The Diffusion of Carbon Dioxide and Water Vapour through Stomata

An account is given of the diffusion of carbon dioxide and ofwater vapour through the stomata of leaves in the presence ofair. It shows that the argument given in K. J. Parkinson andH. L. Penman's paper (1970): ‘A Possible Source of Errorin the Estimation of Stomatal Resistance’ is substantiallyincorrect. However, the correction factors to the sugar beetdata presented in their paper are valid owing to a fortuitousset of circumstances including the similarity in magnitude oftwo mutual diffusion coefficients. The concept of stomatal resistanceis criticized.     

On Photosynthesis and Organic Carbon, Carbon Dioxide, and Oxygen Flows in the Ocean

The modern concept of photosynthesis as a mechanism for utilizing the energy of solar radiation is used as the basis for assessing the scale of photosynthetic production of initial organic matter in the ocean (primary biological production), its destruction, the carbon and carbon dioxide cycles (flows) involved in this process, and the size of oil- and gas-bearing hydrocarbonaceous formations originating in sedimentary deposits.     

Simultaneous Measurement of Oxygen, Carbon Dioxide, and Water Vapour Exchange in Intact Plants

A low flow of air is passed through a temperature-controlledplant chamber in order to obtain relatively large (300–500µl-1) differences in [O₂] between influx and efflux streams.These differences are measured with a stabilized O₂ electrodesystem incorporating elements of gas conditioning electroniczero suppression and signal amplification. Changes in [O₂] of400 µl l-1 can be detected at full scale recorder deflectionagainst a background concentration of 21% O₂. The concentrationsof CO₂ and H₂O within the chamber are held constant by con-trolled-flowCO₂-scrubbing and dehumidifying loops. Carbon dioxide, H₂O,and O₂ fluxes are measured and leaf diffusion resistance andinternal [CO₂] are calculated in essentially ‘real time’.     

Growth of Sclerotiumrolfsiiat Different Concentration of Oxygen and Carbon Dioxide

Sclerotium rolfsii was grown in various atmospheres, the compositionsof which were controlled by the diffusion column technique.Growth-rate of mycelium was constant within a range of oxygenconcentrations from 3 to 21 per cent, but dirminished steadilyas carbon dioxide concentration increased from about 0.03 percent. The rate of sclerotial germination was reduced by oxygenconcentrations less than 6 per cent and by carbon dioxide concentrationsgreater than about 10 per cent. No sclerotia were formed ifthe concentration of oxygen fell below 15 per cent or if thatof carbon dioxide exceeded 4 per cent. The effects of inverserationof gases, from 0 per cent oxygen: 20 per cent carbon dioxideto 21 per cent oxygen: 0 per cent carbon dioxide, were in eachcase similar to the effect of the corresponding carbon dioxideconcentration when combined with 21 per cent oxygen.     

Light-driven Uptake of Oxygen, Carbon Dioxide, and Bicarbonate by the Green Alga Scenedesmus

Mass spectrometric techniques were used to study several aspects of the competition between O₂ and species of inorganic carbon for photosynthetically generated reducing power in the green alga, Scenedesmus.     

Carbon Dioxide, Oxygen and Ethylene Effects on Potato Tuber Dormancy Release and Sprout Growth

The possible roles of oxygen and carbon dioxide treatments inthe presence or absence of ethylene on tuber dormancy releasein potato (Solanum tuberosumL.) were examined. Using two gascompositions (I: 60% CO₂–20% O₂–20% N₂and II: 20%CO₂–40% O₂–40% N₂), the phase of tuber dormancyand previous storage temperature were demonstrated to be importantparameters for dormancy release by these gas mixtures. Gas Icaused decreased abscisic acid (ABA) levels within 24 h regardlessof previous storage temperature, although this effect was reversible.Exogenous C₂H₄, an effective dormancy release agent, also causeddecreased ABA levels within 24 h. It also enhanced dormancyrelease and further promoted ABA losses by gas I. Gas II treatmentled to slight reductions in ABA levels that were further decreasedby C₂H₄. Sprout length was modelled successfully by multipleregression analysis in terms of glucose and ABA levels withinthe apical eye tissues of Russet Burbank tubers immediatelyafter, and regardless of, previous gas treatments or storagetemperatures. Solanum tuberosum,potato, abscisic acid, ethylene, carbon dioxide, oxygen, dormancy.     

Growth Response of Axenic Entamoeba histolytica to Hydrogen, Carbon Dioxide, and Oxygen *,†

Entamoeba histolytica required CO₂ for growth in axenic culture while growth was inhibited by H₂. The organism was tolerant to 5% O₂ in the gas phase and it was able to detoxify products of O₂ reduction in the medium. The ameba did not require a negative oxidation-reduction potential for axenic growth. However, little or no free O₂ was present in media exposed to 5% O₂ in the gas phase. Growth was improved by adding yeast extract to the medium.     

Cross-Modulation of Homeostatic Responses to Temperature,Oxygen and Carbon Dioxide in C. elegans

Different interoceptive systems must be integrated to ensure that multiple homeostatic insults evoke appropriate behavioral and physiological responses. Little is known about how this is achieved. Using C. elegans, we dissect cross-modulation between systems that monitor temperature, O₂ and CO₂. CO₂ is less aversive to animals acclimated to 15°C than those grown at 22°C. This difference requires the AFD neurons, which respond to both temperature and CO₂ changes. CO₂ evokes distinct AFD Ca²⁺ responses in animals acclimated at 15°C or 22°C. Mutants defective in synaptic transmission can reprogram AFD CO₂ responses according to temperature experience, suggesting reprogramming occurs cell autonomously. AFD is exquisitely sensitive to CO₂. Surprisingly, gradients of 0.01% CO₂/second evoke very different Ca²⁺ responses from gradients of 0.04% CO₂/second. Ambient O₂ provides further contextual modulation of CO₂ avoidance. At 21% O₂ tonic signalling from the O₂-sensing neuron URX inhibits CO₂ avoidance. This inhibition can be graded according to O₂ levels. In a natural wild isolate, a switch from 21% to 19% O₂ is sufficient to convert CO₂ from a neutral to an aversive cue. This sharp tuning is conferred partly by the neuroglobin GLB-5. The modulatory effects of O₂ on CO₂ avoidance involve the RIA interneurons, which are post-synaptic to URX and exhibit CO₂-evoked Ca²⁺ responses. Ambient O₂ and acclimation temperature act combinatorially to modulate CO₂ responsiveness. Our work highlights the integrated architecture of homeostatic responses in C. elegans.     

Carbon Dioxide Exchange and Acidity Levels in Detached Pineapple, Ananas comosus (L.), Merr., Leaves during the Day at Various Temperatures, Oxygen and Carbon Dioxide Concentrations

The effects of temperature, O₂, and CO₂ on titratable acid content and on CO₂ exchange were measured in detached pineapple (Ananas comosus) leaves during the daily 15-hour light period. Comparative measurements were made in air and in CO₂-free air. Increasing the leaf temperature from 20 to 35 C decreased the total CO₂ uptake in air and slightly increased the total CO₂ released into CO₂-free air. Between 25 and 35 C, the activation energy for daily acid loss was near 12 kcal mol⁻¹, but at lower temperatures the activation energy was much greater.     

The Response of Oxygen and Carbon Dioxide Exchanges and Root Activity to Short Term Water Stress in Soybean

The gross and net O₂ evolution together with O₂ uptake, CO₂assimilation, transpiration, shoot dark respiration, root respirationand ion uptake of a soybean plant were studied during 19 d whichincluded two periods of water stress. O₂ uptake was measuredusing ¹⁸O₂ as a tracer. Short term water stress induced immediateand lasting effects: (1) reduction of light interception bywilting, (2) limitation of the total reducing equivalent producedby the electron transport chain, (3) decrease of stomatal conductancereducing both losses of water and the entry of CO₂ for assimilation,(4) relative stimulation of O₂ uptake. The ratio of O₂ uptaketo CO₂ assimilation changed from 1.0 before stress to 1.4 forseveral days after. Root respiration was less affected by thestress than ion uptake and shoot gas exchanges. Key words: Photosynthesis, Photorespiration, Transpiration, Shoot and root respiration, Ion uptake, Water stress, Glycine max. L.     

The Wall-stress Footprint of Blood Cells Flowing in Microvessels

It is well known that mechanotransduction of hemodynamic forces mediates cellular processes, particularly those that lead to vascular development and maintenance. Both the strength and space-time character of these forces have been shown to affect remodeling and morphogenesis. However, the role of blood cells in the process remains unclear. We investigate the possibility that in the smallest vessels blood’s cellular character of itself will lead to forces fundamentally different than the time-averaged forces usually considered, with fluctuations that may significantly exceed their mean values. This is quantitated through the use of a detailed simulation model of microvessel flow in two principal configurations: a diameter D=6.5$D=6.5$μ  m tube—a model for small capillaries through which red blood cells flow in single-file—and a D=12$D=12$μm tube—a model for a nascent vein or artery through which the cells flow in a confined yet chaotic fashion. Results in both cases show strong sensitivity to the mean flow speed U  . Peak stresses exceed their means by greater than a factor of 10 when U/D?10$U/D\mathrm{?}10$ s⁻¹, which corresponds to the inverse relaxation time of a healthy red blood cell. This effect is more significant for smaller D cases. At faster flow rates, including those more commonly observed under normal, nominally static physiological conditions, the peak fluctuations are more comparable with the mean shear stress. Implications for mechanotransduction of hemodynamic forces are discussed.     

Effects of Light, Carbon Dioxide, and Temperature on Photosynthesis, Oxygen Inhibition of Photosynthesis, and Transpiration in Solanum tuberosum

Individual leaves of potato (Solanum tuberosum L. W729R), a C₃ plant, were subjected to various irradiances (400-700 nm), CO₂ levels, and temperatures in a controlled-environment chamber. As irradiance increased, stomatal and mesophyll resistance exerted a strong and some-what paralleled regulation of photosynthesis as both showed a similar decrease reaching a minimum at about 85 neinsteins·cm⁻²·sec⁻¹ (about ½ of full sunlight). Also, there was a proportional hyperbolic increase in transpiration and photosynthesis with increasing irradiance up to 85 neinsteins·cm⁻²·sec⁻¹. These results contrast with many C₃ plants that have a near full opening of stomata at much less light than is required for saturation of photosynthesis.     

Effect of Oxygen on the Light-enhanced Dark Carbon Dioxide Fixation in Chlorella Cells

With Chlorella ellipsoidea cells, the effect of oxygen was investigated on the products of enhanced dark ¹⁴CO₂ fixation immediately following preillumination in the absence of CO₂. When the reaction mixture was made aerobic by bubbling air (CO₂-free) throughout preillumination and the following dark ¹⁴CO₂ fixation periods, the initial fixation product was mainly 3-phosphoglyceric acid. When nitrogen gas had been used instead of air, only about one-half of the total radioactivity in the initial fixation products was in 3-phosphoglyceric acid and the rest in aspartic, phosphoenolpyruvic, and malic acids. The percentage distribution of radioactivity incorporated in these initial products rapidly decreased during the rest of the dark period. Concurrent with the decrease in the initial ¹⁴CO₂ fixation products, some increase was observed in the radioactivities of the sugar phosphates. The maximal radioactivity incorporated in sugar mono- and diphosphates accounted for only 10% of total ¹⁴C, under either the aerobic or anaerobic conditions. Under anaerobic conditions most of the ¹⁴C incorporated was eventually transferred to alanine, whereas the main end products under aerobic conditions were aspartate and glutamate. The pattern of ¹⁴CO₂ fixation products was unaffected by the atmospheric condition during the period of preillumination. The preferential flow of the fixed carbon atom to alanine or aspartate depended on the presence or absence of oxygen during the period of dark CO₂ fixation.