糯玉米胚乳淀粉粒粒度分布形成的酶学机理

以7个糯玉米品种为材料,测定其籽粒发育过程中淀粉粒粒度分布及淀粉合成相关酶活性的变化,分析两者之间的关系。结果表明,随着籽粒发育,糯玉米淀粉粒平均粒径逐渐增大,可溶性淀粉合成酶(SSS)和淀粉分支酶(SBE)活性呈单峰曲线变化。籽粒发育前期,小淀粉粒(≤7.4μm)所占体积较大;随着籽粒发育,小淀粉粒所占体积减少,大淀粉粒(>7.4μm)所占体积增多;籽粒发育后期,大淀粉粒所占体积较大。相关分析表明, SSS和SBE活性与大淀粉粒体积增大速率和平均粒径增大速率均呈显著或极显著正相关。因此, SSS和SBE是影响糯玉米胚乳淀粉粒粒度分布形成的主要酶, SSS和SBE活性越高,淀粉粒平均粒径越大,大淀粉粒所占体积越多。     

Amylose Content and Starch Granule Size in Rice Grains are Affected By Growing Season

Amylose content and starch granule size in grains influence rice quality, which differs between the early (ES) and late season (LS). The objective of this study was to determine the variation of amylose content and starch granule size between seasons and find the main reasons (e.g., temperature and solar radiation) for the observed variation. Field experiments with six rice varieties (three high and three low amylose content rice) planted in the ES and LS were conducted in 2016 and 2017, respectively. The mean temperatures during the filling stage were higher in ES, however, the daily temperatures at 7-10 days after flowering (DAF) in 2016, and at 5-10, 13-14 DAF in 2017 were higher in LS. The results showed that amylose content in LS was lower than in ES with high amylose content rice varieties (HACV); the opposite trend occurred with low amylose content rice varieties (LACV). The mean starch granule diameter was higher in LS than ES in 2016, but the opposite result occurred in 2017 with all rice. Our results suggest that higher temperatures increased and decreased the amylose content in HACV and LACV, respectively. Temperatures at 5-15 DAF were important for the formation of starch granules: lower temperatures during 10-14 DAF increased the proportion of larger starch granules (d＞6.21 μm, some with d＞13.3 μm), and higher temperatures at 5-6 DAF increased the proportion of starch granules with diameter 4.24-6.21 μm.     

Size Distribution of Bacterial Cells

By using differential light-scattering measurements of single cells suspended in a laser beam, an effective cell radius has been determined for 141 individual bacteria from suspensions of Staphylococcus epidermidis. The accumulation of these measurements has provided the size distribution for the sampling.     

Body Size Distribution of the Dinosaurs

The distribution of species body size is critically important for determining resource use within a group or clade. It is widely known that non-avian dinosaurs were the largest creatures to roam the Earth. There is, however, little understanding of how maximum species body size was distributed among the dinosaurs. Do they share a similar distribution to modern day vertebrate groups in spite of their large size, or did they exhibit fundamentally different distributions due to unique evolutionary pressures and adaptations? Here, we address this question by comparing the distribution of maximum species body size for dinosaurs to an extensive set of extant and extinct vertebrate groups. We also examine the body size distribution of dinosaurs by various sub-groups, time periods and formations. We find that dinosaurs exhibit a strong skew towards larger species, in direct contrast to modern day vertebrates. This pattern is not solely an artefact of bias in the fossil record, as demonstrated by contrasting distributions in two major extinct groups and supports the hypothesis that dinosaurs exhibited a fundamentally different life history strategy to other terrestrial vertebrates. A disparity in the size distribution of the herbivorous Ornithischia and Sauropodomorpha and the largely carnivorous Theropoda suggests that this pattern may have been a product of a divergence in evolutionary strategies: herbivorous dinosaurs rapidly evolved large size to escape predation by carnivores and maximise digestive efficiency; carnivores had sufficient resources among juvenile dinosaurs and non-dinosaurian prey to achieve optimal success at smaller body size.     

玉米根际与非根际解磷细菌的分布特点

植物光合作用产物约有 12 %～ 5 0 %通过根系进入根际土壤中 ,不同的植物 ,同一植物不同的生长发育时期 ,不仅根际分泌物的数量有差异 ,而且分泌物的种类也不同[4 ] 。这些分泌物不仅是微生物很好的培养基 ,而且一些分泌物可能抑制或有利于甚至刺激某些微生物的繁殖 ,从而导致根际微生物种群结构的变化。根际微生物的数量、活性和群落结构及其变化 ,直接影响到植物吸收水分、养分 ,也影响植物对恶劣环境的抵抗能力 ,尤其是与病菌的侵入和感染关系非常密切[6] 。Ｐ是植物最重要的营养元素之一 ,大多数土壤都具有很强的固定Ｐ的能力 ,Ｐ肥的利…     

Exponential Size Distribution of von Willebrand Factor

Von Willebrand Factor (VWF) is a multimeric protein crucial for hemostasis. Under shear flow, it acts as a mechanosensor responding with a size-dependent globule-stretch transition to increasing shear rates. Here, we quantify for the first time, to our knowledge, the size distribution of recombinant VWF and VWF-eGFP using a multilateral approach that involves quantitative gel analysis, fluorescence correlation spectroscopy, and total internal reflection fluorescence microscopy. We find an exponentially decaying size distribution of multimers for recombinant VWF as well as for VWF derived from blood samples in accordance with the notion of a step-growth polymerization process during VWF biosynthesis. The distribution is solely described by the extent of polymerization, which was found to be reduced in the case of the pathologically relevant mutant VWF-IIC. The VWF-specific protease ADAMTS13 systematically shifts the VWF size distribution toward smaller sizes. This dynamic evolution is monitored using fluorescence correlation spectroscopy and compared to a computer simulation of a random cleavage process relating ADAMTS13 concentration to the degree of VWF breakdown. Quantitative assessment of VWF size distribution in terms of an exponential might prove to be useful both as a valuable biophysical characterization and as a possible disease indicator for clinical applications.     

Egg-Mass Size and Cell Size: Effects of Temperature on Oxygen Distribution

Two processes strongly influence the distribution of oxygenwithin egg masses and cells: the supply of oxygen by diffusionand the consumption of oxygen by embryos and mitochondria. Theseprocesses are differentially sensitive to temperature. The diffusioncoefficient of oxygen depends only weakly on temperature, havinga Q₁₀ of approximately 1.4. In contrast, the consumption ofoxygen depends strongly on temperature, having a Q₁₀ between1.5 and 4.0. Thus, at higher temperatures, the ratio of oxygensupply to demand decreases. I show, by extending a model ofoxygen distribution within metabolizing spheres, that maximalegg-mass sizes and cell sizes are predicted to be smaller athigher temperatures. For egg masses, definitive data are notyet available. For ectothermic cells, this prediction appearsto be supported; cells from a variety of ectothermic organisms,unicellular and multicellular, are smaller when the cells areproduced at warmer temperatures. Establishing a specific connectionbetween this pattern and oxygen distributions requires demonstrationof (1) oxygen concentration gradients within metabolizing spheresand (2) central oxygen concentrations low enough to affect function.Egg masses from a variety of taxa show steep oxygen concentrationgradients and often are severely hypoxic or anoxic in centrallocations. Severe hypoxia appears capable of retarding developmentor killing embryos. Similar kinds of data for ectothermic cellshave not yet been collected, but the literature on oxygen gradientswithin mammalian cells suggests that intracellular gradientsmay be important.     

Size Distribution of "Informational" RNA

Previous investigations suggested that the size of “informational” or “messenger” RNA was confined to sedimentation rates lying between 8 and 14S. These involved procedures permitting extended contact of the RNA with enzymatically active extracts. The present study re-examined the size distribution of T2-complementary RNA isolated by a method which minimized enzymatic degradation. A much greater diversity in size distribution (4S to 25S) was observed. Experiments are described indicating that 8 to 12S informational RNA does not readily attach to the 16S and 23S ribosomal components under the conditions used for sedimentation analysis.     

Exponential Size Distribution of von Willebrand Factor

Von Willebrand Factor (VWF) is a multimeric protein crucial for hemostasis. Under shear flow, it acts as a mechanosensor responding with a size-dependent globule-stretch transition to increasing shear rates. Here, we quantify for the first time, to our knowledge, the size distribution of recombinant VWF and VWF-eGFP using a multilateral approach that involves quantitative gel analysis, fluorescence correlation spectroscopy, and total internal reflection fluorescence microscopy. We find an exponentially decaying size distribution of multimers for recombinant VWF as well as for VWF derived from blood samples in accordance with the notion of a step-growth polymerization process during VWF biosynthesis. The distribution is solely described by the extent of polymerization, which was found to be reduced in the case of the pathologically relevant mutant VWF-IIC. The VWF-specific protease ADAMTS13 systematically shifts the VWF size distribution toward smaller sizes. This dynamic evolution is monitored using fluorescence correlation spectroscopy and compared to a computer simulation of a random cleavage process relating ADAMTS13 concentration to the degree of VWF breakdown. Quantitative assessment of VWF size distribution in terms of an exponential might prove to be useful both as a valuable biophysical characterization and as a possible disease indicator for clinical applications.     

Simulating Stationary Size Distribution of Trees in Rain Forests

A simple dynamic model of the distribution of tree size (trunkdiameter) in natural rain forests is presented. Based on dataof permanent plot measurements in a tropical rain forest anda warm-temperate rain forest, the cumulative basal area densityof trees larger than a given tree, at any particular time, isused to express the effect of suppression, or one-sided competition,on the growth rate of that tree. It also shows that increasingthe basal area density of all trees in the stand depresses therate of recruitment from the pool of seedlings. Mortality istreated as independent of the cumulative basal area. Simulationwith the model, applying the one-dimensional drift-diffusionequation, reproduces the observed course of reforestation afterclear-felling and leads to convergence to a unique stationarysize distribution by 200 years. This concuts with the size distributionobserved in primary forest stands. The present model representsan extension of density-dependent population growth models tosize-structured tree populations. Competition, cumulative basal area, density dependence, equilibrium, population, simulation, size distribution, tropical rain forest, warm—temperate rain forest     

Distribution of Structural Carbohydrates in Corn Plants Across the Southeastern USA

Quantifying lignin and carbohydrate composition of corn (Zea mays L.) is important to support the emerging cellulosic biofuels industry. Therefore, field studies with 0 or 100 % stover removal were established in Alabama and South Carolina as part of the Sun Grant Regional Partnership Corn Stover Project. In Alabama, cereal rye (Secale cereale L.) was also included as an additional experimental factor, serving as a winter cover crop. Plots were located on major soil types representative of their respective states: Compass and Decatur soils in Alabama and a Coxville/Rains-Goldsboro-Lynchburg soil association in South Carolina. Lignin and structural carbohydrate concentrations in the whole (above-ground) plant, cobs, vegetation excluding cobs above the primary ear (top), vegetation below the primary ear (bottom), and vegetation from above the primary ear including cobs (above-ear fraction) were determined using near-infrared spectroscopy (NIRS). The distribution of lignin, ash, and structural carbohydrates varied among plant fractions, but neither inclusion of a rye cover crop nor the stover harvest treatments consistently affected carbohydrate concentrations within locations. Total precipitation and average air temperature during the growing season were strongly correlated with stover composition indicating that weather conditions may have multiple effects on potential biofuel production (i.e., not only yield but also stover quality). When compared to the above-ear fractions, bottom plant partitions contained greater lignin concentrations. Holocellulose concentration was consistently greater in the above-ear fractions at all three locations. Data from this study suggests that the above-ear plant portions have the most desirable characteristics for cellulosic ethanol production via fermentation in the southeastern USA.     

Changes in Vertical Distribution of Pratylenchus scribneri under Potato and Corn

The vertical distribution of Pratylenchus scribneri populations was monitored under irrigated corn and potato grown in loamy sand soil. population estimates were based on the number of nematodes recovered from 100-cm³ soil samples and the roots contained therein. Reproduction was assessed by counting the number of second-stage juveniles. An index of population maturity was computed to evaluate the age structure of populations. At no time were nematodes distributed uniformly among five soil depths from 0 to 37.5 cm deep. During the summer (June-September), changes in the total number of P. scribneri and the number of second-stage juveniles recovered were not consistent among the depths sampled. Early (April-June) and late (September-November) in the season, changes in the abundance, reproduction, and maturity of populations were similar among depths. The timing and pattern of increases in numbers of nematodes suggests that variation in the abundance of P. scribneri in the soil profile beneath potato and corn was caused primarily by reproduction rather than the movement of nematodes.     

Foraging Strategy within African Elephant Family Units: Why Body Size Matters

Differences in intraspecific foraging strategies have been documented between sexes of strongly dimorphic large herbivore species. Body size implications on diet quality requirements, however, can be extended to within‐species age‐specific comparisons. We investigated the hierarchical separation of foraging behavior at the scale of plant type, plant species, plant part and vertically through the canopy. For this, we studied African elephant adult females (lower quality diet required) and weaned calves (higher quality diet) within the elephant family unit, which is socially constrained to traverse the landscape together. Grass and browse were used with similar seasonal frequency. Both females and calves tracked the phenology of woody species, including these species in the diet when new growth was available. Forage utilization differed at the plant part level, with calves selecting for less fibrous and more nutritious plant parts (e.g., stripped leaves), while adult females selected branches, bark and roots with greater frequency. There was displacement of females to higher foraging levels in the canopy when these females fed <3 m away from calves. Elephant family unit foraging strategies were driven by body size, age‐specific nutritional requirements and intraspecific competition. This has broader application to other large herbivore species with great variance in intraspecific body size.     

重症监护病房常见非发酵菌分布及耐药性分析

分析医院重症监护病房非发酵菌感染的耐药情况,以指导临床合理使用抗菌药物。回顾性分析2009~2010年医院自重症监护病房分离的非发酵菌,对其检出率及药敏结果进行统计分析。共检出96株非发酵菌,检出率为19.79%,分离率居前4位的依次为铜绿假单胞菌（46.88%）、鲍氏不动杆菌（21.88%）、嗜麦芽寡养单胞菌（15.63%）、洋葱伯克霍尔德菌（10.42%）;4种常见的非发酵菌对常用的抗菌药物耐药性均较高,头孢哌酮/舒巴坦等含酶抑制剂的复合型抗菌药物对非发酵菌有较高的敏感性。医院重症监护病房非发酵菌检出率高且耐药性强,应加强临床细菌学的检测,按照药敏试验结果合理用药。     

Variability and Bimodal Distribution of Size in Microspores of Aesculus hippocastanum

Size variability of uninucleate microspores was studied in horse chestnut (Aesculus hippocastanum L.). Microspores were isolated from buds of different size (3, 4, and 5 mm) taken from lower, middle and upper segments of inflorescences. All analyzed buds showed bimodal distribution of microspore size which confirmed the presence of pollen dimorphism. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular Size and Chain Length Distribution in Acanthamoeba Cellulose*

SYNOPSIS Evidence obtained by total hydrolysis, partial acetolysis, periodate oxidation, as well as treatment with amylase, emulsin, and Trichoderma virideβ-(1→4)-glucanase, verified that the alkali insoluble component of Acanthamoeba castellanii was pure β-(1→4)-glucan. The weight average chain length of the cellulose varied from DP = 3170 to DP = 4130 (mean DP = 3480) with polysaccharide obtained from seven seemingly identical cultures. Isolation of the cyst-wall cellulose by nondegrading means indicated that alkali extraction was not depolymerizing the polysaccharide. Fractionation of cellulose obtained from a single culture produced fractions from DP = 550 to DP = 4550 (mean DP = 3280; 98.7% of the original cellulose), indicating that the cellulose is polydisperse.     

Uneven Distribution and Size of Rabbit Lens Capsule Proteoglycans

To document the ultrastructural distribution of lens capsule proteoglycans, rabbit lens capsules were fixed and stained overnight in 50mM sodium acetate, pH 5.6, containing 2.5% glutaraldehyde, 0.2% Cuprolinic Blue and 0.2M MgCl2. They were rinsed, stained with 1% aqueous sodium tungstate, embedded in Epon, sectioned (60nm), and examined with an electron microscope at 60kV.Proteoglycan–Cuprolinic Blue complexes mainly appeared as networks of small electron-dense filaments throughout the posterior and anterior capsules. The posterior capsule was a single layer with a network of small proteoglycan filaments gradually decreasing in size from the humoral side (90×10nm) to the lenticular side (30×8nm). The humoral side of the anterior capsule had a thin lamina (400nm) containing large (180×40nm), very electron-dense proteoglycan–Cuprolinic Blue complexes plus small proteoglycans. Below this lamina, the complexes were only seen as filaments slightly smaller than those in the corresponding area of the posterior capsule.Cuprolinic Blue binding of the anterior and posterior lens capsules revealed differences in the size and distribution of their sulphated proteoglycans which do not correspond to the patterns of their immunoreactivity with anti-heparan sulphate proteoglycan. The humoral lamina in the anterior capsules, with large proteoglycan structures, might be a distinct structural and functional compartment.