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21.
Time series diagnosis of tree hydraulic characteristics 总被引:1,自引:0,他引:1
An in vivo method for diagnosing hydraulic characteristics of branches and whole trees is described. The method imposes short-lived perturbations of transpiration and traces the propagation of the hydraulic response through trees. The water uptake response contains the integrated signature of hydraulic resistance and capacitance within trees. The method produces large signal to noise ratios for analysis, but does not cause damage or destruction to tree stems or branches. Based on results with two conifer tree species, we show that the method allows for the simple parameterization of bulk hydraulic resistance and capacitance of trees. Bulk tree parameterization of resistance and capacitance predicted the overall diel shape of water uptake, but did not predict the overshoot water uptake response in trees to shorter-term variations in transpiration, created by step changes in transpiration rate. Stomatal dynamics likely complicated the use of simple resistance-capacitance models of tree water transport on these short time scales. The results provide insight into dominant hydraulic and physiological factors controlling tree water flux on varying time scales, and allow for the practical assessment of necessary tree hydraulic model complexity in relation to the time step of soil- vegetation-atmosphere transport models. 相似文献
22.
荻草谷网蚜Sitobion miscanthi是严重威胁我国小麦生产安全的迁飞性害虫。蜕皮激素是参与蚜虫翅型分化调控的内激素, 在有翅成蚜体内保持高滴度, 且诱导后代产生更高比例的无翅蚜, 其进出靶细胞需要经过细胞膜上特定蛋白的转运。ATP结合盒转运蛋白家族G亚家族(ATP-binding cassette transporter G, ABCG)中的 ABCG1是通过跨膜转运昆虫类固醇、对蜕皮激素信号进行负调控的功能蛋白之一, 在蚜虫中尚未见报道。本文克隆了荻草谷网蚜ABCG1(SmisABCG1)基因, 并进行了序列比对、系统进化分析以及不同组织部位和发育时期表达模式分析。结果显示, SmisABCG1基因的开放阅读框全长为1 851 bp, 编码616个氨基酸, 含7个跨膜结构域, 符合ABCG蛋白家族典型结构特性, 基因登录ID:OP626323。昆虫间ABCG1较保守, 该蛋白系统进化关系与各自物种间亲缘关系的远近保持一致。其中, SmisABCG1与来自豌豆蚜、禾谷缢管蚜、棉蚜、花生蚜和雪松长足大蚜等的ABCG1氨基酸序列高度一致(>87%), 以上蚜虫聚为一支。与SmisABCG1亲缘关系最近的是豌豆蚜的ABCG1, 其次是半翅目的褐飞虱、白背飞虱和灰飞虱, 与膜翅目的新疆菜叶蜂、阿里山潜蝇茧蜂以及鞘翅目的赤拟谷盗、蜂箱小甲虫亲缘关系较远。该基因在伪胚胎和成蚜阶段高表达。包含伪胚胎的有翅、无翅成蚜整蚜SmisABCG1的转录水平无显著差异, 但其在来自有翅成蚜的伪胚胎中的转录水平高于无翅成蚜伪胚胎, 证实无翅成蚜自身的转录水平较高, 而有翅成蚜较低。进一步分析显示这一差异主要是无翅蚜胸部显著高表达所导致。基于该蛋白对蜕皮激素负调控, 与有翅成蚜转录水平低, 但蜕皮激素水平更高相符合。 相似文献
23.
Molecular complexes based on proteins and ionic polysaccharides have considerable potential for encapsulation of functional food components, but their widespread utilization is limited because their structure is highly sensitive to pH and ionic strength. We have investigated the possibility of creating stable hydrogel particles by thermal treatment of protein (beta-lactoglobulin) and cationic polysaccharide (chitosan) mixtures. Mixed solutions of beta-lactoglobulin (0.5 wt %) and chitosan (0.1 wt %) were prepared at various pH's (3-8) and were heated (80 degrees C for 20 min). Prior to heating, the biopolymer mixtures formed molecular complexes at pH values where there was an electrostatic attraction between the protein and the polysaccharide: soluble complexes at pH 4.5; complex coacervates at pH 5.0 and 5.5; precipitates at pH>5.5. After heating, relatively small (d approximately 140 nm) and cationic (zeta>+20 mV) hydrogel particles were formed at pH 4.5, but much larger aggregates were formed at pH 5.0 and higher (d>1000 nm). The thermally treated hydrogel particles formed at pH 4.5 maintained their initial particle size when the pH was subsequently adjusted within the range pH 3-5, but they aggregated when the pH was adjusted to >pH 5 because of a reduction in the magnitude of their electrical charge. This study suggests that hydrogel particles can be formed by heating mixed protein-polysaccharide systems under controlled conditions. These hydrogel particles may be useful for encapsulation of functional food components. 相似文献
24.
Extraction and characterization of oil bodies from soy beans: a natural source of pre-emulsified soybean oil 总被引:1,自引:0,他引:1
Iwanaga D Gray DA Fisk ID Decker EA Weiss J McClements DJ 《Journal of agricultural and food chemistry》2007,55(21):8711-8716
Soybeans contain oil bodies that are coated by a layer of oleosin proteins. In nature, this protein coating protects the oil bodies from environmental stresses and may be utilized by food manufacturers for the same purpose. In this study, oil bodies were extracted from soybean using an aqueous extraction method that involved blending, dispersion (pH 8.6), filtration, and centrifugation steps. The influence of NaCl (0-250 mM), thermal processing (30-90 degrees C, 20 min) and pH (2-8) on the properties and stability of the oil bodies was analyzed using zeta-potential, particle size, and creaming stability measurements. The extracted oil bodies were relatively small ( d 32 approximately 250 nm), and their zeta-potential went from around +12 mV to -20 mV as the pH was increased from 2 to 8, with an isoelectric point around pH 4. The oil bodies were stable to aggregation and creaming at low (pH = 2) and high (pH >/= 6) pH values but were unstable at intermediate values (3 = pH = 5), which was attributed to their relatively low zeta-potential. The oil bodies were stable to aggregation and creaming at relatively low salt concentrations (NaCl = 25 mM, pH 7) but were unstable at higher values as a result of electrostatic screening effects. The oil bodies were stable to thermal processing from 30 to 90 degrees C (0 mM NaCl, pH 7), but there appeared to be a change in their interfacial properties (decrease in zeta-potential) at temperatures exceeding 60 degrees C. These results suggest that oil bodies extracted from soybeans have similar or improved stability compared to soybean oil emulsions produced from bulk ingredients and may provide a new way of creating functional soy products for the food industry. 相似文献
25.
Journal of Pest Science - The present study investigated the feeding behaviour and life-table parameters of the grain aphid Sitobion miscanthi in response to being fed on transgenic wheat lines... 相似文献
26.
Effect of dietary flax oil and hypobaric hypoxia on pulmonary hypertension and haematological variables in broiler chickens. 总被引:1,自引:0,他引:1
1. Three experiments were conducted with broiler chickens using hypobaric chambers and control pens, feeding diets containing 25 or 50 g flax oil/kg food or control diets with equivalent amounts of animal/vegetable (A/V) blend oil for 4 weeks. The effect of these diets on haematological variables and the extent of right ventricular hypertrophy (RVH) leading to ascites was determined. 2. Overall growth rate was not consistently affected by dietary treatment, although feeding the 25 g flax oil/kg diet reduced weight gain in week 4 of one experiment. Feeding the 50 g flax oil/kg diet but not the 25 g flax oil/kg diet reduced RVH in birds exposed to hypobaric conditions compared to feeding control diets. 3. Feeding the 50 g flax oil/kg diet under hypobaric conditions reduced the haematocrit and haemoglobin content, increased the erythrocyte deformability and the proportion of unsaturated fatty acids in the erythrocyte membranes, and reduced the whole blood viscosity compared to feeding control diets. These effects were not seen when the 25 g flax oil/kg diet was fed. The ratio of n-3 to n-6 fatty acids in erythrocyte membranes was increased in the 50 g flax oil/kg treatment group compared to controls. 4. Including 50 g flax oil/kg broiler diet reduces RVH in broiler chickens. This may be attributable in part to an increase in erythrocyte deformability from an increased proportion of unsaturated fatty acids in the erythrocyte membranes. 相似文献
27.
Sarah A. Bekessy Brendan A. Wintle Ascelin Gordon Julian C. Fox Ryan Chisholm Bill Brown Tracey Regan Nick Mooney Steve M. Read Mark A. Burgman 《Biological conservation》2009,142(11):2438-2448
The wedge-tailed eagle is Australia’s largest bird of prey and one of the largest eagles in the world. Aquila audax fleayi is an endemic Tasmanian subspecies isolated for 10,000 years from the nominate subspecies on the Australian mainland. The Tasmanian wedge-tailed eagle is classified nationally and at a State level as endangered due to its small number of breeding pairs, low breeding success and high rate of mortality from unnatural causes. The subspecies experiences mortality throughout its range from shooting, poisoning, trapping, road accidents, electrocutions and collisions with wind turbines, aircraft, fences and overhead wires, which we term ‘un-natural mortality’. A portion of the subspecies’ range is managed for timber production, which can lead to disturbance of nest sites and the loss of nest trees. We use a model of the eagle population from the Bass District in northeast Tasmania to explore the relative importance of different sources of mortality and nesting habitat loss, and the potential for mitigating impacts associated with unnatural mortality, disturbance, nesting habitat loss and human access to forests. We create a habitat map including suitable nest sites and link it to a dynamic landscape population model based on life history traits and disturbance responses. Using the program RAMAS-Landscape, we model alternative forest management scenarios, ranging from no timber harvesting and a natural wildfire regime, to scenarios prescribing native forest harvesting and regeneration and different levels of conversion of native forest to plantation under the same natural wildfire regime. The results indicate that the Tasmanian wedge-tailed eagle is sensitive to unnatural mortality, plantation establishment and native forest harvesting. The predicted decline over the next 160 years (65%) will most likely be driven largely by loss of current and potential future nest sites associated with harvesting activities, exacerbated by unnatural mortality in the wider landscape. Interventions that minimise unnatural mortality, reduce nest disturbance, and retain breeding habitat and nest sites may improve the prospects for the subspecies in the Bass District. If nest disturbance and unnatural mortality continue at the rates modelled here, the species appears to face a high risk of declining substantially in the region. 相似文献
28.
高温蘑菇浙AgH—1种型的鉴定 总被引:1,自引:1,他引:1
本文描述了高温蘑菇浙AgH-1的形态学和生物学特性,该菌株最适出菇温度为27 ̄30℃,子实体能在35 ̄38℃下生长。此外该菌株子实体的口感和风味明显优于以往文献报道的双环蘑菇,因此该菌株是双环蘑菇的一个新的生理型。 相似文献
29.
Chitosan is a cationic biopolymer that has many potential applications in the food industry because of its unique nutritional and physiochemical properties. Many of these properties depend on its ability to interact with anionic surface-active molecules, such as phospholipids, surfactants, and bile acids. The purpose of this study was to characterize the interaction between chitosan and a model anionic surfactant (sodium dodecyl sulfate, SDS) using isothermal titration calorimetry (ITC), surfactant-selective electrode (SSE), and turbidity measurements. ITC and SSE indicated that SDS bound strongly to chitosan via a highly exothermic interaction. The turbidity measurements indicated that chitosan formed insoluble complexes with SDS that strongly scattered light. The chitosan bound approximately 4 mM of SDS per 0.1 wt % chitosan before becoming saturated with surfactant. The SDS-chitosan interaction was weakened appreciably by the presence of 100 mM NaCl, which suggested that it was electrostatic in origin. This study provides information about the origin and characteristics of molecular interactions between chitosan and anionic surface-active lipids that may be useful for the rational design of chitosan-based food ingredients with specific nutritional and functional characteristics, e.g., cholesterol lowering or fat replacement. 相似文献
30.
Lewis J 《Science (New York, N.Y.)》2008,322(5900):399-403
We now have a wealth of information about the molecular signals that act on cells in embryos, but how do the control systems based on these signals generate pattern and govern the timing of developmental events? Here, I discuss four examples to show how mathematical modeling and quantitative experimentation can give some useful answers. The examples concern the Bicoid gradient in the early Drosophila embryo, the dorsoventral patterning of a frog embryo by bone morphogenetic protein signals, the auxin-mediated patterning of plant meristems, and the Notch-dependent somite segmentation clock. 相似文献