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排序方式: 共有191条查询结果,搜索用时 15 毫秒
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Howard S. Neufeld Frederick C. Meinzer Charles S. Wisdom M. Rasoul Sharifi Philip W. Rundel Mollie S. Neufeld Yoram Goldring Gary L. Cunningham 《Oecologia》1988,75(1):54-60
Summary At sites in the United States, creosote bushes (Larrea tridentata (DC.) Cov.) orient foliage clusters predominantly toward the southeast. Foliage of bushes at the southernmost distribution extreme in Mexico shows no predominant orientation. Clusters at all sites are inclined between 33° and 71° from the horizontal. Inclinations are steeper in the drier and hotter Mojave Desert than in the Chihuahuan Desert. Individual leaflets, though not measured, appear more randomly oriented than foliage clusters. In several populations studied, branches were shorter in the southeastern sectors of the crown, reducing self-shading early in the morning. Measurements of direct beam radiation interception by detached branches, using digital image processing, indicated that foliage clusters oriented toward the southeast exhibited less self-shading during spring mornings than clusters oriented northeast. This effect was not apparent at the summer solstice. This type of canopy architecture may tend to minimize self-shading during the morning hours when conditions are more favorable for photosynthesis, resulting in an improved daily water use efficiency. 相似文献
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Cell membranes of colonic epithelial cells (CEC) in ulcerative colitis show structural abnormalities which are specific to the disease and which suggest impaired lipogenesis in CECs. Lipogenesis from [1-14C]-n-butyrate, the chief oxidative fuel of colonic epithelial cells, was measured in isolated CECs under control conditions, with or without glucose and in the presence of mercaptoacetate, a major reducing agent in the colonic lumen- Glucose significantly (p < 0.01) stimulated lipogenesis from [1-14C]-butyrate which was reversed by 5 mM mercaptoacetate. Mercaptoacetate significantly diminished CEC thiolase activity (EC 2.3.1.9). 5-Aminosalicylic acid reversed the adverse effects of mercaptoacetate in the saponifiable fraction of extracted lipids. Changes in lipogenesis due to colonic luminal reducing agents would affect the barrier function of CECs a feature relevant to the disease process of ulcerative colitis. 相似文献
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Tremblay A.; Poehlman E. T.; Nadeau A.; Dussault J.; Bouchard C. 《Journal of applied physiology》1987,62(2):539-544
The present study investigated the role of heredity in determining changes in the energy cost of submaximal exercise in response to short-term overfeeding. Six pairs of monozygotic twins were subjected to a 1,000 kcal/day surplus for 22 days with careful experimental controls over food intake and physical activities. O2 consumption (VO2) was measured during a submaximal treadmill exercise test 165 min postprandially before and the morning after the overfeeding protocol. As expected, overfeeding induced significant increases in body weight and fat mass. No significant increase in mean exercise VO2 was observed after overfeeding. However, the interindividual variation in overfeeding-induced changes in exercise VO2 was large and not randomly distributed. When comparing intrapair variance for changes in exercise VO2 to interpair variance, a moderate to high within-pair resemblance in response, i.e., a genotype-overfeeding interaction, was observed. Changes in exercise VO2 were positively correlated with those in postexercise levels of blood catecholamines, particularly epinephrine. A negative correlation was found between changes in exercise VO2 and body fat gain. These results are consistent with the concept of a role for the sympathoadrenal system in the regulation of adaptive thermogenesis and the predisposition to store fat. Moreover, these data suggest that the sensitivity to adapt in exercise energy expenditure after overfeeding is inherited to a significant extent. 相似文献
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The Lipid Peroxidation Product, 4-Hydroxy-2-trans-Nonenal, Alters the Conformation of Cortical Synaptosomal Membrane Proteins 总被引:6,自引:1,他引:5
‡Ram Subramaniam ‡Fred Roediger Brad Jordan †‡§Mark P. Mattson §Jeffrey N. Keller Georg Waeg ‡§ D. Allan Butterfield 《Journal of neurochemistry》1997,69(3):1161-1169
Abstract: Alzheimer's disease (AD) is widely held to be a disorder associated with oxidative stress due, in part, to the membrane action of amyloid β-peptide (Aβ). Aβ-associated free radicals cause lipid peroxidation, a major product of which is 4-hydroxy-2- trans -nonenal (HNE). We determined whether HNE would alter the conformation of synaptosomal membrane proteins, which might be related to the known neurotoxicity of Aβ and HNE. Electron paramagnetic resonance spectroscopy, using a protein-specific spin label, MAL-6(2,2,6,6-tetramethyl-4-maleimidopiperidin-1-oxyl), was used to probe conformational changes in gerbil cortical synaptosomal membrane proteins, and a lipid-specific stearic acid label, 5-nitroxide stearate, was used to probe for HNE-induced alterations in the fluidity of the bilayer domain of these membranes. Synaptosomal membranes, incubated with low concentrations of HNE, exhibited changes in protein conformation and bilayer order and motion (fluidity). The changes in protein conformation were found to be concentration- and time-dependent. Significant protein conformational changes were observed at physiologically relevant concentrations of 1–10 µ M HNE, reminiscent of similar changes in synaptosomal membrane proteins from senile plaque- and Aβ-rich AD hippocampal and inferior parietal brain regions. HNE-induced modifications in the physical state of gerbil synaptosomal membrane proteins were prevented completely by using excess glutathione ethyl ester, known to protect neurons from HNE-caused neurotoxicity. Membrane fluidity was found to increase at higher concentrations of HNE (50 µ M ). The results obtained are discussed with relevance to the hypothesis of Aβ-induced free radical-mediated lipid peroxidation, leading to subsequent HNE-induced alterations in the structure and function of key membrane proteins with consequent neurotoxicity in AD brain. 相似文献
6.
An understanding of the physiological and behavioral determinants of resting energy requirements is important to nutritional considerations in females. We examined the influence of endurance training and self-reported dietary restraint on resting metabolic rate and fasting plasma hormones in 44 nonobese females characterized for body composition, maximal aerobic power (VO2 max), and daily energy intake. To examine the association of metabolic rate and dietary restraint with hormonal status, fasting plasma levels of insulin, glucose, and thyroid hormones (total and free fractions of thyroxine and triiodothyronine) were determined. In univariate analysis, resting metabolic rate (kcal.min-1) was positively related to VO2 max (L.min-1) (r = 0.54; p less than 0.01). This relationship, however, was partially dependent on body size, since fat-free mass was also related to resting metabolic rate (r = 0.42; p less than 0.01) and VO2 max (L.min-1) (r = 0.75; p less than 0.01). After controlling for fat-free weight using partial correlation analysis, the relation between RMR and VO2 max was weaker but controlling for fat-free weight using partial correlation analysis, the relation between RMR and VO2 max was weaker but still significant (partial r = 0.38; p less than 0.05). On the other hand, high levels of dietary restraint were associated with higher levels of body fat (r = 0.31; p less than 0.05) and a lower resting metabolic rate (r = -0.29; p = 0.07). These associations persisted after control for differences in fat-free mass. Total energy intake as well as total and free levels of triiodothyronine were not related to resting metabolic rate or level of dietary restraint.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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Amjad Horani Steven L. Brody Thomas W. Ferkol David Shoseyov Mollie G. Wasserman Asaf Ta-shma Kate S. Wilson Philip V. Bayly Israel Amirav Malena Cohen-Cymberknoh Susan K. Dutcher Orly Elpeleg Eitan Kerem 《PloS one》2013,8(8)
Background
Primary ciliary dyskinesia (PCD) is a genetic disorder characterized by impaired ciliary function, leading to chronic sinopulmonary disease. The genetic causes of PCD are still evolving, while the diagnosis is often dependent on finding a ciliary ultrastructural abnormality and immotile cilia. Here we report a novel gene associated with PCD but without ciliary ultrastructural abnormalities evident by transmission electron microscopy, but with dyskinetic cilia beating.Methods
Genetic linkage analysis was performed in a family with a PCD subject. Gene expression was studied in Chlamydomonas reinhardtii and human airway epithelial cells, using RNA assays and immunostaining. The phenotypic effects of candidate gene mutations were determined in primary culture human tracheobronchial epithelial cells transduced with gene targeted shRNA sequences. Video-microscopy was used to evaluate cilia motion.Results
A single novel mutation in CCDC65, which created a termination codon at position 293, was identified in a subject with typical clinical features of PCD. CCDC65, an orthologue of the Chlamydomonas nexin-dynein regulatory complex protein DRC2, was localized to the cilia of normal nasal epithelial cells but was absent in those from the proband. CCDC65 expression was up-regulated during ciliogenesis in cultured airway epithelial cells, as was DRC2 in C. reinhardtii following deflagellation. Nasal epithelial cells from the affected individual and CCDC65-specific shRNA transduced normal airway epithelial cells had stiff and dyskinetic cilia beating patterns compared to control cells. Moreover, Gas8, a nexin-dynein regulatory complex component previously identified to associate with CCDC65, was absent in airway cells from the PCD subject and CCDC65-silenced cells.Conclusion
Mutation in CCDC65, a nexin-dynein regulatory complex member, resulted in a frameshift mutation and PCD. The affected individual had altered cilia beating patterns, and no detectable ultrastructural defects of the ciliary axoneme, emphasizing the role of the nexin-dynein regulatory complex and the limitations of certain methods for PCD diagnosis. 相似文献10.
Anderson US Benne M Bloomsmith MA Maple TL 《Journal of applied animal welfare science : JAAWS》2002,5(2):125-137
This study focused on the relationship between nonhuman animal behavior and environment-specifically, between the undesirable behavior exhibited by domestic petting zoo animals in the presence of humans and the spatial design of the petting zoo environment. A spatial feature of a petting zoo referred to as a retreat space was manipulated so that it affected the animals' opportunity for individual control over interaction with humans. Three conditions were tested: no retreat space, semi-retreat space, and a full-retreat space. The subjects of this study were 5 African pygmy goats (Capra hircus) and 2 Romanov sheep (Ovis aries). Investigators used a focal sampling technique to analyze approximately 27 hr of behavioral data collected. The data were analyzed using multiple linear regression methods. The findings suggest that the full-retreat design beneficially moderated both sheep and goat behavior: Undesirable behaviors were lowest in the full-retreat condition. This study provides information that may improve human-animal interactions in a petting zoo setting and may increase animal well-being through exhibit design and management techniques. 相似文献