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1.
Acclimation of nitrogen uptake capacity of rice to elevated atmospheric CO2 concentration 总被引:2,自引:0,他引:2
Background and Aims: Nitrogen (N) is a major factor affecting yield gain of cropsunder elevated atmospheric carbon dioxide concentrations [CO2].It is well established that elevated [CO2] increases root mass,but there are inconsistent reports on the effects on N uptakecapacity per root mass. In the present study, it was hypothesizedthat the responses of N uptake capacity would change with theduration of exposure to elevated [CO2]. Methods: The hypothesis was tested by measuring N uptake capacity inrice plants exposed to long-term and short-term [CO2] treatmentsat different growth stages in plants grown under non-limitingN conditions in hydroponic culture. Seasonal changes in photosynthesisrate and transpiration rate were also measured. Key Results: In the long-term [CO2] study, leaf photosynthetic responsesto intercellular CO2 concentration (Ci) were not affected byelevated [CO2] before the heading stage, but the initial slopein this response was decreased by elevated [CO2] at the grain-fillingstage. Nitrate and ammonium uptake capacities per root dry weightwere not affected by elevated [CO2] at panicle initiation, butthereafter they were reduced by elevated [CO2] by 31–41% at the full heading and mid-ripening growth stages. In theshort-term study (24 h exposures), elevated [CO2] enhanced nitrateand ammonium uptake capacities at the early vegetative growthstage, but elevated [CO2] decreased the uptake capacities atthe mid-reproductive stage. Conclusions: This study showed that N uptake capacity was downregulated underlong-term exposure to elevated [CO2] and its response to elevated[CO2] varied greatly with growth stage. 相似文献
2.
Epidermal strips from either well-watered or water-stressedplants of Commelina communis L. were subjected to a range ofABA concentrations (106103 mol m3)in the presence (330 parts 106 in air) or virtual absence(3 parts 106 in air) of CO2. The stomatal response toCO2 was greater in epidermis from water-stressed plants, althoughthere was a distinct CO2 response in epidermis from well-wateredplants. Additions of ABA via the incubation medium had littleeffect on the relative CO2 response. Stomata responded to ABAboth in the presence and virtual absence of CO2, but the relativeresponse to ABA was greatest in the high CO2 treatment. Whenwell-watered plants were sprayed with a 101 mol m3ABA solution 1 d prior to use, the stomatal response of detachedepidermis to both CO2 and ABA was very similar to that of epidermisdetached from water-stressed leaves. It is hypothesized thata prolonged exposure to ABA is necessary before there is anymodification of the CO2 response of stomata. 相似文献
3.
Temperature Effects on Rice at Elevated CO2 Concentration 总被引:1,自引:0,他引:1
The continuing increase in atmospheric carbon dioxide concentration([CO2]) and projections of possible future increases in globalairtemperatures have stimulated interest in the effects of theseclimate variables on agriculturally important food crops. Thisstudywas conducted to determine the effects of [CO2] and temperatureon rice (Oryza sativa L., cv. IR30). Rice plants weregrownseason-long in outdoor, naturally sunlit, controlled-environment,plant growth chambers in temperature regimes ranging from 25/18/21°Cto 37/30/34°C (daytime dry bulb air temperature/night-timedry bulb air temperature/paddy water temperature)and [CO2] of660 µmol CO2 mol1 air. An ambient chamber was maintainedat a [CO2] of 330 µmol mol1 and temperature regimesof 28/21/25°C. Carbon dioxide enrichment at 28/21/25°Cincreased both biomass accumulation and tillering and increasedgrain yield by 60%. In the 660 µmol mol1 [CO2]treatment, grain yield decreased from 10.4 to 1.0 Mg ha1with increasing temperature from 28/21/25°C to the 37/30/34°Ctemperature treatment. Across this temperature range, the numberof panicles plant1 nearly doubled while the number ofseeds panicle1 declined sharply. These results indicatethat while future increases in atmospheric [CO2] are likelyto be beneficial to rice growth and yield, potentially largenegative effects on rice yield are possible if air temperaturesalso rise. Key words: Oryza sativa, CO2, temperature, growth, yield 相似文献
4.
The circadian rhythm of CO2 output in leaves of Bryophyllumfedtschenkoi damps out after 34 d in continuous darknessand a CO2-free air stream at 15°C. The rhythm is reinitiatedafter a single exposure to white light of 2, 4, 6 or 8 h duration,damps out again after a further 34 d and can be reinitiatedfor a second time by a further exposure to light. During the exposure to light there is a burst of CO2 outputconsistent with the decarboxylation of malate, and the rhythmbegins afterwards with an initial high rate of CO2 fixation.Malate gradually accumulates in the leaves in continuous darknessto attain a maximum value (35 mol m3) at the time whenthe circadian rhythm disappears, and decreases to a low value(19 mol m3) after a 4 h exposure to light which reinitiatesrhythmicity. These results support the hypothesis that damping of the rhythmof CO2 output in continuous darkness is due to the accumulationof malate in the leaf cells, eventually reaching such a levelthat its removal from the cytoplasm into the vacuole cannottake place, with the result that PEPc activity, upon which therhythm of CO2 output depends, remains allosterically inhibited. Key words: CAM, circadian rhythm, Bryophyllum, CO2-fixation, malate metabolism 相似文献
5.
GEHL KATHARINA A.; COOK CATHERINE M.; COLMAN BRIAN 《Journal of experimental botany》1987,38(7):1203-1210
The carbon dioxide compensation point of the unicellular greenalga, Chloretla saccharophila, was determined in aqueous mediumby a gas chromatographic method. Compensation points decreasedmarkedly from 63 cm3 m3 at an external pH of 4.0 to 3.2cm3 m3 at pH 8.0 and were not affected by the O2 concentrationof the medium. The calculated CO2 concentration required tosupport the half-maximum photosynthetic rate of the algal cellsranged from 6.0 mmol m3 at an external pH of 60 to 1.5mmol m3 at pH 8.0 and these values were not affectedby O2 concentration. The Km(CO2) of nbulose-l,5-bisphosphatecarboxylase isolated from cells grown either at pH 4.0 or pH8.0 was determined to be 64 mmol m3. These results indicatethat loss of CO2 by photorespiration does not occur in C. saccharophilacells at acid pH and the disparity between the apparent affinityfor CO2 of the intact cells and that of the carboxylase indicatesthe operation of a CO2 concentrating mechanismin this alga at acid pH. Key words: Acidophilic alga, bicarbonate transport, Chlorella saccharophila, compensation point, CO2 affinity, PH, RuBP carboxylase 相似文献
6.
Effects of Prolonged Darkness on the Sensitivity of Leaf Respiration to Carbon Dioxide Concentration in C3and C4Species 总被引:3,自引:1,他引:2
Predicting responses of plant and global carbon balance to theincreasing concentration of carbon dioxide in the atmosphererequires an understanding of the response of plant respirationto carbon dioxide concentration ([CO2]). Direct effects of thecarbon dioxide concentration at which rates of respiration ofplant tissue are measured are quite variable and their effectsremain controversial. One possible source of variation in responsivenessis the energy status of the tissue, which could influence thecontrol coefficients of enzymes, such as cytochrome-c oxidase,whose activity is sensitive to [CO2]. In this study we comparedresponses of respiration rate to [CO2] over the range of 60to 1000 µmol mol-1in fully expanded leaves of four C3andfour C4herbaceous species. Responses were measured near themiddle of the normal 10 h dark period, and also after another24 h of darkness. On average, rates of respiration were reducedabout 70% by the prolonged dark period, and leaf dry mass perunit area decreased about 30%. In all species studied, the relativedecrease in respiration rate with increasing [CO2] was largerafter prolonged darkness. In the C3species, rates measured at1000 µmol mol-1CO2averaged 0.89 of those measured at 60µmol mol-1in the middle of the normal dark period, and0.70-times when measured after prolonged darkness. In the C4species,rates measured at 1000 µmol mol-1CO2averaged 0.79 of thoseat 60 µmol mol-1CO2in the middle of the normal dark period,and 0.51-times when measured after prolonged darkness. In threeof the C3species and one of the C4species, the decrease in theabsolute respiration rate between 60 and 1000 µmol mol-1CO2wasessentially the same in the middle of the normal night periodand after prolonged darkness. In the other species, the decreasein the absolute rate of respiration with increase in [CO2] wassubstantially less after prolonged darkness than in the middleof the normal night period. These results indicated that increasingthe [CO2] at the time of measurement decreased respiration inall species examined, and that this effect was relatively largerin tissues in which the respiration rate was substrate-limited.The larger relative effect of [CO2] on respiration in tissuesafter prolonged darkness is evidence against a controlling roleof cytochrome-c oxidase in the direct effects of [CO2] on respiration.Copyright 2001 Annals of Botany Company Carbon dioxide, respiration, Abutilon theophrasti(L.), Amaranthus retroflexus(L.),Amaranthus hypochondriacus (L.), Datura stramonium(L.), Helianthus annuus(L.), Solanum melongena(L.), Sorghum bicolor(L. Moench), Zea mays 相似文献
7.
Effects of elevated carbon dioxide and ozone on the growth and yield of spring wheat (Triticum aestivum L.) 总被引:4,自引:0,他引:4
Mulholland B.J.; Craigon J.; Black C.R.; Colls J.J.; Atherton J.; Landon G. 《Journal of experimental botany》1997,48(1):113-122
Spring wheat cv. Minaret was grown under three carbon dioxide(CO2) and two ozone (O3) concentrations from seedling emergenceto maturity in open-top chambers. Under elevated CO2 concentrations,the green leaf area index of the main shoot was increased, largelydue to an increase in green leaf area duration. Biomass increasedlinearly in response to increasing CO2 (ambient, 550 and 680ppm). At anthesis, stem and ear dry weights and plant heightwere increased by up to 174%, 5% and 9 cm, respectively, andbiomass at maturity was 23% greater in the 680 ppm treatmentas compared to the ambient control. Grain numbers per spikeletand per ear were increased by 0.2 and 5 grains, respectively,and this, coupled with a higher number of ears bearing tillers,increased grain yield by up to 33%. Exposure to a 7 h daily mean O3 concentration of 60 ppb inducedpremature leaf senescence during early vegetative growth (leaves17) under ambient CO2 concentrations. Damage to the mainshoot and possible seedling mortality during the first 3 weeksof exposure altered canopy structure and increased the proportionof tillers 1 and 2 which survived to produce ears at maturitywas increased; as a result, grain yield was not significantlyaffected. In contrast to the older leaves, the flag leaf (leaf8) sustained no visible O3 damage, and mean grain yield perear was not affected. Interactions between elevated CO2 andO3 influenced the severity of visible leaf damage (leaves 17),with elevated CO2 apparently protecting against O3-induced prematuresenescence during early vegetative growth. The data suggestthat the flag leaf of Minaret, a major source of assimilateduring grain fill, may be relatively insensitive to O3 exposure.Possible mechanisms involved in damage and/or recovery are discussed. Key words: Carbon dioxide, ozone, spring wheat (cv. Minaret), leaf damage, tiller, yield 相似文献
8.
Plants were grown at either 350 or 1000 µl l-1CO2and inone of three photoperiod treatments: continuous short days (SD),continuous long days (LD), or short switched to long days atday 41 (SDLD). All plants received 9 h of light at 450µmol m-2s-1and LD plants received an additional 4 h oflight at 8 µmol m-2s-1. Growth of SD plants respondedmore positively to elevated CO2than did LD plants, due largelyto differences in the effect of CO2on unit leaf rate. High CO2increasedheight and decreased branching under SD conditions, but hadno effect under LD conditions. Elevated CO2also increased thenumber of buds and open flowers, the effect for flower numberbeing greater in short than in long days. The specific leafarea of plants grown at 1000 µl l-1CO2was reduced regardlessof daylength. High CO2also decreased leaf and increased reproductiveallocation, the magnitude of these effects being greater underSD conditions. Bud formation and flower opening was advancedunder high CO2conditions in SD plants but bud formation wasdelayed and there was no effect on flower opening under LD conditions.The effects of CO2on plants switched from SD to LD conditionswere largely intermediate between the two continuous treatments,but for some parameters, more closely resembled one or the other.The results illustrate that daylength is an important factorcontrolling response of plants to elevated CO2. Petunia hybridaHort. ex Vilm; carbon dioxide; photoperiod; functional growth analysis; daylength; global change; development; phenology 相似文献
9.
Overcoming Incompatibility in Brassica campestris L. by Carbon Dioxide, and Dark Fixation of the Gas by Self- and Cross-pollinated Pistils 总被引:1,自引:0,他引:1
Supplementing pollen suspension cultures with CO2 (35per cent) caused a marked increase in germination and tube growthin vitro in Brassica campestris L. cv. toria. A weakening ofself-incompatibility by increased CO2 levels from 35per cent was observed. The percentage of pollen tubes whichpenetrated the cuticle layer of stigmatic papilla cells in self-pollinatedpistils was high when CO2 level was 5 per cent. Phosphoenolpyruvate (PEP) carboxylase activity was greater in the pollengerminated in 4 per cent CO2 as compared to air (0.03 per cent).A possible role of CO2 for self-recognition and control of pollentube growth is proposed, proposed. Brassica campestris L., carbon dioxide, self-incompatibility, phosphoenol pyruvate carboxylase 相似文献
10.
The poplar clones Columbia River, Beaupre, Robusta and Raspaljehave been investigated under the present (350 µmol mol1)and double the present (700 µmol mol1) atmosphericCO2 concentration. Cuttings were planted in pots and were grownin open-top chambers inside a glasshouse for 92 d. The number of leaves, total length of stem, total leaf area,overall growth rate, total leaf, stem and root d. wt respondedpositively to increased CO2 but the leaf size and biomass allocationshowed no change with CO2 enrichment. Beaupre and Robusta showeda larger growth response than either Columbia River or Raspalje. The effects of CO2 enrichment were restricted to the early phaseof growth at the beginning of the growth season. Leaf cell numbers in all the clones were not affected by CO2enrichment. Leaf thickness was affected; this was mainly theresult of larger mesophyll cells and more extensive intercellularspaces. Poplar clones, CO2 enrichment, growth, leaf anatomy, leaf cell number 相似文献
11.
It has been predicted that the concentration of CO2in the aircould double during the 21st century. Though it is recognizedthat CO2-doubling could increase yield through its effects onplant photosynthesis and stomatal behaviour, it is unclear whetherCO2-doubling will change phasic development in wheat. A phytotronstudy was conducted with two contrasting cultivars of wheat,Condor (spring) and Cappelle Desprez (winter), to determinewhether development is affected by a season-long exposure to360 and 720 ppmv CO2. Plants were vernalized for 50 d (8/4 °C,8 h photoperiod) before their exposure to the CO2treatments. There were significant differences between cultivars in theduration of different phenophases as well as in the final numberof leaves. However, CO2concentration had no effect in eithercultivar on the duration of the early developmental phase toterminal spikelet initiation, or on the final number of leaves,though CO2-doubling did slightly increase the later phase fromterminal spikelet initiation to heading in Cappelle Desprez.Condor and Cappelle Desprez also differed markedly in the dynamicsof leaf appearance. While the former had a constant rate ofleaf appearance throughout development, the latter had a fastrate initially (between leaves 1 and 7), similar to that ofCondor, which was followed by a slower rate after the appearanceof leaf 7. Overall, CO2-doubling did not significantly affectthe rates of leaf appearance nor the shape of the relationship.Phyllochron for the first seven leaves was the same for bothCO2concentrations. However, the change in phyllochron associatedwith CO2-doubling for leaves 712 in Cappelle Desprez,although quite small (4%), accounts for part of the slightlyincreased duration of the phase from terminal spikelet initiationto heading under high CO2concentration in that cultivar. Weconclude that CO2concentration does not influence developmentin wheat to a degree relevant to agronomy. Carbon dioxide; climatic change; development; leaf number; phyllochron 相似文献
12.
Elevated CO2 reduces O3 flux and O3-induced yield losses in soybeans: possible implications for elevated CO2 studies 总被引:2,自引:0,他引:2
Soybeans were grown for three seasons in open-top field chambersto determine (1) whether elevated CO2 (360 versus 700 µmolmol1) alleviates some of the yield loss due to pollutantO3, (2) whether the partial stomatal closure resulting fromchronic O3 exposure (charcoal-filtered air versus 1.5 ambientconcentrations) is a cause or result of decreased photosynthesis,and (3) possible implications of CO2/O3 interactions to climatechange studies using elevated CO2. Leaf conductance was reducedby elevated CO2, regardless of O3 level, or by exposure to O3alone. As.a result of these effects on conductance, high CO2reduced estimated midday O3 flux into the leaf by an averageof 50% in charcoal-filtered air and 35% in the high O3 treatment.However, while exposure to O3 reduced seed yields by 41% atambient CO2 levels, the yield reduction was completely amelioratedby elevated CO2. The threshold midday O3 flux for yield lossappears to be 2030 nmol m2 s1 in this study.Although elevated CO2 increased total biomass production, itdid not increase seed yields. A/Ci curves show a large reductionin the stomatal limitation to photosynthesis due to elevatedCO2 but no effect of O3. These data demonstrate that (1) reducedconductance due to O3 is the result, and not the cause, of reducedphotosynthesis, (2) 700 µmol mol1 CO2 can completelyameliorate yield losses due to O3 within the limits of theseexperiments, and (3) some reports of increased yields underelevated CO2 treatments may, at least in part, reflect the ameliorationof unrecognized suppression of yield by O3 or other stresses. Key words: Stomatal limitation, elevated CO2, O3 flux, Glycine max, yield suppression 相似文献
13.
KENDALL A. C.; TURNER J. C.; THOMAS S. M.; KEYS A. J. 《Journal of experimental botany》1985,36(2):261-273
Spring wheat plants were grown in a cage with a glass roof untilthree days after anthesis and then subjected to treatments inconstant environment rooms with any one of all combinationsof four irradiances and two concentrations of carbon dioxide.The photoperiod was 16 h and day/night temperatures 19?C/14?C.Growth and yield of grain were saturated at the two brightestirradiances. Carbon dioxide enrichment from 350 to 1200 mm3dm3 increased shoot dry weight and grain yield at finalharvest at all irradiances, by averages of 10.5 (not significant)and 23.5 (significant) percent respectively. However, increasingthe irradiance from 150 to 613 µE m2 s1caused much larger yield increases (approximately 3-fold). Increasedgrain production by increased light was caused by both increasesin dry weight per grain and by increases in grain number perspikelet. The increase caused by CO2 enrichment was mainly becauseof increased dry weight per grain. Increase in ear dry weightcaused by CO2 enrichment took place between 30 and 60 d afteranthesis. The increase in shoot dry weight took place immediatelyafter exposure to increased CO2 from 3 to 15 d after anthesis.Net photosynthesis by flag leaves on the main shoots was almostdoubled 16 d after anthesis by the CO2 enrichment even thoughstomatal resistance was also doubled. However, this increasewas not reflected by a proportional increase in yield, probablybecause increased mutual shading by bigger stems and late tillersreduced total assimilation and because of increased respirationby the shoots. The increase in photosynthesis was not due toa decrease in photorespiration but to an increase in gross photosynthesis. Key words: CO2enrichment, Photosynthesis, Photorespiration 相似文献
14.
The mechanism of SO2-induced changes in stomatal conductance(g) of alder was examined to determine if SO2 affects guardcell function directly or indirectly through the SO2-inducedchanges in photosynthesis. During experimental fumigations at SO2 concentrations of 33µmol m3 (0.08 µl l1), stomatal closurepreceded declines in net photosynthetic rate (A), indicatingthat SO2 can directly affect guard cells. From these and otherstudies it appears that the sequence of A and g responses maybe influenced by SO2 concentration as well as by species. Fumigation with SO2 did not cause increases in g, even whenthe intercellular substomatal CO2 concentration (ci) was reducedby 50 µmol mol1. Increases in g are not attributableto SO2 effects on the CO2-based stomatal control system. Key words: Air pollution, Alnus serrulata, gas exchange, stomata, sulphur dioxide 相似文献
15.
Interactions between water availability and elevated atmosphericCO2 concentrations have the potential to be important factorsin determining future forage supply from temperate pastures.Using large turves from an established pasture, the responseof these communities at 350 or 700 l l1 CO2 to a soilmoisture deficit and to recovery from the deficit in comparisonto turves that were well-watered throughout was measured. Priorto this experiment the turves had been exposed to the CO2 treatmentsfor 324 d. Net CO2 exchange continued at elevated CO2 even when the volumetricsoil moisture content was less than 0.10 m3 m3 soil;at the same moisture deficit gas exchange at ambient CO2 waszero. The additional carbon fixed by the elevated CO2 turveswas primarily allocated below-ground as shown by the maintenanceof root length density at the same level as in well-wateredturves. When the dry turves were rewatered there was compensatorygrowth at ambient CO2 so that the above-ground growth rate exceededthat of turves that had not experienced a moisture deficit.At the start of this experiment, the turves that were growingat 700 l I1 CO2 had a greater proportion of legume (principallywhite clover, Trifolium repens L.) in the harvested herbage.There was a trend for the legume content at elevated CO2 tobe reduced under a soil moisture deficit. The results indicate different strategies in response to soilmoisture deficits depending on the CO2 concentration. At ambientCO2, growth stopped, but plants were able to respond stronglyon rewatering; while at elevated CO2 growth continued (particularlybelow-ground), but no additional growth was evident on rewatering.Ecosystem gas exchange measurements taken at the end of theexperiment (after 429 d of exposure to CO2) showed 33% moreCO2 was fixed at elevated CO2 with only a small (12%) and nonsignificantdownward regulation. Key words: Carbon dioxide, climate change, grassland, gas exchange, soil moisture deficit 相似文献
16.
Experiments are reported on the spatial distributions of isotopiccarbon within the mesophyll of detached leaves of the C3 plantVicia faba L. fed 14CO2 at different light intensities. Eachleaf was isolated in a cuvette and ten artificial stomata providedspatial continuity between the ambient atmosphere (0.030.05%v/v CO2) and the mesophyll from the abaxial leaf side. Paradermalleaf layers exhibited spatial profiles of radioactivity whichvaried with the intensity of incident light in 2 min exposures.At low light, when biochemical kinetics should limit CO2 uptake,sections through palisade cells contained most radioactivity.As the light intensity was increased to approximately 20% offull sunlight, peak radioactivity was observed in the spongycells near the geometric mid-plane of the mesophyll. The resultsindicate that diffusion of carbon dioxide within the mesophyllregulated the relative photosynthetic activity of the palisadeand spongy cells at incident photosynthetically active lightintensities as little as 110 µE m2 s1 whenCO2 entered only through the lower leaf surface. Key words: CO2 capture sites, Vicia faba L., Artificial stomata 相似文献
17.
ROWLAND-BAMFORD AMANDA J; ALLEN L HARTWELL JR; BAKER JEFFREY T; BOOTE KEN J 《Journal of experimental botany》1990,41(12):1601-1608
The atmospheric carbon dioxide (CO2) concentration has beenrising and is predicted to reach double the present concentrationsometime during the next century. The objective of this investigationwas to determine the long-term effects of different CO2 concentrationson carbohydrate status and partitioning in rice (Oryza sativaL cv. IR-30). Rice plants were grown season-long in outdoor,naturally sunlit, environmentally controlled growth chamberswith CO2 concentrations of 160, 250, 330, 500, 660, and 900µmolCO2 mol1 air. In leaf blades, the priority between the partitioningof carbon into storage carbohydrates or into export changedwith developmental stage and CO2 concentration. During vegetativegrowth, leaf sucrose and starch concentrations increased withincreasing CO2 concentration but tended to level off above 500µmolmol1 CO2. Similarly, photosynthesis also increased withCO2 concentrations up to 500µmol mol1 and thenreached a plateau at higher concentrations. The ratio of starchto sucrose concentration was positively correlated with theCO2 concentration. At maturity, increasing CO2 concentrationresulted in an increase in total non-structural carbohydrate(TNC) concentration in leaf blades, leaf sheaths and culms.Carbohydrates that were stored in vegetative plant parts beforeheading made a smaller contribution to grain dry weight at CO2concentrations below 330µmol mol1 than for treatmentsat concentrations above ambient Increasing CO2 concentrationhad no effect on the carbohydrate concentration in the grainat maturity Key words: CO2 enrichment, starch, sucrose 相似文献
18.
Studies on frost hardiness in Chlorella ellipsoidea I. Development of frost hardiness of Chlorella ellipsoidea in synchronous culture 总被引:1,自引:0,他引:1
Hatano Shoji; Sadakane Haruo; Tutumi Masakazu; Watanabe Tadao 《Plant & cell physiology》1976,17(3):451-458
Cells of Chlorella ellipsoidea Gerneck (IAM C-27) were synchronouslygrown under a 28-hr light-14-hr dark regime at 25°C. Thealgal cells at different stages during the cell cycle were hardenedat 3°C for 48 hr. The survival rate of hardened cells wasmaximum (70%) at the L2 stage(ripening phase) in the life cycle.The average cell volume of L2 cells increased during hardening,but the process of nuclear division scarcely advanced. The hardinessof L2 cells increasedwith prolongation of hardening time upto 48 hr. Their viability decreased upon increasing the ratof cooling and lowering the final freezing temperature. Butthe hardened cells, which had been prefrozen stepwise, showeda survival rate above 50% even at 196°C when thawedrapidlyin a bath at 25°C. Although L2 cells were somewhathardened in the dark, illumination was the more effective whenused with bubbling gas. Under illumination, bubbling of 1% CO2-airincreased the hardiness more than CO2-free air, but in the dark,this relation was reversed. The hardiness was lowest with nitrogengas bubbling under both conditions. (Received December 3, 1975; ) 相似文献
19.
Long-term effects of atmospheric carbon dioxide concentration(ambient or 700 µmol mol1) and air temperature(simulation of field conditions or + 4 C) on leaf photosyntheticrate were examined in Lolium perenne L. cv. Vigor, exposed tonatural illumination during winter. Photosynthetic capacitywas compared over a range of air temperatures and photon fluxdensities of photosynthetically active radiation which wererepresentative of winter climate (515 C and 0500µmol m2s1), with CO2 level during measurementsimilar to that during the experimental period. Long-term exposureto increased air temperature reduced leaf CO2 fixation capacityby 23% (averaged over all measurement conditions), resultingfrom a decline in lightsaturated uptake rate, but not in incident-lightquantum efficiency. CO2- stimulation was largely absent in plantsgrown in ambient temperature, but pronounced in plants grownunder +4 C, where it compensated for two-thirds of the 23%drop. This enhancing effect of elevated CO2 level on leaf CO2uptake rate observed in the warmer treatment, was strongly dependenton measurement temperature, increasing from 5% at 5 C, to upto 32% at 15 C. Measurements of chlorophyll fluorescence anddry matter corresponded with the observed changes in assimilationcapacity, which could not be attributed to a deteriorated nitrogenstatus of the leaves as there was a similar N content on anarea basis. Several hypotheses are considered to explain theobserved CO2-temperature interactions. Key words: Acclimation, chlorophyll fluorescence, elevated CO2 level, global warming, low temperature 相似文献
20.
Colman, B. and Rotatore, C. 1988. Uptake and accumulation ofinorganic carbon by a freshwater diatom.J. exp Bot 39:10251032. The mechanism of uptake of inorganic carbon and its accumulationhas been studied in the freshwater diatom Navicula pelliculosa.No external carbonic anhydrase could be detected, although itwas detected in cell extracts. The rate of photosynthetic O2evolution, in media in the range pH 7.58.5, exceededthe calculated rate of CO2 supply 2- to 5-fold, indicating thatHCO3 was taken up by the cells. At an external pH of7.5, the internal pH, measured by 14C-dimethyloxazolidine-2,4-dione distribution between the cells and the medium, was pH7.6 in the light and pH 7.4 in the dark. Accumulation of inorganiccarbon was determined by the silicone oil centrifugation methodand inorganic carbon pools of 23.5 mol m3 were found,a concentration 21.6-fold that in the external medium. The resultsindicate an active accumulation of inorganic carbon againstpH and concentration gradients in this diatom, probably by activeHCO3 uptake. Key words: Bicarbonate transport, carbon dioxide, carbonic anhydrase, CO2 affinity, CO2 concentrating mechanism, internal pH, Navicula pelliculosa 相似文献