栲树不同生长发育阶段的枝系特征分析

对浙江天童国家森林公园内常绿阔叶优势树种栲树(Castanopsis fargesii)不同发育阶段植冠内的分枝式样特征进行了统计分析。结果表明：栲树在不同发育阶段的总体分枝率和逐步分枝率有显著变化,幼苗和幼树阶段的分枝率较低,而成株阶段的分枝率较高;幼树阶段的枝条长度、枝倾角和叶倾角明显大于幼苗和成株阶段,表现为明显的高生长对策;叶片配置在不同枝系上有较大差异,叶片主要集中于植冠内一级枝和二级枝上;叶片的大小从幼苗、幼树到成株阶段逐渐增大。研究结果表明栲树在生活史的不同生长发育阶段,分枝式样表现出一定的可塑性,反映了不同的适应对策。     

胚胎肾分支形态发生调控因素

胚胎肾发育最初阶段是中肾导管尾端在胶质细胞源性神经营养因子诱导下向背侧长出输尿管芽,而后成纤维细胞生长因子、肝细胞生长因子、骨形成蛋白、基质金属蛋白酶、整合素和粘附分子相继表达,作用于输尿管芽和间充质细胞,诱导分支形态发生,包括输尿管芽向间充质侵入、延伸以及间充质细胞向上皮转化。上述这些分子在功能上存在部分重叠与拮抗,维持细胞增殖和分化的平衡,从而保证输尿管芽形成正常的分支结构。本文对肾脏发育时期分支形态发生的调控因素进行综述。     

Estimation in a Continuous State Space Branching Process

In some biological studies it is impossible to count the total number of individuals, but the size of the population can be measured by it's weight or volume. The probability of extinction of such populations is an interesting parameter, e.g. in modelling of epidemics. In this paper, the estimation of extinction probability and the moments of the offspring distribution is studied and the asymptotic properties of the estimators are discussed.     

Identification of Multiple Phosphorylation Sites on Maize Endosperm Starch Branching Enzyme IIb,a Key Enzyme in Amylopectin Biosynthesis

Starch branching enzyme IIb (SBEIIb) plays a crucial role in amylopectin biosynthesis in maize endosperm by defining the structural and functional properties of storage starch and is regulated by protein phosphorylation. Native and recombinant maize SBEIIb were used as substrates for amyloplast protein kinases to identify phosphorylation sites on the protein. A multidisciplinary approach involving bioinformatics, site-directed mutagenesis, and mass spectrometry identified three phosphorylation sites at Ser residues: Ser⁶⁴⁹, Ser²⁸⁶, and Ser²⁹⁷. Two Ca²⁺-dependent protein kinase activities were partially purified from amyloplasts, termed K1, responsible for Ser⁶⁴⁹ and Ser²⁸⁶ phosphorylation, and K2, responsible for Ser⁶⁴⁹ and Ser²⁹⁷ phosphorylation. The Ser²⁸⁶ and Ser²⁹⁷ phosphorylation sites are conserved in all plant branching enzymes and are located at opposite openings of the 8-stranded parallel β-barrel of the active site, which is involved with substrate binding and catalysis. Molecular dynamics simulation analysis indicates that phospho-Ser²⁹⁷ forms a stable salt bridge with Arg⁶⁶⁵, part of a conserved Cys-containing domain in plant branching enzymes. Ser⁶⁴⁹ conservation appears confined to the enzyme in cereals and is not universal, and is presumably associated with functions specific to seed storage. The implications of SBEIIb phosphorylation are considered in terms of the role of the enzyme and the importance of starch biosynthesis for yield and biotechnological application.     

植物茎分枝的分子调控

植物茎分枝结构决定了不同植物的不同形态结构.本文从腋生分生组织的发生、腋芽的生长两个方面综述了近年来植物分枝发生发育相关的分子机理研究及其进展.发现在不同植物中腋分生组织形成的基本机制是相似的,LS（lateral suppressor）及其同源基因在不同植物中都参与腋生分生组织的形成,而BL(blind)及其同源基因也参与调控腋生分生组织的形成.腋生分生组织的形成可能也是受激素调控的.目前,对腋芽生长的分子调控机制的认识主要集中于生长素通过二级信使的作用调控腋芽的生长.而生长素调控腋芽生长的机制已经较为清楚的有两条途径：一是生长素通过抑制细胞分裂素合成来调控腋芽的生长;另一途径是一种类胡萝卜素衍生的信号物质参与生长素的运输调控(MAX途径)来调控腋芽的生长.最新研究表明,TB1的拟南芥同源基因在MAX途径的下游负调控腋芽的生长.此外,增强表达OsNAC2也促进腋芽的生长.     

On Branching Processes and the Early Stages of the Spread of an Epidemic

Branchingprocess(BP)isusedtomodeltheearlystagesofthespreadofasexuallytransmitteddisease.TheearlystagesofAIDSspreadwhichistransmittedbothhomosexuallyandheterosexuallyarestudiedasaBP.     

Branching stochastic processes with immigration in analysis of renewing cell populations

This paper considers the utility of a new class of stochastic branching processes with non-homogeneous immigration in modeling complex renewing cell systems. Such systems typically include the population of stem cells that provides an inexhaustible supply of cells necessary for maintaining the cellular composition of a tissue. A stem cell may be induced to transform (differentiate) into a progenitor cell. Progenitor cells retain the ability to proliferate and their function is believed to provide a quick proliferative response to an increased demand for cells in the population. There may be several sub-types of progenitor cells. Terminally differentiated cells do not divide under normal conditions; they are responsible for maintaining tissue-specific functions. Recent advancements in experimental techniques offer considerable scope for quantitative studies of in vivo cell kinetics based on stochastic modeling of renewing cell populations. However, no ready-made theory is currently available to take full advantage of these advancements. This paper introduces such a theory with a special focus on its feasibility in biological applications.     

腐植酸对植物生理活动的影响

本文介绍了腐植酸的形成、提取、分类以及活性基团等方面的特征。腐植酸能影响植物的多种生理活动,包括植物的生长、营养元素的吸收、蛋白质和核酸的合长、光合作用、呼吸作用以及有些酶的活性等。腐植酸对植物的这些作用受自身不同成分、浓度、植物种类、外界营养条件等多方面的影响。本文也从细胞或分子水平讨论了腐植酸促进植物生长、影响营养元素吸收促进呼吸作用的机理。     

Poisson convergence on continuous time Branching Random Walks and multistage carcinogenesis

A theorem for Poisson convergence on realizations of twodimensional Branching Random Walks with an underlying continuous time Markov Branching Process is proved. This result can be used to gain an approximation for the number of cells having sustained a certain deficiency after a long time in multistage carcinogenesis.     

Modeling and numerical simulation of biotin carboxylase kinetics: implications for half-sites reactivity

Biotin carboxylase catalyzes the ATP-dependent carboxylation of biotin and is one component of the multienzyme complex acetyl-CoA carboxylase that catalyzes the first committed step in fatty acid synthesis in all organisms. In Escherichia coli, biotin carboxylase exists as a homodimer where each subunit contains a complete active site. In a previous study (Janiyani, K., Bordelon, T., Waldrop, G.L., Cronan Jr., J.E., 2001. J. Biol. Chem. 276, 29864-29870), hybrid dimers were constructed where one subunit was wild-type and the other contained an active site mutation that reduced activity at least 100-fold. The activity of the hybrid dimers was only slightly greater than the activity of the mutant homodimers and far less than the expected 50% activity for completely independent active sites. Thus, there is communication between the two subunits of biotin carboxylase. The dominant negative effect of the mutations on the wild-type active site was interpreted as alternating catalytic cycles of the active sites in the homodimer. In order to test the hypothesis of oscillating catalytic cycles, mathematical modeling and numerical simulations of the kinetics of wild-type, hybrid dimers, and mutant homodimers of biotin carboxylase were performed. Numerical simulations of biotin carboxylase kinetics were the most similar to the experimental data when an oscillating active site model was used. In contrast, alternative models where the active sites were independent did not agree with the experimental data. Thus, the numerical simulations of the proposed kinetic model support the hypothesis that the two active sites of biotin carboxylase alternate their catalytic cycles.     

桃树修剪分枝模式的模拟

在不同修剪手法下,对栽培桃树(Prunuspersica(L.)Batsch)不同母枝上的分枝模式进行了比较研究.从分枝模式来看:修剪后的母枝基本由3个不同的区域组成,基部是不萌发的潜伏芽形成的未分枝区域;中部是延迟分枝和多次分枝组成的分枝区域(主要的枝条类型有短枝、长枝和多次枝);顶部是被剪除的部分.我们通过隐式半马尔可夫模型来模拟这一分枝模式,主要是定量描述1次枝和多次枝在母枝上的数量及其分布状况.在上述模型中,未分枝区、延迟分枝区和多次分枝区称为瞬时态,被剪除的部分称为吸收态.模拟的结果与观察的结果进行对比后发现,两者具有很好的一致性.这说明隐式半马尔可夫模型是模拟植物分枝过程的一种有效方法,尽管隐式半马尔可夫链模型只是一个描述性的模型,但仍能对其所描述的生物现象进行解释,在预测修剪手法对母枝分枝模式影响方面比传统的方法具有明显的优势.本研究结果是建立三维虚拟桃树树冠分枝结构的基础.     

桃树修剪分枝模式的模拟

在不同修剪手法下,对栽培桃树(Prunuspersica(L.)Batsch)不同母枝上的分枝模式进行了比较研究。从分枝模式来看修剪后的母枝基本由3个不同的区域组成,基部是不萌发的潜伏芽形成的未分枝区域;中部是延迟分枝和多次分枝组成的分枝区域(主要的枝条类型有短枝、长枝和多次枝);顶部是被剪除的部分。我们通过隐式半马尔可夫模型来模拟这一分枝模式,主要是定量描述1次枝和多次枝在母枝上的数量及其分布状况。在上述模型中,未分枝区、延迟分枝区和多次分枝区称为瞬时态,被剪除的部分称为吸收态。模拟的结果与观察的结果进行对比后发现,两者具有很好的一致性。这说明隐式半马尔可夫模型是模拟植物分枝过程的一种有效方法,尽管隐式半马尔可夫链模型只是一个描述性的模型,但仍能对其所描述的生物现象进行解释,在预测修剪手法对母枝分枝模式影响方面比传统的方法具有明显的优势。本研究结果是建立三维虚拟桃树树冠分枝结构的基础。     

Dynamic regulation of growing domains for elongating and branching morphogenesis in plants

With their continuous growth, understanding how plant shapes form is fundamentally linked to understanding how growth rates are controlled across different regions of the plant. Much of a plant's architecture is generated in shoots and roots, where fast growth in tips contrasts with slow growth in supporting stalks. Shapes can be determined by where the boundaries between fast- and slow-growing regions are positioned, determining whether tips elongate, branch, or cease to grow. Across plants, there is a diversity in the cell wall chemistry through which growth operates. However, prototypical morphologies, such as tip growth and branching, suggest there are common dynamic constraints in localizing chemical growth catalysts. We have used Turing-type reaction-diffusion mechanisms to model this spatial localization and the resulting growth trajectories, characterizing the chemistry-growth feedback necessary for maintaining tip growth and for inducing branching. The mechanism defining the boundaries between fast- and slow-growing regions not only affects tip shape, it must be able to form new boundaries when the pattern-forming dynamics break symmetry, for instance in the branching of a tip. In previous work, we used an arbitrary concentration threshold to switch between two dynamic regimes of the growth catalyst in order to define growth boundaries. Here, we present a chemical dynamic basis for this threshold, in which feedback between two pattern-forming mechanisms controls the extent of the regions in which fast growth occurs. This provides a general self-contained mechanism for growth control in plant morphogenesis (not relying on external cues) which can account for both simple tip extension and symmetry-breaking branching phenomena.     

云南地区种子植物多样性分布格局和多样性分化特点研究

利用大尺度的植物分布信息结合地理信息系统和数理统计分析,探讨了云南种子植物多样性的地理分布格局和多样性分化特点。结果表明,从科到属和种,植物多样性和区系分化强度的数据集离散程度均呈递增趋势。相对属和种而言,科的多样性的空间分异和高值区域并不明显,这可能与科、属、种所代表的不同地质历史时期有关;南部地区属和种的多样性明显高于除滇西北以外的大部分地区。种的多样性分布中心主要集中在滇西北地区、云南南部地区、哀牢山、无量山地区和昆明地区,这可能与生境异质性和热量条件有关。相对科而言,属的区系分化强度的空间分异更为明显,并与物种多样性的分布格局比较接近,暗示着植物多样性与区系分化之间的密切联系。相对科而言,属的区系分化中心高值区域更为明显。总体上,云南地区植物多样性的分布格局及其分化可能与其生境、热量条件和地质历史有关。     

内生真菌对植物生长发育及抗逆性的影响

本文从内生真菌的涵义和基本生物学特征出发,以国内外近二十年来关于内生真菌与植物关系的研究情况作了综述。主要包括内生真菌的检测、鉴定和转染,内生真菌对植物生长发育与抗逆性的影响,以及内生真菌在农业及其他相关领域的应用前景。文中提及作者近期开展的关于内生真菌对黑麦草抗旱性影响的研究课题及其初步进展。     

Estimating the Total Rate of DNA Replication Using Branching Processes

Increasing the knowledge of various cell cycle kinetic parameters, such as the length of the cell cycle and its different phases, is of considerable importance for several purposes including tumor diagnostics and treatment in clinical health care and a deepened understanding of tumor growth mechanisms. Of particular interest as a prognostic factor in different cancer forms is the S phase, during which DNA is replicated. In the present paper, we estimate the DNA replication rate and the S phase length from bromodeoxyuridine-DNA flow cytometry data. The mathematical analysis is based on a branching process model, paired with an assumed gamma distribution for the S phase duration, with which the DNA distribution of S phase cells can be expressed in terms of the DNA replication rate. Flow cytometry data typically contains rather large measurement variations, however, and we employ nonparametric deconvolution to estimate the underlying DNA distribution of S phase cells; an estimate of the DNA replication rate is then provided by this distribution and the mathematical model.     

The Growth and Carbon Allocation Patterns of White Clover (Trifolium repens L.) Plants of Contrasting Branching Structure

The growth, morphology and carbon allocation patterns of F1progeny white clover (Trifolium repens L.) plants selected foreither low (‘LBF’) or high (‘HBF’) frequencyof stolon branching were compared in two controlled-environmentexperiments. Selections from within both a small-leaved (‘GrasslandsTahora’) and a large-leaved (‘Grasslands Kopu’)clover cultivar were compared, and plants were grown under arelatively lenient defoliation treatment (expt 1) or under threelevels of defoliation seventy (expt 2). Carbon allocation patternswere measured by ¹⁴CO₂ pulse-chase labelling using fully unfoldedleaves on the main (parent) stolon. LBF and HBF displayed consistent differences in the selectedcharacter though, within cultivars, the difference between selectionswas most pronounced for Kopu. The selections developed fundamentallydifferent branching structures resulting from differences inbranching frequency, with total branch weight per plant averaging122 mg for LBF and 399 mg for HBF (mean of both experiments).More C moved from parent stolon leaves to branches in HBF thanin LBF (mean 22.6% vs. 15.1% respectively of the ¹⁴C exportedfrom source leaves). More C also moved to stolon tissue in HBF,but, counterbalancing this and the difference in allocationto branches, less moved to developing leaves and roots on theparent stolon itself compared to LBF. However, the total weightof developing leaves and roots per parent stolon was generallygreater in HBF than in LBF, probably reflecting greater C importby these sinks from the higher number of branches present perplant in the former selection. HBF plants were consistentlylarger at harvest than LBF plants. There were no defoliationtreatment x selection interactions in C allocation patternsin expt 2. The implications of the results for plant performancein grazed pastures are discussed. Branching, carbon translocation, defoliation, growth, morphology, Trifolium repens, white clover     

Strigolactones,a novel class of plant hormone controlling shoot branching

For several decades, auxin and cytokinin were the only two hormones known to be involved in the control of shoot branching through apical dominance, a process where the shoot apex producing auxin inhibits the outgrowth of axillary buds located below. Grafting studies with high branching mutants and cloning of the mutated genes demonstrated the existence of a novel long distance carotenoid derived signal which acted as a branching inhibitor. Recently, this branching inhibitor has been shown to belong to the strigolactones, a group of small molecules already known to be produced by roots, exuded in the rhizosphere and as having a role in both parasitic and symbiotic interactions.     

植物干旱诱导蛋白研究进展

植物在干旱环境下会产生干旱诱导蛋白.干旱诱导蛋白与干旱诱导基因是当前植物逆境生理学研究的热点之一.根据近年的研究进展,本文就干旱诱导蛋白的类型、特性、功能作了简要综述.