Two-breath CO(2) test detects altered dynamic cerebrovascular autoregulation and CO(2) responsiveness with changes in arterial P(CO(2))

The new two-breath CO(2) method was employed to test the hypotheses that small alterations in arterial P(CO(2)) had an impact on the magnitude and dynamic response time of the CO(2) effect on cerebrovascular resistance (CVRi) and the dynamic autoregulatory response to fluctuations in arterial pressure. During a 10-min protocol, eight subjects inspired two breaths from a bag with elevated P(CO(2)), four different times, while end-tidal P(CO(2)) was maintained at three levels: hypocapnia (LoCO(2), 8 mmHg below resting values), normocapnia, and hypercapnia (HiCO(2), 8 mmHg above resting values). Continuous measurements were made of mean blood pressure corrected to the level of the middle cerebral artery (BP(MCA)), P(CO(2)) (estimated from expired CO(2)), and mean flow velocity (MFV, of the middle cerebral artery by Doppler ultrasound), with CVRi = BP(MCA)/MFV. Data were processed by a system identification technique (autoregressive moving average analysis) with gain and dynamic response time of adaptation estimated from the theoretical step responses. Consistent with our hypotheses, the magnitude of the P(CO(2))-CVRi response was reduced from LoCO(2) to HiCO(2) [from -0.04 (SD 0.02) to -0.01 (SD 0.01) (mmHg x cm(-1) x s) x mmHg Pco(2)(-1)] and the time to reach 95% of the step plateau increased from 12.0 +/- 4.9 to 20.5 +/- 10.6 s. Dynamic autoregulation was impaired with elevated P(CO(2)), as indicated by a reduction in gain from LoCO(2) to HiCO(2) [from 0.021 +/- 0.012 to 0.007 +/- 0.004 (mmHg x cm(-1) x s) x mmHg BP(MCA)(-1)], and time to reach 95% increased from 3.7 +/- 2.8 to 20.0 +/- 9.6 s. The two-breath technique detected dependence of the cerebrovascular CO(2) response on P(CO(2)) and changes in dynamic autoregulation with only small deviations in estimated arterial P(CO(2)).     

Vibrational spectra and structure of M(CO2) and M2(CO2) molecules

Atomic Na, K and Cs were codeposited with CO₂ in excess of matrix gas at the temperature of 12 K. The IR spectra revealed the presence of ionic aggregates corresponding to the molecules M(CO)₂ and M₂(CO₂) (M=Na, K, Cs). Both molecular species have C_2v symmetry; M(CO₂) species have a planar ring structure while M₂(CO₂) have a W-shape structure. M₂(CO₂) molecules with C_s symmetry were also identified. The geometrical parameters of all the molecules were determined by ¹²C/¹³C and ¹⁶O/¹⁸O isotopic shifts. Raman spectra were also recorded and the results are reported in this study. The effect of photolysis on the structure of these molecules was examined. It was determined that photolysis promotes the formation of Na(CO₂) and transforms the M₂(CO₂) molecules with C_2v symmetry into C_s symmetry isomers.     

CO(2)-Enhanced Yield and Foliar Deformation among Tomato Genotypes in Elevated CO(2) Environments

Yield increases observed among eight genotypes of tomato (Lycopersicon esculentum Mill.) grown at ambient CO₂ (about 350) or 1000 microliters per liter CO₂ were not due to carbon exchange rate increases. Yield varied among genotypes while carbon exchange rate did not. Yield increases were due to a change in partitioning from root to fruit. Tomatoes grown with CO₂ enrichment exhibited nonepinastic foliar deformation similar to nutrient deficiency symptoms. Foliar deformation varied among genotypes, increased throughout the season, and became most severe at elevated CO₂. Foliar deformation was positively related to fruit yield. Foliage from the lower canopy was sampled throughout the growing season and analysed for starch, K, P, Ca, Mg, Fe, and Mn concentrations. Foliar K and Mn concentrations were the only elements correlated with deformation severity. Foliar K decreased while deformation increased. In another study, foliage of half the plants of one genotype received foliar applications of 7 millimolar KH₂PO₄. Untreated foliage showed significantly greater deformation than treated foliage. Reduced foliar K concentration may cause CO₂-enhanced foliar deformation. Reduced K may occur following decreased nutrient uptake resulting from reduced root mass due to the change in partitioning from root to fruit.     

Oscillations of the internal CO(2) concentration in tobacco leaves transferred to low CO(2)

Measurement of the internal CO(2) concentration (Ci) in tobacco leaves using a fast-response CO(2) exchange system showed that in the light, switching from 350 microLL(-1) to a low CO(2) concentration of 36.5 microLL(-1) (promoting high photorespiration) resulted in the Ci oscillating near the value of CO(2) compensation point (Gamma*). The oscillations are highly irregular, the range of Ci varying by 2-4 microLL(-1) in substomatal cavities with a period of a few seconds. The statistical properties of the time series became stationary after a transient of approximately 100s following transfer to low CO(2). Attractor reconstruction shows that the observed oscillations are not chaotic but exhibit stochastic behavior. The period of oscillations is consistent with the duration of photorespiratory post-illumination burst (PIB). We suggest that the observed oscillations may be due to a similar mechanism to that which leads to PIB, and may play a role in switching mitochondrial operation between oxidation of the photorespiratory glycine and of the tricarboxylic acid cycle substrates.     

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.     

CO(2) Fixation in Opuntia Roots

Nonautotrophic CO₂ metabolism in Opuntia echinocarpa roots was studied with techniques of manometry and radiometry. The roots were grown in a one-quarter strength nutrient solution for several days; the distal 2 cm was used for physiological studies. The roots assimilated significant quantities of ¹⁴CO₂ and appeared to show a crassulacean-type acid metabolism with respect to quality and quantity. Most of the ¹⁴C activity was associated with the distal portion of the elongating root indicating correlation with metabolic activity. The ¹⁴CO₂ assimilation was comparable to a crassulacean leaf succulent, but 3 times greater than that found for stem tissue of the same Opuntia species.

The rates of O₂ and CO₂ exchange and estimated CO₂ fixation were 180, 123, and 57 μl/g per hour. A respiratory quotient of 0.66 was found.

The products of ¹⁴CO₂ fixation were similar in most respects to reported experiments with leaf succulents. Equilibration of the predominant malic acid with isocitric, succinic, and fumaric acids was not evident. The latter observation was interpreted as metabolic isolation of the fixation products rather than poor citric acid cycle activity.

A rapid turnover of the fixed ¹⁴CO₂ was measured by following decarboxlyation kinetics and by product analysis after a postincubation period. The first order rate constant for the steady state release was 4.4 × 10⁻³ min⁻¹ with a half-time of 157.5 minutes. Amino acids decayed at a more rapid rate than organic acids.

     

Ethylene Contamination of CO(2) Cylinders: Effects on Plant Growth in CO(2) Enrichment Studies

The mechanical extensibilities of stage IVb Phycomyces were measured before and after a humidified wind stimulus. We find that when the humidity of the wind is greater than that of the ambient air, there is an increase in the mechanical extensibility of the cell wall. We also find that a step decrease in wind humidity results in a decrease in the mechanical extensibility of the cell wall.     

Carbon Dioxide Exchanges in Leaves. I. Discrimination Between CO(2) and CO(2) in Photosynthesis

In order to measure CO₂ exchange reactions by leaves using isotopes of CO₂, it is necessary to know precisely the discrimination against ¹⁴CO₂ by leaves. Earlier determinations of discrimination are at variance, and may be inaccurate because of assumptions made about the rate of photorespiration. Maize leaves evolve little or no CO₂ in light, and so provide suitable material for this measurement. Discrimination against ¹⁴CO₂ in photosynthesis by maize leaves is almost precisely the same as in CO₂ absorption by NaOH solution, amounting to 2.1 and 2.0% respectively. The agreement between these values and their close approximation to the relative rates of diffusion of ¹²CO₂ and ¹⁴CO₂, calculated from Graham's law, shows that diffusion into the leaf is primarily responsible for discrimination against ¹⁴CO₂ in photosynthesis.     

Photosynthetic CO(2) Fixation at Air Levels of CO(2) by Isolated Spinach Chloroplasts

A system has been developed for the study of photosynthetic CO₂ fixation by isolated spinach chloroplasts at air levels of CO₂. Rates of CO₂ fixation were typically 20 to 60 micromoles/milligrams chlorophyll per hour. The rate of fixation was linear for 10 minutes but then declined to less than 10% of the initial value by 40 minutes. Ribulose 1,5-bisphosphate (RuBP) levels remained unchanged during this period, indicating that they were not the cause for the decline. The initial activity of the RuBP carboxylase in the chloroplast was high for 8 to 10 minutes and then declined similar to the rate of CO₂ fixation, suggesting that the decline in CO₂ fixation may have been caused by deactivation of the enzyme.     

Laboratory-Produced CO(2) Calibration Gases

A simple, inexpensive apparatus for making mixtures of accurately known amounts of CO₂ and CO₂-free atmospheric air is described. Calibration gases with CO₂ contents of 200 to 1500 microliters per liter produced with the apparatus had concentrations which were within 10 microliters per liter of the target concentration.     

Adaptation to Low CO(2) Level in a Mutant of Anacystis nidulans R(2) which Requires High CO(2) for Growth

The mutant E₁ of Anacystis nidulans R₂ requires high CO₂ concentration for growth but was able to adapt to low CO₂ concentration. This was exhibited by the increased ability to accumulate inorganic carbon within the cells and the large increase in the amount of a 42-kilodalton polypeptide located in the cytoplasmic membrane. The adaptation occurred in E₁ cells at an extracellular CO₂ concentration as high as 0.3%, which was 8 times the concentration for maximal adaptation in R₂ cells. The ability of E₁ cells to exhibit low CO₂ characteristics at a higher CO₂ concentration was attributed to lower intracellular CO₂ concentration.     

Long-distance CO(2) signalling in plants.

Stomatal numbers are tightly controlled by environmental signals including light intensity and atmospheric CO(2) partial pressure. This requires control of epidermal cell development during the early phase of leaf growth and involves changes in both the density of cells on the leaf surface and the proportion of cells that adopt a stomatal fate. This paper reviews the current understanding of how stomata develop and describes recent advances that have given insights into the regulatory mechanisms involved using mutant Arabidopsis plants that implicates a role for long-chain fatty acids in cell-to-cell communication. Evidence is presented which indicates that long-distance signalling from mature to newly developing leaves forms part of the mechanism by which stomatal development responds to environmental cues. Analysis of mutant plants suggests that the plant hormones abscisic acid, ethylene and jasmonates are implicated in the long-distance signalling pathway and that the action may be mediated by reactive oxygen species.     

Photochemical synthesis method of tungsten(II) complexes [WCl2(CO)3PPh3)2] and [WCl2(CO)2(dppe)]

The photochemical oxidation reaction of W(CO)₆ to [W(CO)₄Cl₂]₂ with CCl₄ was applied in the synthesis of [WCl₂(CO)₃(PPh₃)₂] and [WCl₂(CO)₂₋- (dppe)].     

Quantum Yields for CO(2) Uptake in C(3) and C(4) Plants: Dependence on Temperature, CO(2), and O(2) Concentration

The quantum yields of C₃ and C₄ plants from a number of genera and families as well as from ecologically diverse habitats were measured in normal air of 21% O₂ and in 2% O₂. At 30 C, the quantum yields of C₃ plants averaged 0.0524 ± 0.0014 mol CO₂/absorbed einstein and 0.0733 ± 0.0008 mol CO₂/absorbed einstein under 21 and 2% O₂. At 30 C, the quantum yields of C₄ plants averaged 0.0534 ± 0.0009 mol CO₂/absorbed einstein and 0.0538 ± 0.0011 mol CO₂/absorbed einstein under 21 and 2% O₂. At 21% O₂, the quantum yield of a C₃ plant is shown to be strongly dependent on both the intercellular CO₂ concentration and leaf temperature. The quantum yield of a C₄ plant, which is independent of the intercellular CO₂ concentration, is shown to be independent of leaf temperature over the ranges measured. The changes in the quantum yields of C₃ plants are due to changes in the O₂ inhibition. The evolutionary significance of the CO₂ dependence of the quantum yield in C₃ plants and the ecological significance of the temperature effects on the quantum yields of C₃ and C₄ plants are discussed.     

High CO(2) Requiring Mutant of Anacystis nidulans R(2)

Some physiological characteristics of a mutant (E₁) of Anacystis nidulans R₂, incapable of growing at air level of CO₂, are described. E₁ is capable of accumulating inorganic carbon (C_i) internally as efficiently as the wild type (R₂). The apparent photosynthetic affinity for C_i in E₁, however, is some 1000 times lower than that of R₂. The kinetic parameters of ribulose 1,5-bisphosphate carboxylase/oxygenase from E₁ are similar to those observed in R₂. The mutant appears to be defective in its ability to utilize the intracellular C_i pool for photosynthesis and depends on extracellular supply of Ci in the form of CO₂. The very high apparent photosynthetic K_m (CO₂) of the mutant indicate a large diffusion resistance for CO₂. Data obtained here are used to calculate the permeability coefficient for CO₂ between the bulk medium and the carboxylation site of cyanobacteria.     

Quantitation of the O(2)-Dependent, CO(2)-Reversible Component of the Postillumination CO(2) Exchange Transient in Tobacco and Maize Leaves

The postillumination transient of CO₂ exchange and its relation to photorespiration has been examined in leaf discs from tobacco (Nicotiana tabacum) and maize (Zea mays). Studies of the transients observed by infrared gas analysis at 1, 21, and 43% O₂ in an open system were extended using the nonsteady state model described previously (Peterson and Ferrandino 1984 Plant Physiol 76: 976-978). Cumulative CO₂ exchange equivalents (i.e. nanomoles CO₂) versus time were derived from the analyzer responses of individual transients. In tobacco (C₃), subtraction of the time course of cumulative CO₂ exchange under photorespiratory conditions (21 or 43% O₂) from that obtained under nonphotorespiratory conditions (1% O₂) revealed the presence of an O₂-dependent and CO₂-reversible component within the first 60 seconds following darkening. This component was absent in maize (C₄) and at low external O₂:CO₂ ratios (i.e. <100) in tobacco. The size of the component in tobacco increased with net photosynthesis as irradiance was increased and was positively associated with inhibition of net photosynthesis by O₂. This relatively simple and rapid method of analysis of the transient is introduced to eliminate some uncertainties associated with estimation of photorespiration based on the maximal rate of postillumination CO₂ evolution. This method also provides a useful and complementary tool for detecting variation in photorespiration.     

Photoreduction of O(2) Primes and Replaces CO(2) Assimilation

A mass spectrometer with a membrane inlet system was used to monitor directly gaseous components in a suspension of algae. Using labeled oxygen, we observed that during the first 20 seconds of illumination after a dark period, when no net O₂ evolution or CO₂ uptake was observed, O₂ evolution was normal but completely compensated by O₂ uptake. Similarly, when CO₂ uptake was totally or partially inhibited, O₂ evolution proceeded at a high (near maximal) rate. Under all conditions, O₂ uptake balanced that fraction of the O₂ evolution which could not be accounted for by CO₂ uptake.