排序方式: 共有19条查询结果,搜索用时 15 毫秒
1.
Katny MA Hoffmann-Thoma G Schrier AA Fangmeier A Jäger HJ van Bel AJ 《Journal of plant physiology》2005,162(4):429-438
Potato plants (Solanum tuberosum cv. Bintje) were grown in open top chambers under ambient (400 microL L(-1)) and elevated CO2 (720 microL L(-1)). After 50 days one half of each group was transferred to the other CO2 concentration and the effects were studied in relation to leaf age (old, middle-aged and young leaves) in each of the four groups. Under long-term exposure to elevated CO2, photosynthesis increased between 10% and 40% compared to ambient CO2. A subsequent shift of the same plants to ambient CO2 caused a 20-40% decline in photosynthetic rate, which was most pronounced in young leaves. After shifting from long-term ambient to elevated CO2, photosynthesis also increased most strongly in young leaves (90%); these experiments show that photosynthesis was downregulated in the upper young fully expanded leaves of potato growing long-term under elevated CO2. Soluble sugar content in all leaf classes under long-term exposure was stable irrespective of the CO2 treatment, however under elevated CO2 young leaves showed a strongly increased starch accumulation (up to 400%). In all leaf classes starch levels dropped in response to the shift from 720 to 400 microL L(-1) approaching ambient CO2 levels. After the shift to 720 microL L(-1), sucrose and starch levels increased, principally in young Leaves. There is clear evidence that leaves of different age vary in their responses to changes in atmospheric CO2 concentration. 相似文献
2.
Maria Ponec Arij Weerheim Louis Havekes Johannes Boonstra 《Experimental cell research》1987,171(2):426-435
The relationship among keratinocyte differentiation capacity, lipid synthesis, low-density lipoprotein (LDL) metabolism, plasma membrane composition, and epidermal growth factor (EGF) binding has been studied in SCC-12F2 cells. The differentiation capacity of the cells, i.e., ionophore-induced cornified envelope formation, was inhibited by various retinoids and stimulated by hydrocortisone. Retinoids that caused a significant reduction of cornified envelope formation, i.e., retinoic acid and 13-cis-retinoic acid, caused only minor changes in lipid synthesis and plasma membrane composition. Arotinoid ethylsulfone, having a minor effect on cornified envelope formation, caused a drastic inhibition of cholesterol synthesis, resulting in changes in the plasma membrane composition. Hydrocortisone stimulated cornified envelope formation but had only minor effects on lipid synthesis and plasma membrane composition. Of all retinoids tested, only arotinoid ethylsulfone caused a drastic increase in EGF binding, while hydrocortisone had no effect. Retinoic acid, arotinoid ethylsulfone, and hydrocortisone had no effects on LDL binding and only minor effects on LDL degradation. These results clearly demonstrate that the plasma membrane composition is not related to keratinocyte differentiation capacity, but most likely does determine EGF binding. Furthermore, EGF binding does not determine keratinocyte differentiation capacity. 相似文献
3.
Acylceramides and lanosterol-lipid markers of terminal differentiation in cultured human keratinocytes: Modulating effect of retinoic acid 总被引:1,自引:0,他引:1
J. Brod E. Bavelier P. Justine A. Weerheim M. Ponec 《In vitro cellular & developmental biology. Animal》1991,27(2):163-168
Summary Epidermal differentiation is accompanied by profound changes in the synthesis of a variety of intracellular proteins and intercellular
lipids. In conventional, submerged culture keratinocytes have been shown to lose the ability to synthesize the protein markers
of differentiation. They re-express them, however, when they are cultured in medium supplemented with delipidized [retinoic
acid (RA)-depleted] serum or in air-exposed cultures using de-epidermized dermis (DED) as a substrate. Recent studies have
revealed that acylceramides (AC) and lanosterol (LAN), which are present only in trace amounts in cultures of keratinocytes
grown under submerged conditions on DED in medium supplemented with normal serum, become expressed in significant amounts
when the culture is lifted to the air-liquid interface. Inasmuch as culture conditions may markedly affect the extent of keratinocyte
differentiation, the present study aimed to investigate the effect of normal (RA-containing) or delipidized (RA-depleted)
serum and of RA administration on lipid composition (especially of the AC and LAN contents) in cells cultured under submerged
and air-exposed conditions. To test a possible effect of dermal substrate (used in the air-exposed model), the lipid composition
of keratinocytes grown under submerged conditions on a plastic and on a dermal substrate (de-epidermized dermis, DED) has
also been compared. The results revealed that under all culture conditions, RA deprivation of fetal bovine serum resulted
in a marked increase of total ceramide content. Even under submerged conditions, the presence of both AC and LAN could be
detected. In air-exposed culture, the content of these lipids was markedly increased. Addition of RA at 1 μM concentration to cultures grown in RA-depleted medium induced marked changes in lipid composition under all culture conditions
tested. In cells grown under submerged conditions (both on plastic and on DED) AC and LAN were no longer present in detectable
amounts. Also in air-exposed culture, a marked decrease in the content of these lipids was observed. These results suggest
that liposoluble serum components, like RA, control the synthesis of lipids that are present in later stages of epidermal
differentiation. 相似文献
4.
We have studied the relationship between differentiation capacity, plasma membrane composition, and epidermal growth factor (EGF) receptor expression of normal keratinocytes in vitro. The plasma membrane composition of the cells was modulated experimentally by cholesterol depletion, using specific inhibitors of cholesterol synthesis, such as 25-hydroxycholesterol and mevinolin. Exposure of the cells towards these inhibitors resulted in a drastic decrease of cholesterol biosynthesis, as determined from 14C-acetate incorporation into the various lipid fractions. This effect on cholesterol biosynthesis was reflected by changes in plasma membrane composition, as determined by lipid analysis of isolated plasma membrane fractions, these resulting in a decreased cholesterol-phospholipid ratio. The experimental modulation of plasma membrane composition by 25-hydroxycholesterol or mevinolin were accompanied by a decreased cornified envelope formation and by high expression of EGF binding sites. These phenomena were more pronounced in cells induced to differentiate by exposure of cells grown under low Ca2+ to normal Ca2+ concentrations, as compared to cells grown persistently under low Ca2+ concentrations. These results suggest a close correlation between plasma membrane composition, differentiation capacity, and EGF receptor expression. 相似文献
5.
Zhang X Daou A Truong TM Bertram R Roper MG 《American journal of physiology. Endocrinology and metabolism》2011,301(4):E742-E747
Pancreatic islets secrete insulin in a pulsatile manner, and the individual islets are synchronized, producing in vivo oscillations. In this report, the ability of imposed glucose waveforms to synchronize a population of islets was investigated. A microfluidic system was used to deliver glucose waveforms to ~20 islets while fura 2 fluorescence was imaged. All islets were entrained to a sinusoidal waveform of glucose (11 mM median, 1 mM amplitude, and a 5-min period), producing synchronized oscillations of fura 2 fluorescence. During perfusion with constant 11 mM glucose, oscillations of fura 2 fluorescence were observed in individual islets, but the average signal was nonoscillatory. Spectral analysis and a synchronization index (λ) were used to measure the period of fura 2 fluorescence oscillations and evaluate synchronization of islets, respectively. During perfusion with glucose waveforms, spectral analysis revealed a dominant frequency at 5 min, and λ, which can range from 0 (unsynchronized) to 1 (perfect synchronization), was 0.78 ± 0.15. In contrast, during perfusion with constant 11 mM glucose, the main peak in the spectral analysis corresponded to a period of 5 min but was substantially smaller than during perfusion with oscillatory glucose, and the average λ was 0.52 ± 0.09, significantly lower than during perfusion with sinusoidal glucose. These results indicated that an oscillatory glucose level synchronized the activity of a heterogeneous islet population, serving as preliminary evidence that islets could be synchronized in vivo through oscillatory glucose levels produced by a liver-pancreas feedback loop. 相似文献
6.
J. G. Sivak H. C. Howland J. West J. Weerheim 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1989,165(6):771-777
Summary Multiple refractive state measurements were made on a male and female hooded seal (Cystophora cristata) when the eyes were exposed to air and to water. The measures, made by conventional retinoscopy and by photorefraction, show that the seals are moderately hyperopic (2–3 diopters) in water and moderately myopic (2–4 diopters) in air. No significant astigmatism was noted in either medium. The absence of refractive state variation over time suggests that an accommodative mechanism is insignificant or absent, although histological study indicates that the ciliary muscle is well developed.Photokeratoscopy, carried out on two animals with two keratoscopic instruments, show that the cornea is relatively flat (30 mm, or about one-half the diameter of the eye). Furthermore the cornea is only slightly astigmatic (less than 1 diopter). The refractive power of the external corneal surface (in air), calculated from a measurement of corneal refractive index of 1.378, amounts to only 10 or 11 diopters.As in the typical fish eye, hooded seal lenses are spherical or nearly spherical in shape (24–23 mm), and have short focal lengths (30–32 mm). Focal measures for rays at varying distances from the lens center indicate that spherical aberration is well corrected.There is no indication in this seal species, of a previously reported adaptation involving a highly astigmatic cornea which together with a slit pupil can minimize the optical effect of movement from water to air. 相似文献
7.
Maria Ponec Arij Weerheim Johanna Kempenaar Peter M. Elias Mary L. Williams 《In vitro cellular & developmental biology. Plant》1989,25(8):689-696
Summary Differentiation in keratinocytes can be experimentally modulated by changing the culture conditions. When cultured under conventional,
submerged conditions, the extent of cellular differentiation is reduced in the presence of low calcium medium and is enhanced
in medium containing physiologic calcium concentrations. Moreover cultures grown at the air-medium interface or on a dermal
substrate, or both, differentiate even further. Herein we report the effect of culture conditions on lipid composition in
normal human keratinocytes and three squamous carcinoma cell (SCC) lines that vary in their capacity to differentiate as assessed
by cornified envelope formation. Under submerged conditions, the total phospholipid content was lower, triglyceride content
higher, and phospholipid: neutral lipid ratio lower in direct correlation to the degree of differentiation in these cultures.
When grown at the air-medium interface on the-epidermized dermis, evidence of further morphologic differentiation was found
only for well-differentiated SCC cells and normal keratinocytes. Similarly, the phospholipid content remained high in poorly
differentiated SCC cells and it, decreased modestly in well-differentiated SCC cells and markedly in normal keratinocytes.
In all cell lines the triglyceride content was increased and cholesterol content decreased when compared to parallel submerged
cultures, but these differences were most pronounced in well-differentiated cell lines. Acylceramides and acylglucosylceramides
were found only in normal keratinocytes and only under the most differentiation-enhancing conditions. These studies demonstrate
differentiation-related changes in the lipid content of both normal and neoplastic keratinocytes.
This work was supported in part by NATO Scientific Award (RG 8510056). 相似文献
8.
Arij Mechergui Wafa Achour Assia Ben Hassen 《World journal of microbiology & biotechnology》2014,30(8):2181-2188
We aimed to compare accuracy of genus and species level identification of Neisseria spp. using biochemical testing and 16S rRNA sequence analysis. These methods were evaluated using 85 Neisseria spp. clinical isolates initially identified to the genus level by conventional biochemical tests and API NH system (Bio-Mérieux®). In 34 % (29/85), more than one possibility was given by 16S rRNA sequence analysis. In 6 % (5/85), one of the possibilities offered by 16S rRNA gene sequencing, agreed with the result given by biochemical testing. In 4 % (3/85), the same species was given by both methods. 16S rRNA gene sequencing results did not correlate well with biochemical tests. 相似文献
9.
Ng T Chand D Song L Al Chawaf A Watson JD Boutros PC Belsham DD Lovejoy DA 《Regulatory peptides》2012,174(1-3):79-89
10.