共查询到20条相似文献,搜索用时 187 毫秒
1.
2.
3.
A D Bangham 《Biophysical journal》1995,68(4):1630-1633
4.
5.
6.
W K Moore 《BMJ (Clinical research ed.)》1978,2(6132):277-278
7.
8.
E. V. Seliverstova N. P. Prutskova 《Journal of Evolutionary Biochemistry and Physiology》2012,48(3):295-305
The structure and function of small intestine epithelium have been studied in overwintering frogs at various stages of hibernation. Experiments on the in vitro absorption of arginine vasotocin (AVT) have shown that the epithelium ability for absorption of this nonapeptide without hydrolysis persists during hibernation. However, there is a decline in AVT absorption observed in January–February and later on (as compared with that in October–December) which is most pronounced in March–April. Changes in the epithelial structure appear by midwinter and are growing towards spring. In April–May, enterocyte height decreased by 33%, microvilli length by 40%, and number of mitochondria by 57% relative to the values at the beginning of hibernation. The absence of signs of breakdown attests to the adaptive nature of the observed changes. The dynamics of the studied parameters reveals morphological and functional plasticity of small intestinal epithelium in Rana temporaria over the hibernation period. 相似文献
9.
10.
M. Scott Morrison Paul A. Cobine Eric L. Hegg 《Journal of biological inorganic chemistry》2007,12(8):1129-1139
The crystal structure of Cnx1G, an enzyme involved in the biosynthesis of the molybdenum cofactor (Moco) in Arabidopsis thaliana, revealed the remarkable feature of a copper ion bound to the dithiolene unit of a molybdopterin intermediate (Kuper et al. Nature 430:803-806, 2004). To characterize further the role of copper in Moco biosynthesis, we examined the in vivo and/or in vitro activity of two Moco-dependent enzymes, dimethyl sulfoxide reductase (DMSOR) and nitrate reductase (NR), from cells grown under a variety of copper conditions. We found the activities of DMSOR and NR were not affected when copper was depleted from the media of either Escherichia coli or Rhodobacter sphaeroides. These data suggest that while copper may be utilized during Moco biosynthesis when it is available, copper does not appear to be strictly required for Moco biosynthesis in these two organisms. 相似文献
11.
RAFAEL G. ALBALADEJO A. APARICIO S. SILVESTRE 《Botanical journal of the Linnean Society. Linnean Society of London》2004,145(1):97-108
Hybridization seems to be common in the genus Phlomis (Lamiaceae) in the Iberian Peninsula, especially in the P. × composita complex. In order to detect patterns of morphological variation linked to eco- and geographical variation, ecological (cluster and canonical correspondence) and morphometric (principal component and discriminant function) analyses were performed. Character count procedure was applied to discern between divergence and reticulate events for the origin of the morphologically intermediate plants. Following these analyses clear patterns were detected suggesting the existence of four independent morphological groups also supported by the ecogeographical data. These are P. crinita ssp. crinita (Levante, eastern Spain), P. crinita ssp. malacitana (Andalusia, southern Spain) and P. lychnitis (widespread) being the extremes of the morphological variation, and P. × composita including all the morphologically intermediate individual plants. Furthermore, at the population level significant differences in hybrid plant frequencies between areas were also found. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 97–108. 相似文献
12.
J O Drife D B McClelland A Pryde M M Roberts I I Smith 《BMJ (Clinical research ed.)》1976,2(6034):503-506
Nulliparous women have a greater risk of developing breast cancer than women who have borne children, but so far no functional differences in breast tissue have been reported between parous women and nulliparae. Macroscopically and histologically normal breast tissue was obtained from 74 women of reproductive age during biopsy of benign breast lesions and was examined for the presence of plasma cells by immunfluorescence. Immunoglobulin synthesis was detected by an in-vitro culture technique. Synthesis of IgA was detected in 81% of specimans of IgG in 45%, and of IgM in 3%. IgA synthesis much more intense than IgG or IgM synthesis. Plasma cells containing IgA were seen in 71% of the specimens examined, and 88% of specimens had deposits of IgA in the ductules. The findings were not significantly incluenced by the nature of the condition necessitating biopsy or by oral contraception. Nulliparous women showed no cyclical changes, but among parous women IgA synthesis was more intense during luteal phase of the menstrual cycle. This suggests that after the first pregnancy the breast is more sensitive to progesterone. 相似文献
13.
Klaus Lunau Katrin Unseld Franziska Wolter 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2009,195(12):1121-1130
Many flowers display colour patterns comprising a large peripheral colour area that serves to attract flower visitors from
some distance, and a small central, contrastingly coloured area made up by stamens or floral guides. In this study, we scaled
down the size of floral guides to detect the minimal size bumblebees (Bombus terrestris) and honeybees (Apis mellifera) require for guidance. We analyzed the approach and the precise contact of the antennal tips with the floral guide of artificial
flowers which precedes landing and inspection. Both bumblebees and honeybees were able to make antennal contact with circular
floral guides which were 2 mm in diameter; bumblebees performed better than honeybees and antennated also at floral guides
smaller than 2 mm. In discrimination experiments with bumblebees, a minimum floral guide size of 2 mm was required for discrimination
between artificial flowers with and without floral guides. With increasing experience bumblebees targeted close to the site
of reward instead of making antennal contact with the floral guide, whereas honeybees did not alter their initial behaviour
with growing experience. Bumblebees and honeybees spontaneously target diminutive floral guides to achieve physical contact
with flowers by means of their antennae which helps them to inspect flowers. 相似文献
14.
T. D. Dubatolova N. V. Dorogova L. V. Omel’yanchuk L. -Sh. Chang 《Russian Journal of Genetics》2011,47(4):404-408
The cell cycle duration was estimated in Drosophila melanogaster mutants for the tumor suppressor Merlin with the use of different approaches. Experiments on induction of mosaic clones in tissues of the larval wing imaginal disc
showed that the cell cycle in mutant discs is shorter than that in control. Flow fluorescence cytometry revealed no differences
between mutant and normal animals in the relative duration of the cell cycle phases, which suggests proportional shortening
of the cell cycle phases. The study with pulselabeled mitoses confirmed these results and showed that the length of the cell
cycle is 7 h (S phase duration 3 h) in control individuals and 5 h (S phase duration 2 h) in Merlin gene mutants. 相似文献
15.
16.
17.
18.
19.
Kenji Konishi Tsutomu Tamura Ryoko Zenitani Takeharu Bando Hidehiro Kato Lars Walløe 《Polar Biology》2008,31(12):1509-1520
The annual trend in energy storage in the Antarctic minke whale was examined using catch data from all 18 survey years in
the Japanese Whale Research Program (JARPA). Regression analyses clearly showed that blubber thickness, girth and fat weight
have been decreasing for nearly 2 decades. The decrease per year is estimated at approximately 0.02 cm for mid-lateral blubber
thickness and 17 kg for fat weight, corresponding to 9% for both measurements over the 18-year period. Furthermore, “date”,
“extent of diatom adhesion”, “sex”, “body length”, “fetus length”, “latitude”, “age” and “longitude” were all identified as
partially independent predictors of blubber thickness. The direct interpretation of this substantial decline in energy storage
in terms of food availability is difficult, since no long-term krill abundance series is available. However, an increase in
the abundance of krill feeders other than minke whales and a resulting decrease in the krill population must be considered
as a likely explanation. 相似文献