Carbohydrate partitioning between upper and lower regions of the crown in oat and rye during cold acclimation and freezing

Carbohydrates have long been recognized as an important aspect of freezing tolerance in plants but the association between these two factors is often ambiguous. To help clarify the relationship, the allocation of carbohydrates between specific tissues within the over wintering organ (crown) of winter cereals was measured. A winter-hardy and non-winter-hardy oat (Avena sativa L.), and a rye (Secale cereale L.) cultivar were grown and frozen under controlled conditions. Crown tissue was fractionated into an upper portion, called the apical region, and a lower portion, called the lower crown. These tissues were ground in liquid N and extracted with water. Extracts were analyzed by HPLC for the simple sugars, sucrose, glucose, fructose, and for fructan of various size classes. After 3 weeks of cold acclimation at 3 degrees C, carbohydrates accounted for approximately 40% of the dry weight of oats and 60% of the dry weight of rye. The apical region, which is the tissue within the crown that acclimates to the greatest extent, was generally 10% higher in total carbohydrates than the lower crown. During a mild freeze, various carbohydrates were allocated differently between specific tissues in the three genotypes. When frozen, fructan generally decreased to a greater extent in the lower crown than in the apical region but sugars increased more in the apical region than in the lower crown. Results suggest that to understand how carbohydrates relate to freezing tolerance, regions of the crown that endure freezing stress differently should be compared.     

A reusable magnetic nickel nanoparticle based catalyst for the aqueous synthesis of diverse heterocycles and their evaluation as potential anti-bacterial agent

A library of biologically important heterocycles, viz. pyrazolyl pyrimidine-triones, bis(heterocyclyl)methanes were successfully synthesised by the condensation of barbituric acid, pyrazolone with an aldehyde and dimedone/4-hydoxy coumarin with various substituted aldehydes in aqueous medium at room temperature catalysed by nickel nanoparticles which proved to be an efficient magnetically recyclable catalyst. The method is simple, eco-friendly and gave excellent yields of the products without taking recourse to column chromatographic separation procedures. Computational method was employed to elucidate the selective formation of uncyclised product in reaction course. The biological activity of the synthesized compounds were investigated and the results demonstrated profound antibacterial activity.     

The effect of the presence of crown ether on ion transport across the lipid bilayer

We studied the electric properties of phosphatidylcholine bilayers modified with crown ether (dibenzo[18] crown-6). The studies were carried out for various crown ether concentrations in forming solutions and various potassium ion concentrations in electrolyte solutions. The presence of crown ether in the membrane influences the membrane's impedance; there is a reduction in its resistivity, a decrease in its resistance of phase transfer and an increase in its capacity of phase transfer with an increase in crown ether concentration in the bilayer and in K(+) ion concentration in the electrolyte solution.     

Synthesis of five libraries of 6,5-fused heterocycles to establish the importance of the heterocyclic core for antiplasmodial activity

Research has indicated that N-myristoyl transferase, an enzyme that catalyzes the addition of a myristate group to the N-terminal glycine residues of proteins, is involved in the myristoylation of more than 100 proteins. Genetic knockdown of the enzyme proved detrimental for the viability of the parasite P. knowlesi. A crystal structure of P. vivax N-myristoyl transferase (pvNMT), containing a 3-methyl benzofuran ligand has made it possible to assess key amino acid residue-ligand interactions. We synthesized five libraries of 6,5-fused heterocycles to establish the importance of the heterocycles as core scaffolds, as well as introduced various aromatic amides and esters to determine which carbonylic group affects the potency of each heterocyclic antiplasmodial agent.     

丛栽茶树树冠小气候及其对新梢生育和生化成分的影响

1 引言 为了获得优质高产的茶叶,需通过修剪养蓬等方法,使茶树形成宽广而整齐的树冠。丛栽茶树的树冠多呈馒头形,由于方位不同,形成了树冠内光、温、湿、风等因子的差异,因而影响了茶树的物候期及生理生化变化。因此,探讨树冠小气候特征及其对茶树新梢生育和生化成分的影响,在理论和生产实践上均有意义。有关这方面研究已有一些报道,但对茶树树冠小气候特征及其茶树新梢生育和品质成分的影响尚未见报     

Effect of second-sphere coordination 12. Adduct formation behavior of crown ethers with ammine complexes of ruthenium containing a protic ligand of other type than ammine

Adduct formation of pentaammineruthenium complexes involving a different type of protic ligand, such as imidazole, was investigated for a series of crown ethers with different ring size. Changes in redox potential and in absorption spectra of the complex were measured on addition of crown ether to the complex solution. The magnitude of the change in both properties is dependent on the ring size of crown ethers. ¹H-NMR spectra of the complex were measured in the presence of crown ethers in order to elucidate hydrogen bonding sites. The chemical shifts of NH proton of imidazol and ammine protons were measured at various concentrations of crown ethers. Adduct formation was discussed based on the features of dependences of those chemical shifts on crown ether concentration.     

Crown allometries are less responsive than stem allometry to tree size and habitat variations in an Indian monsoon forest

While theoretical allometric models postulate universal scaling exponents, empirical relationships between tree dimensions show marked variability that reflects changes in the biomass allocation pattern. As growth of the various tree compartments may be controlled by different functions, it is hypothesized that they may respond differently to factors of variation, resulting in variable tree morphologies and potentially in trade-offs between allometric relationships. We explore the variability of tree stem and crown allometries using a dataset of 1,729 trees located in an undisturbed wet evergreen forest of the Western Ghats, India. We specifically test whether species adult stature, terrain slope, tree size and crown light exposure affect the relationships between stem diameter and stem height (stem allometry), and between stem diameter and crown width, crown area and crown volume (crown allometries). Results show that both stem and crown allometries are subject to variations in relation to both endogenous (tree size, species adult stature) and exogenous (terrain slope, crown light exposure) factors. Stem allometry appears to be more affected by these factors than are crown allometries, including the stem diameter–crown volume relationship, which proved to be particularly stable. Our results support the idea that height is a prevailing adjustment factor for a tree facing variable growth (notably light) conditions, while stem diameter–crown volume allometry responds more to internal metabolic constraints. We ultimately discuss the various sources of variability in the stem and crown allometries of tropical trees that likely play an important role in forest community dynamics.     

Autotomy in a polychaete: Abscission zone at the base of the tentacular crown of Sabella penicillus

Summary Under various circumstances the tentacular crown of some sabellid polychaetes becomes detached from the body. Separation occurs always at a preestablished zone of abscission at the base of the crown. We used electron microscopy to study the abscission zone of Sabella penicillus, both in specimens whose crown was intact and in those whose crown had separated.The abscission zone is within the intermediate layer, between the crown skeleton and the body wall musculature, and only structures supported by the crown skeleton separate from the animal's body. Abscission involves a rupture of the paramyosin muscle cells which form bridges connecting extensions from the epimysium of the body wall musculature and from the cartilage matrix of the crown. After abscission the anterior and posterior ends of the cells remain in place on the crown and body respectively. Sabella penicillus appears able to control the loss of its tentacular crown, so this abscission is a kind of autotomy. Under some circumstances autotomy of the crown may permit escape or confer some surgical benefit to the animal. Using standard histology we found the same anatomical provision for crown abscission in a variety of sabellids. We conclude that differences in their capacities to autotomize the crown have a behavioral/physiological basis rather than an anatomical one.     

Effect of Crown Asymmetry on Size-Structure Dynamics of Plant Populations

The effect of crown asymmetry on the size–structure dynamicsof populations was evaluated using a spatial competition modelincorporating crown asymmetry. Computer simulations were carriedout with various combinations of density levels, spatial patterns,and degrees of asymmetry in competition to assess how they modifythe effect of crown asymmetry on size–structure dynamics. In the model, crown asymmetry is expressed by the crown-vector,or the vector linking the stem base and the centre of the projectedarea of the crown on the horizontal plane. Crown-vectors areassumed to develop in the manner by which crowns repel eachother. As crown-vectors develop, the positions of the crown-centresmove. Competition between individuals is expressed by a neighbourhoodmodel, in which individual growth is determined by the distancefrom, and size of, the neighbours' crown-centres. Generally, populations of individuals which developed asymmetriccrowns had larger survivorship, larger mean size, smaller coefficientsof variation and skewness, and a more regular spatial patternthan populations of individuals which developed symmetric crowns.The effect of crown symmetry is generally stronger in populationswith high density and a clumped spatial pattern. The effectof mortality caused by one-sided competition on size-structuredynamics was similar to that of crown asymmetry; mortality increasedmean size, reduced size hierarchy, and made the spatial patternmore regular. Because mortality was heavier in populations withoutcrown asymmetry, its effect on size-structure dynamics cancelledout, or overwhelmed, the effect of crown asymmetry in latergrowth stages. If crown asymmetry is associated with a reductionin growth, the effect of crown asymmetry is reduced. Nevertheless,the resultant population structure is different from that ofpopulations without crown asymmetry. Competition; crown asymmetry; morphological plasticity; neighbourhood interference model; size-structure dynamics     

Novel lopinavir analogues incorporating heterocyclic replacements of six-member cyclic urea--synthesis and structure-activity relationships

The HIV protease inhibitor ABT-378 (lopinavir) has a six-member cyclic urea in the P-2 position. A series of analogues in which the six-member cyclic urea is replaced by various heterocycles was synthesized and the structure-activity relationships explored.     

A conceptual model of tree behaviour improves the visual assessment of tree condition

A conceptual model describing the response of two Australian floodplain eucalypts, river red gum (Eucalyptus camaldulensis) and black box (Eucalyptus largiflorens), to changes in water availability was developed based on field observations. This model was incorporated into a percentage based visual method estimating two tree crown parameters, crown extent and density. Extent is the amount of foliage at the periphery of the assessable crown; density is the density of assessable crown foliage. Polychoric correlation was used to determine the level of agreement between two experienced observers assessing river red gum and black box trees using a simple percentage scale and a percentage scale supported by the conceptual model. Trees were evaluated using the model by determining their position on a trajectory of water stress related decline and response. In both cases observer estimates of crown extent and density were significantly correlated. With the exception of red gum crown density the correlation coefficients were higher for the model supported scale. Using a conceptual model of tree response to water availability improved observer agreement. Supporting subjective assessment systems with a conceptual model is recommended to improve observer agreement in cases where a distinct model of the dominant stressor can be defined.     

Root-infecting fungi associated with a decline of longleaf pine in the southeastern United States

A 35-year-old longleaf pine stand exhibited trees in various stages of decline. A study was conducted to determine root-infecting fungi and other abnormalities associated with varying degrees of crown symptoms. A four-class crown symptom rating system was devised according to ascending symptom severity. Leptographium procerum and L. terebrantis were significantly associated with increasing crown symptom severity. Heterobasidion annosum was also isolated in higher frequency as crown symptoms increased. Also, evidence of insects on roots increased as did amount of resinosis observed. Edaphic and silvicultural factors may interact with these pathogens and insects to pose a pathological limitation on longer-term management objectives. Further research is needed to determine relationships among various edaphic, silvicultural, and biological factors associated with the decline syndrome on this site. This revised version was published online in June 2006 with corrections to the Cover Date.     

Carbohydrate concentrations in crown fractions from winter oat during hardening at sub-zero temperatures

BACKGROUND AND AIMS: Contradictory results in correlation studies of plant carbohydrates with freezing tolerance may be because whole crown tissue is analysed for carbohydrates while differences exist in the survival of specific tissue within the crown. The aim of this study was to see if carbohydrate changes in tissue within oat crowns during second phase hardening (sub-zero hardening) are tissue specific. METHODS: The lower portion of oat (Avena sativa) crowns was exposed to mild grinding in a blender and the remaining crown meristem complex, consisting of tough root-like vessels, was ground in a device developed specifically for grinding cereal crown tissue. Carbohydrates were extracted by water and measured by HPLC. Carbohydrate concentrations were compared in the two regions of the crown before and after hardening at sub-zero temperatures. KEY RESULTS: Fructan of all size classes except DP>6 decreased during sub-zero hardening in both stems (base of leaf sheath) and crown meristem complex. Total simple sugar increase, including sucrose, was significantly higher in the crown meristem complex than in the stem. CONCLUSIONS: Results support the hypothesis that carbohydrate change in mildly frozen plants is tissue specific within crowns and underscore the need to evaluate specific tissue within the crown when correlating the biochemistry of plants with freezing tolerance.     

刺槐对降雨的截持作用

基于林冠截持和干流现象的物理机制,通过进行一些假设简化,建立了刺槐单株林木的林冠截持量和干流量的模型,并对它们的应用简单地提出了建议。     

Thermo-Mechanical Analysis of Restored Molar Tooth using Finite Element Analysis

The aim of the study is to find most optimum combination of crown material and adhesive to avoid loosening and thereby failure of restored tooth. This study describes the Thermo-Mechanical analysis of restored molar tooth crown for determination of the stress levels due to thermal and mechanical loads on restored molar tooth. The potential use of the 3-D model was demonstrated and analyzed using different materials for crown. Thermal strain, stress and deformation were measured at hot and cold conditions in ANSYS and correlated with analytical calculation and existing experimental data for model validation and optimization. It is concluded that amongst various material porcelain crown with composite resin adhesive cement closely simulates the behavior of natural crown and should ideally result into long lasting restoration.     

Bis[(benzo-15-crown-5)-15-yl methyl] pimelate forms ion channels in planar lipid bilayer: a novel model ion channel

Some crown ethers translocate cations across the liposomal membrane either by a carrier mechanism or by forming ion channels. We report formation of ion channels in lipid bilayer membranes by bis[(benzo-15-crown-5)-15-yl methyl] pimelate, a crown ether known to form ion inclusion complexes with alkali metal cations. The channels have characteristic long openings lasting several seconds and a low conductance (4 pS in 500 mM KCl and 2.5 pS in 500 mM NaCl). A model of the crown ether channel formed by stacking of four monomers is proposed. A large database of structural information on crown ethers and their ion inclusion complexes as well as large family of crown ethers with a variety of substitutions in the ring are commercially available. Thus the crown ether channel is an attractive model system to study the role of various chemical moieties in ion conduction which may provide deeper insight into understanding the mechanism(s) of selectivity, ion transport, etc. in biological ion channels.     

Models relating stem growth to crown length dynamics: application to loblolly pine and Norway spruce

We derive and analyze a model that relates the growth rate of cross-sectional area (‘csa’) at any height on the central stem of a tree to crown-length dynamics. The derivation is based, in part, on assumptions that (a) active csa on the central stem relates allometrically to the length of crown above the cross section, and (b) inactive csa is proportional to active csa within the crown. We also assume that the deactivation rate of csa beneath the crown is determined, in part, by the rate of crown rise. Integration of the growth-rate model under an additional assumption—that total crown length is constant after stand closure—provides a simple model of annual or periodic growth of total csa that can be fit to standard growth data. Three implications of the assumptions and integration are notable: (1) total csa within the crown scales allometrically with stem length above the cross section; (2) for a special case, total csa beneath the crown scales with stem length above the cross section; more generally, csa scales with a linear combination of the stem and crown lengths; and (3) the stem beneath the crown forms to approximate a frustum of a quadratic paraboloid. Basal area data from a loblolly pine (Pinus taeda L.) spacing trial show good agreement with (1) and (2), and with an empirical model developed from the special case of (2). Data from the plots of a Norway spruce (Picea abies (L.) Karst.) thinning trial, where crown length remained approximately constant, show good agreement with (2) and the empirical model. Prediction (3) is demonstrated by simulation.     

The crown-gap ratio (C) and crown cover: Derivation and simulation study

The crown-gap ratio C is defined as the mean distance between adjacent crowns divided by the mean crown diameter. Previous field studies have established that for a limited range of vegetation stands crown cover is related to C by a general function, viz. crown cover = k/(1 + C)², where k is a constant. In the present study we investigated the general derivation of the function which relates crown cover to C. The function was then used to determine values for k, a range of point distributions being simulated from semi-regular to clumped, with mixtures of crown sizes. The relationship between crown cover and 1/(1 + C)² was linear in all cases tested (R²= 1.0). The value of k was shown to depend on the sampling technique used, the degree of clumping, and the range in crown sizes permitted. The variation in k was reduced by using a specific sampling method and limiting the range of spatial distributions and crown sizes considered. The constraints imposed were:

• 1 Sampling followed a zig-zag transect (Delaunay two-sided model).
• 2 Point distributions were not overly clumped.
• 3 The range of crown diameters approximated a Gaussian distribution with a relative range of 1–4.

Given these constraints the value of k was determined to be 0.806 with a variance of less than 2%. A table is given to convert values for C into crown cover percentages and, if required, to calculate foliage cover per cent. The constraints imposed are considered to be within conditions normally encountered in the field, making the use of C an accurate and simple method by which to estimate crown or foliage cover per cent.     

辽东栎林内不同小生境下幼树植冠构型分析

以黄土高原黄龙山林区辽东栎林内3个小生境（林下、林隙、林缘）下辽东栎天然更新幼树为研究对象,采用典型抽样法对辽东栎幼树侧枝、叶片和树冠的空间分布状况以及生物量分配状况进行调查分析,探讨微生境与幼树植冠构型特征的关系,明确辽东栎幼树对不同小生境的适应策略,为栎林经营和林分结构优化提供理论依据。结果显示：（1）3种生境下辽东栎幼树构型发生了可塑性变化,林下幼树树冠层次比较单一,林隙与林缘的幼树树冠层次更加丰富。（2）由林下至林缘,幼树的树高、枝下高呈逐渐减小的趋势,而地径变化趋势与之相反;幼树的冠幅、树冠面积、树冠率呈先增加后减小的趋势,并且林下与林隙、林缘的差异显著;幼树的总体分枝率、逐步分枝率、枝径比呈先增加后减小的趋势。（3）3种生境下,幼树的一级枝的枝长、直径与倾角随着树高的增加而呈减小的趋势,但3种生境的差异不显著;林下一级枝主要分布在冠层中上部,而林隙与林缘一级枝主要分布在冠层中下、中上部。（4）由林下至林缘幼树叶长、叶宽、单叶面积和比叶面积逐渐降低,而单株叶数、叶总面积、叶面积指数呈先增大后减小趋势;与其他2种生境相比林下叶片分布趋于冠层上部。（5）幼树地上部分生物量中林下主干生物量占83%,枝和叶生物量只占17%;而林隙与林缘虽然各部位生物量有所差异但比例基本一致,其中主干占66%左右,枝和叶生物量占34%左右。研究表明,林隙生境下幼树的构型优于林缘和林下生境,在今后栎林的经营中,可以通过适当间伐来增加林隙数量,为森林更新和结构的优化提供有利条件。     

Cyclopentane-nucleobase coupling in the synthesis of carbocyclic L-nucleosides: is a SN2-reaction an alternative to the Mitsunobu-reaction?

Several carbocyclic L-nucleosides have been synthesized by coupling a cyclopentane-system with heterocycles according to a modified Mitsunobu-protocol. This reaction gave two regioisomers, the N1-alkylated product and an unwanted O(2)-product. A simple S(N)2-reaction has been investigated as an alternative for such couplings.