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排序方式: 共有99条查询结果,搜索用时 15 毫秒
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The use of stem or progenitor cells from bone marrow, or peripheral or umbilical cord blood is becoming more common for treatment of diabetic foot problems. These cells promote neovascularization by angiogenic factors and they promote epithelium formation by stimulating cell replication and migration under certain pathological conditions. We investigated the role of CD34 + stem cells from human umbilical cord blood in wound healing using a rat model. Rats were randomly divided into a control group and two groups with diabetes induced by a single dose of 55 mg/kg intraperitoneal streptozocin. Scarred areas 5 mm in diameter were created on the feet of all rats. The diabetic rats constituted the diabetes control group and a diabetes + stem cell group with local injection into the wound site of 0.5 × 106 CD34 + stem cells from human umbilical cord blood. The newly formed skin in the foot wounds following CD34 + stem cell treatment showed significantly improvement by immunohistochemistry and TUNEL staining, and were closer to the wound healing of the control group than the untreated diabetic animals. The increase in FGF expression that accompanied the local injection of CD34 + stem cells indicates that FGF stimulation helped prevent apoptosis. Our findings suggest a promising new treatment approach to diabetic wound healing. 相似文献
24.
An overview of models of stomatal conductance at the leaf level 总被引:4,自引:0,他引:4
GAËLLE DAMOUR THIERRY SIMONNEAU HERVÉ COCHARD LAURENT URBAN 《Plant, cell & environment》2010,33(9):1419-1438
Stomata play a key role in plant adaptation to changing environmental conditions as they control both water losses and CO2 uptake. Particularly, in the context of global change, simulations of the consequences of drought on crop plants are needed to design more efficient and water‐saving cropping systems. However, most of the models of stomatal conductance (gs) developed at the leaf level link gs to environmental factors or net photosynthesis (Anet), but do not include satisfactorily the effects of drought, impairing our capacity to simulate plant functioning in conditions of limited water supply. The objective of this review was to draw an up‐to‐date picture of the gs models, from the empirical to the process‐based ones, along with their mechanistic or deterministic bases. It focuses on models capable to account for multiple environmental influences with emphasis on drought conditions. We examine how models that have been proposed for well‐watered conditions can be combined with those specifically designed to deal with drought conditions. Ideas for future improvements of gs models are discussed: the issue of co‐regulation of gs and Anet; the roles of CO2, absissic acid and H2O2; and finally, how to better address the new challenges arising from the issue of global change. 相似文献
25.
Background
The cell shape and morphology of plant tissues are intimately related to structural modifications in the primary cell wall that are associated with key processes in the regulation of cell growth and differentiation. The primary cell wall is composed mainly of cellulose immersed in a matrix of hemicellulose, pectin, lignin and some structural proteins. Xyloglucan is a hemicellulose polysaccharide present in the cell walls of all land plants (Embryophyta) and is the main hemicellulose in non-graminaceous angiosperms. 相似文献26.
迁徙水鸟保护对生物多样性保护具有重要意义。开展水鸟种群数量和幼鸟比例监测,对科学评估其种群变化趋势、制定长期保护策略具有重要价值。长江中下游湿地是东亚-澳大利西亚迁徙路线上重要的水鸟越冬区之一。本研究采用野外同步调查等方法对该区域87个湿地的亟需保护和具有代表性的10种大型越冬水鸟,其中雁形目6种,分别是鸿雁Anser cygnoides、豆雁A.fabalis、灰雁A.grus、白额雁A.albifrons、小白额雁A.erythropus和小天鹅Cygnus columbianus;鹤形目4种,分别是白鹤Leucogeranus leucogeranus、白枕鹤Antigone vipio、灰鹤Grus grus和白头鹤G.monacha,进行了长期监测(2003—2019年冬季),并结合相关文献,评估其种群变化趋势、幼鸟比例和死亡率。研究结果如下:(1)2005—2019年3种水鸟(豆雁、灰雁和灰鹤)的种群数量呈上升趋势,7种水鸟(鸿雁、白额雁、小白额雁、小天鹅、白鹤、白枕鹤和白头鹤)种群数量呈下降趋势;(2)种群趋势下降组(N=7)和上升组(N=3)的幼鸟比例均值在2016—2... 相似文献
27.
Galbeta1-3GalNAc (T-disaccharide) and related molecules were assayed to
describe the structural requirements of carbohydrates to bind Agaricus
bisporus lectin (ABL). Results provide insight into the most relevant
regions of T-disaccharide involved in the binding of ABL. It was found that
monosaccharides bind ABL weakly indicating a more extended
carbohydrate-binding site as compared to those involvedin the T-
disaccharide specific lectins such as jacalin and peanut agglutinin.
Lacto-N-biose (Galbeta1-3GlcNAc) unlike T-disaccharide, is unable to
inhibit the ABL interaction, thus showing the great importance of the
position of the axial C-4 hydroxyl group of GalNAc in T-disaccharide. This
finding could explain the inhibitory ability of Galbeta1-6GlcNAc and
lactose because C-4 and C-3 hydroxyl groups of reducing Glc, respectively,
occupy a similar position as reported by conformational analysis. From the
comparison of different glycolipids bearing terminal T-disaccharide bound
to different linkages, it can be seen than ABL binding is even more
impaired by an adjacent C-6 residual position than by the anomeric
influence of T-disaccharide. Furthermore, the addition of beta-GlcNAc to
the terminal T-disaccharide in C-3 position of Gal does not affect the ABL
binding whereas if an anionic group such as glucuronic acid is added to
C-3, the binding is partially affected. These findings demonstrate that ABL
holds a particular binding nature different from that of other
T-disaccharide specific lectins.
相似文献
28.
Slipped-strand mispairing: a major mechanism for DNA sequence evolution 总被引:141,自引:13,他引:128
Simple repetitive DNA sequences are a widespread and abundant feature of
genomic DNA. The following several features characterize such sequences:
(1) they typically consist of a variety of repeated motifs of 1-10
bases--but may include much larger repeats as well; (2) larger repeat units
often include shorter ones within them; (3) long polypyrimidine and poly-CA
tracts are often found; and (4) tandem arrangements of closely related
motifs are often found. We propose that slipped-strand mispairing events,
in concert with unequal crossing- over, can readily account for all of
these features. The frequent occurrence of long tandem repeats of
particular motifs (polypyrimidine and poly-CA tracts) appears to result
from nonrandom patterns of nucleotide substitution. We argue that the
intrahelical process of slipped-strand mispairing is much more likely to be
the major factor in the initial expansion of short repeated motifs and
that, after initial expansion, simple tandem repeats may be predisposed to
further expansion by unequal crossing-over or other interhelical events
because of their propensity to mispair. Evidence is presented that
single-base repeats (the shortest possible motifs) are represented by
longer runs in mammalian introns than would be expected on a random basis,
supporting the idea that SSM may be a ubiquitous force in the evolution of
the eukaryotic genome. Simple repetitive sequences may therefore represent
a natural ground state of DNA unselected for coding functions.
相似文献
29.
GA McFeters FP Yu BH Pyle PS Stewart 《Journal of industrial microbiology & biotechnology》1995,15(4):333-338
This report reviews the development of a rapidin situ approach to study the physiological responses of bacteria within biofilms to disinfectants. One method utilized direct viable counts (DVC) to assess the disinfection efficacy when thin biofilms were exposed to chlorine or monochloramine. Results obtained using the DVC method were one log higher than plate count (PC) estimates of the surviving population after disinfection. Other methods incorporated the use of fluorogenic stains, a cryotomy technique to yield thin (5-m) sections of biofilm communities and examination by fluorescence microscopy. The fluorogenic stains used in this approach included 5-cyano-2,3-ditolyl tetrazolium chloride (CTC), which indicates cellular electron transport activity and Rhodamine 123, which responds specifically to proton motive force. The use of these stains allowed the microscopic discrimination of physiologically active bacteria as well as heterogeneities of active cells within thicker biofilms. The results of experiments using these techniques with pure culture and binary population biofilms on stainless steel coupons indicated biocidal activity of chlorine-based disinfectants occurred initially at the bulk-fluid interface of the communities and progressed toward the substratum. This approach provided a unique opportunity to describe the spatial response of bacteria within biofilms to antimicrobial agents and address mechanisms explaining their comparative resistance to disinfection in a way that has not been possible using traditional approaches. Results obtained using this alternative approach were also consistently higher than PC data following disinfection. These observations suggest that traditional methods involving biofilm removal and bacterial enumeration by colony formation overestimate biocide efficacy. Hence the alternative approach described here more accurately indicates the ability of bacteria surviving disinfection to recover and grow as well as demonstrate spatial heterogeneities in cellular physiological activities within biofilms. 相似文献
30.
Complete sequences of the rRNA genes of Drosophila melanogaster 总被引:19,自引:0,他引:19
In this, the first of three papers, we present the sequence of the
ribosomal RNA (rRNA) genes of Drosophila melanogaster. The gene regions of
D. melanogaster rDNA encode four individual rRNAs: 18S (1,995 nt), 5.8S
(123 nt), 2S (30 nt), and 28S (3,945 nt). The ribosomal DNA (rDNA) repeat
of D. melanogaster is AT rich (65.9% overall), with the spacers being
particularly AT rich. Analysis of DNA simplicity reveals that, in contrast
to the intergenic spacer (IGS) and the external transcribed spacer (ETS),
most of the rRNA gene regions have been refractory to the action of
slippage-like events, with the exception of the 28S rRNA gene expansion
segments. It would seem that the 28S rRNA can accommodate the products of
slippage-like events without loss of activity. In the following two papers
we analyze the effects of sequence divergence on the evolution of (1) the
28S gene "expansion segments" and (2) the 28S and 18S rRNA secondary
structures among eukaryotic species, respectively. Our detailed analyses
reveal, in addition to unequal crossing-over, (1) the involvement of
slippage and biased mutation in the evolution of the rDNA multigene family
and (2) the molecular coevolution of both expansion segments and the
nucleotides involved with compensatory changes required to maintain
secondary structures of RNA.
相似文献