共查询到20条相似文献,搜索用时 15 毫秒
1.
Laura Riboni Antonella Caminiti Rosaria Bassi Guido Tettamanti 《Journal of neurochemistry》1995,64(1):451-454
Abstract: Gangliosides GM1 [3 H-labeled at the sphingosine (Sph) moiety] and GM2 [3 H-labeled at the Sph or N -acetylgalactosamine (GalNAc) moiety] were administered to cultured Neuro2a cells for varying pulse (1–4 h) and chase (up to 4 h) periods, and their metabolic processing was followed. The main and earliest formed 3 H-metabolites of [ Sph -3 H]GM1 were GM2, asialo-GM1, asialo-GM2, and lactose-ceramide, and those of [ Sph -3 H]GM2 were asialo-GM2 and lactose-ceramide. The asialo-GM1 and asialo-GM2 formed were isolated and chemically characterized. [3 H]Asialo-GM2 was produced in identical amounts after treatment with equimolar [ Sph -3 H]GM2 and [ GalNAc -3 H]GM2. At low temperature or in the presence of chloroquine, the formation of all 3 H-metabolites, including asialo-GM2 and asialo-GM1, was undetectable, indicating that ganglioside metabolic processing was an endocytosis- and lysosome-dependent process. These results demonstrate that in Neuro2a cells exogenous GM1 (and GM2) is mainly degraded through the pathway GM1 → GM2 → asialo-GM2 →→ Sph, with a minor fraction of GM1 undergoing degradation with the sequence GM1 → asialo-GM1 → asialo-GM2 →→ Sph. These findings are consistent with the hypothesis that Neuro2a cells contain a sialidase (likely of lysosomal nature) affecting ganglioside GM1 and GM2. The sialidase-mediated degradative pathway of GM1 and GM2 in Neuro2a cells might be related to the tumoral nature of these cells. 相似文献
2.
The acquisition and accumulation of inorganic carbon by the unicellular green alga Chlorella ellipsoidea 总被引:3,自引:0,他引:3
Abstract. The uptake and accumulation of inorganic carbon has been investigated in Chlorella ellipsoidea cells grown at acid or alkaline pH. Carbonic anhydrase (CA) was detected in ceil extracts but not in intact cells and CA activity in acid-grown cells was considerably less than that in alkali-grown cells. Both cell types demonstrates low K1/2 (CO2 ) values in the range pH 7.0–8.0 and these were unaffected by O2 concentration. The CO2 compensation concentrations of acid- and alkali-grown cells suspended in aqueous media were not significantly different in the range of pH 6.0–8.0, but at pH 5.0, the CO2 compensation concentrations of acid-grown cells (57.4cm3 m−3 ) were lower than those of alkali-grown cells (79.2cm3 m−3 ). The rate of photo-synthetic O2 evolution in the range pH 7.5–8.0 exceeded the calculated rate of CO2 supply two- to three-fold, in both acid- and alkali-grown cells, indicating that HCO3 − was taken up by the cells. Accumulation of inorganic carbon was measured at pH 7.5 by silicone-oil centri-fugation, and the concentration of unfixed inorganic carbon was found to be 5.1 mol m−3 in acid-grown and 6.4mol m−3 in alkali-grown cells. These concentrations were 4.6- and 5.9-fold greater than in the external medium. These results indicate that photorespiration is suppressed in both acid- and alkali-grown cells by an intracellular accumulation of inorganic carbon due, in part, to an active uptake of bicarbonate. 相似文献
3.
The effects of the carbonic anhydrase (CA) inhibitors acetazolamide (AZ) and dextran-bound sulfonamide (DBS) on HCO3 − -dependent O2 evolution in Chlorella saccharophila were evaluated. Addition of 4 μ M AZ or 0.4 mg ml−1 DBS to photosynthesizing cells reduced the O2 evolution rate at low dissolved inorganic carbon (DIC) concentration, decreased the size of the intracellular acid-labile carbon pool, and decreased the apparent affinity of the cells for DIC. Measurement of the whole-cell affinity of cells for CO2 and HCO3 − in the presence and absence of inhibitors indicated that active HCO3 − transport was inhibited by AZ and DBS. The inhibition of HCO3 − transport was independent of the inhibition of external and internal CA. These results suggest that the active uptake of HCO3 − occurs initially by the interaction of HCO3 − and a CA-like transporter. 相似文献
4.
Abstract. Measurements of the water-relation parameters of the giant subepidermal cells (volume, V = 0.119 to 1.658 mm3 ; = 0.53±0.35 mm3 , SD, n = 23) and the smaller mesocarp parenchyma cells ( V = 0.10 to 0.79×10−3 mm3 ; = 0.36±0.27×10−3 mm3 , SD, n = 6) of the inner pericarp surface of Capsicum annuum L. were made using the Jülich pressure probe. The volumetric elastic modulus ɛ for the large cells was between 1.5 and 27 MPa for a pressure range of 0.09 to 0.41 MPa. For the small cells ɛ was 0.1 to 0.6 MPa for a pressure range of 0.22 to 0.39 MPa. The turgor pressure P , the half-time of water exchange T 1/2 , and the hydraulic conductivity L p were as follows, with SD and number of replicates: large cells, P = 0.27±0.06 MPa (23), T 1/2 =2.7±2.2 s (46), L p =5.8±3.7 pm s−1 Pa− (46); small cells, P = 0.33±0.07 MPa (6), T 1/2 = 33±10s (12), L p =0.21±0.07 pm s−1 Pa−1 (12). The determination of these basic water-relation parameters is considered as a prerequisite for future ecotoxicological and phytopathological studies. The differences between the large and the small cells are discussed in relation to a desirable biophysical definition of succulence. Further, for the large cells a pressure and volume dependence of ɛ was demonstrated. 相似文献
5.
YOSHIKO BANNO YUKIO OKANO KIYOSHI FURUKAWA ARNO TIEDTKE AKIRA KOBATA YOSHINORI NOZAWA 《The Journal of eukaryotic microbiology》1993,40(4):515-520
ABSTRACT. The proteolytic processing and secretion of a lysosomal enzyme, acid α-glucosidase, was studied by pulse-chase labeling with [35 S]methionine in Tetrahymena thermophila CU-399 cells treated with ammonium chloride. This cell secreted a large amount of acid α-glucosidase into the cultured medium during starvation. the secretion was found to be repressed by addition of ammonium chloride (NH4 Cl). Acid α-glucosidase was produced as a precursor form (108 kDa) and then processed to a mature polypeptide (105 kDa) within 60 min. This mature enzyme was secreted into the media within 2-3 h after chase, whereas the precursor form was not secreted by either control cells or NH4 Cl-treated cells. NH4 Cl did not affect the processing of the precursor acid α-glucosidase. Processing profile of this enzyme was apparently indistinguishable from that of the mutant MS-1 defective in lysosomal enzyme secretion. Furthermore, the purified extracellular (CU-399) and intracellular (MS-1) acid a-glucosidases were the same in molecular mass (105 kDa) and enzymatic properties. They contained no mannose 6-phosphate residues in N-linked oligosaccharides. These results suggested that unlike mammalian cells, Tetrahymena acid α-glucosidase may be transferred to lysosomes by a mannose 6-phosphate receptor-independent mechanism, and also that low pH was not essential for the proteolytic processing of precursor polypeptide. 相似文献
6.
Clones of Rosa damascena Mill. cv. Gloire de Guillan, selected for growth in solid medium containing 56 m M NaClO3 , were studied to determine the reason for their resistance to this toxic salt. The cells grew on medium containing nitrate as the only nitrogen source, and they synthesized nitrate reductase (EC 1.6.6.2) in the presence of nitrate. The cells were resistant in the presence of nitrate. However, their resistance was greatly increased by the presence of glutamate in the medium. The cells took up [36 Cl]-ClO3 - and reduced it to ClO2 − , but the fraction of ClO3 − that they reduced under our experimental conditions was less than that reduced by wild type. The slower production of ClO2 − apparently accounted for the resistance of the cells to ClO3 − . We suggest several possible reasons for the low rate of reduction of ClO3 − . 相似文献
7.
Jesús A. G. Ochoa de Alda María I. Tapia Fabrice Franck María J. Llama Juan L. Serra 《Physiologia plantarum》1996,97(1):69-78
In an attempt to clarify the interactions between the available nitrogen source and the photosystems in cyanobacteria, O2 exchange and fluorescence emission were monitored in spheroplasts and intact cells of the non N2 -fixing cyanobacterium Phormidium laminosum (strain OH-1-p.Cl1 ) growing on different nitrogen sources or in the absence of nitrogen. Short-term (time scale of seconds to minutes), NH+ 4 addition to NO− 3 -growing or N-starved cells and, to a minor extent, NO− 3 addition to N-starved cells, induced state 2 transitions both in light and dark. Long term (time scale of days), the fluorescence yield of PSII relative to that of PSII at 77 K was higher in NO− 3 - than in NH+ 4 growing cells, and even higher in N-starved cells. In the dark, the plastoquinone pool was more reduced in NH+ 4 - than in NO− 3 -growing cells. Both PSII and PSI activities and the degree of linking between both photosystems were affected in the long term, so that non-cyclic electron transport decreased in parallel to the ferredoxin requirement to assimilate each nitrogen source. Results indicate that nitrogen metabolism exerts short- and long-term control over the photosynthetic apparatus, which acclimates to the energy requirement of the available nitrogen source. 相似文献
8.
Summary. Soluble potassium concentrations were determined for the slightly vacuolated, unicellular, walled alga Chlorella emersonii. Sap of cells grown in 1 mol m−3 NaCI contained 140 mol m−3 K+ and sap of cells grown in 125, 200, and 335 mol m−3 NaCI contained 160-180 mol m−3 K + .
The possible regulation of K+ concentrations by a system of lurgor and volume maintenance was investigated by supplying 3-0-methylglucose. This solute accumulates to 85-230 mol m−3 in C. emersonii , but is not metabolized. Accumulation of 3-0-methylglucose increased the volume of cells grown at both low and high NaCI by about 10%. Furthermore, accumulation of 3-0-methylglucose also increased turgor pressures of cells grown in 1 and 125 mol m−3 NaCI by 0.3 and 0.2 MPa, respectively. (Similar measurements were not attempted for cells grown in 200 and 335 mol m−3 NaCI, because of the insensitivity of available methods to measure turgor pressure of cells exposed to high external osmotic pressures.)
At all NaCI concentrations, the K+ concentrations of cells which had accumulated 3-0-methylglucose were only 10-20 mol m−3 lower than K+ in cells which had not been supplied with 3-0-methylglucose. In contrast, accumulation of 3-0-methylglucose greatly decreased concentrations of the endogenous osmotic solutes, proline and sucrose, which accumulated in cells grown in 125 mol m−3 and higher NaCI concentrations.
It is concluded that K+ concentrations in Chlorella emersonii are not controlled by a system of turgor and volume maintenance. 相似文献
The possible regulation of K
At all NaCI concentrations, the K
It is concluded that K
9.
Native Serotonin 5-HT3 Receptors Expressed in Xenopus Oocytes Differ from Homopentameric 5-HT3 Receptors 总被引:1,自引:0,他引:1
Johannes A. van Hooft Angélique P. Kreikamp Henk P. M. Vijverberg 《Journal of neurochemistry》1997,69(3):1318-1321
Abstract: Efficacies of the 5-hydroxytryptamine (serotonin) 5-HT3 receptor (5-HT3 R) agonists 2-methyl-5-HT, dopamine, and m -chlorophenylbiguanide on 5-HT3 R native to N1E-115 cells and on homopentameric 5-HT3 R expressed in Xenopus oocytes were determined relative to that of 5-HT. Efficacies of 2-methyl-5-HT and dopamine on 5-HT3 R native to differentiated N1E-115 cells are high (54 and 36%) as compared with their efficacies on homopentameric 5-HT3 R-AL and 5-HT3 R-As receptors expressed in oocytes (4–8%). m -Chlorophenylbiguanide does not distinguish between 5-HT3 R in N1E-115 cells and in oocytes. The distinct pharmacological profile of 5-HT3 R native to differentiated N1E-115 cells is conserved when poly(A)+ mRNA from these cells is expressed in oocytes. The results indicate that, apart from the known 5-HT3 R subunits, N1E-115 cells express additional proteins involved in 5-HT3 R function. 相似文献
10.
KIYOTA GOSHIMA HACHIRO YAMANAKA GORO EGUCHI SHIGEO YOSHINO 《Development, growth & differentiation》1978,20(2):191-204
Increase in the extracellular Ca2+ concentration from low (≤ 10−7 M) to normal (10−3 M) caused morphological changes of cultured myocardial cells obtained from fetal mouse heart. The extracellular Na+ and K+ concentrations of the normal medium (10−3 M Ca2+ ) did not significantly affect the genesis of these morphological changes. Like Ca2+ , Ba2+ and Sr2+ , but not Mg2+ , Co2+ or Ni2+ , could induce morphological changes. Increase in the extracellular Ca2+ concentration from 10−8 M to 10−3 M also caused excess uptake of 45 Ca2+ by cultured myocardial cells. B–16CW 1 cells, which did not show these morphological changes, did not take up excess 45 Ca2+ on this treatment. Treatments, such as addition of verapamil or incubation at pH 6.3, which reduced the genesis of morphological changes, reduced the rate of 45 Ca2+ uptake by myocardial cells. These facts show that the morphological changes of myocardial cells induced by increasing the extracellular Ca2+ concentration from low to normal are due to excess uptake of Ca2+ by the myocardial cells.
The morphological changes of cultured myocardial cells induced by increasing the extracellular Ca2+ concentration from low to normal were reversed on further incubation of the cells in medium with or without Ca2+ . 相似文献
The morphological changes of cultured myocardial cells induced by increasing the extracellular Ca
11.
Sunhee C. Lee Wei Liu Dennis W. Dickson Celia F. Brosnan 《Journal of neurochemistry》1995,64(4):1800-1807
Abstract: In human astrocyte cultures established from second-trimester fetal brain tissue, ∼5–10% of total astrocyte population in unstimulated cultures were GD3+ /glial fibrillary acidic protein (GFAP)+ . The GD3+ cells were always GFAP+ and grew as flat, highly spread cells but changed to process-bearing cells after interleukin-1β (IL-1β) stimulation. It is interesting that IL-1β, a known mitogen for rat astrocytes, suppressed human fetal astrocyte proliferation as determined by [3 H]thymidine incorporation, bromodeoxyuridine (BrdU) labeling, and cell counting. The GD3+ population, however, consistently increased in absolute number after IL-1β stimulation, in a dose- and time-dependent manner. The IL-1β-mediated increase in number of GD3+ astrocytes was independent of initial cell density or serum concentration. By flow cytometry, IL-1β enhanced both the mean fluorescence intensity and the percentage of GD3+ cells. To investigate whether the increase in GD3+ astrocyte cell number was due to proliferation of preexisting GD3+ astrocytes or due to conversion of GD3− to GD3+ cells, we performed BrdU/GD3 double immunocytochemistry. BrdU/GD3 double-positive cells were extremely rare in both control and IL-1β-stimulated cultures. Moreover, an increase in number of GD3+ astrocytes was still observed in control and IL-1β-stimulated cultures where GD3+ cells had been initially eliminated by cell sorting. These results indicate that GD3+ astrocytes in human fetal culture may represent a postmitotic, differentiated, distinct phenotype. 相似文献
12.
P. C. Wood R. J. H. Wojcikiewicz J. Burgess† C. M. Castleden S. R. Nahorski 《Journal of neurochemistry》1994,62(6):2219-2223
Abstract: The effects of aluminium (as Al3+ ) on carbachol-induced inositol 1,4,5-trisphosphate (lnsP3 ) production arid Ca2+ mobilisation were assessed in electropermeabilised human SH-SY5Y neuroblastoma cells. Al3+ had no effect on lnsP3 -induced Ca2+ release but appreciably reduced carbachol-induced Ca2+ release (lC50 of ∼90 μ M ). Aβ3+ also inhibited lnsP3 production (lC60 of ∼15 μ M ). Dimethyl hydroxypyridin-4-one, a potent Al3+ chelator (K5 = 31), at 100 μ M was able to abort and reverse the effects of Al3+ on both Ca2+ release and lnsP3 production. These data suggest that, in permeabilised cells, the effect of Al3+ on the phosphoinositide-mediated signalling pathway is at the level of phosphatidylinositol 4,5-bisphosphate hydrolysis. This may reflect interference with receptor-G protein-phospholipase C coupling or an interaction with phosphatidylinositol 4,5-bisphosphate. 相似文献
13.
R. O. Duffard P. H. Fishman R. M. Bradley C. J. Lauter R. O. Brady E. G. Trams 《Journal of neurochemistry》1977,28(6):1161-1166
Abstract— Cultured mouse neuroblastoma cells (clone N18) contained a homologous series of gangliosides, GM3 , GM2 , GM1 and GD1a ; the total lipid bound sialic acid (LBSA) was 3.3 nmol per mg of protein, of which GD1a comprised two-thirds. In contrast, neonatal hamster astrocytes (clone NN) and human glioblastoma cells (Cox clone) contained mainly GM3 , which represented 95% of the 2 nmol of LBSA per mg protein in these cells. When the cells were grown in the presence of [14 C]galactose, label was incorporated into all of the gangliosides isolated from the cells. The labeling pattern corresponded to the ganglioside composition of the cell lines; GD1a was more extensively labeled in N18 cells and GM3 was the major labeled ganglioside extracted from glial cells. In addition to in rivo biosynthesis, in vitro synthesis of gangliosides was also determined. The activities of five glycosyltransferases of the ganglioside biosynthetic pathway were measured in homogenates of the three cell lines. The neuroblastoma cells contained all five enzyme activities whereas the two glial cell lines were deficient in UDP- N -acetylgalactosamine: GM3 N -acetylgalactosaminyltransferase activity, which catalyzes the synthesis of GM2 from GM3 . The results indicated that cells of neuronal origin contain the more complex gangliosides associated with CNS and the requisite biosynthetic enzymes and that cells of glial origin are missing these complex gangliosides and the key glycosyltransferase required for their synthesis. 相似文献
14.
Abstract The sulfur cycle in a microbial mat was studied by determining viable counts of sulfate-reducing bacteria, chemolithoautotrophic sulfur bacteria and anoxygenic phototrophic bacteria. All three functional groups of sulfur bacteria revealed a maximum population density in the uppermost 5 mm of the mat: 1.1 × 108 cells of sulfate reducers cm−3 sediment, 2.0 × 109 cells of chemolithoautotrophs cm−3 sediment, and 4.0 × 107 cells of anoxygenic phototrophs cm−3 sediment. Bacterial dynamics were studied by sulfate reduction rate measurements, both under anoxic conditions (dark incubation) and oxic conditions (incubation in the light), and determination of the vertical distribution of the potential rate of thiosulfate consumption under oxic conditions. Sulfate reduction rates in the top 5 mm of the sediment were 566 nmol cm−3 d−1 in the absence of oxygen, and 123 nmol cm−3 d−1 in the presence of oxygen. In the latter case, the maximum rate was found in the 5–10-mm depth horizon (361 nmol cm−3 d−1 ). Biological consumption of amended thiosulfate was rapid and decreased with depth, while in the presence of molybdate, thiosulfate consumption decreased to 10–30% of the original rate. 相似文献
15.
†‡ Gunnar K. Gouras ‡Huaxi Xu ‡Jasmina N. Jovanovic ‡Joseph D. Buxbaum §Rong Wang ‡Paul Greengard †Norman R. Relkin Sam Gandy 《Journal of neurochemistry》1998,71(5):1920-1925
Abstract: Studies of processing of the Alzheimer β-amyloid precursor protein (βAPP) have been performed to date mostly in continuous cell lines and indicate the existence of two principal metabolic pathways: the "β-secretase" pathway, which generates β-amyloid (Aβ1–40/42 ; ∼4 kDa), and the "α-secretase" pathway, which generates a smaller fragment, the "p3" peptide (Aβ17–40/42 ; ∼3 kDa). To determine whether similar processing events underlie βAPP metabolism in neurons, media were examined following conditioning by primary neuronal cultures derived from embryonic day 17 rats. Immunoprecipitates of conditioned media derived from [35 S]methionine pulse-labeled primary neuronal cultures contained 4- and 3-kDa Aβ-related species. Radiosequencing analysis revealed that the 4-kDa band corresponded to conventional Aβ beginning at position Aβ(Asp1 ), whereas both radio-sequencing and immunoprecipitation-mass spectrometry analyses indicated that the 3-kDa species in these conditioned media began with Aβ(Glu11 ) at the N terminus, rather than Aβ(Leu17 ) as does the conventional p3 peptide. Either activation of protein kinase C or inhibition of protein phosphatase 1/2A increased soluble βAPPα release and decreased generation of both the 4-kDa Aβ and the 3-kDa N-truncated Aβ. Unlike results obtained with continuously cultured cells, protein phosphatase 1/2A inhibitors were more potent at reducing Aβ secretion by neurons than were protein kinase C activators. These data indicate that rodent neurons generate abundant Aβ variant peptides and emphasize the role of protein phosphatases in modulating neuronal Aβ generation. 相似文献
16.
Zhong-Juan Li Katsuhiko Omoe Kunihiro Shinagawa Junji Yagi Ken'ichi Imanishi 《Microbiology and immunology》2009,53(8):451-459
Specific superantigens activate different T-cell fractions with distinct TCR Vβ elements in association with MHC class II molecules and also induce SDCC against MHC class II+ target cells. In the present study, to determine whether the responsiveness of each CD8+ T-cell fraction expressing a different TCR Vβ element is primarily determined by the TCR Vβ, we compared the levels of proliferation and SDCC in Vβ3+ and Vβ11+ T cells upon stimulation with SEA. Upon stimulation with SEAwt , the levels of proliferation were higher in Vβ3+ T cells than in Vβ11+ T cells. The levels of SDCC were also higher for the combination of Vβ3+ T cells and SEAwt than for the combination of Vβ11+ T cells and SEAwt during both the induction phase and the effector phase. In addition, upon stimulation with SEAm , the levels of proliferation were higher in Vβ11+ T cells than in Vβ3+ T cells. And then, the levels of SDCC were also higher for the combination of Vβ11+ T cells and SEAm than for the combination of Vβ3+ T cells and SEAm during both the induction phase and the effector phase. These results suggest that the SAG-responsiveness of each CD8+ T-cell fraction expressing a different TCR Vβ element is primarily determined by the interaction between the TCR Vβ element and the SAG. 相似文献
17.
Abstract: Cells dissociated from the postnatally developing rat cerebellum retain their high-affinity carrier-mediated transport systems for [3 H]GABA ( K t =1.9 μM, V = 1.8 pmol/106 cells/min) and [3 H]glutamate ( K t = 10 μM, V = 7.9 pmol/106 cells/min). Using a unit gravity sedimentation technique it was demonstrated that [3H]GABA was taken principally into fractions that were enriched in inhibitory neurons (Purkinje, stellate and basket cells). [3 H]β-alanine (which is taken up specifically by the glial GABA transport system) and [3 H]glutamate were concentrated by glial-enriched fractions. However [3 H]glutamate uptake was minimal in fractions enriched in precursors of granule cells, which may utilise this amino acid as their neurotransmitter. These results are discussed in relation to reports of high-affinity [3 H]glutamate uptake by glia. The role of glutamate transport in glutamatergic cells is also considered. The data suggest that high-affinity glutamate transport is a property of glial cells but not granule neurons. 相似文献
18.
Abstract. Mass spectrometry has been used to measure the rates of CO2 uptake of acid- and alkali-grown cells of the green algae Chlorella ellipsoidea (UTEX 20) and C. saccharophila (UTEX 27). The time course of CO2 formation on addition of 100mmol m−3 K2 CO3 to cells in the dark was used as an assay for external carbonic anhydrase (CA). No external CA was detected in acid-grown cells of either species or in alkali-grown cells of C. ellipsoidea but was present in alkali-grown C. saccharophila . In the absence of external CA, or when it was inhibited by 5mmol m−3 acetazolamide, cells of both species, on illumination, rapidly depleted the free CO2 in the medium at pH 7.5 to near zero concentrations before maximum photosynthetic O2 evolution rates were established. Addition of bovine CA rapidly restored the equilibrium CO2 concentration in the medium, indicating that the cells were selectively taking up CO2 . Transfer of cells to the dark caused a rapid increase in the CO2 concentration in the medium largely due to the efflux of inorganic carbon from the cells as CO2 . This rapid light-dependent CO2 uptake takes place against pH and concentration gradients and, thus, has the characteristics of active transport. 相似文献
19.
The effects of UV-C (254 nm), UV-A (365 nm) and broad-band UV (280–380 nm) on guard cells of Vicia faba L. cv. Long Pod were investigated in the presence of white light (450 μmol m−2 s−1 ). UV-C (7 μmol m−2 s−1 ) was found to cause leakage of 86 Rb+ from guard cells, while UV-A (0.3 μmol m−2 s−1 ) stimulated increased uptake in these cells. A relatively small stimulatory effect was observed by broad-band UV (3 μmol m−2 s−1 ) during the first 30 min of irradiation with an apparent equilibration of influx and efflux thereafter. Leakage of 86 Rb+ from guard cells continued despite the removal of UV-C and an increase in the amount of white light from 450 to 1500 μmol m−2 s−1 , suggesting that membranes were irreversibly damaged. Irradiation of guard cells with UV-C for 30, 45 and 90 min indicated that these cells began to be affected already by 30 min UV-C irradiation. 相似文献
20.
Anne Ojala 《Nordic Journal of Botany》1993,13(6):697-705
The effects of light and temperature on cell size and cellular composition (chlorophyll, protein, carbohydrate) of two freshwater cryptophytes were studied with batch cultures. Neither of the species had a constant cell size but the size varied with growth conditions. At each temperature the smallest cells were recorded at the lowest experimental photon flux density. The smallest cells of Cryptomonas 979/67 had an average volume of 232 μm3 and the largest ones 1 020 μm3 . In Cryptomonas 979/62 the smallest and largest cells measured 4 306 μm3 and 12 450 μm3 . Both species increased their cellular chlorophyll content when PFB dropped below 110–120 μmol m-2 s-1 . The highest and lowest chlorophyll contents of 979/67 were 7.45 fg μm-3 and 0.55 fg μm-2 respectively. For 979/62 the corresponding values were 10.23 fg μm-3 and 0.93 fg μm-3 . In both species the protein content remained stable at PFDs higher than 110–120 μmol m-2 S-1 . The highest content of protein measured in 979/67 was 638 fg μm-3 and the lowest 147 fg μm-3 . For 979/62 these values were 1 036 fg μm-3 and 148 fg μm-3 respectively. The carbohydrate results were less clear and no pattern either in response to photon flux density or temperature was obvious. The lowest and highest contents recorded for 979/67 were 62 fg μm-3 and 409 fg μ-3 and for 979162, 36 fg μm-3 and 329 fg μm-3 相似文献