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排序方式: 共有363条查询结果,搜索用时 9 毫秒
1.
YONG-JIANG ZHANG FREDERICK C. MEINZER GUANG-YOU HAO FABIAN G. SCHOLZ SANDRA J. BUCCI FREDERICO S. C. TAKAHASHI RANDOL VILLALOBOS-VEGA JUAN P. GIRALDO KUN-FANG CAO WILLIAM A. HOFFMANN & GUILLERMO GOLDSTEIN 《Plant, cell & environment》2009,32(10):1456-1466
Size-related changes in hydraulic architecture, carbon allocation and gas exchange of Sclerolobium paniculatum (Leguminosae), a dominant tree species in Neotropical savannas of central Brazil (Cerrado), were investigated to assess their potential role in the dieback of tall individuals. Trees greater than ∼6-m-tall exhibited more branch damage, larger numbers of dead individuals, higher wood density, greater leaf mass per area, lower leaf area to sapwood area ratio (LA/SA), lower stomatal conductance and lower net CO2 assimilation than small trees. Stem-specific hydraulic conductivity decreased, while leaf-specific hydraulic conductivity remained nearly constant, with increasing tree size because of lower LA/SA in larger trees. Leaves were substantially more vulnerable to embolism than stems. Large trees had lower maximum leaf hydraulic conductance ( K leaf ) than small trees and all tree sizes exhibited lower K leaf at midday than at dawn. These size-related adjustments in hydraulic architecture and carbon allocation apparently incurred a large physiological cost: large trees received a lower return in carbon gain from their investment in stem and leaf biomass compared with small trees. Additionally, large trees may experience more severe water deficits in dry years due to lower capacity for buffering the effects of hydraulic path-length and soil water deficits. 相似文献
2.
JUAN CARLOS ALONSO LUIS MARIANO GONZALEZ† BORJA HEREDIA† JOSE LUIS GONZALEZ‡ 《Ibis》1987,129(S1):212-224
The behaviour of five broods of radio-tagged Spanish Imperial Eagles Aquila heliaca adalberti was studied in Doñana National Park, Spain during the post-fledging period. The distance between perching sites and nest, the mean flight duration and distance, the percentage of time spent flying and the home range all increased exponentially with age. As the young got older, the parents spent less time in their vicinity. Young were not seen hunting, but depended on their parents for food. They begged and chased their parents throughout the post-fledging period, with higher intensity at the end. Nevertheless, the adults became progressively more reluctant to feed them, as reflected in the decrease in feeding frequency and in the number of approaching flights towards the young. At the end of the post-fledging period, adults often performed aerial displays and frequently chased their offspring. The age of independence of the different young studied varied between 123 and 145 days. The correlations between individual independence and the dates when the young were last fed by their parents, and when the highest intensity of parental aggressive behaviour occurred, were higher than correlations with the variables related to the maturation of flying. Therefore, it is suggested that parental 'meanness' and aggressive behaviour may be the factors determining the date of juvenile independence and dispersal from the home territory. 相似文献
3.
辣椒素引起脊髓P物质释放及其对血压的影响 总被引:5,自引:0,他引:5
为进一步研究脊髓 P 物质(SP)在调节心血管活动中的作用,在大鼠脊髓蛛网膜下腔注射(ith)辣淑素(cap),以刺激脊髓 SP 能神经末梢释放 SP,结果引起血浆去甲肾上腺素(NA)和肾上腺素(AD)含量增高,及具有剂量依赖性的动脉血压上升,心率升高。ith 具有高度特异性的 SP 受体拮抗剂或 SP 抗血清均可阻断 cap 引起的升压效应,免疫组化测定也观察到注入的cap 剂量越大,脊髓胸段 SP 样免疫阳性反应物的致密度越低,这些观察结果支持 cap 可以引起脊髓内 SP 的释放的说法。在第一颈段(C_1)横断脊髓后 ith cap 所引起的升压效应与完整动物 ith cap 的升压效应无显著差异。以上结果提示脊髓 SP 能神经末梢释放的 SP 可以通过交感肾上腺髓质系统引起心血管兴奋效应,SP 可能是引起交感节前神经元兴奋的神经递质。 相似文献
4.
Ribosomes,G-factor and Siomycin 总被引:13,自引:0,他引:13
G-factor interacts with the 50S ribo-somal subunit at a site which is distinct from the peptidyl transferase centre and which is inactivated by siomycin. 相似文献
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We studied the distribution and spread of the invasive social wasp Vespula germanica in Argentina, focusing on the contribution of queen dispersal to territorial expansion. Vespula germanica is native to Eurasia and has invaded several regions of the world, including Southern Argentina. Flight potential of field‐collected queens was measured using flight mills. Also, by means of an extensive survey we estimated the rate of spread by analysing the relationship between years since arrival and distance from the introduction locality. The mean distance flown by wasp queens in flight mills was 404.7 ± 140.8 m (mean ± SE, n = 59), while the rate of spread of V. germanica was estimated at 37.2 ± 2.1 km year?1 (mean ± SE, n = 67), although faster towards the south. The observed spread rate of V. germanica wasps in Argentina confirms the invasive potential shown by several Hymenoptera species worldwide. Still, a stratified geographical expansion pattern does not match observed queen dispersal abilities, suggesting that human‐aided transport of hibernating queens is the central driver of the current distribution of these wasps. We suggest that despite several life‐history traits known for social insects that contribute to successful invasion, wasp spread must still rely strongly on human mediated pathways. This observation sheds light on those factors that are crucial for managing invasions of this and related pestiferous wasps. 相似文献
8.
Abstract: Examination of newly collected brachiopods from the Eusebio Ayala Formation of Paraguay reveals the occurrence of Arenorthis paranaensis sp. nov., Plectothyrella? itacurubiensis sp. nov., Hindella sp. and Eostropheodonta conradii (Harrington). Associated graptolites of the N. persculptus Zone indicate that the age of the fossiliferous beds is Hirnantian. The overall generic composition of the fauna is similar to that of the atypical Hirnantia Fauna of the Bani Province. The record in Paraguay of Arenorthis, hitherto only known from North Africa, together with species of Plectothyrella? and Eostropheodonta different from those recorded in the Kosov Province, emphasizing the affinities between the Paraguayan fauna and the low‐diversity African assemblages. Stratigraphic and faunal evidence indicates that biogeographical links between South America and Africa already existed by the end of the Ordovician when most of the intra‐cratonic basins of Gondwana were flooded during the postglacial sea level rise. 相似文献
9.
JUAN L. BENEDETTO 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2013,46(2):170-179
Benedetto, J.L. 2013: Presence of punctae in the ‘plectorthoidean’ brachiopod Famatinorthis turneri (Middle Ordovician) from western Argentina: implications for early diversification of punctate orthides. Lethaia, Vol. 46, pp. 170–179. Famatinorthis Levy & Nullo is a distinctive orthide brachiopod of Dapingian age from the volcaniclastic rocks of the Famatina Range of western Argentina. Although it was originally classified among the plectorthoideans, a new collection from the La Escondida Formation has yielded exceptionally well‐preserved moulds of Famatinorthis turneri in which silicified infillings of punctae are clearly visible, leading to the reassignment of the genus to the dalmanellidines. In this paper, phylogenetic analyses are used to determine the evolutionary relationships of Famatinorthis, the Tremadocian linoporellid Lipanorthis, and other Ordovician Gondwanan genera. The placement of Plectorthoidea in the same major clade as linoporellids, and the separation of Dalmanellidina as an independent clade are the most important features of all shortest trees, supporting the idea that linoporellids may have originated from a plectorthoid ancestor. Cladistic analysis reveals that Lipanorthis lies close to the ancestry of the linoporellid lineage, and Famatinorthis clusters within the more derived taxa of the clade with which it shares a large septalium. It seems that the presence of endopunctae in the orthides does not necessarily indicate close phylogenetic relationships as it could have occurred at different times in different clades. If the homoplasic nature of endopunctae in the order Orthida is supported by further morphologic and phylogenetic studies, the fundamental division of orthides in non‐punctate (Orthidina) and punctate (Dalmanellidina) may need revision. □Brachiopods, Ordovician, Gondwana, Famatina, phylogeny, punctate orthides. 相似文献
10.
The K+/H+ antiporter LeNHX2 increases salt tolerance by improving K+ homeostasis in transgenic tomato 总被引:1,自引:0,他引:1
RAÚL HUERTAS LOURDES RUBIO OLIVIER CAGNAC MARÍA JESÚS GARCÍA‐SÁNCHEZ JUAN DE DIOS ALCHÉ KEES VENEMA JOSÉ ANTONIO FERNÁNDEZ MARÍA PILAR RODRÍGUEZ‐ROSALES 《Plant, cell & environment》2013,36(12):2135-2149
The endosomal LeNHX2 ion transporter exchanges H+ with K+ and, to lesser extent, Na+. Here, we investigated the response to NaCl supply and K+ deprivation in transgenic tomato (Solanum lycopersicum L.) overexpressing LeNHX2 and show that transformed tomato plants grew better in saline conditions than untransformed controls, whereas in the absence of K+ the opposite was found. Analysis of mineral composition showed a higher K+ content in roots, shoots and xylem sap of transgenic plants and no differences in Na+ content between transgenic and untransformed plants grown either in the presence or the absence of 120 mm NaCl. Transgenic plants showed higher Na+/H+ and, above all, K+/H+ transport activity in root intracellular membrane vesicles. Under K+ limiting conditions, transgenic plants enhanced root expression of the high‐affinity K+ uptake system HAK5 compared to untransformed controls. Furthermore, tomato overexpressing LeNHX2 showed twofold higher K+ depletion rates and half cytosolic K+ activity than untransformed controls. Under NaCl stress, transgenic plants showed higher uptake velocity for K+ and lower cytosolic K+ activity than untransformed plants. These results indicate the fundamental role of K+ homeostasis in the better performance of LeNHX2 overexpressing tomato under NaCl stress. 相似文献