共查询到20条相似文献,搜索用时 663 毫秒
1.
Ca2+ influx through alpha1S DHPR may play a role in regulating Ca2+ release from RyR1 in skeletal muscle 总被引:1,自引:0,他引:1
Shtifman A Paolini C López JR Allen PD Protasi F 《American journal of physiology. Cell physiology》2004,287(1):C73-C78
Skeletal muscle fiber types differ in their contents of total phosphate, which includes inorganic phosphate (Pi) and high-energy organic pools of ATP and phosphocreatine (PCr). At steady state, uptake of Pi into the cell must equal the rate of efflux, which is expected to be a function of intracellular Pi concentration. We measured 32P-labeled Pi uptake rates in different muscle fiber types to determine whether they are proportional to cellular Pi content. Pi uptake rates in isolated, perfused rat hindlimb muscles were linear over time and highest in soleus (2.42 ± 0.17 µmol·g1·h1), lower in red gastrocnemius (1.31 ± 0.11 µmol·g1·h1), and lowest in white gastrocnemius (0.49 ± 0.06 µmol·g1·h1). Reasonably similar rates were obtained in vivo. Pi uptake rates at plasma Pi concentrations of 0.31.7 mM confirm that the Pi uptake process is nearly saturated at normal plasma Pi levels. Pi uptake rate correlated with cellular Pi content (r = 0.99) but varied inversely with total phosphate content. Sodium-phosphate cotransporter (PiT-1) protein expression in soleus and red gastrocnemius were similar to each other and seven- to eightfold greater than PiT-1 expression in white gastrocnemius. That the PiT-1 expression pattern did not match the pattern of Pi uptake across fiber types implies that other factors are involved in regulating Pi uptake in skeletal muscle. Furthermore, fractional turnover of the cellular Pi pool (0.67, 0.57, and 0.33 h1 in soleus, red gastrocnemius, and white gastrocnemius, respectively) varies among fiber types, indicating differential management of intracellular Pi, likely due to differences in resistance to Pi efflux from the fiber. inorganic phosphate; sodium-inorganic phosphate transporters; PiT-2; inorganic phosphate efflux 相似文献
2.
The photosynthetic response to CO2 concentration, light intensityand temperature was investigated in water hyacinth plants (Eichhorniacrassipes (Mart.) Solms) grown in summer at ambient CO2 or at10000 µmol(CO2) mol1 and in winter at 6000 µmol(CO2)mol1 Plants grown and measured at ambient CO2 had highphotosynthetic rate (35 µmo1(CO2) m2 s1),high saturating photon flux density (15002000) µmolm2 s1 and low sensitivity to temperature in therange 2040 °C. Maximum photosynthetic rate (63 µmol(CO2)m2 s1) was reached at an internal CO2 concentrationof 800 µmol mol1. Plants grown at high CO2 in summerhad photosynthetic capacities at ambient CO2 which were 15%less than for plants grown at ambient CO2, but maximum photosyntheticrates were similar. Photosynthesis by plants grown at high CO2and high light intensity had typical response curves to internalCO2 concentration with saturation at high CO2, but for plantsgrown under high CO2 and low light and plants grown under lowCO2 and high light intensity photosynthetic rates decreasedsharply at internal CO2 concentrations above 1000 µmol1. Key words: Photosynthesis, CO2, enrichment, Eichhornia crassipes 相似文献
3.
Photoadaptation in Antarctic phytopfankton: variations in growth rate, chemical composition and P versus I curves 总被引:1,自引:0,他引:1
The response of phytoplankton to variations in the light regimewas studied during the VULCAN and ACDA cruises in the Antarctic.Unenriched batch cultures of 1219 days' duration reachedchl concentrations of 1050 µg1 and exhibitedexponential growth rates, with the maximal rate being 0.41 doubl,day1. Ice edge algae exhibited maximum growth rates atphoton flux densities (PFD) of 30100 µE m2S1and the growth rate was reduced by about 30% at 5001000µE m2S1 The chl/C ratio ranged between 0.004and 0.018, with the lowest ratios at PFDs above 500 µEm2S1 chl/C ratios were also below maximum at PFDsbelow 4050 µE m2S1 The C:N:P ratioswere close to the Redfield ratios; the Si/C ratio averaged 0.16(atoms), and the ATP/C ratio averaged from 0.0024 to 0.0050in different culture senes. When thawed after having been frozenfor 10 days, shade-adapted cultures were in a much better conditionthan sun-adapted ones. P versus I data showed that the maximumassimilation number varied from 0.75 to 4.4 µg C (µgchl)1h1. It varied inversely with the chl/C ratio;therefore the maximum carbon turnover rate varied little betweensamples (0.024/0.035 h1). Low biomass communities exhibitedrelatively high values for (the initial slope of P versus Icurves), low values for 1sat (160330 µE m2S1),and they were susceptible to photoinhibition. In contrast, communitiesdominated by Odontella weissflogii exhibited low values for, a high value for Isat (560 µE m2S1 andthey tolerated high PFDs. The photo-adaptational status of thephytoplankton in natural water samples is discussed relativeto the profile of water column stability and mixing processes. 相似文献
4.
Microbial ammonium cycling in the Mississippi River plume during the drought spring of 2000 总被引:1,自引:0,他引:1
Jochem Frank J.; McCarthy Mark J.; Gardner Wayne S. 《Journal of plankton research》2004,26(11):1265-1275
Microbial potential uptake and regeneration rates of ammonium(NH4+) were studied along a salinity gradient (salinities 0.234.4)in the Mississippi River plume during an extreme drought inspring 2000. Chlorophyll concentrations up to 30 µg L1were highest in the low- and mid-salinity regions (salinities8.528.2) and comparable to records of other years butextended over smaller areas than during periods of normal riverflow. Bacterial biomass (5.128.3 µg C L1)was at the low end of the range observed in normal flow years,decreased with distance from the river mouth and did not peakwith chlorophyll. Heterotrophic nanoflagellate abundance (1.44.0µg C L1) did not reflect phytoplankton and bacterialspatial distribution but peaked at 9.2 µg C L1at salinity 8.5. Microbial NH4+ regeneration rates were estimatedby 15NH4+ isotope dilution experiments for the whole microbialcommunity, under light and dark conditions, and for the <2µm bacterium-dominated size fraction. Microbial NH4+ regenerationrates (0.0180.124 µmol N L1 h1) werelow relative to previous reports and peaked at salinity 28.Total NH4+ regeneration rates were higher than those in the<2 µm size fraction at only four stations, suggestingthat bacterial mineralization was a significant component ofNH4+ recycling in some parts of the river plume. Higher NH4+regeneration in whole-water samples versus <2 µm fractionsprovided evidence for microbial grazing in regions where chlorophylland regeneration rates peaked and at two full-salinity stations. 相似文献
5.
Fisher Tamar; Shurtz-Swirski Revital; Gepstein Shimon; Dubinsky Zvy 《Plant & cell physiology》1989,30(2):221-228
Exponentially growing cultures of the chlorophyta Tetraedronminimum were allowed to photoadapt to low (50µmole quantam2s1) and high (500µmole quanta m21)irradiance levels. In these cultures, various aspects of theorganization of the photosynthetic apparatus and related differencesin its performance were studied. In this organism, the observed five-fold increase in pigmentationof low-light adapted cells was due to increases in the numbersof PSU's, while their sizes remained constant. Using radioimmunoassay technique, we found that high-light adaptedalgae had over five times more Rubisco per PSU than their low-lightadapted counterparts. The high-light adapted algae also exhibited far higher (x2.3)light saturated photosynthetic rates per chl a. This increasewas the result of a reduction of tau, , the turnover time ofPS II reaction centers. We propose that the increase in Rubisco per PSU in high-lightadapted algae explains the reduction in , which results in thehigher Pmax rates per chl a in these algae. The relationship is non linear, since the increase in Rubiscoper PSU was x5.3 whereas that in PmM per chl a was only x2.3. (Received July 30, 1988; Accepted December 2, 1988) 相似文献
6.
Acclimation of single plants of Lolium temulentum to changing[CO2] was studied on plants grown in controlled environmentsat 20°C with an 8 h photoperiod. In the first experimentplants were grown at 135 µ;mol m2 s1 photosyntheticphoton flux density (PPFD) at 415µl l1 or 550µll1 [CO2] with some plants transferred from the lowerto the higher [CO2] at emergence of leaf 4. In the second experimentplants were grown at 135 and 500 µmol m2 s1PPFD at 345 and 575 µl l1 [CO2]. High [CO2] during growth had little effect on stomatal density,total soluble proteins, chlorophyll a content, amount of Rubiscoor cytochrome f. However, increasing [CO2] during measurementincreased photosynthetic rates, particularly in high light.Plants grown in the higher [CO2] had greater leaf extension,leaf and plant growth rates in low but not in high light. Theresults are discussed in relation to the limitation of growthby sink capacity and the modifications in the plant which allowthe storage of extra assimilates at high [CO2]. Key words: Lolium, carbon dioxide, photosynthesis, growth, stomatal density 相似文献
7.
Effect of Elevated CO2 on the Photosynthesis, Respiration and Growth of Perennial Ryegrass 总被引:1,自引:0,他引:1
Single, seed-grown plants of ryegrass (Lolium perenne L. cv.Melle) were grown for 49 d from the early seedling stage ingrowth cabinets at a day/night temperature of 20/15 C, witha 12 h photoperiod, and a CO2 concentration of either 340 or680µI 11 CO2. Following complete acclimation tothe environmental regimes, leaf and whole plant CO2 effluxesand influxes were measured using infra-red gas analysis techniques.Elevated CO2 increased rates of photosynthesis of young, fullyexpanded leaves by 3546% and of whole plants by morethan 50%. For both leaves and whole plants acclimation to 680µI1 CO2 reduced rates of photosynthesis in bothCO2 regimes, compared with plants acclimated to 340µll1. There was no significant effect of CO2 regime onrespiration rates of either leaves or whole plants, althoughleaves developed in elevated CO2 exhibited generally lower ratesthan those developed in 340µI I1 CO2. Initially the seedling plants in elevated CO2 grew faster thantheir counterparts in 340µI I1 CO2, but this effectquickly petered out and final plant weights differed by onlyc. 10%. Since the total area of expanded and unexpanded laminaewas unaffected by CO2 regime, specific leaf area was persistently1340% lower in elevated CO2 while, similarly, root/shootratio was also reduced throughout the experiment. Elevated CO2reduced tissue nitrogen contents of expanded leaves, but hadno effect on the nitrogen contents of unexpanded leaves, sheathsor roots. The lack of a pronounced effect of elevated CO2 on plant growthwas primarily due to the fact that CO2 concentration did notinfluence tiller (branch) numbers. In the absence of an effecton tiller numbers, any possible weight increment was restrictedto the c. 2.5 leaves of each tiller. The reason for the lackof an effect on tillering is not known. Key words: Lolium perenne, ryegrass, elevated CO2, photosynthesis, respiration, growth, development 相似文献
8.
On the causes of interspecific differences in the growth-irradiance relationship for phytoplankton. II. A general review 总被引:5,自引:0,他引:5
The causes of interspecific differences in the µ-l relationshipare examined in the context of a mechanistic model which relatesµ to irradiance in terms of six factors:, kc photosyntheticquotient (PQ), Chl a:C, respiration and excretion. The effectof cell size on the light saturated growth rate is also considered.It is shown that photosynthetic efficiency and PQ exhibit remarkablylittle interspecific variability, and average 0.024 ±0.005 µg C(µg Chl a)1 h1 (µEm2 s1)1 and 1.5 ± 0.2 mol 02 molC1 (when NO3 is the nitrogen source) respectively.Two useful relationships were derived: (i) between growth efficiency,g and Chl a:C at µ. = 0; (ii) between the compensationintensity, Ic and the Chl a-specific maintenance respirationrate. Both relationships were independent of temperature anddaylength. Species best adapted to growth at low light werefound to exhibit high Chl a:C ratios and low maintenance respirationrates. As a group, diatoms were consistently the best adaptedfor growth at low irradiance. Chiorophytes, haptophytes, chrysophytesand cryptophytes were intermediate in their performance at lowirradiance. Dinoflagellates exhibited extreme diversity, withspecies spanning the spectrum from very good performance atlow irradiance to very poor. A new µmax-cell carbon relationshipis given based on growth rates normalized to 15°C. Evidenceis presented to show that noise in this relationship can besignificantly reduced by using only carbon-specific growth ratesand using only data for species grown at the same daylength. 相似文献
9.
Single clonal plants of white clover (Trifolium repens L) grownfrom explants in a Perlite rooting medium, and dependent fornitrogen on N2 fixation in root nodules, were grown for severalweeks in controlled environments which provided two regimesof CO2, and temperature 23/18 °C day/night temperaturesat 680 µmol mol1 CO2, (C680), and 20/15 °Cday/night temperatures at 340 µmol mol1 CO2 (C340)After 34 weeks of growth, when the plants were acclimatedto the environmental regimes, leaf and whole-plant photosynthesisand respiration were measured using conventional infra-red gasanalysis techniques Elevated CO2 and temperature increased ratesof photosynthesis of young, fully expanded leaves at the growthirradiance by 1729%, despite decreased stomatal conductancesand transpiration rates Water use efficiency (mol CO2 mol H2O1)was also significantly increased Plants acclimated to elevatedCO2, and temperature exhibited rates of leaf photosynthesisvery similar to those of C340 leaves instantaneouslyexposed to the C680 regime However, leaves developed in theC680 regime photosynthesised less rapidly than C340 leaves whenboth were exposed to a normal CO2, and temperature environmentIn measurements where irradiance was varied, the enhancementof photosynthesis in elevated CO2 at 23 °C increased graduallyfrom approx 10 % at 100 µmol m1 s1 to >27 % at 1170 µmol m2 s1 In parallel, wateruse efficiency increased by 2040 % at 315 µmolm2 s1 In parallel, water use efficiency increasedby 2040 % at 315 µmol m2 s1 In parallel,water use efficiency increased by 2040 % at 315 µmolm2 s1 In parallel, water use efficiency increasedby 2040 % at 315 µmol m2 s1 to approx100 % at the highest irradiance Elevated CO2, and temperatureincreased whole-plant photosynthesis by > 40 %, when expressedin terms of shoot surface area or shoot weight No effects ofelevated CO2 and temperature on rate of tissue respiration,either during growth or measurement, were established for singleleaves or for whole plants Dependence on N2, fixation in rootnodules appeared to have no detrimental effect on photosyntheticperformance in elevated CO2, and temperature Trifolium repens, white clover, photosynthesis, respiration, elevated CO2, elevated temperature, water use efficiency, N2 fixation 相似文献
10.
Photosynthetic Carbon Sources of Stream Macrophytes 总被引:15,自引:0,他引:15
Rates of photosynthesis of four submerged stream macrophyteswere examined under varying pH and composition of inorganiccarbon species. Callitriche stagnatis and Sparganium simplexused only CO2 for photosynthesis. Potamogeton crispus and P.pectinatus used HCO3 in addition to CO2, but with much lowerefficiency. The photosynthetic rates at air equilibrium anda total inorganic carbon concentration of 5.0 mM were 23times lower than maximum rates at CO2 saturation for the HCO3users and 1014 times lower for the CO2 users. The CO2compensation point of entire plants of Callitriche (2.5 µM)and Sparganium (6.0µM) was well below the equilibriumconcentration (15 µM). and the low saturation points (250500µM) also pointed to efficient use of CO2. Callitricheand Sparganium compete successfully with HCO3 users inhardwater streams, which have a higher exchange and generationcapacity of CO2 than stagnant and more soft waters. Rates ofphotosynthesis of Potamogeton crispus and P. pectinatus decreasedat high pH. Depending on the two alternative hypotheses forHCO3use, this decline can be explained by CO3inhibition of HCO3 uptake or by increasing capacity tobuffer H+efflux from the plant. Habitats subject to high pH,e. g. small ponds with dense vegetation, may have a strong selectionfor efficient mechanisms of HCO3 use. Key words: Photosynthesis, Macrophytes, Carbon-source 相似文献
11.
A mechanistic model of competition on a single resource wastested experimentally with two freshwater rotifers, Brachionusrubens and B.calyciflorus, both grown on the alga Chlorellapyrenoidosa. Using open culture systems for each species wemeasured: (i) the resource-saturated exponential growth rate,µmax, and (ii) the relationship between specific growthrate, µ, at steady-state and the residual algal concentrationover a range of system turnover rates, or dilution rates, D.The µmax of B.calyciflorus was {small tilde}60% higherthan B. rubens. These results were then used to construct agraphical model for predicting the victor in interspecific competitionbetween the two rotifers. Since the two resource-dependent growthrates crossed, one species, B.calyciflorus, was predicted tobe the victor at a high D while B. rubens was predicted as thevictor at low D. Finally, the outcome of competition was determinedfor two turnover rates. As predicted by the graphical competitionmodels, B.calyciflorus was the dominant species at rapid D (0.029h1) and B.rubens was dominant at slow D (0.0044 h1).These studies support recent conclusions that mechanistic competitionmodels may be applied to predict dominant species from a prioriinformation on growth potential and resource levels, which isnot possible with traditional Lotka-Volterra models. 相似文献
12.
Photosynthetic 14C fixation by Characean cells in solutionsof high pH containing NaH14CO3 gave a measure of the abilityof these cells to take up bicarbonate (H14CO3). Whereascells of Nitella translucens from plants collected and thenstored in the laboratory absorbed bicarbonate at 11.5µµmoles cm2 sec1, rates of 38µµmoles cm2 sec1 were obtained withN. translucens cells from plants grown in the laboratory. Influxesof 56 µµmoles cm2 sec1 wereobtained with Chara australis, 38 µµmolescm2 sec1 with Nitellopsis obtusa, and 15µµmoles cm2 sec1 with Tolypella intricata.It is considered that these influxes represent the activityof a bicarbonate pump, which may be an electrogenic process. In solutions of lower pH, H14CO3 uptake would be maskedby rapid diffusion of 14CO2 into the cells: the four Characeanspecies fixed 14CO2 at maximum rates of 3040 µµmolescm2 sec1 (at 21° C). 相似文献
13.
The Uptake of Gaseous Ammonia by the Leaves of Italian Ryegrass 总被引:5,自引:0,他引:5
Lockyer, D. R. and Whitehead, D. C. 1986. The uptake of gaseousammonia by the leaves of Italian ryegrass.J. exp. Bot.37: 919927. Plants of Italian ryegrass (Lolium multiflorum Lam.) grown insoil with two rates of added 15N-labelled nitrate were exposed,in chambers, for 40 d to NH3 in the air at concentrations of16, 118 and 520 µg m3. At the highest concentrationof NH3, this source provided 47?3% of the total nitrogen inplants grown with the lower rate of nitrate addition (100mgN kg1 dry soil) and 35?2% with the higher rate (200mgN kg1 dry soil) At the intermediate concentration ofNH3, the contributions to total plant N were 19?6% and 10?8%,respectively, at low and high nitrate while, at the lowest concentrationof NH3, they were 5?1% and 32%. Most of the N derived from theNH3 remained in the leaves, but some was transported to theroots. The amount of N derived from the NH3 that was presentin the leaves was not reduced by washing the leaves in waterat pH 5?0 before harvesting, indicating that the N was assimilatedby the plant and not adsorbed superficially. Rates of uptakeof NH3 per unit leaf area ranged from 1?7 µg dm2h1 at a concentration of 16 µg m3 to 29?0µg dm2 h1 at a concentration of 520 µgm3 and with the lower rate of nitrate addition. Increasingthe supply of nitrate to the roots slightly reduced the rateof uptake of NH3 per unit leaf area. Uptake of N from the higherrate of nitrate was reduced at the highest concentration ofNH3 in the air. Key words: Ammonia, nitrogen, leaf sorption, Lolium multiflorum 相似文献
14.
Respiratory rates in the cladoceran Ceriodaphnia dubia in Lake Rotongaio, a monomictic lake 总被引:2,自引:0,他引:2
The experimentally measured oxygen consumption rate by the cladoceran,Ceriodaphnia dubia, showed a linear increase between 5 and 20°C.Oxygen consumption rates of C. dubia were estimated in situfrom respiratory electron transport system (ETS) activity inLake Rotongaio during summer stratification and winter mixing.Oxygen consumption was 0.002 µl O2 animal1 h1in the hypolimnion and 0.076 µl O2 animal1 h1in the epilimnion during stratification. Implications of respiredoxygen for metabolic carbon requirements are discussed. 相似文献
15.
Mistletoes usually have slower rates of photosynthesis thantheir hosts. This study examines CO2assimilation, chlorophyllfluorescence and the chlorophyll content of temperate hostparasitepairs (nine hosts parasitized by Ileostylus micranthus and Carpodetusserratus parasitized by Tupeia antarctica). The hosts of I.micranthus had higher mean annual CO2assimilation (3.59 ±0.41 µmol m-2 s-1) than I. micranthus(2.42 ± 0.20µmol m-2 s-1), and C. serratus(2.41 ± 0.43 µmolm-2 s-1) showed higher CO2assimilation than T. antarctica(0.67± 0.64 µmol m-2 s-1). Hosts saturated at significantlyhigher electron transport rates (ETR) and light levels thanmistletoes. The positive relationship between CO2assimilationand electron transport suggests that the lower CO2assimilationrates in mistletoes are a consequence of lower electron transportrates. When photosynthetic rates, ETR and chlorophyll a /b ratioswere adjusted for photosynthetically active radiation, hostsdid not have significantly higher CO2assimilation (3.21 ±0.37 µmol m-2 s-1) than mistletoes (2.54 ± 0.41µmol m-2 s-1), but still had significantly higher ETRand chlorophyll a / b ratios. The electron transport rates,saturating light and chlorophyll a / b ratios of sun leavesfrom mistletoes were similar to host shade leaves. These responsesindicate that in comparison with their hosts, mistletoe leaveshave the photosynthetic characteristics of the leaves of shadeplants. Copyright 2000 Annals of Botany Company CO2assimilation, photosynthetic active radiation (PAR), chlorophyll fluorescence, electron transport rate (ETR), photochemical quenching (qp), non-photochemical quenching (qn), sun and shade leaves, chlorophyll content, Ileostylus micranthus, Tupeia antarctica, New Zealand 相似文献
16.
Apparatus is described for exposing plants to low concentrationsof SO2 (50500µg m3 in air) and for measuringeffects on photosynthesis, dark respiration, and transpiration.Temperature, humidity, and irradiance in the chambers were controlledindependently, and fans ensured that leaf boundary layer resistanceswere low. Experiments with plants of Vicia faba in clean andpolluted air showed that: (i) a depression of net photosynthesisby 50 µg m3 SO2 depended on boundary layer resistanceand on irradiance; (ii) stomatal resistance was increased ordecreased by 50 µg m3 SO2 when relative humidityin the chambers was low (35% r.h., 22 °C) or high (50% r.h.,22 °C) respectively. 相似文献
17.
Kaneko Y Ishikawa T Amano S Nakayama K 《American journal of physiology. Cell physiology》2003,284(5):C1215-C1222
Inisolated rat pancreatic -cells, the nitric oxide (NO) donor NOC-7 at1 µM reduced the amplitude of the oscillations of cytosolicCa2+ concentration ([Ca2+]c)induced by 11.1 mM glucose, and at 10 µM terminated them. In thepresence of NG-nitro-L-arginine(L-NNA), however, NOC-7 at 0.5 and 1 µM increased theamplitude of the [Ca2+]c oscillations,although the NO donor at 10 µM still suppressed them. Aqueous NOsolution also had a dual effect on the[Ca2+]c oscillations. The soluble guanylatecyclase inhibitor LY-83583 and the cGMP-dependent protein kinaseinhibitor KT5823 inhibited the stimulatory effect of NO, and8-bromo-cGMP increased the amplitude of the[Ca2+]c oscillations. Patch-clamp analyses inthe perforated configuration showed that 8-bromo-cGMP inhibited wholecell ATP-sensitive K+ currents in the isolated ratpancreatic -cells, suggesting that the inhibition by cGMP ofATP-sensitive K+ channels is, at least in part, responsiblefor the stimulatory effect of NO on the[Ca2+]c oscillations. In the presence ofL-NNA, the glucose-induced insulin secretion from isolatedislets was facilitated by 0.5 µM NOC-7, whereas it was suppressed by10 µM NOC-7. These results suggest that NO facilitatesglucose-induced [Ca2+]c oscillations of-cells and insulin secretion at low concentrations, which effectsare mediated by cGMP, whereas NO inhibits them in a cGMP-independentmanner at high concentrations. 相似文献
18.
Defoliation in White Clover: Nodule Metabolism, Nodule Growth and Maintenance, and Nitrogenase Functioning During Growth and Regrowth 总被引:1,自引:0,他引:1
In two experiments, the functioning and metabolism of nodulesof white clover, following a defoliation which removed abouthalf the shoot tissue, were compared with those of undefoliatedplants. In one experiment, the specific respiration rates of nodulesfrom undefoliated plants varied between 1160 and 1830 µmolCO2 g1h1, of which nodule growth and maintenanceaccounted for 22 ± 2 per cent, or 27 ± 3.6 percent, according to method of calculation. Defoliation reducedspecific nodule respiration and nodule growth and maintenancerespiration by 6070 per cent, and rate of N2 fixationby a similar proportion. The original rate of nodule metabolismwas re-established after about 5 d of regrowth; during regrowthnodule respiration was quantitatively related to rate of N2,fixation: 9.1 µmol CO2 µmol1N2. With the possible exception of nodules examined 24 h after defoliation,the efficiency of energy utilization in nitrogenase functioningin both experiments was the same in defoliated and undefoliatedplants: 2.0±0.1 µmol CO2 µmol1 C2H4;similarly, there was no change in the efficiency of nitrogenasefunctioning as rate of N2 fixation increased with plant growthfrom 1 to 22 µmol N2 per plant h1. Exposure of nodulated white clover root systems to a 10 percent acetylene gas mixture resulted in a sharp peak in rateof ethylene production after 1.52.5 min; subsequently,rate of ethylene production declined rapidly before stabilisingafter 0.51 h at a rate about 50 per cent of that initiallyobserved. Regression of peak rate of ethyleneproduction on rate of N2 fixation indicated a value of 2.9 µmolC2H4 µmol1 N2, for rates of N2 fixation between1 and 22 µmol N2 per plant h1. The relationshipsbetween nitrogenase respiration, acetylene reduction rates andN2 fixation rates are discussed. Trifolium repens, white clover, defoliation, nodule respiration, N2, fixation, nitrogenase 相似文献
19.
Quantitative determinations of chemical composition and oxygenconsumption rates were made for a deep-living population ofthe lobate ctenophore Bolinopsis infundibulum. Animals werecollected in the Gulf of Maine with the submersible Johnson-Sea-Linkduring September 1989 at depths ranging from 120 to 240 m. Carbonand nitrogen contents were similar to values reported for epipelagicctenophores. Lipid and protein levels were lower than valuestypical of epipelagic ctenophores, but higher than those ofmesopelagic species. Carbohydrate was nearly an order of magnitudehigher than previously recorded for B.infundibulum. Oxygen consumptionrates ranged from 0.004 to 0.235 µl O2 mg1 dryweight h at temperatures ranging from 5 to 7°C. Carbon-specificmetabolic rates ranged from 0.21 to 12.73 µl O2 mg1C h1. Energy expenditures estimated from respirationdata ( 相似文献
20.
We grew water hyacinth [Eichhornia crassipes (Mart.) Solms]for 60 days in a greenhouse under natural light and in a controlledenvironment room at 31/25?C day/night temperatures and 90, 320and 750/µEm2sec1. We then determined maximumphotosynthetic rates in 21% and 1% oxygen, stomatal diffusionresistances, contents of chlorophyll and soluble protein, andthe size and density of the photosynthetic units (PSU) in representativeleaves from the four treatments. In air containing 21% oxygen,maximum photosynthetic rates were 14, 27 and 29 mg CO2 dm2hr1for plants grown in artificial light at 90, 320 and 750µEm2sec1,respectively. Plants grown in natural light (maximum of 2000µEm2sec1) had maximum photosynthetic ratesof 34 mg CO2 dm2hr1. In all treatments, photosyntheticrates in 1% oxygen were about 50% greater than rates in normalair, indicating the presence of photorespiration in water hyacinth.There was no apparent relationship between maximum photosyntheticrate per unit leaf area and stomatal conductance, chlorophyllcontent per unit area, or PSU density per unit area. However,the higher maximum photosynthetic rates were associated withgreater mesophyll conductances, specific leaf weights and proteincontents per unit area. When plants grown at 90µEm2sec1for 120 days were transferred to 750µEm2sec1for 5 days, only young leaves that were just beginning to expandat the time of transfer exhibited adaptation to the higher irradiance.The 40% increase in light-saturated photosynthetic rate in theseyoung leaves was associated with increases in mesophyll conductance,soluble protein content per unit area, and specific leaf weight.
1 Mississippi Agricultural and Forestry Experiment Station cooperating. (Received July 19, 1978; ) 相似文献