共查询到20条相似文献,搜索用时 125 毫秒
1.
L. Romo-Parada L.-P. Vézina P. M. Charest F. Castaigne C. Willemot 《Physiologia plantarum》1991,83(4):664-674
Differences in mitochondrial membrane composition and ultrastructure were studied after storage of cauliflower ( Brassica oleracea , L., Botrytis group) for 5 days at 25°C in air or under controlled atmospheres: 3% O2 , 21% O2 + 15% CO2 or 3% O2 + 15% CO2 . In air, postharvest senescence involved a 20% decrease in mitochondrial phospholipid content. A large reduction in the relative abundance of phosphati-dylcholine (PC) and in the degree of unsaturation of PC and phosphatidyl ethanolamine (PE) was observed. However, the degree of unsaturation increased in cardiolipin (CL). Storage under 3% O2 did not prevent phospholipid breakdown. Low O2 prevented the relative decrease in PC observed during storage in air and the loss of linoleic acid from PC, but not from PE. This relative protection offered by the low O2 atmosphere was lost under 3% O2 + 15% CO2 . The high CO2 atmospheres caused twice as much loss in phospholipids as that observed during storage in air. Extensive loss of mitochondrial protein, a marked decrease in phospholipid to protein ratio, and electron micrograph observations suggest structural alterations in the presence of high CO2 . 相似文献
2.
Regulation of DOPA Decarboxylase Activity in Brain of Living Rat 总被引:4,自引:1,他引:3
Paul Cumming Hiroto Kuwabara Ariel Ase Albert Gjedde 《Journal of neurochemistry》1995,65(3):1381-1390
Abstract: To test the hypothesis that l -DOPA decarboxylase (DDC) is a regulated enzyme in the synthesis of dopamine (DA), we developed a model of the cerebral uptake and metabolism of [3 H]DOPA. The unidirectional blood-brain clearance of [3 H]DOPA ( K D 1 ) was 0.049 ml g−1 min−1 . The relative DDC activity ( k D 3 ) was 0.26 min−1 in striatum, 0.04 min−1 in hypothalamus, and 0.02 min−1 in hippocampus. In striatum, 3,4-[3 H]dihydroxyphenylacetic acid ([3 H]DOPAC) was formed from [3 H]DA with a rate constant of 0.013 min−1 , [3 H]homovanillic acid ([3 H]HVA) was formed from [3 H]DOPAC at a rate constant of 0.020 min−1 , and [3 H]HVA was eliminated from brain at a rate constant of 0.037 min−1 . Together, these rate constants predicted the ratios of endogenous DOPAC and HVA to DA in rat striatum. Pargyline, an inhibitor of DA catabolism, substantially reduced the contrast between striatum and cortex, in comparison with the contrast seen in autoradiograms of control rats. At 30 min and at 4 h after pargyline, k D 3 was reduced by 50% in striatum and olfactory tubercle but was unaffected in hypothalamus, indicating that DDC activity is reduced in specific brain regions after monoamine oxidase inhibition. Thus, DDC activity may be a regulated step in the synthesis of DA. 相似文献
3.
繁殖是植物生命活动的重要环节, 了解植物的繁殖特征是解释植物生态适应性和制定有效管理措施的重要依据。该研究以荒漠草原猪毛蒿(Artemisia scoparia)种群为研究对象, 通过测定不同土壤类型的理化性质和猪毛蒿的繁殖特征, 以期探讨影响其繁殖特征的主要土壤驱动因子。结果表明: 灰钙土、风沙土和基岩风化残积土的水溶性碳含量、全氮含量、全磷含量、全盐含量、土壤水分含量、土壤硬度存在显著差异。猪毛蒿平均个体大小、单株头状花序的平均质量和数量均以灰钙土生境下最大, 基岩风化残积土最小。繁殖分配在不同土壤类型下无显著差异, 但与单个头状花序质量、单株头状花序数量和质量间呈极显著正相关关系。单株头状花序数量与单个头状花序质量间呈负相关关系。在风沙土生境下, 单株头状花序质量主要受到土壤水溶性碳含量、土壤水分含量以及pH值的共同影响; 单株头状花序数量受全盐含量的影响最大; 繁殖分配和单个头状花序质量主要受全碳含量的影响。灰钙土生境下, 单株头状花序质量与土壤水溶性碳含量、土壤水分含量和有机碳含量呈正相关关系; 速效氮含量显著影响着单株头状花序数量。而基岩风化残积土生境下, 繁殖特征的变异主要受到土壤水溶性碳含量、土壤硬度、土壤水分含量、全磷和速效磷含量的影响。综合分析发现, 土壤因子对猪毛蒿繁殖特征的影响程度不同, 其中单株头状花序数量和质量极显著地受到土壤水溶性碳含量和土壤水分含量的影响, 繁殖分配和单个头状花序质量与土壤水溶性碳含量、土壤水分含量呈负相关关系。因此, 土壤水溶性碳含量和土壤水分是荒漠草原地区影响猪毛蒿种群繁殖特征的主要土壤因子。 相似文献
4.
Keiichi Miyamoto Yoshiyuki Shimonishi Masayuki Tokita Takashi Komai 《International journal of biological macromolecules》2001,29(4-5):219-223
Cryogel, prevalent in the plasma of rheumatoid arthritis patients, is a plasma fibronectin (pFN)-extra domain A containing FN [EDA(+)FN]-fibrinogen (Fbg) aggregate formed by the addition of heparin (Hep) at low temperature. Although EDA(+)FN is not usually present in normal plasma, its prevalence in rheumatic patients induces cryogelation. In this study, we determined the hydrodynamic radius (Rh) ratio (Rh/Rh30) of the cryogel component by dynamic light scattering in vitro. Rh/Rh30 was normalized to Rh at 30 °C (Rh30) at several temperatures. The Rh/Rh30 of Fbg was found to increase only by self-aggregation, whereas the Rh/Rh30 of FNs does not increase in response to temperature changes. The Rh/Rh30 of the Fbg/FN aggregate is increased by the addition of Hep, and the Rh/Rh30 (12.5) of the Hep-induced EDA(+)FN/Fbg aggregate is greater than that (2.5) of the pFN/Fbg aggregate. These results suggest that cryogelation requires Fbg self-aggregation and the interaction between EDA(+)FN and Hep. 相似文献
5.
Following a series of continuous exposures to 14CO2 for different lengths of time, leaves from Neurachne munroi (C4), N. minor (C3-C4) and N. tenuifolia (C3| were estimated to assimilate 100%, 9% and 2–4%, respectively, of atmospheric CO2 by the C4 pathway. The percentage of 14C-label appearing in malate and aspartate in leaves of N. minor progressively increased with longer exposure times indicating that a significant proportion of its C4 acids are formed as secondary products. In 14CO2/12CO2 pulse/chase experiments, the 14C-label in leaves of N. munroi was rapidly transferred from C4 acids to sugar monophosphates plus sugar diphosphates, and finally to sucrose. In leaves of N. minor, the 14C-label was slowly metabolized from the C-4 carboxyl of malate and asparate (apparent half-time = 250 s), and the formation of C4 acids as secondary products was again evident. 14C-label in serine/glycine accumulated to comparable magnitudes in both N. minor and in N. tenuifolia, but there was an initial lag phase in the accumulation of label in N. minor. C4 photosynthesis is apparently of minimal importance in reducing photorespiration in N. minor, but leaf anatomical specializations and a possible compartmentation of photorespiratory metabolism may be of considerable importance. 相似文献
6.
In the temperate-zone woody species Salix pentandra elongation growth is regulated by the photoperiod. Long days sustain active growth, whereas short days induce cessation of apical growth, which is a prerequisite for winter hardening. It is shown that this is correlated to quantitative changes in levels of endogenous GA19 GA20 , and GA1 . Within two short days the amount of the active GA1 and its immediate precursor GA20 , decreased markedly in young leaves us well as in stem tissue. Also, the amount of GA19 , declined, but the decrease was delayed relative to that of GA1 and GA20 . The ability of S. pentandra seedlings to respond to exogenous GA19 , decreased with increasing numbers of short days. Observations that support the hypothesis that the level of GA1 in S. pentandra is regulated by the photoperiod in a quantitative mode with conversion of GA19 , to GA20 , being one target for control.
Different distribution of GAs in various plant parts was observed. The level of GA was higher in young leaves than in other plant parts, and the amount of GA19 was 5–10 times higher in stem tissue than in leaves and roots. The ratios of GA8 to GA1 and GA20 , were higher in roots as compared with other parts, as rods contained very low levels of GA1 and GA20 , but amounts of GA20 comparable with other parts. 相似文献
Different distribution of GAs in various plant parts was observed. The level of GA was higher in young leaves than in other plant parts, and the amount of GA
7.
Comparison of endogenous gibberellins in roots and shoots of elongating Salix pentandra seedlings 总被引:1,自引:0,他引:1
Gibberellins GA1 , GA8 . GA19 . GA29 . GA20 and GA56 (2-epi-GA8 ). were identified by combined gas chromatography-mass spectrometry in root extracts of elongating Salix pentandra L. seedlings. The presence of GA8 was also demonstrated for the first time in S. pentandra shoots. The levels of GA1 , GA8 , GA19 , GA20 in shoot tissue and in roots were estimated by selected ion monitoring. While the amounts of GA8 and GA19 were similar in both plant parts. the levels of the biologically active GA1 and its immediate precursor GA20 . were found to be much lower in roots than in shoots. 相似文献
8.
9.
Andrés P. Sanz Conrado Moreno-Vivián José M. Maldonado Agustín González-Fontes 《Physiologia plantarum》1995,95(1):39-44
The effect of the nitrogen source on carbohydrate and protein contents and on several enzymatic activities involved in the carbon and nitrogen metabolism was studied in Anabaena variabilis ATCC 29413 cells grown under a constant supply of either N, NO− 3 or NH+ 4 at different concentrations. An enhancement of protein content accompanied by a parallel decrease of carbohydrates was observed with increasing NO− 3 or NH+ 4 concentrations in the medium. In cultures containing 0.1 m M NO− 3 or 0.1 m M NH+ 4 nitrogenase (EC 1.18.6.1) activity was 74 and 66%, respectively, of that found in N2 -grown cells. This activity was still present with 1 m M NO− 3 or 1 m M NH+ 4 in the medium and even with 10 m M NO− 3 , but it was completely inhibited by 5 m M NH+ 4 . Ferredoxin-nitrate reductase (EC 1.7.7.2) activity was detected only in NO− 3 grown cells and simultaneously with nitrogenase activity. Increasing concentrations of combined nitrogen in the medium, especially NH+ 4 , promoted a concomitant decline of glutamine synthetase (EC 6.3.1.2), NADP+ -isocitrate dehydrogenase (EC 1.1.1.42), and NAD+ -malate dehydrogenase (EC 1.1.1.37) activities, suggesting that these enzymes play an important role in the regulation of carbon-nitrogen metabolism in cyanobacteria. 相似文献
10.
Ionic Composition of Cisternal CSF in Acute Respiratory Acidosis: Lack of Effect of Large Dose Bumetanide 总被引:1,自引:0,他引:1
Abstract: Sodium/chloride cotransport carrier is known to be involved in transepithelial fluid absorption and secretion in various tissues. Recent studies indicate that Na,K,2CI cotransport carrier also exists in the choroid plexus cells and inhibition of the carrier alters ionic composition of the choroidal tissue. In this study, we report the effects of large dose intravenous bumetanide, a potent inhibitor of Na,K,2CI carrier, on cisternal CSF ionic composition in acute respiratory acidosis in pentobarbital-anesthetized mechanically ventilated dogs. Renal pedicles were ligated to prevent bumetanide-induced diuresis. The experirnental group (Group II, n = 7) received 50 mg/kg of bumetanide intravenously and Group I (the control group, n = 7) received the vehicle. Analysis of serum and choroidal plexus tissue revealed bumetanide concentration of ∼10− -5 mol/L in Group II. During 5 h of acute respiratory acidosis in both groups, the mean Paco2 increased ∼25 mm Hg, with comparable changes in CSF Pco2 . In both groups, CSF [HCO3 − ] and [H+ ] increased ∼3 mEq/L and 20 nEq/L, respectively. Furthermore, changes in CSF [Na+ ], [K+ ], [Ca2+ ], [Mg2+ ], [CI− ], and [Na+ -CI− ] were also similar and were not significantly different from each other. These data show that bumetanide, at the dose that inhibits NaCl cotransport carrier, does not significantly affect ionic composition of cisternal CSF. 相似文献
11.
We have searched for the exclusivity of common sequence motifs of the mitochondrial uncoupling proteins (UCP1, UCP2, UCP3, UCP4, BMCP1, and plant UCP [PUMP]) within the gene family of mitochondrial anion carrier proteins. The UCP-specific sequences, "UCP signatures", were found in the first, second, and fourth alpha-helices. First: Ala/Ser-Cys/Thr/n-n/Phe-Ala/Gly-[negatively charged residue]-n/Phe-n/Cys-Thr-Phe/n; second: Gly/Ala-Ile/Leu-Gln/X-[positively charged residue]-NH-n/Cys-Ser/nphi/X-n/Ser-OH/Gly-n-[positively charged residue]-Ile/Met-Gly/Val-n/Thr; fourth: Pro-Asn/ Thr-n-X-[positively charged residue]-Asn/Ser/Ala-n-n-Ile/Leu-n-Asn/Val-Cys/n-n/Thr-[negatively charged residue]-n-n/Thr/Pro-OH/Val (n, nonpolar; phi, aromatic; (positively charged residue/negatively charged residue, charged residue). The second and part of the third signature are also present in the yeast dicarboxylate transporter. The UCP signature excluding BMCP1 was also found in the second matrix segment: [positively charged residue]-(Pro/ del-Leu/del)-[positively charged residue]-phi-X-Gly/Ser-Thr/n-X-NH/[negatively charged residue]-Ala-phi. These UCP signatures are thought to be involved in fatty acid anion binding and translocation. 相似文献
12.
Chloride transport in sheath and blade tissue and the cellular distribution of Cl- were investigated in an attempt to determine the physiological basis of the preferential accumulation of Cl- in sheaths of salt-stressed sorghum ( Sorghum bicolor L.). Import and export of 36 Cl- in leaf sheaths and blades of intact sorghum were followed over a 2 week period. X-ray microanalysis of frozen-hydrated bulk tissue samples was used to determine the accumulation of Cl- and other elements in the vacuoles of sheath and blade cells.
Sheath tissue accumulated Cl- despite a relatively high Cl- turnover rate. Chloride was shown to accumulate in most cell types of the sheath, particularly in adaxial epidermal cells. After an initial increase in the concentration of Cl- , blade tissue regulated Cl- levels within certain limits. Chloride levels in blades were greater in the abaxial and adaxial epidermal cells than in other cell types. The epidermal cells of blades accumulated Cl- to approximately the same concentration as sheath epidermal cells. The Cl- concentration in the photosynthetically active mesophyll and bundle sheath cells, however, remained low.
Thus, the partitioning of Cl- previously observed in the leaves of salinized sorghum apparently results from the ability of bundle sheath and mesophyll cells to maintain concentrations of Cl- at lower levels than do epidermal cells. In addition, the relatively large sheath parenchyma cells tend to serve as reservoirs for the storage of Cl- . 相似文献
Sheath tissue accumulated Cl
Thus, the partitioning of Cl
13.
Eric N. Powell George M. Staff Robert J. Stanton Jr W. Russell Callender 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2001,34(2):97-118
We evaluate onshore-offshore trends in age-frequency distributions and trophic transfer efficiencies using 11 modern death assemblages off the Texas coast. Trophic transfer efficiencies within trophic levels offer little insight over that achieved by a size-frequency distribution. Production/biomass ratios will always be 1 in the fossil record. Within trophic-level estimates of paleogrowth efficiency, the ratio of paleoproduction to paleoingestion (Piglt/Iilt where i indicates the ith trophic level and lt indicates the time-averaged value) follow the expected ecological trend precisely in that paleogrowth efficiency is consistently higher in primary consumers than in predators in all 11 death assemblages. Paleoutilization efficiency, the ratio of predator paleoingestion to prey paleoproduction, I2lt°/P1glt°, may provide information on the degree of bias in the preservation of primary (1 °) and secondary (2 °) consumer trophic groups. I2lt°/P1glt° fell below 0.1 in most cold-seep and bay assemblages, indicating a large surplus of primary consumers. In sharp contrast, I2lt°/P1glt° 相似文献
14.
Inhibition of electron transport through photosystem II (PS II) by formate (HCO− 2 ) or nitrite (NO− 2 ) in the presence or absence of chloride ions was studied. The inhibition induced by HCO− 2 or NO− 2 is overcome by HCO− 3 more in the presence, than in the absence of Cl− . The data on electron transport are supported by chlorophyll a fluorescence measurements. In experiments. In experiments in which water oxidation was blocked. Cl− was found to facilitate electron transport between bound quinone A (Q− A ) and the plastoquinone (PQ) pool. It can thus be concluded that in addition to the well known site of action of Cl− on water oxidation, another site of Cl− action is between Q− A and the PQ pool. 相似文献
15.
Seol CA Kim J Kim WT Ha JM Choe H Jang YJ Shim EB Youm JB Earm YE Leem CH 《Progress in biophysics and molecular biology》2008,96(1-3):132-151
Atrial fibrillation is the most prevalent arrhythmia, but the mechanisms by which it develops are not clear. Recently, over 90% of paroxysmal atrial fibrillation was found to be located inside the main pulmonary veins (PVs). We found that single cardiac myocytes isolated from the main PVs of rabbits generate spontaneous action potentials (SAP). We therefore assayed the electrical characteristics of these cardiomyocytes. Among the diverse ionic currents identified were INa, ICa,L, IK1, IKr, IKs, Ito, IKsus, Incx, Ipump, IKH and ICl,Ca. In contrast, IK1 was minimal, IKs could be detected only in the presence of 10 μM forskolin, and we were unable to detect If and ICa,T, the most important currents for pacemaking activity in sinoatrial node cells. To identify the main cause of SAP, we developed a model that can explain the electrical properties of these cardiomyocytes. After reconstructing the ionic currents based on experimental observations, we were able to use our model to successfully reconstruct the characteristics of the SAP of PV cardiomyocytes. The simulation showed that the major currents contributing to pacemaking depolarization were ICaL, IKr, a background current and Na+–K+ pump current. Deactivation kinetics of IKr was one of the major determinants of the rate of pacemaking depolarization. The steady state inactivation of Ito was shifted to the negative voltage and the activity of Ito was minimal in the range of the SAP. The major currents for the repolarization were IKr and Ipump. The amplitude of most currents in these cardiac myocytes was small and no currents did not exceed 30 pA during the SAP, indicating that slight activation of other inward or outward currents will have profound effects on the SAP. To our knowledge, this report is the first to show the simulation of SAP of PV cardiomyocytes. This model may help to study on the electrophysiological basis of paroxysmal atrial fibrillation originating from PVs. 相似文献
16.
Simultaneous Measurement of Nitrite and Nitrate Levels as Indices of Nitric Oxide Release in the Cerebellum of Conscious Rats 总被引:2,自引:0,他引:2
Abstract: We examined the modulation of nitric oxide production in vivo by measuring levels of nitrite (NO2 − ) and nitrate (NO3 − ) in the dialysate of the cerebellum in conscious rats, by using an in vivo brain microdialysis technique. The levels of both NO2 − and NO3 − were decreased by the intraperitoneal injection of N G -nitro- l -arginine methyl ester, an inhibitor of nitric oxide synthase, whereas N G -nitro- d -arginine methyl ester had no effect. l -Arginine by itself increased NO2 − and NO3 − levels and diminished the reduction of their levels caused by N G -nitro- l -arginine methyl ester. Direct infusion of l -glutamate, N -methyl- d -aspartate, or KCl into the cerebellum through a dialysis probe resulted in an increase in NO2 − and/or NO3 − levels. The effects of N -methyl- d -aspartate and KCl were dependent on extracellular calcium. Furthermore, the stimulatory effects of l -glutamate and N -methyl- d -aspartate were inhibited by N G -nitro- l -arginine methyl ester and (±)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP), an N -methyl- d -aspartate receptor antagonist. These results suggest that NO2 − and NO3 − levels may be related to nitric oxide production in vivo. 相似文献
17.
Biochemical and immunological properties of the C-terminal domain of the alpha-toxin of Clostridium perfringens 总被引:2,自引:0,他引:2
Abstract The C-terminal domain of the alpha-toxin (cpa247–370 ) of Clostridium perfringens has been expressed in Escherichia coli and purified. Antiserum raised against cpa247–370 reacted in an identical manner to anti-alpha-toxin serum when used to map epitopes in the C-terminal domain, suggesting that cpa247–370 was immunologically and structurally identical to this region in the alpha-toxin. The isolated cpa247–370 was devoid of sphingomyelinase activity or haemolytic activity and was not cytotoxic for mouse lymphocytes. Haemolytic activity was detected when cpa247–370 was tested with the N-terminal domain of the alpha-toxin (cpa1–249 ), confirming that cpa247–370 confers haemolytic properties on the phospholipase C activity of the alpha-toxin. Haemolytic activity was not detected if cpa247–370 was tested with the Bacillus cereus phosphatidylcholine phospholipase C, nor if cpa1–249 and cpa247–370 were incubated sequentially with erythrocytes. 相似文献
18.
The effect of natural selection on estimates of genetic divergence among populations of the Atlantic salmon 总被引:2,自引:0,他引:2
The effect of natural selection on the m MEP-2 * locus on measures of genetic divergence among Atlantic salmon populations was investigated by examining the pattern of change in the level of genetic differentiation (FST ) averaged over loci when data on the m MEP-2 * locus were either included or excluded. The level of FST among populations at various geographic scales was estimated from allele frequencies at up to four loci (s AAT-4 *, IDDH-1 *, IDHP-3 *, and m MEP-2 *). At smaller geographic scales (within river systems or limited geographic regions) levels of variance in m MEP-2 * allele frequencies were reduced relative to mean levels. At larger geographic scales (across continents or the species range) variation in m MEP-2 * allele frequencies was greater than mean levels. These results suggest an a priori hypothesis for the effect of selection on the m MEP-2 * locus which may be applied in future studies on variation in protein coding or other (e.g. mini- and microsatellite) loci in the Atlantic salmon. It is recommended that estimates of gene flow among populations of the Atlantic salmon based on mean F ST estimates which include data on the m MEP-2 * locus should be viewed with caution. 相似文献
19.
J. JOSEPH BLUM 《The Journal of eukaryotic microbiology》1991,38(3):229-233
Leishmania major promastigotes were washed and resuspended in an iso-osmotic buffer. The rate of oxidation of 14 C-labeled substrates was then measured as a function of osmolality. An acute decrease in osmolality (achieved by adding H2 O to the cell suspension) caused an increase in the rates of 14 CO2 production from [6-14 C]glucose and, to a lesser extent, from [1, (3)-14 C]glycerol. An acute increase in osmolality (achieved by adding NaCl, KCl, or mannitol) strongly inhibited the rates of 14 CO2 production from [1-: 14 C]alanine, [1-14 C]glutamate, and [1, (3)-14 C]glycerol. The rates of 14 CO2 formation from [1-14 C]laurate, [1-14 C]acetate, and [2-14 C]glucose (all of which form [1-14 C]acetyl CoA prior to oxidation) were also inhibited, but less strongly, by increasing osmolality. These data suggest that with increasing osmolality there is an inhibition of mitochondrial oxidative capacity, which could facilitate the increase in alanine pool size that occurs in response to hyper-osmotic stress. Similarly, an increase in oxidative capacity would help prevent a rebuild up of the alanine pool after its rapid loss to the medium in response to hypo-osmotic stress. 相似文献
20.
Studies were carried out on the polymorphism of alkaline ribonuclease in Black-and-White cattle in the north-eastern region of Poland. Leucocytes isolated from peripheral blood were used. Three phenotypes were defined, consisting of the combination of two alleles. The gene frequency was: q4 = 0,7082, qB = 0,2918. In calves the frequency of allele RNA-aseB and number of RNA-aseA / RNA -aseB heterozygotes were higher than in adult animals. 相似文献