Effects of hyperchloremia on blood oxygen binding in healthy calves

Three different levels of hyperchloremia wereinduced in healthy Friesian calves to study the effects of chloride onblood oxygen transport. By infusion, the calves received either 5 ml/kg of 0.9% NaCl (low-level hyperchloremia; groupA), 5 ml/kg of 7.5% NaCl (moderate hyperchloremia;group B), or 7.5 ml/kg of 7.5% NaCl(high-level hyperchloremia; groupC). Blood was sampled from the jugular vein and thebrachial artery. Chloride concentration, hemoglobin content, arterialand venous pH, PCO₂, and PO₂ were determined. At each timepoint (0, 15, 30, 60, and 120 min), the whole blood oxygen equilibriumcurve (OEC) was measured under standard conditions. Ingroups B andC, hyperchloremia was accompanied by asustained rightward shift of the OEC, as indicated by the significantincrease in the standard PO₂ at 50%hemoglobin saturation. Infusion of hypertonic saline also inducedrelative acidosis. The arterial and venous OEC were calculated, withbody temperature, pH, and PCO₂ valuesin arterial and venous blood taken into account. The degree of blooddesaturation between the arterial and the venous compartments[O₂ exchange fraction(OEF%)] and the amount of oxygen released at tissue level by 100 ml of bovine blood (OEF vol%) were calculated from the arterial andvenous OEC combined with the PO₂ andhemoglobin concentration. The chloride-induced rightward shift of theOEC was reinforced by the relative acidosis, but the alteredPO₂ values combined with the lowerhemoglobin concentration explained the absence of any significantdifference in OEF (% and vol%). We conclude that infusion ofhypertonic saline induces hyperchloremia and acidemia, which canexplain the OEC rightward shift observed in arterial and peripheralvenous blood.

     

Regeneration of Ribulose 1,5-bisphosphate and Ribulose 1,5-bisphosphate carboxylase/oxygenase Activity Associated with Lack of Oxygen Inhibition of Photosynthesis at Low Temperature

The nature of the lack of oxygen inhibition of C₃-photosynthesisat low temperature was investigated in white clover (Trifoliumrepens L.). Detached leaves were brought to steady-state photosynthesisin air (34 Pa p(CO²), 21 kPa p(O₂), balance N₂) at temperaturesof 20°C and 8°C, respectively. Net photosynthesis, ribulose1,5-bisphosphate (RuBP) and ATP contents, and ribulose 1,5-bisphosphatecarboxylase/oxygenase (RuBPCO) activities were followed beforeand after changing to 2·0 kPa p(O₂). At 20°C, lowering p(O₂) increased net photosynthesis by37%. This increase corresponded closely with the increase expectedfrom the effect on the kinetic properties of RuBPCO. Conversely,at 8°C net photosynthesis rapidly decreased following adecrease in p(O₂) and then increased again reaching a steady-statelevel which was only 7% higher than at 21 kPa p(O₂). The steady-staterates of RuBP and associated ATP consumption were both estimatedto have decreased. ATP and RuBP contents decreased by 18% and33% respectively, immediately after the change in p(O₂) suggestingthat RuBP regeneration was reduced at low p(O₂) due to reducedphotophosphorylation. Subsequently, RuBP content increased again.Steady-state RuBP content at 2·0 kPa p(O₂) was 24% higherthan at 21 kPa p(O₂). RuBPCO activity decreased by 22%, indicatingcontrol of steady-state RuBP consumption by RuBPCO activity. It is suggested that lack of oxygen inhibition of photosynthesisat low temperature is due to decreased photophosphorylationat low temperature and low p(O₂). This may be due to assimilateaccumulation within the chloroplasts. Decreased photophosphorylationseems to decrease RuBP synthesis and RuBPCO activity, possiblydue to an acidification of the chloroplast stroma. Key words: Oxygen inhibition, photosynthesis, ribulose bisphosphate carboxylase/oxygenase     

Response of Wheat Seedlings to Low O2 Concentrations in Nutrient Solution: II. K +/Na+ SELECTIVITY OF ROOT TISSUES9

This paper reports the effects of low O₂ concentration (0–01,0–055, and 0.115mol m^–3) in nutrient solutions onK⁺/Na⁺ selectivity of growing and mature root tissues of 6-to 8-d-old, intact, wheat (Triticum aestivum cv. Gamenya) seedlings. Increases in anaerobic catabolism and decreases in O₂ uptake,K⁺ uptake and K⁺/Na⁺ selectivity were all more pronounced and/oroccurred at higher external O₂ concentrations in the apex (0–2mm) than in the expanding tissues (2–4 mm); these growingtissues were, in turn, more affected than the expanded tissuesof the roots (4–12 mm). Selectivity for K⁺ over Na⁺ in roots and shoots was particularlysensitive to O₂ deficiency. For example, in apical tissues (0–2mm) K ⁺ /Na⁺ selectivity was already reduced at 0.115 mol m^–3O₂, yet at this O₂ concentration there was no effect on eithergrowth or (K⁺/Na⁺) uptake. Upon transfer from 0.01 to 0.26 mol m^–3 O₂, a detailedstudy of the 12 mm root tips showed that 70% of these tips regainedhigh (K⁺ + Na⁺) concentrations and K⁺/^Na+ ratios. In contrast,there was no recovery in the remaining 30% of the 12 mm roottips. Net K⁺ transport to the shoots during the period afterre-aeration was negative for the population as a whole. Theseverity of these effects supports the view that the root tipsand the stele were more susceptible to O2 deficiency than wasthe cortex of the fully-developed root tissues. Key words: Hypoxia, K⁺/Na⁺ selectivity, expanded and expanding tissues     

A microsensor for direct measurement of O2 partial pressure within plant tissues3

Widespread use of O₂ microsensors to measure O₂ partial pressure(pO₂) in plant tissues has been limited in part because of difficultyof construction and other technical obstacles. By modifyingpublished techniques, an O₂ microsensor was constructed thatcombined the advantages of Clark-type microsensors with lesscomplicated construction techniques. The specifications andsome performance characteristics of the microsensor are: tipdiameter 1–5 µm; sensitivity 7.5–25 pA kPa^–1;negligible stir-induced current; response time 540 ms. The microsensorcan be used in air or solution, and each sensor can be usedfor several experiments. The sensitivity of the microsensorwas unchanged during measurements over the physiological rangeof pO₂ in intact, growing maize (Zea mays L.) primary roots,and was thus unaffected by cellular fluids and turgor pressure.Use of the microsensor to compare pO₂ profiles in vermiculite-and solution-grown roots is described. The O₂ microsensor couldfind application in studies in which information on tissue pO₂is needed, but for which conventional O₂ probes are too large. Key words: Oxygen microsensor, Zea mays L., roots, oxygen partial pressure     

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.     

Reactive oxygen species as causative agents in the ichthyotoxicity of the red tide dinoflagellate Cochlodinium polykrikoides

The underlying toxic mechanisms of the red tide dinoflagellate,Cochlodinium polykrikoides, were studied with respect to thereactive oxygen species-mediated toxic effect. Cochlodiniumpolykrikoides generates superoxide anion (O₂^–) and hydrogenperoxide (H₂O₂), as measured by the cytochrome c reduction methodand scopoletin–peroxidase method, respectively. The capabilityof C.polykrikoides to generate these oxygen radicals was relatedto the growth phase: the highest rate in the exponential phaseand a gradual decrease in the stationary phase. Other phytoplankton,such as Eutreptiella gymnastica, Heterosigma akashiwo, Prorocentrummicans, Gymnodinium sanguineum and Alexandrium tamarense, alsoproduce H₂O₂; the rate of H₂O₂ generation by these species waslower than that of C.polykrikoides. The exposure of liposomalsamples to intact or ruptured individuals of C.polykrikoidesresulted in severe membrane damage, such as liposomal lipidperoxidation. Cochlodinium polykrikoides-induced lipid peroxidationwas significantly reduced by oxygen radical scavengers, superoxidedismutase, benzoquinone, catalase and mannitol. In addition,lipid peroxidation of gill tissue of flatfish exposed to C.polykrikoidesincreased with increasing algal cell density. These resultssuggest that reactive oxygen species generated from C.polykrikoidesare responsible for oxidative damage leading to fish kills.     

Effect of Oxygen on Photosynthetic 14CO2 Fixation in Chroomonas sp. (Cryptophyta) II. Effects of Inhibitors, Uncouplers and an Artificial Electron Mediator on the Inhibition of 14CO2 Fixation by Anaerobiosis

In "air-grown" Chroomonas sp. cells, low concentrations of DCMU(less than 0.1 µM) could prevent the inhibition of ¹⁴CO₂fixation by anaerobiosis under light-saturating conditions (morethan 40 W.m^–2), with phenazine methosulfate showing asimilar effect. Antimycin A, carbonyl cyanide m-chlorophenylhydrazone(CCCP), and N,N'-dicyclohexylcarbodiimide strongly inhibitedanaerobic photosynthesis at concentrations which did not significantlyinhibit the rate under 2% O₂ at high light intensity (200 W.m^–2),although 0.2 µM CCCP stimulated the rate under 2% O₂ tosome extent. On the other hand, KCN inhibited the rate muchmore strongly under 2% O₂ than N₂, although it inhibited therate very strongly at concentrations above 5 µM both underN₂ and 2% O₂. These results suggest that the inhibition of photosynthetic¹⁴CO₂ fixation by anaerobiosis in this alga result from ATPdeficiency caused by over-reduction of electron carriers ofthe cyclic electron flow and that oxygen can prevent the over-reduction.Cyclic electron flow seems to be necessary to provide additionalATP for CO₂ reduction under anaerobic conditions, although itseems to be less necessary under aerobic conditions. (Received July 21, 1983; Accepted January 23, 1984)     

Peripheral circulatory factors limit rate of increase in muscle O2 uptake at onset of heavy exercise

We used anexercise paradigm with repeated bouts of heavy forearm exercise to testthe hypothesis that alterations in local acid-base environment thatremain after the first exercise result in greater blood flow andO₂ delivery at the onset of the second bout of exercise.Two bouts of handgrip exercise at 75% peak workload were performed for5 min, separated by 5 min of recovery. We continuously measured bloodflow using Doppler ultrasound and sampled venous blood forO₂ content, PCO₂, pH, and lactateand potassium concentrations, and we calculated muscle O₂uptake (O₂). Forearm blood flow waselevated before the second exercise compared with the first andremained higher during the first 30 s of exercise (234 ± 18 vs. 187 ± 4 ml/min, P < 0.05). Flow was notdifferent at 5 min. Arteriovenous O₂ content difference waslower before the second bout (4.6 ± 0.9 vs. 7.2 ± 0.7 mlO₂/dl) and higher by 30 s of exercise(11.2 ± 0.7 vs. 10.8 ± 0.7 ml O₂/dl,P < 0.05). Muscle O₂was unchanged before the start of exercise but was elevated during thefirst 30 s of the transition to the second exercise bout(26.0 ± 2.1 vs. 20.0 ± 0.9 ml/min, P < 0.05). Changes in venous blood PCO₂, pH, andlactate concentration were consistent with reduced reliance onanaerobic glycolysis at the onset of the second exercise bout. Thesedata show that limitations of muscle blood flow can restrict theadaptation of oxidative metabolism at the onset of heavy muscular exertion.

     

Quantifying the sensitivity of barley seed germination to oxygen, abscisic acid, and gibberellin using a population-based threshold model

Barley (Hordeum vulgare L.) seeds (grains) exhibit dormancyat maturity that is largely due to the presence of the glumellae(hulls) that reduce the availability of oxygen (O₂) to the embryo.In addition, abscisic acid (ABA) and gibberellins (GAS) interactwith O₂ to regulate barley seed dormancy. A population-basedthreshold model was applied to quantify the sensitivities ofseeds and excised embryos to O₂, ABA, and GA, and to their interactiveeffects. The median O₂ requirement for germination of dormantintact barley seeds was 400-fold greater than for excised embryos,indicating that the tissues enclosing the embryo markedly limitO₂ penetration. However, embryo O₂ thresholds decreased by anotherorder of magnitude following after-ripening. Thus, increasesin both permeability of the hull to O₂ and embryo sensitivityto O₂ contribute to the improvement in germination capacityduring after-ripening. Both ABA and GA had relatively smalleffects on the sensitivity of germination to O₂, but ABA andGA thresholds varied over several orders of magnitude in responseto O₂ availability, with sensitivity to ABA increasing and sensitivityto GA decreasing with hypoxia. Simple additive models of O₂–ABAand O₂–GA interactions required consideration of theseO₂ effects on hormone sensitivity to account for actual germinationpatterns. These quantitative and interactive relationships amongO₂, ABA, and GA sensitivities provide insight into how dormancyand germination are regulated by a combination of physical (O₂diffusion through the hull) and physiological (ABA and GA sensitivities)factors. Key words: Abscisic acid, barley, germination, gibberellin, Hordeum vulgare L., model, oxygen, sensitivity Received 2 August 2007; Revised 14 November 2007 Accepted 19 November 2007     

Sources of error in A-aDO2 calculated from blood stored in plastic and glass syringes

Wu, Eugene Y., Khalid W. Barazanji, and Robert L. Johnson,Jr. Sources of error in A-aD_O2calculated from blood stored in plastic and glass syringes.J. Appl. Physiol. 82(1):196-202, 1997.We studied the effects of time delay on bloodgases, pH, and base excess in blood stored in glass and plasticsyringes on ice and the effects of resulting errors on calculatedalveolar-to-arterial PO₂ difference(A-aD_O2).Matched samples of dog whole blood were tonometered with gasmixtures of 5% CO₂-12%O₂-83% N₂ (mixtureA), 10% CO₂-5%O₂-85%N₂ (mixtureB), and 2.88%CO₂-4% O₂-93.12%N₂ (mixtureC). Tonometered blood samples were transferred to5-ml glass (5G), 5-ml plastic (5P), and 3-ml plastic (3P) syringes andstored on ice. Blood gases were measured every 1 h up to 6 h. In 5G,PO₂ progressively decreased in bloodtonometered with mixture A but rose inblood tonometered with mixtures B and C.O₂ saturation progressively fellin all cases. In 5G, blood PCO₂progressively rose regardless of which gas mixture was used, and pH aswell as base excess progressively fell. The rise inPO₂ was faster in plastic than inglass syringes, and O₂ saturationalways rose in plastic syringes. Differences between storage in plasticand glass syringes on PO₂ change weregreatest when initial blood PO₂ washighest (mixture A). At the highestPO₂,O₂ exchange was faster in 3P thanin 5P. The rise of PCO₂ was just asfast in plastic as in glass syringes, but in both the rise inPCO₂ was faster at a higher initialPCO₂ (mixtureB) than at lower initialPCO₂ (mixturesB and C). Rates ofPO₂ andPCO₂ change in matched samples weresignificantly faster in 3P than in 5P. Errors due to rises inPCO₂ andPO₂ cause additive errors incalculatedA-aD_O2,and when blood is stored in plastic syringes for >1 h significant errors result. Errors are greater in normoxic blood, in which estimatedA-aD_O2decreased by >10 Torr after 6 h on ice in plastic syringes, than inhypoxic blood.

     

Reactive oxygen species formation in the transition to hypoxia in skeletal muscle

Many tissues produce reactive oxygen species (ROS) during reoxygenation after hypoxia or ischemia; however, whether ROS are formed during hypoxia is controversial. We tested the hypothesis that ROS are generated in skeletal muscle during exposure to acute hypoxia before reoxygenation. Isolated rat diaphragm strips were loaded with dihydrofluorescein-DA (Hfluor-DA), a probe that is oxidized to fluorescein (Fluor) by intracellular ROS. Changes in fluorescence due to Fluor, NADH, and FAD were measured using a tissue fluorometer. The system had a detection limit of 1 µM H₂O₂ applied to the muscle superfusate. When the superfusion buffer was changed rapidly from 95% O₂ to 0%, 5%, 21%, or 40% O₂, transient elevations in Fluor were observed that were proportional to the rise in NADH fluorescence and inversely proportional to the level of O₂ exposure. This signal could be inhibited completely with 40 µM ebselen, a glutathione peroxidase mimic. After brief hypoxia exposure (10 min) or exposure to brief periods of H₂O₂, the fluorescence signal returned to baseline. Furthermore, tissues loaded with the oxidized form of the probe (Fluor-DA) showed a similar pattern of response that could be inhibited with ebselen. These results suggest that Fluor exists in a partially reversible redox state within the tissue. When Hfluor-loaded tissues were contracted with low-frequency twitches, Fluor emission and NADH emission were significantly elevated in a way that resembled the hypoxia-induced signal. We conclude that in the transition to low intracellular PO₂, a burst of intracellular ROS is formed that may have functional implications regarding skeletal muscle O₂-sensing systems and responses to acute metabolic stress. dihydrofluorescein; tissue fluorometer; ebselen; N-acetylcysteine; rat     

Changes in Nitrogenase Activity and Nodule Diffusion Resistance of Subterranean Clover in Response to pO2

Diffusion resistance to oxygen within nodules was calculatedusing the respiratory quotient (RQ) of nodules from intact plantsof subterranean clover (Trifolium subterraneum L.) cv. SeatonPark nodulated by Rhizobiun trifolii WU95. From 21 to 52% O₂,the RQ remained between 0.94 and 1.04, whereas at 10% O₂, theRQ was 1.65. When nodulated roots of intact plants were exposedto sub-ambient pO₂ in a continuous flow-through system, respirationdeclined immediately, followed by a partial recovery within30 min. The magnitude of the final respiration rate was dependentupon the pO₂ in the gas stream. Initial rates of respirationwere re-established after 24 h at sub-ambient pO₂ as a resultof changes in the resistance of the variable barrier to oxygendiffusion within the nodules. Nitrogenase activity also decreasedlinearly with decreasing pO₂ in the gas stream, but partialrecovery occurred after 24 h incubation at sub-ambient pO₂.Maximum rates of nitrogenase activity occurred at rhizosphereoxygen concentrations between 21% and 36% O₂. Resistance tothe diffusion of oxygen within the nodules increased at supra-ambientpO₂ and at oxygen concentrations above 36% O₂, resulted in adecrease in both nitrogenase activity and nodulated root respiration.The diffusion resistance of nodules to oxygen increased rapidlyin the presence of either supra-ambient pO₂ or saturating pC₂H₂.Reductions in nodule diffusion resistance either during recoveryfrom exposure to 10% acetylene or to sub-ambient pO₂ occurredmore slowly. It is concluded that subterranean clover is welladapted for maximum nitrogen fixation at ambient pO₂. Key words: Nitrogenase activity, oxygen, subterranean clover, diffusion resistance     

EFFECTS OF TEMPERATURE ON CHRONIC HYPOXIA TOLERANCE IN THE NON-INDIGENOUS BROWN MUSSEL, PERNA PERNA (BIVALVIA: MYTILIDAE) FROM THE TEXAS GULF OF MEXICO

Effects of temperature (15°, 20° and 25°C), O₂ partialpressure (P_O2=0, 1, 2, 4, and 6 kPa), and individual size(12–79 mm shell length; SL) on survivorship of specimensof the non-indigenous, marine, brown mussel, Perna perna, fromTexas were investigated to assess its potential distributionin North America. Its hypoxia tolerance was temperature-dependent,survivorship being significantly extended at lower temperaturesunder all tested lethal P_O2. Incipient tolerated P_O2 was 4 and6 kPa at 15 and 20°C, respectively, with >50% mortalityoccurring at 25°C at all tested levels of hypoxia. P_O2 hadless of an effect on survival of hypoxia than temperature. At25°C, survivorship was not different over a P_O2 range of0–2 kPa and increased only at 4 and 6 kPa. Survivorshipwas size-dependent. Median survival times increased with increasingSL in anoxia and P_O2=1 kPa, but at 2, 4 and 6 kPa,smaller individuals survived longer than larger individuals.With tolerance levels similar to other estuarine bivalve species,P. perna should withstand hypoxia encountered in estuarine environments.Thus, its restriction to intertidal rocky shores may be dueto other parameters, particularly its relatively low temperaturetolerance. (Received 26 January 2004; accepted 31 March 2005)     

Importance of glucose-6-phosphate dehydrogenase activity in cell death

The intracellular redox potential plays an important role incell survival. The principal intracellular reductant NADPH is mainlyproduced by the pentose phosphate pathway by glucose-6-phosphate dehydrogenase (G6PDH), the rate-limiting enzyme, and by6-phosphogluconate dehydrogenase. Considering the importance of NADPH,we hypothesized that G6PDH plays a critical role in cell death. Ourresults show that 1) G6PDHinhibitors potentiatedH₂O₂-inducedcell death; 2) overexpression ofG6PDH increased resistance toH₂O₂-induced cell death; 3) serum deprivation, astimulator of cell death, was associated with decreased G6PDH activityand resulted in elevated reactive oxygen species (ROS);4) additions of substrates for G6PDHto serum-deprived cells almost completely abrogated the serumdeprivation-induced rise in ROS; 5)consequences of G6PDH inhibition included a significant increase inapoptosis, loss of protein thiols, and degradation of G6PDH; and6) G6PDH inhibition caused changesin mitogen-activated protein kinase phosphorylation that were similarto the changes seen withH₂O₂.We conclude that G6PDH plays a critical role in cell death by affectingthe redox potential.     

Presence of the distinct systems responsible for superoxide anion and hydrogen peroxide generation in red tide phytoplankton Chattonella marina and Chattonella ovata

Raphidophycean flagellates, Chattonella marina and C. ovata,are harmful red tide phytoplankters; blooms of these phytoplanktersoften cause severe damage to fish farming. Previous studieshave demonstrated that C. marina and C. ovata continuously producereactive oxygen species (ROS) such as superoxide anion (O₂^–)hydrogen peroxide (H₂O₂) under normal growth conditions, andan ROS-mediated toxic mechanism against fish and other marineorganisms has been proposed. Although the exact mechanism ofROS generation in these phytoplankters still remains to be clarified,our previous study suggested that NADPH oxidase-like enzymelocated on the cell surface of C. marina may be involved inO₂^– generation. To investigate the localization of O₂^–and H₂O₂ generation in C. marina and C. ovata, we employed 2-methyl-6(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin-3-oneand 5-(and-6)-carboxy-2',7'-dichlorodihydrodihydrofluoresceindictate, acetyl ester, which are specific fluorescent probefor detecting O₂^– and H₂O₂, respectively. Observationby fluorescence microscopy of live phytoplankters incubatedwith each probe revealed that O₂^– is mainly generatedon the cell surface, whereas H₂O₂ is generated in the intracellularcompartment in these phytoplankters. When the cells were rupturedby ultrasonic treatment, O₂^– levels of C. marina and C.ovata decreased significantly, whereas a few times higher levelsof H₂O₂ were detected in the ruptured cell suspensions whencompared with the levels of the live cell suspension. In immunoblottinganalysis, the protein recognized by anti-human gp91 phox wasdetected in both species. These results suggest that, in bothphytoplankters, the underlying mechanisms of O₂^– and H₂O₂generation may be distinct and such systems are independentlyoperating in the cells.     

Relationships between the effect of O2 on energy metabolism and RNA synthesis in Rhodotorula gracilis

In the aerobic yeast Rhodotorula gracilis, a decrease in O₂availability, from saturating conditions (pO₂ = 100 mm Hg) topO₂ = 1 mm Hg, causes a decrease in the growth rate accompaniedby a fall in the accumulation rate of RNA and, to a lesser extent,of proteins. At pO₂ = 1, no relevant changes in the levels oftriphosphate nucleotides (ATP, GTP, CTP and UTP) are observedwith respect to the controls, while the ADP and AMP levels markedlyincrease. The uptake of labelled precursors and qualitative analysis ofRNA suggest that the decrease in the RNA accumulation rate atpO₂ = 1 is due to a decreased RNA synthesis rate. This paper examines the mechanism by which low availabilityof O₂ causes a decrease in the RNA synthesis rate even thoughtotal triphosphate nucleotide levels remain high. (Received December 28, 1977; )     

Thermal Dependence of Air Convection Requirement and Blood Gases in the Snake Coluber constrictor

In this report I discuss ventilatory and circulatory adjustmentsthat prov for increased O₂transport associated with increasedbody temperature in the snake Coluber constrictor. Also includedis the effect of temperature upon acid-base status. Minute ventilationincreases with rising body temperature but does not keep pacewith the increment in resting O₂ consumption. The decrease inair convection requirement (i.e., ventilation ÷ oxygenconsumption) causes lung pO₂ and arterial oxygen contentto falland lung pCO₂ to rise. With the rise in lung pCO₂, systemicarterial pCO₂ and H⁺; concentration increase while plasma bicarbonateconcentration does not change. The effect of temperature uponair convection requirement, arterial pCO₂, and pH are most pronouncedat body temperatures above about 27°C whereColuber behavesapproximately as an alphastat pH regulator. Despite the inverserelationship between temperature and lung pO₂, systemic arterialpO₂ is about 80 torr lower at 15°C than at 35°C. Thisdecline in arterial pO₂ as temperature falls is explained byleft shifting the oxygen dissociation curve in the presenceof aconstant right-to-left intracardiac shunt.     

Assessing the genetic relatedness of higher ozone sensitivity of modern wheat to its wild and cultivated progenitors/relatives

Modern wheat (Triticum aestivum L.) is one of the most ozone(O₃)-sensitive crops. However, little is known about its geneticbackground of O₃ sensitivity, which is fundamental for breedingO₃-resistant cultivars. Wild and cultivated species of winterwheat including donors of the A, B and D genomes of T. aestivumwere exposed to 100 ppb O₃ or charcoal-filtered air in opentop chambers for 21 d. Responses to O₃ were assessed by visibleO₃ injury, gas exchange, chlorophyll fluorescence, relativegrowth rate, and biomass accumulation. Ozone significantly decreasedlight-saturated net photosynthetic rate (–37%) and instantaneoustranspiration efficiency (–42%), but increased stomatalconductance (+11%) and intercellular CO₂ concentration (+11%).Elevated O₃ depressed ground fluorescence (–8%), maximumfluorescence (–26%), variable fluorescence (–31%),and maximum photochemical efficiency (–7%). Ozone alsodecreased relative growth rate and the allometric coefficient,which finally reduced total biomass accumulation (–54%),but to a greater extent in roots (–77%) than in the shoot(–44%). Winter wheat exhibited significant interspeciesvariation in the impacts of elevated O₃ on photosynthesis andgrowth. Primitive cultivated wheat demonstrated the highestrelative O₃ tolerance followed by modern wheat and wild wheatshowed the lowest. Among the genome donors of modern wheat,Aegilops tauschii (DD) behaved as the most O₃-sensitive followedby T. monococcum (AA) and Triticum turgidum ssp. durum (AABB)appeared to be the most O₃-tolerant. It was concluded that thehigher O₃ sensitivity of modern wheat was attributed to theincreased O₃ sensitivity of Aegilops tauschii (DD), but notto Triticum turgidum ssp. durum (AABB) during speciation. Key words: Biomass, Chl a fluorescence, genome, ozone sensitivity, relative growth rate, stomatal conductance, winter wheat Received 20 September 2007; Revised 30 November 2007 Accepted 16 January 2008     

Effects of a Range of O2 Concentrations on Porosity of Barley Roots and on their Sugar and Protein Concentrations

Barley was grown at a range of oxygen concentrations (0.5–9mg l^–1), in nutrient solutions. Growth of both shootsand seminal roots was restricted by O₂ concentrations lowerthan 2–3 mg l^–1) but nodal root growth was not. Root porosities were increased even at those O₂ concentrationswhich did not restrict growth, and were inversely proportionalto the protein levels of the roots. Sugar concentrations increasedappreciably only at those O₂ concentrations which also restrictedgrowth. Hordeum vulgare L., barley, root porosity, sugar, protein, oxygen concentration     

Response of Wheat Seedlings to Low O2 Concentrations in Nutrient Solution: I. GROWTH, O2 UPTAKE AND SYNTHESIS OF FERMENTATIVE END-PRODUCTS BY ROOT SEGMENTS

Root growth of 7-d-old wheat (Triticum aestivum cv. Gamenya)seedlings was impaired at dissolved O₂ concentrations of 0.01and 0.055 mol m^–3 O₂, while growth at 0.115 mol m^–3O₂ was the same as that in continuously aerated controls (0.26mol m^–3 O2). Oxygen uptake by apical (0–2 mm), expanding (2–4mm) and expanded (10–12 mm) tissues of the roots decreasedbelow 0.16, 0.09 and 0.05 mol m^–3 O₂, respectively. Thishierarchy is consistent with the metabolic rates of these tissues.There was a small (c. 9%) inhibition of O₂ uptake and some netsynthesis of ethanol and alanine in root apices at 0.115 molm^–3 O₂. Significant amounts of anaerobic end-productsaccumulated at 0.055 mol m^–3 O₂ and even more so at 0.01mol m^–3 O₂, indicating that oxidative phosphorylationwas strongly inhibited. Net alanine synthesis increased in fully expanded (10–16mm) tissues exposed to <0.003–0.01 mol m^–3 O₂,and this increase was accompanied either by a proportionallysmaller increase in the concentration of other free amino acidsor by a net decrease in free amino acid levels excluding alanine.This suggests that alanine was synthesized as an end-productof anaerobic catabolism and did not accumulate simply becauseof decreased net protein synthesis. Comparing the carbon flow to CO₂, ethanol, lactate and alaninein roots at 0.01 mol m^–3 O₂ with carbon loss as CO₂ inaerated roots suggests that carbon flow to products of metabolismwas not greatly enhanced due to O₂ deficiency. This infers,but does not prove that, in wheat, generation of energy duringperiods of O₂ deficiency is not enhanced due to a Pasteur effect. Key words: Anaerobic, fermentation, oxygen, wheat