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排序方式: 共有173条查询结果,搜索用时 15 毫秒
71.
G N Smith K R Sinervo L Carmichael J Patrick A D Bocking J F Brien 《Journal of developmental physiology》1991,16(4):239-242
A study was performed to examine the role of prostaglandins (PGs) in the mechanism of the ethanol-induced suppression of FBM, in which the objective was to test the hypothesis that fetal administration of PGE2 can suppress the incidence of FBM following reversal of ethanol-induced suppression of FBM by indomethacin, a fatty acid cyclooxygenase inhibitor. Instrumented near-term pregnant ewes received 1-h maternal infusion of ethanol (1 g/kg maternal body weight) followed 0.5 h later by a 3-h fetal infusion of indomethacin (1 mg/kg fetal body weight/h), and then a 2-h fetal infusion of PGE2 (400 ng/kg fetal body weight/min). Prior to drug administration, FBM occurred approximately 36.1 +/- 2.6% of the time. FBM were suppressed during the period of ethanol infusion (9.6 +/- 1.7%); the ethanol-induced suppression of FBM was reversed by fetal indomethacin treatment (77.5 +/- 14.1%); shortly after the onset of fetal PGE2 infusion, the incidence of FBM decreased to a 2-h mean incidence of 14.1 +/- 4.2%, which was similar in magnitude to that observed after maternal ethanol infusion. After the completion of PGE2 infusion, the incidence of FBM rapidly increased to a peak incidence of 83.4 +/- 19.2%, which was indicative of a prolonged effect of indomethacin on FBM. The data indicate that PGs mediate the ethanol-induced suppression of ovine FBM and that the action of indomethacin to antagonize ethanol-induced suppression of FBM is primarily due to its inhibition of PG synthesis. 相似文献
72.
Thermal sensitivity of growth rate in hatchling Sceloporus lizards: environmental,behavioral and genetic aspects 总被引:2,自引:0,他引:2
Summary To investigate the physiological, behavioral, and genetic contributions to growth rate, we studied the thermal sensitivity of growth rate in hatchlings of the iguanid lizards Sceloporus occidentalis and S. graciosus in the laboratory. We used a cycling thermal regime patterned after thermal environments found in nature. Growth rates increased with duration of access to radiant heat. Thus, variation in the thermal environment can cause phenotypic variation in growth rate and hence body size. The two species differed in both the magnitude and thermal sensitivity of growth rate, and these differences were associated with differences in behavioral thermoregulation. Thus, growth is determined interactively by both behavior and physiology. We found evidence of among-family variation in the growth rates of S. occidentalis, suggesting that growth rate has the genetic potential to evolve. In S. occidentalis, both growth rate and egg size affected body size of hatchlings at several weeks of age. In turn, hatchling size may affect fitness: for example, larger S. occidentalis hatchlings had higher sprint speeds and may therefore be more adept at capturing prey or evading predators. Our results demonstrate that growth rate has genetic, behavioral, and physiological components, and that the resulting effects on body size may have important consequences for ecological performance e.g., sprint speed. 相似文献
73.
Spatial variation in selection has long been recognized as promoting population divergence and in maintaining genetic polymorphisms, but selection at a fine spatial scale is seldom measured directly. We analyzed spatial and temporal variation in selective regimes on egg size using long-term population data of the side-blotched lizard (Uta stansburiana). Juvenile survival rates varied between years at a small spatial scale that was reflected as a strong interaction between the local neighborhood level and year. Spatially and temporally variable selection acted jointly on egg mass, which presumably would facilitate the maintenance of high additive genetic variance for this trait. Local selection gradients calculated at the neighborhood level were significantly correlated with the annual global selection gradients calculated at the metapopulation level. However, there was substantial variance in these local selective regimes, which suggests that strong local selection could go undetected if the analysis was limited to the global level. We also investigated the degree of spatial synchronization among outcrop in local selection gradients. The degree of synchrony was higher among later-clutch hatchlings than among first-clutch hatchlings, and we suggest that more intense density- and frequency-dependent selection on egg size later in the season is responsible for this effect. 相似文献
74.
Samuilova O Krogerus C Pöyry T Hyypiä T 《The Journal of biological chemistry》2004,279(36):37822-37831
The functional properties of the nonstructural 2A protein are variable among different picornaviruses. The 2A protein of the human parechovirus 1 (HPEV1) has been shown to lack the proteolytic activity found in many other picornaviruses, but no particular function has been identified for HPEV1 2A. To obtain information about the role of HPEV1 2A in the viral life cycle, the protein was expressed in Escherichia coli. A polyclonal antibody was then raised against the protein and employed to investigate its subcellular localization in the infected cells by immunofluorescence microscopy. Typically, a diffuse cytoplasmic staining pattern, concentrated to the perinuclear area, was observed in the infected cells. However, at late stages of infection some infected cells also exhibited diffuse nuclear staining. Viral RNA, visualized by fluorescent in situ hybridization, partly colocalized with 2A in the perinuclear region. Three experimental approaches including Northwestern blot, UV cross-linking, and gel retardation demonstrated that 2A possesses RNA binding activity. Competition experiments with various single-stranded RNA molecules addressed the specificity of 2A binding. These studies revealed that the 2A protein bound RNA corresponding to the 3'-untranslated region (UTR) of the viral genome with highest affinity. At the N- and C-terminal ends of the protein, two regions, necessary for RNA binding, were identified by mutagenesis. In addition, we demonstrated that 2A has affinity to double-stranded RNA containing 3'UTR(+)-3'UTR(-). In conclusion, our experiments showed that HPEV1 2A binds to viral 3'UTR RNA, a feature that could be important for the function of the protein during HPEV1 replication. 相似文献
75.
Tiimonen H Aronen T Laakso T Saranpää P Chiang V Ylioja T Roininen H Häggman H 《Planta》2005,222(4):699-708
Transgenic silver birch (Betula pendula Roth) lines were produced in order to modify lignin biosynthesis. These lines carry COMT (caffeate/5-hydroxyferulate O-methyltransferase) gene from Populus tremuloides driven by constitutive promoter 35S CaMV (cauliflower mosaic virus) or UbB1 (ubiquitin promoter from sunflower). The decreased
syringyl/guaiacyl (S/G) ratio was found in stem and leaf lignin of 35S CaMV-PtCOMT transgenic silver birch lines when compared
to non-transformed control or UbB1–PtCOMT lines. In controlled feeding experiments the leaves of transgenic birch lines as
well as controls were fed to insect herbivores common in boreal environment, i.e., larvae of Aethalura punctulata, Cleora cinctaria and Trichopteryx carpinata (Lepidoptera: Geometridae) as well as the adults of birch leaf-feeding beetles Agelastica alni (Coleoptera: Chrysomelidae) and Phyllobius spp. (Coleoptera: Curculionidae). The feeding preferences of these herbivores differed in some cases among the tested birch
lines, but these differences could not be directly associated to lignin modification. They could as well be explained by other
characteristics of leaves, either natural or caused by transgene site effects. Growth performance of lepidopteran larvae fed
on transgenic or control leaves did not differ significantly. 相似文献
76.
Ammon Corl Ke Bi Claudia Luke Akshara Sree Challa Aaron James Stern Barry Sinervo Rasmus Nielsen 《Current biology : CB》2018,28(18):2970-2977.e7
77.
Jari P. T. Valkonen Marjo Keskitalo Tuija Vasara Leena Pietilä Dr. K. V. Raman 《植物科学评论》1996,15(1):1-20
Steroidal glycoalkaloids (SGAs) are produced following the general steroid biosynthesis pathway, starting from acetyl-coenzyme A and followed by the intermediates mevalonic acid, squalene, cycloartenol, and cholesterol. α-Chaconine and α-solanine are the main SGAs of the cultivated potato (Solanum tuberosum), whereas many other SGAs are known in the wild potato species. Low concentrations of SGAs improve the taste of potato, but concentrations greater than 200 mg/kg can have toxic effects on animals and humans. SGAs have antimicrobial activity and confer resistance to some insects, but many such pests of potato are not greatly affected. Certain environmental conditions and wounding enhance SGA accumulation in tubers in the field and storage. Low production of SGAs is a dominant character inherited in a relatively simple manner and can be selected for in potato-breeding programs, whereas the use of wild potato germplasm tends to increase the SGA accumulation in the breeding lines. Further efforts are likely to be directed toward the reduction of the SGA content in the edible potato products through breeding and biotechnological methodologies, whereas potato genotypes with high SGA production may be developed for use in the pharmaceutical industry. 相似文献
78.
Optimal feeding is often constrained by predation avoidance, which may direct feeding to take place on more sheltered, but less profitable, parts of the habitat. Though constrained, feeding preferences and/or digestive capabilities should co-evolve with the energetic and nutritional needs of the animal. These needs, as well as risk taking for these goals, may differ between the sexes. We studied sexual differences in the utilization of the brown alga Fucus vesiculosus by the marine isopod Idotea baltica . In a feeding preference test with small pieces of alga both sexes prefer the apical, newly grown parts to the basal parts. However, males show stronger preference than females. When isopods are reared on the apical or basal part of the alga alone, sexes grow differently on these parts. Females gain weight equally well and their intermolt duration is the same on both parts of the alga, while males perform clearly worse on the basal than on the apical part. Despite the better quality of the apical parts of the alga, in a grazing experiment in a "semi-natural" environment with whole bushes of F. vesiculosus also the basal parts are consumed, and even preferred over apical parts by females. We suggest that feeding preferences are subordinate to microhabitat choice, and therefore predation avoidance constrains optimal feeding. We hypothesize that the better ability of females than that of males to utilize the basal parts of the alga for growth is a co-adaptation to their risk-averse general reproductive strategy. We discuss the sexual differences in host plant utilization in the context of reproductive strategies of the sexes, especially different risk sensitivity of foraging, and its potential consequences on plant-herbivore interaction. 相似文献
79.
Tuija Palin-Palokas 《Gerodontology》1990,9(4):103-110
A representative sample of urban elderly living at home were studied for their perceived problems of oral health, treatment need felt for these problems, and their utilization of oral health care services. The majority of these elderly were denture wearers. Nearly all of the denture-wearing elderly had problems with their dentures, and about half of the dentate elderly had problems with their remaining teeth. The number of problems perceived increased with deteriorating health and decreasing income. Half of the elderly with denture problems and two-thirds of those who had problems with remaining teeth felt they needed dental treatment. Multivariate analyses found the number of perceived problems, having some natural teeth, and perceived general health to be the most important determinants of their perceived treatment need. Although two-thirds of the studied elderly felt no barriers to seeking treatment, only half of them had made their last dental visit less than five years ago. Having some teeth remaining, oral health education experiences, and income were found to be the best predictors of service utilization. Altogether, affective and cognitive factors rather than socio-demographic differences appeared to determine the elderly's perceptions about treatment need and their actual utilization of dental services, emphasizing the necessity of oral health education approaches designed for the elderly. 相似文献
80.