr^–1, respectively) much greater than that of control, air-treated soil (40.2 ppm and 4.35 nmol cm^–3 hr^–1, respectively). In the H₂ treated soils, O₂, CO₂ and H₂ exchange rates were measured simultaneously in the presence of various pH₂. With increasing pH₂, a 5-fold increase was observed in O₂ uptake, and CO₂ evolution declined such that net CO₂ fixation was observed in treatments of 680 ppm H₂ or more. At the H₂ exposure rate used to pretreat the soil, 60% of the electrons from H₂ were passed to O₂, and 40% were used to support CO₂ fixation. The effect of H₂ on the energy and C metabolism of soil may account for the well-known effect of legumes in promoting soil C deposition.     

CO2 and O2 dependence of PS II activity in C4 plants having genetically produced deficiencies in the C3 or C4 cycle

The CO2 dependence of rates of CO2 fixation (A) and photochemistry of PS II at 5, 15 and 30% O2 were analyzed in the C4 plant Amaranthus edulis having a C4 cycle deficiency [phosphoenolpyruvate carboxylase (PEPC) mutants], and in the C4 plant Flaveria bidentis having a C3 cycle deficiency [Rubisco small subunit antisense (SSU)]. In the wild type (WT) A. edulis and its heterozygous mutant having less than 50% WT PEPC activity there was a similar dependence of A and PS II photochemistry on varying CO2, although the CO2 saturated rates were 25% lower in heterozygous plants. The homozygous plants having less than 2% PEPC of the WT had significant levels of photorespiration at ambient levels of CO2 and required about 30 times ambient levels for maximum rates of A. Despite variation in the capacity of the C4 cycle, more than 91% of PS II activity was linearly associated with A under varying CO2 at 5, 15 and 30% O2. However, the WT plant had a higher PS II activity per CO2 fixed under saturating CO2 than the homozygous mutant, which is suggested to be due to elimination of the C4 cycle and its associated requirement for ATP from a Mehler reaction. In the SSU F. bidentis plants, a decreased rate of A (35%) and PS II activity (33%) accompanied a decrease in Rubisco capacity. There was some increase in alternative electron sinks at high CO2 when the C3 cycle was constrained, which may be due to increased flux through the C4 cycle via an ATP generating Mehler reaction. Nevertheless, even with constraints on the function of the C4 or C3 cycle by genetic modifications, analyses of CO2 response curves under varying levels of O2 indicate that CO2 assimilation is the main determinant of PS II activity in C4 plants.     

Differential effects of oligomycin on carotid chemoreceptor responses to O2 and CO2 in the cat

Effects of oligomycin on carotid chemoreceptor responses to O2 and CO2 were investigated using an in situ perfusion technique. Cats were anesthetized, paralyzed, and artificially ventilated. To avoid a possible reaction between an oligomycin-ethanol mixture and blood, we administered oligomycin to the carotid body via cell- and protein-free perfusate. Except for the perfusion periods, the carotid body received its own natural blood supply. Responses to O2, CO2, sodium cyanide, and nicotine of the same carotid chemoreceptor afferents were studied before and after each perfusion. An appropriate low dose of oligomycin completely blocked carotid chemoreceptor response to O2 while preserving the CO2 response. At the same time cyanide response was attenuated leaving nicotine response intact. Additional doses of oligomycin attenuated carotid chemoreceptor response to CO2 as well. Perfusion with a blank solution containing ethanol did not change the carotid body chemoreceptor responses. These effects of oligomycin on carotid chemoreceptor responses to O2 and CO2 were reversible, and restoration of the response to CO2 preceded that to O2. In addition, oligomycin administered into the blood with close intra-arterial injection produced similar differential blockade of O2 and CO2 chemoreception, preserving the nicotine and dopamine effects. This study confirmed the previous findings and provided new evidence showing that 1) the responses of carotid chemoreceptor to O2 and CO2 were separable by oligomycin due to the inhibition of oxidative phosphorylation and 2) the responses to nicotine and dopamine were intact even after blockade of O2 response.     

Synthesis of biomolecules from N2, CO,and H2O by electric discharge

A model primitive gas containing a mixture of N₂, CO and water vapor over a water pool (300 mL, 37 °C) was subjected to electric discharges. The discharge vessel (7 L in volume) was equipped with a CO₂ absorber (The CO₂ being formed during the discharge), thus simulating possible absorption of CO₂ in the primitive ocean. The vessel also has a cold trap ( –15 °C), which protects the primary products against the further decomposition in the discharge phase by enabling these products to adhere to the trap. Since the partial pressures of CO and N₂ decreased at rates of 1.5–1.7 cmHg day^–1 and 0.1–0.2 cmHg day^–1, respectively, the gases were added at regular intervals. The solution was analyzed at regular intervals for HCN, HCHO and urea, and maximum concentrations of about 50, 2, and 140 mM were observed. The discharge phase was continued for 6 months. In the solution, glycine (5.6% yield based on the carbon), glycylglycine (0.64%), orotic acid (0.004%) and small amounts of the other amino acids were found.     

Biomethanation: Anaerobic fermentation of CO2, H2 and CO to methane

Studies to examine the microbial fermentation of coal gasification products (CO₂, H₂ and CO) to methane have been done with a mixed culture of anaerobic bacteria selected from an anaerobic sewage digestor. The specific rate of methane production at 37°C reached 25 mmol/g cell hr. The stoichiometry for methane production was 4 mmol H₂/mol CO₂. Cell recycle was used to increase the cell concentration from 2.5 to 8.3 g/liter; the volumetric rate of methane production ran from 1.3 to 4 liter/liter hr. The biogasification was also examined at elevated pressure (450 psi) and temperature to facilitate interfacing with a coal gasifier. At 60°C, the specific rate of methane production reached 50 mmol/g cell hr. Carbon monoxide utilization by the mixed culture of anaerobes and by a Rhodopseudomonas species was examined. Both cultures are able to carry out the shift conversion of CO and water to CO₂ and hydrogen.     

Effects of Atmospheric CO(2) Enrichment on Photosynthesis, Respiration, and Growth of Sour Orange Trees

Numerous net photosynthetic and dark respiratory measurements were made over a period of 4 years on leaves of 24 sour orange (Citrus aurantium) trees; 8 of them growing in ambient air at a mean CO₂ concentration of 400 microliters per liter, and 16 growing in air enriched with CO₂ to concentrations approaching 1000 microliters per liter. Over this CO₂ concentration range, net photosynthesis increased linearly with CO₂ by more than 200%, whereas dark respiration decreased linearly to only 20% of its initial value. These results, together with those of a comprehensive fine-root biomass determination and two independent aboveground trunk and branch volume inventories, suggest that a doubling of the air's current mean CO₂ concentration of 360 microliters per liter would enhance the growth of the trees by a factor of 3.8.     

Effects of 2,5-norbornadiene on cocklebur seed germination and rice coleoptile elongation in response to CO2 and C2H4

To examine in more detail the mechanisms of cocklebur (Xanthium pennsylvanicum Wallr.) seed germination and rice (Oryza sativa L. cv. Sasanishiki) coleoptile elongation that were responsive to both C₂H₄ and CO₂, the effects of NBD (2,5-norbornadiene), a cyclic olefin known as a competitive inhibitor of C₂H₄, on those phenomena were tested under various conditions. NBD strongly inhibited germination of cocklebur seeds and their axial and cotyledonary growth. The NBD effects were significantly negated by endogenously evolved and exogenously applied CO₂ regardless of incubation temperature. Similarly, the inhibitory NBD effect was negated by C₂H₄ at 23°C, but at 33°C a low concentration (3 1/L) of C₂H₄ rather enhanced the inhibitory NBD effect. This phenomenon reflected the growth responses of the tip zone of axial tissues in cocklebur seeds to NBD and C₂H₄, in which both gases were antagonistic in regulating the axial growth at 23°C but additive in inhibiting it at 33°C. Maximal negation of these inhibitory NBD effects was brought about by simultaneous application of CO₂ and C₂H₄. Similarly, elongation of rice coleoptiles was suppressed by NBD, and when they were immature, its inhibitory action was counteracted by both C₂H₄ and CO₂, especially during simultaneous application. However, the inhibitory NBD effect was completely negated by C₂H₄ applied alone at concentrations above 500 1/L regardless of the physiological age of coleoptiles. These inhibitory NBD effects are additional evidence suggesting that C₂H₄ acts as a growth regulator in both cocklebur seed germination and rice coleoptile elongation. That NBD was capable of counteracting CO₂ action in some cases but was incapable of negating inhibitory C₂H₄ action, such as that observed in cocklebur seeds, suggests that NBD acts with some side effects besides being a competitive inhibitor of C₂H₄ actions.     

Responses of C4 grasses to atmospheric CO2 enrichment

Summary The growth and photosynethetic responses to atmospheric CO₂ enrichment of 4 species of C₄ grasses grown at two levels of irradiance were studied. We sought to determine whether CO₂ enrichment would yield proportionally greater growth enhancement in the C₄ grasses when they were grown at low irradiance than when grown at high irradiance. The species studied were Echinochloa crusgalli, Digitaria sanguinalis, Eleusine indica, and Setaria faberi. Plants were grown in controlled environment chambers at 350, 675 and 1,000 l 1^-1 CO₂ and 1,000 or 150 mol m^-2 s^-1 photosynthetic photon flux density (PPFD). An increase in CO₂ concentration and PPFD significantly affected net photosynthesis and total biomass production of all plants. Plants grown at low PPFD had significantly lower rates of photosynthesis, produced less biomass, and had reduced responses to increases in CO₂. Plants grown in CO₂-enriched atmosphere had lower photosynthetic capacity relative to the low CO₂ grown plants when exposed to lower CO₂ concentration at the time of measurement, but had greater rate of photosynthesis when exposed to increasing PPFD. The light level under which the plants were growing did not influence the CO₂ compensation point for photosynthesis.