共查询到20条相似文献,搜索用时 31 毫秒
1.
[14C]-assimilation rates were measured on cultures of two unicellulargreen algae (Chlamydomonas sp. and Oocystis sp.) as a functionof light intensities (saturation curves), under steady lightand also under rapidly alternating high and low light intensities.Assimilation rates vary according to the frequency of the intermittentlight regime and it falls under two categories: (1) at 0.1 and0.2 Hz, the assimilation rate is equal to the average of therates observed at high and low light intensities under steadylight, and (2) under 1.0, 1.6 and 10 Hz the assimilation rateis equal to the rate observed under a mean steady irradiance.Moreover, the range of assimilation rates at a given frequencydepends on the difference between the high and the low intensities.Batch cultures of Oocystis sp. have been grown under intermittentlight of 0.1, 1.0 and 10.0 Hz (same mean intensity). Growthrate under intermittent light of 0.1 Hz is 40% lowerthan the control under steady light. Photosynthetic potential(PBmax)and efficiency () change with the growth stages of thecultures. At the end of the logarithmic growth phase, both photosyntheticparameters are maximum at 1.0 Hz and minimum at 0.1 Hz. Averagecell concentrations of chlorophyll a increase as the frequencyof the light regime decreases. During the log phase, concentrationof carotenoids relative to chlorophyll a increases at 1.0 Hz,decreases at 0.1 Hz, and remains constant at 10.0 Hz. Underclear sky conditions, wave-induced light fluctuations in thephotic layer may therefore enhance primary production, especially(1) in the lower part of the photic layer, where low frequencylight changes might cause cell chlorophyll a to increase, and(2) at a depth of 14 m, where the main frequencies (ofthe order of 1.0 Hz), might cause a significant increase ofboth the photosynthetic potential (PBmax)and efficiency ().
1Contribution au programme du GIROQ (Groupe interuniversitairede recherches océanographiques du Québec)
2Adresse actuelle: Centre de recherches en nutrition, UniversitéLaval, Québec, Qué. G1K 7P4, Canada 相似文献
2.
Les diatomes Nitzschia turgiduloides et Chaetoceros deflandrei,rcoltes en fvrierMars 1980 dans le secteur indiende l'Ocan Antarctique, ont t maintenues en culture au laboratoire,sous des intensits himineuss variant de 140 2 µE m2s2. The production versus intensite lumineuse, tabliespar cellule et par unit de chlorophylle a, suggrent, selonla mthode de Richardson et al. (1983), une adaptation des espcesantarctiques la lumire par variation de la taille (estimepar la valeur Ik) et du nombre (volution de la pente initiale) des units photosynthtiques. Au plan ecologique, les valeursdes paramtres photosynthetiques en lumire Bmitante et en lumiresaturante sont faibles, caractristiques des algues d'ombre:concentration en chlorophylle a et productivit par celluleplus fortes quand les espces sont acclimates a des faiblesintensites lumineuses. Ce travail met ainsi en vidence I'importancedu facteur lumineux par rapport la basse temprature sur laproduction primaire de l'Ocan Antarctique. 相似文献
3.
Dans le Miocène moyen du Sud-Est de l'Europe on rencontretrès rarement des exemplaires fossiles de lamellibrancheslithophages, quelques-uns de ceux-ci appartenant au genre Lithophagaet d'autres au Pholas, Clavagella, Saxicava, Petricola, et Barnea.Certaines especes de Pholas et de Barnea sont rélativementsouvent rencontrees non seulement dans le Miocène moyen(etage Tortonien), mais aussi dans le Miocène supérieur(étage Sarmatien). En génèral ces espèces se rencontrent surun substrat calcaire. Å la fin du Miocène les espècesde lamellibranches fossiles lithophages disparaissent du basinde la Mer Noire, a cause que celui-ci est devenu un basin d'eaudouce. Mais, dans le temps actuel trois espèces de lamellibrancheslithophages vivent aussi dans la Mer Noire, venues dans le Quaternairede la Mer Mediterranee. C'est-à-dire: Pholas dactylusL., Barnea Candida var. pontica Mil., qui vivent sur un substratformé surtout de marnes argileuses ou de marnes calcaires.Sur un substrat de grès dures calcaire se rencontre presqueexclusivement Petricola lithophaga Retzius, sur la plateformerocheuse du sud de Constantza (Roumanie). 相似文献
4.
为了比较C4荒漠植物猪毛菜(Salsola collina)和木本猪毛菜(S. arbuscula)的抗旱结构和适应环境的光合作用特征, 在二者混生的群落中, 选择代表性植株, 采集叶片进行叶片解剖结构分析, 在自然条件下测定了二者叶片的气体交换参数。研究结果表明:猪毛菜叶片具表皮毛, 具有更发达的薄壁贮水组织;木本猪毛菜叶片具有更厚的角质层, 表皮下有1层下皮细胞, 其栅栏组织细胞较长, 排列更紧密。猪毛菜的净光合速率明显高于木本猪毛菜, 日平均值分别为21.5和15.7 μmol CO2·m–2·s–1。猪毛菜的蒸腾速率也明显高于木本猪毛菜, 日平均值分别为14.9和10.2 mmol·m–2·s–1。猪毛菜和木本猪毛菜的水分利用效率的日平均值分别为1.39和1.53 μmol CO2·mmol–1 H2O, 特别是在14:00时分别为1.61和2.30 μmol CO2·mmol–1 H2O, 木本猪毛菜高出猪毛菜约42%。猪毛菜的光补偿点低于木本猪毛菜, 而光饱和点和光量子效率较高, 具有更低的CO2补偿点。这表明:二者的旱生结构不同, 木本猪毛菜具有更显著的荒漠植物特征;在适于二者混生的环境下, 猪毛菜比木本猪毛菜的光合能力更强, 而木本猪毛菜的水分利用效率更高。 相似文献
5.
A novel photorespiratory mutant of Arabidopsis thaliana, designatedgld2, was isolated based on a growth requirement for abnormallyhigh levels of atmospheric CO2. Photosynthetic CO2 fixationwas inhibited in the mutant following illumination in air butnot in atmosphere containing 2% O2. Photosynthetic assimilationof 14CO2 in an atmosphere containing 50% O2 resulted in accumulationof 48% of the soluble label in glycine in the mutant comparedto 9% in the wild type. The rate of glycine decarboxylationby isolated mitochondria from the mutant was reduced to 6% ofthe wild type rate. In genetic crosses, the mutant complementedtwo previously described photorespiratory mutants of A. thalianathat accumulate glycine during photosynthesis in air due todefects in glycine decarboxylase (glyD, now designated gld1)and serine transhydroxymethylase (stm). Because glycine decarboxylaseis a complex of four enzymes, these results are consistent witha mutation in a glycine decarboxylase subunit other than thataffected in the gld1 mutant. The two gld loci were mapped tochromosomes 2 and 5, respectively.
3Present address: Department of Crop and Soil Sciences, MichiganState University, East Lansing, MI 48824, U.S.A.
4Present address: Department of Applied Bioscience, Facultyof Agriculture, Hokkaido University, Kita-Ku, Sapporo, 060 Japan
5Present address: Department of Biology, Carnegie Institutionof Washington, 290 Panama Street, Standford, CA 94305, U.S.A. 相似文献
6.
THE RATIO OF CALCAREOUS AND ORGANIC SHELL COMPONENTS OF FRESHWATER SPHAERIID CLAMS IN RELATION TO WATER HARDNESS AND TROPHIC CONDITIONS 总被引:1,自引:0,他引:1
BURKY ALBERT J.; BENJAMIN MICHELE A.; CATALANO DENNIS M.; HORNBACH DANIEL J. 《Journal of Molluscan Studies》1979,45(3):312-321
Shells from 14 populations of sphaeriid clams including Sphaeriumstriatinum, S. simile, Pisidium walkeri, Musculim partumeiumand M. iransversum were analyzed for organic carbon (µgCmg1 shell), nitrogen (µg,N mg1 shell) andCaCOs (%CaCO3 of total clam dry weight). Habitat waters wereassessed for total hardness (expressed as ppm CaCo3), ppm Ca,ppm Mg, conductivity (µmho) and suspended organic Carbon(µgCl1). For all populations, shell organic C andN are positively correlated and there is an inverse relationshipbetween the amounts of shell CaCO3 and shell organic carbon.Trophic considerations give the best correlation with shelltype at the generic level of consideration since species ofMusculium are found at the opposite end of the trophic scale(eutrophic) from all other populations studied. For S. striatinum,the most extensively studied species, the amount of shell CaCO3is inversely related to water hardness. The selection of shellsin the Sphaeriidae is discussed in relation to structural-functionalneeds and habitat conditions
1 Present Address: Department of Biology, Syracuse University,Syracuse, New York 13210, U.S.A.
2 Present Address: Department of Zoology, Miami University,Oxford, Ohio 45056, U.S.A. (Received 5 December 1978; 相似文献
7.
Isolation of the ALG6 locus of Saccharomyces cerevisiae required for glucosylation in the N-linked glycosylation pathway 总被引:1,自引:0,他引:1
Reiss Gilles; Heesen Stephen te; Zimmerman Jenet; Robbins Phillips; Aebi Markus 《Glycobiology》1996,6(5):493-498
N-Linked protein glycosylation in most eukaryotic cells initiateswith the transfer of the oligosaccharide Glc3Man9GlcNAc2 fromthe lipid carrier dolichyl pyrophosphate to selected asparagineresidues. In the yeast Saccharomyces cerevisiae, alg mutationswhich affect the assembly of the lipid-linked oligosaccharideat the membrane of the endoplasmic reticulum result in the accumulationof lipid-linked oligosaccharide intermediates and a hypoglycosylationof proteins. Exploiting the synthetic growth defect of alg mutationsin combination with mutations affecting oligosaccharyl transferaseactivity (Stagljar et al., 1994), we have isolated the ALG6locus. alg6 mutants accumulate lipid-linked Man9GlcNAc2, suggestingthat this locus encodes an endoplasmic glucosyltransferase.Alg6p has sequence similarity to Alg8p, a protein required forglucosylation of Glc1Man9GlcNAc2. Saccharomyces cerevisiae endoplasmic reticulum glycosyltransferase dolichol 相似文献
8.
Distinct K+ conductive pathways are required for Cl- and K+ secretion across distal colonic epithelium 总被引:1,自引:0,他引:1
Secretion of Cl and K+ in the colonic epithelium operates through a cellular mechanism requiring K+ channels in the basolateral and apical membranes. Transepithelial current [short-circuit current (Isc)] and conductance (Gt) were measured for isolated distal colonic mucosa during secretory activation by epinephrine (Epi) or PGE2 and synergistically by PGE2 and carbachol (PGE2 + CCh). TRAM-34 at 0.5 µM, an inhibitor of KCa3.1 (IK, Kcnn4) K+ channels (H. Wulff, M. J. Miller, W. Hänsel, S. Grissmer, M. D. Cahalan, and K. G. Chandy. Proc Natl Acad Sci USA 97: 81518156, 2000), did not alter secretory Isc or Gt in guinea pig or rat colon. The presence of KCa3.1 in the mucosa was confirmed by immunoblot and immunofluorescence detection. At 100 µM, TRAM-34 inhibited Isc and Gt activated by Epi (4%), PGE2 (30%) and PGE2 + CCh (60%). The IC50 of 4.0 µM implicated involvement of K+ channels other than KCa3.1. The secretory responses augmented by the K+ channel opener 1-EBIO were inhibited only at a high concentration of TRAM-34, suggesting further that KCa3.1 was not involved. Sensitivity of the synergistic response (PGE2 + CCh) to a high concentration TRAM-34 supported a requirement for multiple K+ conductive pathways in secretion. Clofilium (100 µM), a quaternary ammonium, inhibited Cl secretory Isc and Gt activated by PGE2 (20%) but not K+ secretion activated by Epi. Thus Cl secretion activated by physiological secretagogues occurred without apparent activity of KCa3.1 channels but was dependent on other types of K+ channels sensitive to high concentrations of TRAM-34 and/or clofilium. epinephrine; prostaglandin E2; cholinergic; Kcnn4; TRAM-34; clofilium 相似文献
9.
K+ channel KVLQT1 located in the basolateral membrane of distal colonic epithelium is not essential for activating Cl- secretion 总被引:1,自引:0,他引:1
Liao T Wang L Halm ST Lu L Fyffe RE Halm DR 《American journal of physiology. Cell physiology》2005,289(3):C564-C575
The cellular mechanism for Cl and K+ secretion in the colonic epithelium requires K+ channels in the basolateral and apical membranes. Colonic mucosa from guinea pig and rat were fixed, sectioned, and then probed with antibodies to the K+ channel proteins KVLQT1 (Kcnq1) and minK-related peptide 2 (MiRP2, Kcne3). Immunofluorescence labeling for Kcnq1 was most prominent in the lateral membrane of crypt cells in rat colon. The guinea pig distal colon had distinct lateral membrane immunoreactivity for Kcnq1 in crypt and surface cells. In addition, Kcne3, an auxiliary subunit for Kcnq1, was detected in the lateral membrane of crypt and surface cells in guinea pig distal colon. Transepithelial short-circuit current (Isc) and transepithelial conductance (Gt) were measured for colonic mucosa during secretory activation by epinephrine (EPI), prostaglandin E2 (PGE2), and carbachol (CCh). HMR1556 (10 µM), an inhibitor of Kcnq1 channels (Gerlach U, Brendel J, Lang HJ, Paulus EF, Weidmann K, Brüggemann A, Busch A, Suessbrich H, Bleich M, and Greger R. J Med Chem 44: 38313837, 2001), partially (50%) inhibited Cl secretory Isc and Gt activated by PGE2 and CCh in rat colon with an IC50 of 55 nM, but in guinea pig distal colon Cl secretory Isc and Gt were unaltered. EPI-activated K+-secretory Isc and Gt also were essentially unaltered by HMR1556 in both rat and guinea pig colon. Although immunofluorescence labeling with a Kcnq1 antibody supported the basolateral membrane presence in colonic epithelium of the guinea pig as well as the rat, the Kcnq1 K+ channel is not an essential component for producing Cl secretion. Other K+ channels present in the basolateral membrane presumably must also contribute directly to the K+ conductance necessary for K+ exit during activation of Cl secretion in the colonic mucosa. HMR1556; K+ secretion; epinephrine; prostaglandin E2; cholinergic 相似文献
10.
Lee, H. S. J. and Griffiths, H. 1987. Induction and repressionof CAM in Sedurn relephluni L. in response to photopcnod andwater stress.J. exp. Bot. 38: 834841. The introduction and repression of CAM in Sedurn telephiunmL, a temperate succulent, was investigated in watered, progressivelydrouglited and rewatered plants in growth chambers. Measurementswere made of water vapour and CO2 exchange, titratable acidity(TA) and xylem sap tension. Effects of photoperiod were alsostudied. CAM was induced by drought under long or short days,although when watered no CAM activity was expressed. C3-CAM intermediate plants were used for the investigation ofwater supply. Those which had received water and those drought-stressedboth displayed a similar nocturnal increase in TA, with a day-nightmaximum (H+) of 69 µmol g1 fr. wt. The wateredplants took up CO2 at a maximum rate of 2?2 µmol m2s1 only in the light period, while the droughted plantsshowed a maximum nocturnal CO2 uptake rate of 0?69 µmolm2 s1. Subsequently, as CAM was repressed, thewatered S. telephiwn displayed little variation in TA, withconstant levels at 42 µmol g1 fr. wt. (day 10).After 10 d of drought stress, the CAM characteristics of S.telephiurn were aLso affected, with reduced net CO2 uptake andH+. The transition between C3 and CAM in S. telephium can be describedas a progression in terms of the proportion of respiratory CO2which is recycled and refixed at night as malic acid, in comparisonwith net CO2 uptake. Recycling increased from 20% (day 1) to44% (day 10) as a result of the drought stress and was highin both the CAM-C3 stage (no net CO2 uptake at night) and alsoin the drought-stressed CAM stage (reduced net CO2 uptake atnight). The complete C3-CAM transition occurred in less than8 d, and the stages could be characterized by xylem sap tensionmeasurements: CAM = 0?50 MPa C3-CAM = 0?36 MPa C3 = 0?29 MPa. Key words: CAM, Sedum telephium L., recycling 相似文献
11.
In myogenic C2C12 cells, 5 mM creatine increased the incorporation of labeled [35S]methionine into sarcoplasmic (+20%, P < 0.05) and myofibrillar proteins (+50%, P < 0.01). Creatine also promoted the fusion of myoblasts assessed by an increased number of nuclei incorporated within myotubes (+40%, P < 0.001). Expression of myosin heavy chain type II (+1,300%, P < 0.001), troponin T (+65%, P < 0.01), and titin (+40%, P < 0.05) was enhanced by creatine. Mannitol, taurine, and -alanine did not mimic the effect of creatine, ruling out an osmolarity-dependent mechanism. The addition of rapamycin, the inhibitor of mammalian target of rapamycin/70-kDa ribosomal S6 protein kinase (mTOR/p70s6k) pathway, and SB 202190, the inhibitor of p38, completely blocked differentiation in control cells, and creatine did not reverse this inhibition, suggesting that the mTOR/p70s6k and p38 pathways could be potentially involved in the effect induced by creatine on differentiation. Creatine upregulated phosphorylation of protein kinase B (Akt/PKB; +60%, P < 0.001), glycogen synthase kinase-3 (+70%, P < 0.001), and p70s6k (+50%, P < 0.001). Creatine also affected the phosphorylation state of p38 (–50% at 24 h and +70% at 96 h, P < 0.05) as well as the nuclear content of its downstream targets myocyte enhancer factor-2 (–55% at 48 h and +170% at 96 h, P < 0.05) and MyoD (+60%, P < 0.01). In conclusion, this study points out the involvement of the p38 and the Akt/PKB-p70s6k pathways in the enhanced differentiation induced by creatine in C2C12 cells. protein synthesis; insulin-like growth factor; mitogen-activated protein kinase; extracellular signal-regulated kinase 1/2; 70-kDa ribosomal S6 protein kinase 相似文献
12.
Yang T Esteve E Pessah IN Molinski TF Allen PD López JR 《American journal of physiology. Cell physiology》2007,292(5):C1591-C1598
Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle triggered in susceptible individuals by inhalation anesthetics and depolarizing skeletal muscle relaxants. This syndrome has been linked to a missense mutation in the type 1 ryanodine receptor (RyR1) in more than 50% of cases studied to date. Using double-barreled Ca2+ microelectrodes in myotubes expressing wild-type RyR1 (WTRyR1) or RyR1 with one of four common MH mutations (MHRyR1), we measured resting intracellular Ca2+ concentration ([Ca2+]i). Changes in resting [Ca2+]i produced by several drugs known to modulate the RyR1 channel complex were investigated. We found that myotubes expressing any of the MHRyR1s had a 2.0- to 3.7-fold higher resting [Ca2+]i than those expressing WTRyR1. Exposure of myotubes expressing MHRyR1s to ryanodine (500 µM) or (2,6-dichloro-4-aminophenyl)isopropylamine (FLA 365; 20 µM) had no effects on their resting [Ca2+]i. However, when myotubes were exposed to bastadin 5 alone or to a combination of ryanodine and bastadin 5, the resting [Ca2+]i was significantly reduced (P < 0.01). Interestingly, the percent decrease in resting [Ca2+]i in myotubes expressing MHRyR1s was significantly greater than that for WTRyR1. From these data, we propose that the high resting myoplasmic [Ca2+]i in MHRyR1 expressing myotubes is due in part to a related structural conformation of MHRyR1s that favors "passive" calcium leak from the sarcoplasmic reticulum. ryanodine; FLA 365; bastadin 5; resting intracellular calcium concentration; sarcoplasmic reticulum 相似文献
13.
Green Light Drives CO2 Fixation Deep within Leaves 总被引:5,自引:0,他引:5
Maximal l4CO2-fixation in spinach occurs in the middle of thepalisade mesophyll [Nishio et al. (1993) Plant Cell 5: 953],however, ninety percent of the blue and red light is attenuatedin the upper twenty percent of a spinach leaf [Cui et al. (1991)Plant Cell Environ. 14: 493]. In this report, we showed thatgreen light drives 14CO2-fixation deep within spinach leavescompared to red and blue light. Blue light caused fixation mainlyin the palisade mesophyll of the leaf, whereas red light drovefixation slightly deeper into the leaf than did blue light.14CO2-fixation measured under green light resulted in less fixationin the upper epidermal layer (guard cells) and upper most palisademesophyll compared to red and blue light, but led to more fixationdeeper in the leaf than that caused by either red or blue light.Saturating white, red, or green light resulted in similar maximal14CO2-fixation rates, whereas under the highest irradiance ofblue light given, carbon fixation was not saturated, but itasymptotically approached the maximal 14CO2-fixation rates attainedunder the other types of light. The importance of green lightin photosynthesis is discussed.
1Supported in part by grants from Competitive Research GrantsOffice, U.S. Department of Agriculture (Nos. 91-37100-6672 and93-37100-8855). 相似文献
14.
Sink-limited conditions, defined as treatment with continuousillumination, cause a reduction in the rate of photosyntheticfixation of CO2 in single-rooted leaves of soybean (Glycinemax. Merr. cv. Turunoko). We suggested previously that thisreduction is due to a deactivation of ribulose-1,5-bisphosphatecarboxylase (RuBPcase, E.C. 4.1.1.39
[EC]
) that is caused by a decreasein the level of Pi in the leaves [Sawada et al. (1989) PlantCell Physiol. 30: 691, Sawada et al. (1990) Plant Cell Physiol.31: 697]. In the present study, the mechanism of regulationof RuBPcase activity by Pi was examined. The activity of RuBPcasein the sink-limited leaves, exposed for 6 or 7 d to continuousillumination to alter the source/sink balance, was enhancedwith increasing concentrations of Pi, in a CO2-free preincubationmedium in the presence of 5 mM MgCl2 The maximum value [6.3µmole CO2 (mg Chl)1 min1] was obtained atapproximately 5 mM Pi after a 5 min incubation, being 3 timesof the activity without the preincubation. The activity of acrude preparation of RuBPcase that had been deactivated by removalof CO2 and Mg2+ ions by the gel filtration was 5.29.3nmole CO2 (mg protein)1 min1 and was also enhancedby Pi plus Mg2+ ions. The maximum value [147151 nmoleCO2 (mg protein)1 min1] was attained at 5 mM Piafter a 5 min incubation. The cycle of activation and inactivationof deactivated crude RuBPcase was perfectly reversible by additionof Pi to the enzyme and removal of Pi from the enzyme. Levelsof free Pi and of esterified phosphate in the sink-limited leaveswere 69% and 31% of the total phosphate, respectively. By contrast,in the control leaves, these values were 87% and 13%, respectively.These results support our previously stated hypothesis and indicatean important role for free Pi in the regulation of RuBPcaseactivity, in particular in sink-limited plants. (Received February 21, 1992; Accepted July 23, 1992) 相似文献
15.
Vol. II, N. S. No. 5 (January 1938), article by A. H. K. PETRIEand j . G. WOOD. In Table VII, p. 53, all values of the coefficientsof A2R and A2T should be preceded by minus signs. 相似文献
16.
Millhouse, J. and Strother, S. 1987. Further characteristicsof salt-dependent bicarbonate use by the seagrass Zostera muelleri.J.exp. Bot. 38: 10551068. The contribution of HCO3to photosynthetic O2 evolutionin the seagrass Zostera muelleri Irmisch ex Aschers. increasedwith increasing salinity of the bathing seawater when the inorganiccarbon concentration was kept constant. K1/2 (seawater salts)for HCO3 -dependent photosynthesis was 66% of seawatersalinity. Both short- and long-term pretreatment at low salinitiesstimulated photosynthesis in full strength seawater. Twentyfour hours pre-incubation of seagrass plants in 3·0 molm3 NaHCO3 resulted in increased photosynthesis at allsalinities, apparently due to stimulation of HCO3 use(K1/2 (seawater salts) = 26%). Vmax (HCO3) was not affectedby low salinity pretreatment. The kinetics of HCO3 stimulationby the major seawater cations was investigated. Ca2+ was themost effective cation with the highest Vmax (HCO3) andwith K1/2(Ca2+) = 14 mol m3. Mg2+ was also very effectiveat less than 50 mol m3 but higher concentrations wereinhibitory. This inhibition cannot be accounted for solely byprecipitation of MgCO3. Na+ and K+ were both capable of stimulatingHCO3 use. Stimulation was in two distinct parts. Up to500 mol m3, both citrate and chloride salts gave similarresults (K1/2(Na+) 81 mol m3, Vmax(HCO3) 0·26µmol O2 mg1 chl min1), but use of citratesalts above 500 mol m2 caused a second stimulation ofHCO3 use (K1/2(Na+) 830 mol m3, Vmax(HCO3)0·68 µmol O2 mg1 chl min1). Vmax(HCO3)for the second-phase Na+ or K+ stimulation was of the same orderas for Ca2+-stimulated HCO3 use. To further characterizesalt-dependent HCO3 use, the sensitivity of photosynthesisto Tris and TES buffers was investigated. The effects of Trisappear to be due to the action of Tris+ causing stimulationof HCO3 -dependent photosynthesis in the absence of salt,but inhibition of HCO3 use in saline media. TES has noeffect on photosynthesis. External carbonic anhydrase, althoughimplicated in salt-dependent HCO3 use in Z. muelleri,could not be detected in whole leaves. Key words: Zostera muelleri, HCO3 use, salinity 相似文献
17.
The capacity for C4 photosynthesis in Panicum milioides, a specieshaving reduced levels of photorespiration, was investigatedby examining the activity of certain key enzymes of the C4 pathwayand by pulse-chase experiments with 14CO2. The ATP$P1 dependentactivity of pyruvate,P1 dikinase in the species was extremelylow (0.140.18 µmol mg chlorophyll1 min1).Low activity of the enzyme was also found in Panicum decipiensand Panicum hians (related species with reduced photorespiration)and in Panicum laxum (a C3 species). The antibody to pyruvate,P1dikinase caused about 70% inhibition of the ATP$P1 dependentactivity of the enzyme in P. milioides. The activity of NAD-malicenzyme and NADP-malic enzyme in P. milioides was equally low(approximately 0.10.2 µmol mg chlorophyll1min1) and similar to the activity in P. decipiens, P.hians and P. laxum. Photosynthetic pulse-chase experiments underatmospheric conditions showed a typical C3-like pattern of carbonassimilation including the labelling of glycine and serine asexpected during photorespiration. During the pulse with 14CO2only about 1% of the labelled products appeared in malate and23% in aspartate. During a chase in atmospheric levelsof CO2 for up to 6 min there was a slight increase in labellingin the C4 acids. The amount of label in carbon 4 of aspartatedid not change during the chase, indicating little or no turnoverof the C4 acid via decarboxylation. The results indicate thatunder atmospheric conditions P. milioides assimilates carbondirectly through the C3 pathway. Photorespiration as indicatedby the CO2 compensation point may be repressed in the speciesby a more efficient recycling of photorespired CO2. (Received June 8, 1982; Accepted July 22, 1982) 相似文献
18.
We investigated the effects of 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one(DCEBIO) on the Cl secretory response of the mouse jejunum using the Ussing short-circuit current (Isc) technique. DCEBIO stimulated a concentration-dependent, sustained increase in Isc (EC50 41 ± 1 µM). Pretreating tissues with 0.25 µM forskolin reduced the concentration-dependent increase in Isc by DCEBIO and increased the EC50 (53 ± 5 µM). Bumetanide blocked (82 ± 5%) the DCEBIO-stimulated Isc consistent with Cl secretion. DCEBIO was a more potent stimulator of Cl secretion than its parent molecule, 1-ethyl-2-benzimidazolinone. Glibenclamide or NPPB reduced the DCEBIO-stimulated Isc by >80% indicating the participation of CFTR in the DCEBIO-stimulated Isc response. Clotrimazole reduced DCEBIO-stimulated Isc by 67 ± 15%, suggesting the participation of the intermediate conductance Ca2+-activated K+ channel (IKCa) in the DCEBIO-activated Isc response. In the presence of maximum forskolin (10 µM), the DCEBIO response was reduced and biphasic, reaching a peak response of the change in Isc of 43 ± 5 µA/cm2 and then falling to a steady-state response of 17 ± 10 µA/cm2 compared with DCEBIO control tissues (61 ± 6 µA/cm2). The forskolin-stimulated Isc in the presence of DCEBIO was reduced compared with forskolin control tissues. Similar results were observed with DCEBIO and 8-BrcAMP where adenylate cyclase was bypassed. H89, a PKA inhibitor, reduced the DCEBIO-activated Isc, providing evidence that DCEBIO increased Cl secretion via a cAMP/PKA-dependent manner. These data suggest that DCEBIO stimulates Cl secretion of the mouse jejunum and that DCEBIO targets components of the Cl secretory mechanism. 1-ethyl-2-benzimidazolinone; forskolin; glibenclamide; clotrimazole; H89 相似文献
19.
Ko EA Burg ED Platoshyn O Msefya J Firth AL Yuan JX 《American journal of physiology. Cell physiology》2007,293(3):C928-C937
Mice are useful animal models to study pathogenic mechanisms involved in pulmonary vascular disease. Altered expression and function of voltage-gated K+ (KV) channels in pulmonary artery smooth muscle cells (PASMCs) have been implicated in the development of pulmonary arterial hypertension. KV currents (IK(V)) in mouse PASMCs have not been comprehensively characterized. The main focus of this study was to determine the biophysical and pharmacological properties of IK(V) in freshly dissociated mouse PASMCs with the patch-clamp technique. Three distinct whole cell IK(V) were identified based on the kinetics of activation and inactivation: rapidly activating and noninactivating currents (in 58% of the cells tested), rapidly activating and slowly inactivating currents (23%), and slowly activating and noninactivating currents (17%). Of the cells that demonstrated the rapidly activating noninactivating current, 69% showed IK(V) inhibition with 4-aminopyridine (4-AP), while 31% were unaffected. Whole cell IK(V) were very sensitive to tetraethylammonium (TEA), as 1 mM TEA decreased the current amplitude by 32% while it took 10 mM 4-AP to decrease IK(V) by a similar amount (37%). Contribution of Ca2+-activated K+ (KCa) channels to whole cell IK(V) was minimal, as neither pharmacological inhibition with charybdotoxin or iberiotoxin nor perfusion with Ca2+-free solution had an effect on the whole cell IK(V). Steady-state activation and inactivation curves revealed a window K+ current between –40 and –10 mV with a peak at –31.5 mV. Single-channel recordings revealed large-, intermediate-, and small-amplitude currents, with an averaged slope conductance of 119.4 ± 2.7, 79.8 ± 2.8, 46.0 ± 2.2, and 23.6 ± 0.6 pS, respectively. These studies provide detailed electrophysiological and pharmacological profiles of the native KV currents in mouse PASMCs. KV channels 相似文献
20.
Alvarez LJ Zamudio AC Candia OA 《American journal of physiology. Cell physiology》2005,289(1):C138-C147
Experiments were conducted to determine whether the Cl secretagogue, 1-ethyl-2-benzimidazolinone (EBIO), stimulates Cl transport in the rabbit conjunctival epithelium. For this study, epithelia were isolated in an Ussing-type chamber under short-circuit conditions. The effects of EBIO on the short-circuit current (Isc) and transepithelial resistance (Rt) were measured under physiological conditions, as well as in experiments with altered electrolyte concentrations. Addition of 0.5 mM EBIO to the apical bath stimulated the control Isc by 64% and reduced Rt by 21% (P < 0.05; paired data). Under Cl-free conditions, Isc stimulation using EBIO was markedly attenuated. In the presence of an apical-to-basolateral K+ gradient and permeabilization of the apical membrane, the majority of the Isc reflected the transcellular movement of K+ via basolateral K+ channels. Under these conditions, EBIO in combination with A23187 elicited nearly instantaneous 6090% increases in Isc that were sensitive to the calmodulin antagonist calmidazolium and the K+ channel blocker tetraethyl ammonium. In the presence of an apical-to-basolateral Cl gradient and nystatin permeabilization of the basolateral aspect, EBIO increased the Cl-dependent Isc, an effect prevented by the channel blocker glibenclamide (0.3 mM). The latter compound also was used to determine the proportion of EBIO-evoked unidirectional 36Cl fluxes in the presence of the Cl gradient that traversed the epithelium transcellularly. Overall, EBIO activated apical Cl channels and basolateral K+ channels (presumably those that are Ca2+ dependent), thereby suggesting that this compound, or related derivatives, may be suitable as topical agents to stimulate fluid transport across the tissue in individuals with lacrimal gland deficiencies. Ussing chamber; short-circuit current; electrolyte transport; chloride secretagogue; potassium conductance; 1-ethyl-2-benzimidazolinone; 1,10-phenanthroline 相似文献