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21.
Hedgehog signaling in pancreas development and disease 总被引:6,自引:0,他引:6
Since its discovery, numerous studies have shown that the Hedgehog (Hh) signaling pathway plays an instrumental role during
diverse processes of cell differentiation and organ development. More recently, it has become evident that Hh signaling is
not restricted to developmental events, but retains some of its activity during adult life. In mature tissues, Hh signaling
has been implicated in the maintenance of stem cell niches in the brain, renewal of the gut epithelium and differentiation
of hematopoietic cells. In addition to the basal function in adult tissue, deregulated signaling has been implicated in a
variety of cancers, including basal cell carcinoma, glioma and small cell lung cancer. Here, we will focus on the role of
Hh signaling in pancreas development and pancreatic diseases, including diabetes mellitus, chronic pancreatitis and pancreatic
cancer.
Received 5 August 2005; received after revision 4 November 2005; accepted 22 November 2005 相似文献
22.
Responses of ephemeral plant germination and growth to water and heat conditions in the southern part of Gurbantunggut Desert 总被引:3,自引:0,他引:3
WANG Xueqing JIANG Jin WANG Yuanchao LUO Weilin SONG Chunwu CHEN Junjie 《科学通报(英文版)》2006,51(A01):110-116
Ephemeral plants in the southern part of Gurbantunggut Desert were systematically monitored from 2002 to 2004 and the meteorological data and soil moisture during the same period were analyzed. The results show that the ephemeral plants germination and growth are sensitive to the changes of water and heat condition. The time for daily temperature over 0℃ in early spring in 2003 was delayed nearly 10 d compared with that in 2002, while the soil water changed little in the same period. Observation showed that there were 28 ephemeral species germinated in 2002, their life period was about 70 d in spring, and the maximum cover of ephemeral synusia reached 46.4%. However, only 17 ephemeral species germinated in 2003, their life period was about 50 d in spring, and their maximum cover was only 20.8%. The height of ephemeral plants was significantly higher in 2002 than that in 2003. It can be seen that ephemeral plant germination and growth in spring are strongly dependent on temperature. The changes of water conditions can affect ephemerals germination and growth as well. Because no heavy precipitation occurred during summer in 2002, only a few ephemerophytes were observed in autumn after ephemerals completed their life circle in early spring. However, about 60 mm precipitation was recorded from July to August both in 2003 and in 2004. Some ephemerals such as Erodium oxyrrhynchum and Carex physodes, etc. covered the dune surface rapidly with a cover 〉10%. Therefore, the ephemerals not only germinate in autumn after the early spring, some species may germinate in summer if adequate rainfall occurs. The study on responses of ephemerals growth to water and heat conditions not only has a certain ecological significance but also contributes a better understanding to the effect of climate changes on the desert surface stability. 相似文献
23.
植物水势系数及其应用实例 总被引:5,自引:0,他引:5
本文提出了植物水势系数的概念与计测公式,即植物水势系数是植物水势占大气水势和土壤水势对植物水势产生直接影响力那部分水势之和的比值。并对在塔克拉玛干沙漠生长的沙生柽柳进行了应用实例的验证。结果表明,在自然状态下,植物水势系数可作为衡量植物对环境胁迫反应强弱的一个指标。 相似文献
24.
遥感、GIS支持下的浑善达克沙漠化土地最新特征分析 总被引:10,自引:1,他引:9
通过对浑善达克沙地土地沙漠化的遥感调查发现,2000年沙地沙漠化土地面积达318.54万hm^2,占沙地总面积的58.84%。其中,轻度沙漠化土地占沙漠化土地的52.34%之多,是浑善达克沙地沙漠化土地的主体。在空间分布上,除了沙地北部的锡林浩特市之外,其余旗县都有大面积的沙漠化土地分布。从作业区的分析情况来看,沙漠化态势比较严重的是阿巴嘎旗和正蓝旗。与1995年对比分析表明,5年来浑善达克沙地在整体上基本稳定,沙漠化土地面积没有太大的扩展,但部分旗县仍以沙漠化的加重为主,区域差异很大。 相似文献
25.
在艾比湖保护区内多个样地风速测点选择荒漠植被,开展防风防沙研究。在实地测量的基础上通过比照不同地形、不同植被类型以及不同植被覆盖率防风及输沙率的影响,分析在不同风速范围的效果,对干旱地区防治风蚀及沙尘暴提供理论依据,课题研究对艾比湖国家湿地自然保护区生态恢复有着极其重要的意义。 相似文献
26.
27.
腾格里沙漠南缘土门剖面52L~41FD层段由3层风成沙丘砂、2层湖相沉积、2层古土壤和5层砂黄土构成. 分析结果表明:微量元素含量的高低变化依次为Mn、P、Sr、Rb、Cr、V、Zn、Ni、Cu、Nb,各元素含量在砂黄土、古土壤和湖相沉积中表现为相对峰态,而在沙丘砂层段中则呈现为相对谷态;在垂直方向上,各微量元素含量随着各沉积相的多次更替,构成了10条峰谷交替的锯齿状形态的元素波动过程线. 结合研究区地理位置与微量元素特征,认为可用Zn(ppm)、P(ppm)为代表作为气候替代性指标,指示本区东亚冬夏季风变化. 据此划分出了8个冷暖波动事件:冷干事件,即C1(11 870~11 640 a BP)、C2(12 650~12 050 a BP)、C3(13 340~13 010 a BP)、C4(13 810~13 620 a BP), 暖湿事件, 即W1(12050~11870 a BP)、W2(13010~12650 a BP)、W3(13620~13340 a BP)、W4(14850~13810 a BP). 本研究与格陵兰GRIP冰芯和中国南京葫芦洞H82石笋之间较高的同步性,这表明,腾格里沙漠南缘气候波动可能与格陵兰气候变化受相同的高纬动力驱动. 相似文献
28.
Late Pleistocene/Holocene wetland events recorded in southeast Tengger Desert lake sediments, NW China 总被引:4,自引:0,他引:4
D.B.Madsen CHENFahu Ch.G.Oviatt ZHUYan P.J.Brantinaham R.GoElston R.L.Bettinger 《科学通报(英文版)》2003,48(14):1423-1429
The area along the eastern and southeastern margins of the Tengger Desert, NW China, which is sensitive to the summer monsoon variations, was selected for studying the environmental conditions surrounding the transition between Paleolithic foragers and Neolithic farmer/pastoral-ists. Short cores were obtained from four lake basins in the southwestern Tengger using a hand-driven piston coringdevice. Proxies from these cores were supplemented by ra-diocarbon ages obtained from lake sediment cores, shoreline features and spring mound deposits. Together these records provide evidence of millennial-scale climate change eventsfrom the Pleistocene-Holocene transition to the present.Lake/wetland events, representing periods of more intensive summer monsoon, occur in the records at-12.7-11.6,-10.1, -9.3, -8.0, -5.4, -1.5, and -0.8 ka BP. They do suggest that century- to miliennial-seale climatic cycles are characteristic of the Holocene in the southeastern Tengger Desert although the chronology must be considered extremely tentative. 相似文献
29.
在第四纪沉积物研究中,特别是现代沉积环境的研究中,沉积物的地球化学特征在分析物源和重建古环境等方面发挥积极的作用.通过采集了巴丹吉林沙漠不同区域、不同类型沙丘、不同地貌部位的沙样,分析了巴丹吉林沙漠沉积物的地球化学特征,得出巴丹吉林沙漠沉积物在矿物学上和沉积学上的成熟度较低,但是具有很好的均质性的结论.这一结论对于推断巴丹吉林沙漠沉积物的物源有很好的指示意义,同时对于研究巴丹吉林沙漠高大沙山的成因也有一定的线索意义. 相似文献
30.
This study was conducted on the desert riparian forest along the lower reach of the inland Tarim River, which is located in the arid region of Northwest China. Fifteen plant species in 10 families were collected from five monitoring sections, and examined for the infection ofarbuscular mycorrhizal fungi (AMF). The impact of different soil factors on AMF infection rate and intensity was compared using the principal component analysis (PCA) method. The results indicate that 11 species are AM and only 4 are non-AM plants. The estimated capacity of AMF infection depends on families of plants and also the parameters (infection rate, infection intensity, fungal spore density) used. The density of fungal spores was relatively higher in Phragmites communis and Populus euphratica in Graminaceae and Salicaceae families, respectively. The infection rate was above 50% in all the AM plants, except Calligonumjunceum. The highest infection rate appeared in Alhagi sparsifolia (97%) and Glycyrrhizainflata (92%). However, when compared by AMF infection intensity, Tamarix spp. became the top one, followed by Alhagi sparsifolia, and Glycyrrhiza inflata was in the middle range of all the species. The PCA has identified that soil total salt, moisture, organic matter, total nitrogen, total P, available K and pH were closely associated with the AMF infection. 相似文献