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1.
Obara K Nobe K Nobe H Kolodney MS De Lanerolle P Paul RJ 《American journal of physiology. Cell physiology》2000,279(3):C785-C796
We used a reconstituted fiber formed when 3T3fibroblasts are grown in collagen to characterize nonmusclecontractility and Ca2+ signaling. Calf serum (CS) andthrombin elicited reversible contractures repeatable for >8 h. CSelicited dose-dependent increases in isometric force; 30% produced thelargest forces of 106 ± 12 µN (n = 30), whichis estimated to be 0.5 mN/mm2 cell cross-sectionalarea. Half times for contraction and relaxation were 4.7 ± 0.3 and 3.1 ± 0.3 min at 37°C. With imposition of constant shortening velocities, force declined with time, yieldingtime-dependent force-velocity relations. Forces at 5 s fit thehyperbolic Hill equation; maximum velocity(Vmax) was 0.035 ± 0.002 Lo/s.Compliance averaged 0.0076 ± 0.0006 Lo/Fo. Disruption of microtubules with nocodazole in a CS-contracted fiber had no net effects on force, Vmax, or stiffness; force increased in 8, butdecreased in 13, fibers. Nocodazole did not affect baselineintracellular Ca2+ concentration([Ca2+]i) but reduced (~30%) the[Ca2+]i response to CS. The force afternocodazole treatment was the primary determinant of stiffness andVmax, suggesting that microtubules were not amajor component of fiber internal mechanical resistance. Cytochalasin Dhad major inhibitory effects on all contractile parameters measured butlittle effect on [Ca2+]i. 相似文献
2.
The population dynamics of the cyanobacterium Microcystis aeruginosain a hypertrophic, subtropical lake (Hartbeespoort Dam, SouthAfrica) were followed over 4.5 years. We examined the hypothesisthat M.aeruginosa dominated (>80% by volume) the phytoplanktonpopulation up to 10 months of each year because it maintaineditself within shallow diurnal mixed layers and was thus ensuredaccess to light, the major limiting resource. Wind speeds overHartbeespoort Dam were strong enough to mix the entire epilimnionthrough Langmuir circulations only 12% of the time. At othertimes solar heating led to the formation of diurnal mixed layers(z1) that were shallower (<2 m) than the euphotic zone (zcu;mean = 3.5 m, range: 0.458.4 m) while the seasonal mixedlayer (zm) was always deeper than zcu (range: 718 m).By means of its buoyancy mechanism M.aeruginosa maintained thebulk of its population within z1, while non-buoyant speciessank into dark layers. Adaptation to strong light intensitywas implicated from low cellular chlorophyll a content (0.132µg/106 cells) and high Ik (up to 1230 µE m2s1). Ensured access to light, the post-maximum summerpopulations persisted throughout autumn and winter, despitesuboptimal temperatures, by sustaining low losses. Increasedsedimentation losses caused a sharp decline of the populationat the end of winter each year, and a short (23 months)successional episode followed, but by late spring M.aeruginosawas again dominant. The data from Hartbeespoort Dam point outthe importance of distinguishing between zm and z1, and showthe profound effect that the daily pattern of z1 as opposedto the seasonal pattern of zm, can have on phytoplankton populationspecies composition. 相似文献
3.
This study examined the scaling relationships ofnet O2 uptake [O2(net) = O2 restingO2] to body mass(MB) andcombined mass (MC = MB + bicycle)during uphill treadmill bicycling. It was hypothesized thatO2(net)(l/min) would scale proportionally withMC [i.e.,O2(net) M1.0C] and less than proportionally withMB [i.e.,O2(net) MB].Twenty-five competitive cyclists [73.9 ± 8.8 and 85.0 ± 9.0 (SD) kg forMB andMC,respectively] rode their bicycles on a treadmill at 3.46 m/s andgrades of 1.7, 3.5, 5.2, and 7.0% whileO2 was measured. Multiplelog-linear regression procedures were applied to the pooledO2(net)data to determine the exponents forMC andMB afterstatistically controlling for differences in treadmill grade anddynamic friction. The regression models were highly significant (R2 = 0.95, P < 0.001). Exponents forMC (0.99, 95%confidence interval = 0.80-1.18) andMB (0.89, 95%confidence interval = 0.72-1.07) did not differ significantly fromeach other or 1.0. It was concluded that the 0.99 MC exponent wasdue to gravitational resistance, whereas theMB exponent was<1.0 because the bicycles were relatively lighter for heaviercyclists. 相似文献
4.
Perianth MP, gynoecium MG, and androecium MA dry-weight biomass(in g) of 39 species of perfect flowers was measured. Thesedata were pooled with published data from an additional 51 speciesand used to determine size-dependent variations in (MG and MA)in terms of the hypothesis that the quotient of MG and MA exceeds1·0 for out-breeding (xenogamous) species and less than1·0 for in-breeding (autogamous) species. Ordinary leastsquare regression of the pooled data (n = 90) showed MG = 0·118M0·916P (r2 = 0·884) and MA = 0·186 M0·975P(r2 = 0·865), indicating that the biomass of the gynoeciumproportionally decrease as floral size increases. The exponentsof these regressions indicate that the ratio of gynoecial toandroecial biomass decreased with increasing floral size suchthat comparatively small flowers (MP < 0·0021 g) hadMG/MA > 1·0 (predicted for 'out-breeders') while comparativelylarger flowers (MP > 0·0021 g) had MG /MA < 1·0(predicted for 'in-breeders'). Thus, on average, the type ofbreeding system was a size-dependent phenomenon. To test whether the biomass of a floral organ-type is a legitimateindicator of gender reproductive effort, the biomass (in g)of stamen filaments Mm and anther sacs MAS of 39 species wasdetermined. Least square regression of these data showed MAS= 0·188 M0·854fil (r2 = 0·967), indicatingthat species with larger stamen filaments, on the average, boreproportionally smaller anther sacs and thereby cautioning againstthe uncritical use of the allocation of biomass to floral organ-typeas a strict gauge of gender-function investment. To determine whether the loss of one gender-function resultsin proportional reallocation of biomass to the remaining gender-function,the size-dependency of androecial and gynoecial biomass wasdetermined for a total of 33 perfect and imperfect flowers ofCucumis melo. Regression of the data obtained from perfect flowersyielded MA = 0·402 M1·47P (r2 = 0·898)and MG = 4·63 M1·36P (r2 = 0·842). SinceMG/MA M0·11P , the biomass allocation to the gynoeciumrelative to the androecium decreased with increasing floralsize. This result was consistent with the broad interpecificcomparison based on 90 species with perfect flowers . Regressionof the data for imperfect flowers yielded MA = 0·151M1·02P (r2 = 0·675) and MG = 4·68 M1·47P(r2 = 0·996), indicating a near allometric relation forthe androecium and a strong positive anisometry for the gynoecium.Thus, for flowers of comparable size, a loss of female genderobtains a modest to significant again in androecial biomasswhereas the loss of male gender yields only a slight increasein gynoecial biomass. Collectively, the results of these studies indicate that biomassallocation patterns are size-dependent phenomena whose complexitieshave been largely ignored in the literature.Copyright 1993,1999 Academic Press Allometry, floral biomass, reproduction 相似文献
5.
Imbibition of seeds of oil seed rape (Brassica napus cv Jetneuf)in 103 M aminoethoxyvinylglycine (AVG) or 102silver thiosulphate (Ag+) had no effect on germination nor onthe emergence of seedlings from uncompacted or lightly compressedsoil, but significantly reduced emergence from moderately compressedsoil of 68.4 or 143.3 N cm2 impedance. Exertion of force by emerging control seedlings against a staticcantilever bar fitted with strain gauges reached a maximum (Fmax)of 6 g over 10 h. Higher axial forces were achieved when theseedlings were emerging from compressed soil, without any changein the time required to reach Fmax, so that the build-up offorce was considerably (1.8 fold) faster than in uncompressedsoil. This adaptive response to soil impedance was modified by theseed pretreatments employed. Seedlings from AVG or Ag+pretreatedseeds produced lower axial forces than controls, and neitherFmax nor the rate at which force developed showed any responseto soil compression. After pretreatment in 103 ethephon or 104 naphthaleneacetic acid (NAA) the seedlings achieved similar Fmax to controlseedlings, but responded more rapidly to soil compression sothat the rate of build up of emergence force was 2.3 fold (NAA)or 2.8 fold (ethephon) faster in compressed than in uncompressedsoil. The results suggest that the exertion of force by a seedlingagainst a barrier involves a dynamic response to impedance onthe part of the seedling. This response can be either enhancedor suppressed by substances which affect ethylene productionor ethylene action. Such compounds may have promise for modifyingseedling emergence from impeding soils. Brassica napus, oil seed rape, seedling emergence, soil compaction, ethylene, Ethrel, silver, aminoethoxyvinylglycine, naphthalene acetic acid 相似文献
6.
Arellano Rogelio O.; Garay Edith; Miledi Ricardo 《American journal of physiology. Cell physiology》1998,274(2):C333
Ionic currents elicited via purinergic receptors located in themembrane of Xenopus follicles werestudied using electrophysiological techniques. Follicles responded toATP-activating inward currents with a fast time course(Fin). InRinger solution, reversal potential (Erev) ofFin was 22mV, which did not change with external substitutions ofNa+ orK+, whereas solutions containing50 or 5% of normal Clconcentration shiftedErev to about +4and +60 mV, respectively, and decreasedFin amplitude,indicating thatFin was carriedby Cl.Fin had an onsetdelay of ~400 ms, measured by application of a brief jet of ATP froma micropipette positioned near the follicle (50 µm).Fin was inhibitedby 50% in follicles pretreated with pertussis toxin. This suggests a Gprotein-mediated receptor channel pathway.Fin was mimickedby 2-MeSATP and UTP, the potency order (half-maximal effectiveconcentration) was 2-MeSATP (194 nM) > UTP (454 nM) > ATP(1,086 nM). All agonists generatedCl currents and displayedcross-inhibition on the others.Fin activation byacetylcholine also cross-inhibitedFin-ATPresponses, suggesting that all act on a common channel-activationpathway. 相似文献
7.
Oh-oka Hirozo; Kakutani Saki; Matsubara Hiroshi; Malkin Richard; Itoh Shigeru 《Plant & cell physiology》1993,34(1):93-101
The photoactive reaction center (RC) complex from the greensulfur bacterium Chlorobium limicola f. thiosulfatophilum, strainLarsen, was isolated after solubilization and ammonium sulfatefractionation followed by ion-exchange chromatography. The spectrumof the complex was almost identical with that of the similarRC complex isolated by Feiler et al. [(1992) Biochemistry 31:26082614] except for the presence of cytochrome c551instead of c553 in the latter study. A molecular ratio of BChla to P840 of the isolated RC complex was assayed to be 2535.SDSPAGE analysis revealed that the isolated complex containedthree major polypeptides with apparent molecular masses of 68,41 and 21 kDa, respectively. The 21-kDa polypeptide was identifiedto be a heme-binding protein by staining the gel for peroxidaseactivity. The cytochrome c551 was oxidized by flash light ina biphasic manner with half times of 90 and 390 µs, respectively,that coincided with the reduction half times of P840+. Threedistinct iron-sulfur centers assigned to FA, FB and Fx, respectively,from their g-values were detected by EPR spectroscopy at cryogenictemperature. These results suggest that the present preparationcontains a minimal functional unit of the RC of this bacterium,and that this complex appears to lie on a evolutionary linebetween RC's of purple bacteria and photosystem I. (Received August 18, 1992; Accepted October 28, 1992) 相似文献
8.
Iturriaga, Rodrigo, and Julio Alcayaga. Effects ofCO2-on catecholamine efflux from cat carotid body. J. Appl. Physiol. 84(1): 60-68, 1998.Using achronoamperometric technique with carbon-fiber microelectrodes andneural recordings, we simultaneously measured the effects of thefollowing procedures on catecholamine efflux (CA) andfrequency of chemosensory discharges (fx) fromsuperfused cat carotid body: 1) theaddition ofCO2- to Tyrode solution previously buffered withN-2-hydroxyethylpiperazine-N -2-ethanesulfonicacid, maintaining pH at 7.40; 2)hypercapnia (10% CO2, pH 7.10);3) hypoxia(PO2 h 40 Torr) with andwithoutCO2-;and 4) the impact of several bolusesof dopamine (DA; 10-100 µg) on hypoxic and hypercapnic challenges. WithCO2-,hypoxia increased fx which preceded CAincreases, whereas hypercapnia raised fx but didnot consistently increase CA. Repeated stimuli induced similarfx increases, but attenuated CA. AfterDA, hypoxia produced larger CA, which preceded chemosensoryresponses. WithoutCO2-, hypoxia produced a similar pattern of CA andfx responses. Switching to Tyrode solution withCO2-at pH 7.40 raised fx but did not increase CA.WithCO2- and after DA, hypoxic-induced CAs were larger than in its absence. Results suggest that DA release is not essential for chemosensory excitation. 相似文献
9.
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
10.
The Effect of Drying Rate on the Survival of Three Desiccation-tolerant Angiosperm Species 总被引:7,自引:1,他引:6
FARRANT JILL M.; COOPER KEREN; KRUGER LYNETTE A.; SHERWIN HEATHER W. 《Annals of botany》1999,84(3):371-379
The effect of drying rate on the survival of three angiospermresurrection plants, Craterostigma wilmsii (homoiochlorophyllous),Xerophyta humilis (poikilochlorophyllous) and Myrothamnus flabellifolius(homoiochlorophyllous) was examined. All species survived slowdrying, but only C. wilmsii was able to survive rapid drying.C. wilmsii was rapidly able to induce protection mechanismssuch as folding of cell walls to prevent mechanical stress andcurling of leaves to minimize light stress, and thus survivedfast drying. Rapid drying of X. humilis andM. flabellifoliusappeared to allow insufficient time for complete induction ofprotection mechanisms. In X. humilis, there was incomplete replacementof water in vacuoles, the photosynthetic apparatus was not dismantled,plasma membrane disruption occurred and quantum efficiency ofphotosystem II (FV/FM) did not recover on rehydration. Rapidlydried leaves of M. flabellifolius did not fold tightly againstthe stem and FV/FMdid not recover. Ultrastructural studies showedthat subcellular damage incurred during drying was exacerbatedon rehydration. The three species co-occur in environments inwhich they experience high desiccation pressures. C. wilmsiihas few features to retard water loss and thus the ability forrapid induction of subcellular protection is vital to survival.X. humilis and M. flabellifolius are able to retard water lossand protection is acquired relatively slowly. Copyright 1999Annals of Botany Company Chlorophyll fluorescence, Craterostigma wilmsii, drying rate, Myrothamnus flabellifolius, resurrection plant, ultrastructure, Xerophyta humilis. 相似文献
11.
Effects of themenstrual cycle on heat loss and heat production(M) and core and skin temperatureresponses to cold were studied in six unacclimatized female nonsmokers(18-29 yr of age). Each woman, resting supine, was exposed to acold transient (ambient temperature = mean radiant temperature = 20 to5°C at 0.32°C/min, relative humidity = 50 ± 2%, wind speed = 1 m/s) in the follicular (F) phase(days 2-6) and midluteal (L)phase (days 19-23) of her menstrual cycle. Clothed in each of two ensembles with different thermal resistances, women performed multiple experiments in the F andL phases. Thermal resistance was 0.2 and 0.4 m2 · K · W1for ensembles A andB, respectively. Esophagealtemperature (Tes), mean weightedskin temperature(sk),finger temperature (Tfing), andarea-weighted heat flux were recorded continuously. Rate of heat debt(S) and integrated mean bodytemperature(b,i)were calculated by partitional calorimetry throughout the cold ramp. Extensive peripheral vasoconstriction in the F phase during early periods of the ramp elevated Tesabove thermoneutral levels. Shivering thermogenesis(M = M Mbasal,W /m2) was highly correlated withdeclines insk andTfing(P <0.0001). There was a reducedslope in M as a function ofb,i inthe L phase with ensembles A(P < 0.02) andB (P < 0.01). Heat flux was higher andS was less in the L phases withensemble A(P < 0.05). An analytic modelrevealed thatsk andTes contribute as additive inputsand Tfing has a multiplicativeeffect on the total control of Mduring cold transients(R2 = 0.9).Endogenous hormonal levels at each menstrual cycle phase, coretemperature andskinputs, vascular responses, and variations in body heat balance must beconsidered in quantifying thermoregulatory responses in women duringcold stress. 相似文献
12.
Extracellular acidification elicits a chloride current that shares characteristics with ICl(swell) 总被引:1,自引:0,他引:1
Nobles M Higgins CF Sardini A 《American journal of physiology. Cell physiology》2004,287(5):C1426-C1435
A Cl current activated by extracellular acidification, ICl(pHac), has been characterized in various mammalian cell types. Many of the properties of ICl(pHac) are similar to those of the cell swelling-activated Cl current ICl(swell): ion selectivity (I > Br > Cl > F), pharmacology [ICl(pHac) is inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), 1,9-dideoxyforskolin (DDFSK), diphenylamine-2-carboxylic acid (DPC), and niflumic acid], lack of dependence on intra- or extracellular Ca2+, and presence in all cell types tested. ICl(pHac) differs from ICl(swell) in three aspects: 1) its rate of activation and inactivation is very much more rapid, currents reaching a maximum in seconds rather than minutes; 2) it exhibits a slow voltage-dependent activation in contrast to the fast voltage-dependent activation and time- and voltage-dependent inactivation observed for ICl(swell); and 3) it shows a more pronounced outward rectification. Despite these differences, study of the transition between the two currents strongly suggests that ICl(swell) and ICl(pHac) are related and that extracellular acidification reflects a novel stimulus for activating ICl(swell) that, additionally, alters the biophysical properties of the channel. cell swelling-activated chloride current; patch clamp; pH 相似文献
13.
Yin X Denton J Yan X Strange K 《American journal of physiology. Cell physiology》2007,292(1):C269-C277
An inwardly rectifying swelling- and meiotic cell cycle-regulated anion current carried by the ClC channel splice variant CLH-3b dominates the whole cell conductance of the Caenorhabditis elegans oocyte. Oocytes also express a novel outwardly rectifying anion current termed ICl,OR. We recently identified a worm strain carrying a null allele of the clh-3 gene and utilized oocytes from these animals to characterize ICl,OR biophysical properties. The ICl,OR channel is strongly voltage dependent. Outward rectification is due to voltage-dependent current activation at depolarized voltages and rapid inactivation at voltages more hyperpolarized than approximately +20 mV. Apparent channel open probability is zero at voltages less than +20 mV. The channel has a 4:1 selectivity for Cl over Na+ and an anion selectivity sequence of SCN > I > Br > Cl > F. ICl,OR is relatively insensitive to most conventional anion channel inhibitors including DIDS, 4,4'-dinitrostilbene-2,2'-disulfonic acid, 9-anthracenecarboxylic acid, and 5-nitro-2-(3-phenylpropylamino)benzoic acid. However, the current is rapidly inhibited by niflumic acid, metal cations including Gd3+, Cd2+, and Zn2+, and bath acidification. The combined biophysical properties of ICl,OR are distinct from those of other anion currents that have been described. During oocyte meiotic maturation, ICl,OR activity is rapidly downregulated, suggesting that the channel may play a role in oocyte Cl homeostasis, development, cell cycle control, and/or ovulation. chloride channel; ovulation; cell cycle; meiotic maturation 相似文献
14.
Zhan Wen-Zhi; Watchko Jon F.; Prakash Y. S.; Sieck Gary C. 《Journal of applied physiology》1998,84(4):1260-1268
Postnatal transitions in myosin heavy chain (MHC) isoformexpression were found to be associated with changes in both isometric and isotonic contractile properties of rat diaphragm muscle(Diam). Expression of MHCneo predominated inneonatal Diam fibers but was usually coexpressed withMHCslow or MHC2A isoforms. Expression ofMHCneo disappeared by day 28. Expression ofMHC2X and MHC2B emerged at day 14 andincreased thereafter. Associated with these MHC transitions in theDiam, maximum isometric tetanic force (Po), maximum shortening velocity, and maximum power output progressively increased during early postnatal development. Maximum power output ofthe Diam occurred at ~40% Po at days0 and 7 and at ~30% Po in older animals.Susceptibility to isometric and isotonic fatigue, defined as a declinein force and power output during repetitive activation, respectively,increased with maturation. Isotonic endurance time, defined as the timefor maximum power output to decline to zero, progressively decreasedwith maturation. In contrast, isometric endurance time, defined as thetime for force to decline to 30-40% Po, remained>300 s until after day 28. We speculate that with thepostnatal transition to MHC2X and MHC2Bexpression energy requirements for contraction increase, especiallyduring isotonic shortening, leading to a greater imbalance betweenenergy supply and demand. 相似文献
15.
Cala S. J.; Kenyon C. M.; Ferrigno G.; Carnevali P.; Aliverti A.; Pedotti A.; Macklem P. T.; Rochester D. F. 《Journal of applied physiology》1996,81(6):2680-2689
Cala, S. J., C. M. Kenyon, G. Ferrigno, P. Carnevali, A. Aliverti, A. Pedotti, P. T. Macklem, and D. F. Rochester. Chest wall and lung volume estimation by optical reflectance motion analysis.J. Appl. Physiol. 81(6):2680-2689, 1996.Estimation of chest wall motion by surfacemeasurements only allows one-dimensional measurements of the chestwall. We have assessed an optical reflectance system (OR), which tracksreflective markers in three dimensions (3-D) for respiratory use. Weused 86 (6-mm-diameter) hemispherical reflective markers arrangedcircumferentially on the chest wall in seven rows between the sternalnotch and the anterior superior iliac crest in two normal standingsubjects. We calculated the volume of the entire chest wall andcompared inspired and expired volumes with volumesobtained by spirometry. Marker positions were recorded by four TVcameras; two were 4 m in front of and two were 4 m behind the subject.The TV signals were sampled at 100 Hz and combined with gridcalibration parameters on a personal computer to obtain the 3-Dcoordinates of the markers. Chest wall surfaces were reconstructed bytriangulation through the point data, and chest wall volume wascalculated. During tidal breathing and vital capacity maneuvers andduring CO2-stimulated hyperpnea, there was a very close correlation of the lung volumes(VL) estimated by spirometry[VL(SP)] and OR[VL(OR)]. Regressionequations of VL(OR)(y) vs.VL(SP)(x,BTPS in liters) for the two subjects were given by y = 1.01x 0.01 (r = 0.996) andy = 0.96x + 0.03 (r = 0.997), and byy = 1.04x + 0.25 (r = 0.97) andy = 0.98x + 0.14 (r = 0.95) for the two maneuvers,respectively. We conclude spirometric volumes can be estimated veryaccurately and directly from chest wall surface markers, and wespeculate that OR may be usefully applied to calculations of chest wallshape, regional volumes, and motion analysis. 相似文献
16.
Kwa Siew-Hwa; Wee Yeow-Chin; Lim Tit-Meng; Kumar Prakash P. 《Journal of experimental botany》1995,46(10):1535-1542
Gametophyte-derived callus cultures of Platycerium coronariumcould be maintained under photoautotrophic conditions on Murashigeand Skoog medium supplemented with 2µM 2,4-dichlorophenoxyaceticacid (2,4-D) and with CO2 enrichment. Progressive reductionof sucrose from the medium resulted in a reduction in growth,but an increase in total chlorophyll content. When subculturingwas delayed beyond 2 weeks, callus cells differentiated intogametophytes on the medium with 0.2 sucrose and no CO2 enrichment.Enriching the photoautotrophic cultures on 2µM 2, 4-Dwith 1% CO2 resulted in about 1.7-fold increase in fresh weightwithin 42 d. Total chlorophyll content was generally higherwith 1% CO2 enrichment than with 10%. Fv/Fm ratio was higherfor callus on low levels of sucrose (>0.5%) than that onsucrose 1.0%. An increase in autofluorescence of chloroplasts,but not the size, was observed with decreasing sucrose levelsin the medium. Autofluorescence decreased with increase in CO2from 0.03%. Our data are in agreement with the view that long-termexposure to high levels of decrease in photosynthetic capacity. Key words: Platycerium coronarium, stag's horn fern, autofluorescence of chloroplasts, confocal laser scanning microscope, Fv/Fm ratio, photoautotrophic callus 相似文献
17.
Ferris, Daniel P., and Claire T. Farley. Interaction ofleg stiffness and surface stiffness during human hopping.J. Appl.Physiol. 82(1): 15-22, 1997.When mammals run,the overall musculoskeletal system behaves as a single linear "legspring." We used force platform and kinematic measurements todetermine whether leg spring stiffness(kleg) isadjusted to accommodate changes in surface stiffness(ksurf) whenhumans hop in place, a good experimental model for examiningadjustments tokleg in bouncinggaits. We found thatkleg was greatlyincreased to accommodate surfaces of lower stiffnesses. The seriescombination ofkleg andksurf[total stiffness(ktot)]was independent ofksurf at a givenhopping frequency. For example, when humans hopped at a frequency of 2 Hz, they tripled theirkleg on the leaststiff surface(ksurf = 26.1 kN/m; kleg = 53.3 kN/m) compared with the most stiff surface(ksurf = 35,000 kN/m; kleg = 17.8 kN/m). Values forktot were notsignificantly different on the least stiff surface (16.7 kN/m) and themost stiff surface (17.8 kN/m). Because of thekleg adjustment,many aspects of the hopping mechanics (e.g., ground-contact time andcenter of mass vertical displacement) remained remarkably similardespite a >1,000-fold change inksurf. This studyprovides insight into howkleg adjustmentscan allow similar locomotion mechanics on the variety of terrainsencountered by runners in the natural world. 相似文献
18.
19.
Partially purified homoserine dehydrogenase was prepared frompea seedlings. The optimum pH for this enzyme is approximately 5.4. The Kmvaluesfor ASA and TPNH are 4.6xl04Af and 7.7xl05M, respectively.This enzyme can also utilize DPNH but less effectively thanTPNH. In contrast with yeast homoserine dehydrogenase whichis insensitive to SH reagents, the pea enzyme is inhibitedalmost completely by 104MPCMB and 105MHgCl2, theinhibition being removed by 102M thioglycolate. Homoserinedehydrogenase was found not only in decotylized seedlings, butalso in cotyledons. The significance of this enzyme in homoserine biosynthesis ingerminating pea seeds has been discussed. (Received February 20, 1961; ) 相似文献
20.
Water Transport in Isolated Maize Roots 总被引:3,自引:0,他引:3
A simple model has been devised which predicts the concentration,Cxs, of salt (e.g. KCl) in the exudate from isolated roots asa function of the salt concentration, C0s, in the medium. Thechief assumption, made in deriving the relationship betweenCxs and C05, is that the exudation of water, J, from the rootsconsists of two components (one being osmotic, Ø, inorigin and the other, Ø0, flowing in the absence of anosmotic gradient). The exudation of salt, Js, calculated asJ Cxs, was found to be dependent on C0s. Our investigationson maize roots were concerned with estimations of Lp and Øvand determinations of Cxs as a function of C0s. Satisfactoryagreement between prediction and experiment was found in thesepreliminary studies. It is considered that water movement inisolated roots can be explained by a simple osmotic model withthe additional possibility that a relatively small non-osmoticwater flow occurs. 相似文献