共查询到20条相似文献,搜索用时 15 毫秒
1.
Effects of temperature (15°, 20° and 25°C), O2 partialpressure (PO2=0, 1, 2, 4, and 6 kPa), and individual size(1279 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 PO2. Incipient tolerated PO2 was 4 and6 kPa at 15 and 20°C, respectively, with >50% mortalityoccurring at 25°C at all tested levels of hypoxia. PO2 hadless of an effect on survival of hypoxia than temperature. At25°C, survivorship was not different over a PO2 range of02 kPa and increased only at 4 and 6 kPa. Survivorshipwas size-dependent. Median survival times increased with increasingSL in anoxia and PO2=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) 相似文献
2.
Germination of three populations of Kochia indica Wight fromcontrasting soil types were studied under various levels ofsalinity, alkalinity and osmotic stress with a view to evaluatetheir potential to establish through seeds in saline and alkalineenvironments of various magnitudes. The seeds were germinatedunder controlled conditions in Petri dishes using salinizedsolutions of NaCl, Na2SO4, MgCI2 and CaSO4 (electrical conductivity,EC, 416 ds m), sodium carbonate solutions (pH8.5100), mannitol solutions ( 2.5 to 100 bar) and de-ionised distilled water (control). Inter-populationdifferences were very marked, showing selective adaptation ofthe populations to a particular stress type. In general, allpopulations exhibited salt tolerance but were rather sensitiveto high osmotic stress. Kochia indica Wight (bui), germination, population, salinity, alkalinity, osmotic stress 相似文献
3.
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 相似文献
4.
Germination of three populations of Kochia indica Wight fromcontrasting soil types were studied under various levels ofsalinity, alkalinity and osmotic stress with a view to evaluatetheir potential to establish through seeds in saline and alkalineenvironments of various magnitudes. The seeds were germinatedunder controlled conditions in Petri dishes using salinizedsolutions of NaCl, Na2SO4, MgCl2 and CaSO4 (electrical conductivity,EC, 416 dsm1), sodium carbonate solutions (pH 8.5ndash;10.0), mannitol solutions ( 2.5 to 10.0 bar) andde-ionised distilled water (control). Inter-population differenceswere very marked, showing selective adaptation of the populationsto a particular stress type. In general, all populations exhibitedsalt tolerance but were rather sensitive to high osmotic stress. Kochia indicaWight (bui), germination, populatio, salinity, alkalinity, osmotic stress 相似文献
5.
Kayar, Susan R., and Erich C. Parker. Oxygen pulse inguinea pigs in hyperbaric helium and hydrogen. J. Appl. Physiol. 82(3): 988-997, 1997.We analyzedO2 pulse, the total volume of O2 consumed per heart beat, inguinea pigs at pressures from 10 to 60 atmospheres. Animals were placedin a hyperbaric chamber and breathed 2%O2 in either helium (heliox) orhydrogen (hydrox). Oxygen consumption rate(O2) was measured by gaschromatographic analysis. Core temperature and heart rate were measuredby using surgically implanted radiotelemeters. TheO2 was modulated over afourfold range by varying chamber temperature from 25 to 36°C. There was a direct correlation betweenO2 and heartrate, which was significantly different for animals in heliox vs.hydrox (P = 0.003). By usingmultivariate regression analysis, we identified variables that weresignificant to O2 pulse: bodysurface area, chamber temperature, core temperature, and pressure.After normalizing for all nonpressure variables, the residualO2 pulse was found to decreasesignificantly (P = 0.02) with pressurefor animals in heliox but did not decrease significantly(P = 0.38) with pressure for animalsin hydrox over the range of pressures studied. This amounted to aroughly 25% lower O2 pulse fornormothermic animals in 60 atmospheres heliox vs. hydrox. These resultssuggest that reduction of cardiovascular efficiency in a hyperbaricenvironment can be mitigated by the choice of breathing gas. 相似文献
6.
Clipson, N. J. W. 1987. Salt tolerance in the halophyte Suaedamaritima L. Dum. Growth, ion and water relations and gas exchangein response to altered salinity.J. exp. Bot. 38: 19962004. Shoot and root fresh and dry weights and shoot sodium, chlorideand potassium contents were measured and shoot relative growthrates calculated in seedlings of Suaeda maritima over a periodof 11 d following a raising of culture solution salinity from0 to 200 mol m3 NaCl. Growth, growth rates and sodiumand chloride contents, as compared to plants growing in theabsence of salt were increased whilst potassium contents declined.Shoot sodium accumulation rate and the rate of transport ofsodium from root to shoot, osmotic potential, and rates of photosynthesisand transpiration were also measured for up to 72 h after transferof plants originally growing at 0 and 200 mol3 NaCl to200 and 400 mol m3 NaCl respectively. Ion uptake andtransport rates were maximal 6-12 h after transfer and thendeclined to new steady-state levels within 48 h; osmotic potentialswere lowered over a 72 h period on average by approximately1·0 MPa; and after 9 h photosynthetic and transpirationrates were reduced by about 20percnt; and 30% respectively.Results are discussed in terms of the ability of halophytesto adjust to fluctuating salinity and to salt tolerance mechanismsin general. Key words: Suaeda maritima, salinity, gas exchange, growth, ion and water relations 相似文献
7.
Bruce Douglas; Popovic Radovan; Vidaver William; Colbow Konrad 《Plant & cell physiology》1983,24(5):877-882
The kinetics of the flash induced 518 nm absorbance change (A518)in lettuce leaves were found to be dependent on O2 concentration.(1) Either a lower O2 partial pressure or the addition of weakred background illumination accelerated the decay of (A518)while far-red background light induced a transient acceleration.(2) In the presence of background red light the accelerateddecay could be restored to the original dark level by the additionof O2. A linear relationship was found between the intensityof red background light and the O2 pressure required for thisrestoration. (3) The O2 dependence of (A518) decay halftimewas biphasic, the sensitive phase saturating at 0.3 atmospheresO2 independent of input light energy while the O2 concentrationneeded to saturate the second phase increased with increasinginput light energy (increasing flash frequency). (4) Treatmentwith N, N'-dicyclohexylcarbodiimide (DCCD) or KCN eliminatedall O2 and background light effects and DCMU treatment inhibitedall but the sensitive phase of the O2 dependence on (A518) decayhalftime. (5) The extent of the lag phase in the dark recoveryof (A518) normally present after preillumination induced accelerationof decay was decreased with added O2 or KCN. (6) It was concludedthat O2 competes directly with background red light inducedelectron transport to PS I acceptors to influence the (A518)decay. A possible mechanism involving the O2 sensitive ferredoxin-thioredoxin-reductaseactivation of chloroplast coupling factor 1 ATP-hydrolase activitywas discussed. (Received December 17, 1982; Accepted April 28, 1983) 相似文献
8.
Possible physiological mechanisms for production of hydrogen peroxide by the ichthyotoxic flagellate Heterosigma akashiwo 总被引:2,自引:0,他引:2
Blooms of the toxic red tide phytoplankton Heterosigma akashiwo(Raphidophyceae) are responsible for substantial losses withinthe aquaculture industry. The toxicological mechanisms of H.akashiwoblooms are complex and to date, heavily debated. One putativetype of ichthyotoxin includes the production of reactive oxygenspecies (ROS) that could alter gill structure and function,resulting in asphyxiation. In this study, we investigated thepotential of H.akashiwo to produce extracellular hydrogen peroxide,and have investigated which cellular processes are responsiblefor this production. Within all experiments, H.akashiwo producedsubstantial amounts of hydrogen peroxide (up to 7.6 pmol min1104 cells1), resulting in extracellular concentrationsof ~0.5 µmol l1 H2O2. Measured rates of hydrogenperoxide production were directly proportional to cell density,but at higher cell densities, accuracy of H2O2 detection wasreduced. Whereas light intensity did not alter H2O2 production,rates of production were stimulated when temperature was elevated.Hydrogen peroxide production was not only dependent on growthphase, but also was regulated by the availability of iron inthe medium. Reduction of total iron to 1 nmol l1 enhancedthe production of H2O2 relative to iron replete conditions (10µmol l1 iron). From this, we collectively concludethat production of extracellular H2O2 by H.akashiwo occurs througha metabolic pathway that is not directly linked to photosynthesis. 相似文献
9.
Champattanachai V Marchase RB Chatham JC 《American journal of physiology. Cell physiology》2008,294(6):C1509-C1520
We have previously reported that glucosamine protected neonatal rat ventricular myocytes against ischemia-reperfusion (I/R) injury, and this was associated with an increase in protein O-linked-N-acetylglucosamine (O-GlcNAc) levels. However, the protective effect of glucosamine could be mediated via pathways other that O-GlcNAc formation; thus the initial goal of the present study was to determine whether increasing O-GlcNAc transferase (OGT) expression, which catalyzes the formation of O-GlcNAc, had a protective effect similar to that of glucosamine. To better understand the potential mechanism underlying O-GlcNAc-mediated cytoprotection, we examined whether increased O-GlcNAc levels altered the expression and translocation of members of the Bcl-2 protein family. Both glucosamine (5 mM) and OGT overexpression increased basal and I/R-induced O-GlcNAc levels, significantly decreased cellular injury, and attenuated loss of cytochrome c. Both interventions also attenuated the loss of mitochondrial membrane potential induced by H2O2 and were also associated with an increase in mitochondrial Bcl-2 levels but had no effect on Bad or Bax levels. Compared with glucosamine and OGT overexpression, NButGT (100 µM), an inhibitor of O-GlcNAcase, was less protective against I/R and H2O2 and did not affect Bcl-2 expression, despite a 5- to 10-fold greater increase in overall O-GlcNAc levels. Decreased OGT expression resulted in lower basal O-GlcNAc levels, prevented the I/R-induced increase in O-GlcNAc and mitochondrial Bcl-2, and increased cellular injury. These results demonstrate that the protective effects of glucosamine are mediated via increased formation of O-GlcNAc and suggest that this is due, in part, to enhanced mitochondrial Bcl-2 translocation. mitochondria; apoptosis; necrosis, O-linked-N-acetylglucosamine 相似文献
10.
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. 相似文献
11.
Panicum hians and Panicum milioides were found to have characteristicsintermediate to those of C3 and C4 species with respect to CO2compensation point, percentage inhibition of photosynthesisby O2 at various O2/CO2 solubility ratios, and water use efficiency.C4 species have a higher carboxylation efficiency than eitherthe intermediate or C3 species. During photosynthesis, evenunder 2.5% O2, C4 species have a higher affinity for intercellularCO2 (Km 1.6 µM) apparently due to the initial carboxylationthrough PEP carboxylase. Under low O2 the intermediate and C3species had a similar affinity for intercellular CO2 duringphotosynthesis (Km 57 µM) consistent with carboxylationof atmospheric CO2 through RuDP carboxylase. There were considerablevariation in photosynthesis/unit leaf area at saturating CO2levels in the species examined which in part is due to differencesin RuDP carboxylase /unit leaf area. The highest rates of photosynthesis/unitleaf area under CO2-saturating conditions were with the C3 specieswhich had a correspondingly high level of RuDP carboxylase/unitleaf area. Possibilities for the greater efficiency of P. hiansand P. milioides in comparison to C3 species in utilizing lowlevels of CO2 in the presence of atmospheric O2 are discussed.
1 This research was supported by the College of Agriculturaland Life Sciences, University of Wisconsin, Madison; and theUniversity of Wisconsin Research Committee with funds from theWisconsin Alumni Research Foundation. (Received June 25, 1977; ) 相似文献
12.
The influence of hydrogenase in Bradyrizobum-Phaseoleae symbioseswas studied ex-planta and in-planra in soybean (Glycine max)and cowpea (Vigna unguiculata). The hydrogenase was activatedby the addition of hydrogen in the incubation gas phase whichmodified the response of nitrogenase activity of Hup+ (hydrogenuptake positive) symbiosis to the external oxygen partial pressure.For bacteroids the hydrogenase expression increased nitrogenaseactivity at supraoptimal pO2, acting possibly as a respiratoryprotection of nitrogenase. However, at suboptimal pO2, nitrogenaseactivity of Hup+ bacteroids decreased with hydrogen, a phenomenonattributed to the lower efficiency of ATP synthesis from hydrogenthan from carbon substrates oxidation. For undisturbed nodules,the hydrogenase expression in soybean increased the optimalpO2 for ARA (COP), from 35.3 to 40.3 kPa O2, and the ARA atsupraoptimal pO2; at suboptimal PO2 there was a negative effectof hydrogenase on ARA, although this inhibition was less thanon bacteroids and was not detected if plants were grown at 15°C rather than 20 °C root temperature. No H2 effectwas detected on cowpea nodules. The results on soybean nodulesare consistent with the concept that symbiotic nitrogen fixationis oxygen-limited and that hydrogenase activity has no beneficialeffect on nitrogen fixation in O2 limitation. Key words: Glycine max, hydrogenase, nitrogenase, nitrogen fixation, nodules, Vigna unguiculata 相似文献
13.
Robinson MA Baumgardner JE Good VP Otto CM 《American journal of physiology. Cell physiology》2008,294(4):C1079-C1087
Nitric oxide (NO) production by inducible NO synthase (iNOS) is dependent on O2 availability. The duration and degree of hypoxia that limit NO production are poorly defined in cultured cells. To investigate short-term O2-mediated regulation of NO production, we used a novel forced convection cell culture system to rapidly (response time of 1.6 s) and accurately (±1 Torr) deliver specific O2 tensions (from <1 to 157 Torr) directly to a monolayer of LPS- and IFN-stimulated RAW 264.7 cells while simultaneously measuring NO production via an electrochemical probe. Decreased O2 availability rapidly (30 s) and reversibly decreased NO production with an apparent KmO2 of 22 (SD 6) Torr (31 µM) and a Vmax of 4.9 (SD 0.4) nmol·min–1·10–6 cells. To explore potential mechanisms of decreased NO production during hypoxia, we investigated O2-dependent changes in iNOS protein concentration, iNOS dimerization, and cellular NO consumption. iNOS protein concentration was not affected (P = 0.895). iNOS dimerization appeared to be biphasic [6 Torr (P = 0.008) and 157 Torr (P = 0.258) >36 Torr], but it did not predict NO production. NO consumption was minimal at high O2 and NO tensions and negligible at low O2 and NO tensions. These results are consistent with O2 substrate limitation as a regulatory mechanism during brief hypoxic exposure. The rapid and reversible effects of physiological and pathophysiological O2 tensions suggest that O2 tension has the potential to regulate NO production in vivo. inducible nitric oxide synthase; substrate limitation; nitric oxide consumption 相似文献
14.
Haseler Luke J.; Richardson Russell S.; Videen John S.; Hogan Michael C. 《Journal of applied physiology》1998,85(4):1457-1463
There isevidence that the concentration of the high-energy phosphatemetabolites may be altered during steady-state submaximal exerciseby the breathing of different fractions of inspiredO2 (FIO2). Whereasit has been suggested that these changes may be the result ofdifferences in time taken to achieve steady-state O2 uptake(O2) at differentFIO2 values, we postulated that they are due to a direct effect ofO2 tension. We used31P-magnetic resonancespectroscopy during constant-load, steady-state submaximal exercise todetermine 1) whether changes inhigh-energy phosphates do occur at the sameO2 with variedFIO2 and2) that these changes are not due todifferences in O2onset kinetics. Six male subjects performed steady-state submaximal plantar flexion exercise [7.2 ± 0.6 (SE) W] for 10 minwhile lying supine in a 1.5-T clinical scanner. Magnetic resonancespectroscopy data were collected continuously for 2 min beforeexercise, 10 min during exercise, and 6 min during recovery. Subjectsperformed three different exercise bouts at constant load with theFIO2 switched after 5 min ofthe 10-min exercise bout. The three exercise treatments were1)FIO2 of 0.1 switched to0.21, 2)FIO2 of 0.1 switched to1.00, and 3)FIO2 of 1.00 switched to0.1. For all three treatments, theFIO2 switch significantly (P 0.05) altered phosphocreatine:1) 55.5 ± 4.8 to 67.8 ± 4.9% (%rest); 2) 59.0 ± 4.3 to72.3 ± 5.1%; and 3) 72.6 ± 3.1 to 64.2 ± 3.4%, respectively. There were no significantdifferences in intracellular pH for the three treatments. The resultsdemonstrate that the differences in phosphocreatine concentration withvaried FIO2 are not theresult of different O2onset kinetics, as this was eliminated by the experimental design.These data also demonstrate that changes in intracellular oxygenation,at the same work intensity, result in significant changes in cell homeostasis and thereby suggest a role for metabolic control by O2 even during submaximalexercise. 相似文献
15.
Kim Daekyung; Nakashima Takuji; Matsuyama Yukihiko; Niwano Yoshimi; Yamaguchi Kenichi; Oda Tatsuya 《Journal of plankton research》2007,29(3):241-247
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 O2and 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. 相似文献
16.
Resistance of Photosynthesis to Hydrogen Peroxide in Algae 总被引:18,自引:0,他引:18
The effects of H2O2 on the photosynthetic fixation of CO2 andon thiol-modulated enzymes involved in the photosynthetic reductionof carbon in algae were studied in a comparison with those inchloroplasts isolated from spinach leaves. In both systems,H2O2-scavenging enzymes were inhibited by addition of 0.1 mMNaN3 1 h prior to the addition of H2O2. A concentration (10-4M) of H2O2 caused strong inhibition of the CO2 fixation by intactspinach chloroplasts, as observed by Kaiser [(1976) Biochim.Biophys. Acta 440: 476], but not that by Euglena and Chlamydomonascells. The same results were also obtained with cells of thecyanobacteria Synechococcus PCC 7942 and Synechocystis PCC 6803in the presence of 1 mM hydroxylamine. These results indicatethat algal photosynthesis is rather resistant to H2O2. The insusceptibilityto H2O2 of thiolmodulated enzymes, namely, fructose-1,6-bisphosphatase,NADP-glyceraldehyde-3-phosphate dehydrogenase, and ribulose-5-phosphatekinase, was also observed in the chloroplasts of Euglena andChlamydomonas and in cyanobacterial cells. It seems likely thatthe resistance of photosynthesis to H2O2 is due in part to theinsusceptibility of the algal thiol-modulated enzymes to H2O2. (Received April 22, 1995; Accepted June 29, 1995) 相似文献
17.
Wu Eugene Y.; Barazanji Khalid W.; Johnson Robert L. Jr. 《Journal of applied physiology》1997,82(1):196-202
Wu, Eugene Y., Khalid W. Barazanji, and Robert L. Johnson,Jr. Sources of error in A-aDO2calculated 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-aDO2).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-aDO2,and when blood is stored in plastic syringes for >1 h significant errors result. Errors are greater in normoxic blood, in which estimatedA-aDO2decreased by >10 Torr after 6 h on ice in plastic syringes, than inhypoxic blood. 相似文献
18.
Oxygenconsumption (O2)was measured in normoxia as ambient temperature(Ta) was lowered from 40 to15°C, at the rate of 0.5°C/min (thermoneutrality ~33°C).In 2-day-old rats born in hypoxia after hypoxic gestation, theTa-O2relationship was as in controls; their interscapular brown adiposetissue (IBAT) was hypoplastic (less proteins and DNA), with lowerconcentration of the mitochondrial uncoupling proteinthermogenin. In 8-day-old rats exposed to hypoxiapostnatally (day 2 today 8), at anyTa below thermoneutralityO2 was higher than incontrols; also, in this group IBAT was hypoplastic with decreasedthermogenin. Additional measurements under variousexperimental conditions indicated that the increased thermogeniccapacity was not explained by the smaller body mass and increased bloodoxygen content or by the eventuality of intermittent cold stimuliduring the chronic hypoxia. On the other hand, chronic hypercapnia (3%CO2 in normoxia, fromday 2 to day8) also resulted in increased normoxic thermogenesis. We conclude that chronic hypoxia in the perinatal period1) reduces IBAT mass andthermogenin concentration and2) can increase the newborn's thermogenic capacity because of stress-related mechanisms not specific to hypoxia. 相似文献
19.
Maintenance Respiration and Carbon Balance of Plants at Low Levels of Sodium Chloride Salinity 总被引:7,自引:0,他引:7
The daily course of carbon influx and efflux was measured inyoung plants of Phaseolus vulgaris, Xanthium strumarium, Zeamays, and Atriplex halimus, exposed to low levels of salinity(NaCl) and varying daytime light intensities. Maintenance respiration(RM) was calculated. In Phaseolus, Xanthium, and Atriplex, RMrose with increasing salinity, approximately up to those levelsof salinity above which apparent signs of toxicity appear. Athigher levels of salinity RM declined. There was no responseof RM to salinity in Zea. At the levels of salinity tested,salinity did not affect the ratio of growth respiration to photosynthesis. At 5 x 105 Pa of NaCl salinity, the increase in RM inXanthium was calculated to account for 24% of the growth reductioncaused by salt. The remainder could be ascribed to reduced photosynthesis.The increase of RM is considered to be indicative of an adaptivemechanism, not present in the very salt-sensitive Zea. 相似文献
20.
This study analyses the effects of salt on the effective symbiosisof faba bean (Vicia faba L. var. minor cv. Alborea) and salt-tolerantRhizobium leguminosarum biovar. viciae strain GRA19 grown withtwo KNO3 levels (2 and 8 mM). The addition of 8 mM KNO3 to thegrowth medium increases plant tolerance to salinity even witha concentration of 100 mM NaCl. This KNO3 level in control plantsreduced the N2 fixation. For 2 and 8 mM KNO3 the plants treatedwith NaCl reduced N2 fixation to identical values. The activityof the enzymes mediating ammonium assimilation in nodules (GS,NADH-GOGAT and NADH-GDH) was decreased by high KNO3 levels.The results show that NADH-GOGAT activity was more markedlyinhibited than was GS activity by salinity, therefore NADH-GOGATlimits the ammonium assimilation by nodules in V. faba undersalt stress. The total proline content in the nodule was notrelated to salt tolerance and thus does not serve as a salttoleranceindex for V. faba. Key words: Glutamate synthase, glutamine synthetase, N2 fixation, nitrate, salinity 相似文献