Mechanical Forces Program the Orientation of Cell Division during Airway Tube Morphogenesis

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Quantitative Analyses of Cell Division in Plants

At the molecular level regulatory interactions between cell cycle genes are being uncovered rapidly, but less progress is made in unravelling how these molecular events regulate growth processes at the level of cells and of the whole organism. The main obstacle is the absence of a set of analytical tools that are powerful enough to determine pertinent parameters and, at the same time, relatively easy to use by non-specialized laboratories. Appropriate methodology to obtain this type of data has been pioneered in the first half of the last century and is now commonly defined as ‘kinematic analysis’. Unfortunately, the laborious nature of these analyses and the relatively complex numerical methods used, have limited their use to only a handful of specialized research groups. In this article we attempt to present an accessible entry to this methodology, particularly in terms of the mathematical framework. We start describing the simplest possible system, i.e., a virtually homogenous cell suspension culture. Then, we outline the analysis of dicotyledonous leaves, root tips, monocotyledonous leaves, and finally shoot apical meristems. For each of these systems we discuss the details of the calculation of cell division parameters such as cell cycle duration, size of the meristem and number of cells contained in it, which enables answering fundamental questions about the relative contribution of differences in cell production and cell size to variation in growth. In addition, we discuss the assumptions and limitations of these and alternative methodologies with the aim to facilitate the choice of appropriate analyses depending on the specific research question.     

SLC/AGO1基因控制拟南芥细胞分裂与定向伸长

植物通过控制细胞分裂和伸长决定器官的形状。为了研究器官形状决定的分子机理,通过EMS诱变分离得到一个叶形细长的拟南芥突变体。细胞生物学观察发现,该基因突变不仅影响了生长点中的细胞分裂,也影响了叶片细胞的形状和数目,其表皮细胞凸起数明显减少,呈单轴向伸长,因此将该突变体定名为slender leaves and cells（slc）。有趣的是,不同组织内细胞分裂和伸长受到不同程度的影响,说明SLC基因在协调细胞分裂和伸长过程中起关键作用。图位克隆结果表明,SLC与小RNA介导的基因沉默相关基因AGO1等位,其第574位组氨酸突变为酪氨酸。slc和ago1杂交F1代植物呈现突变体表型,证明AGO1和SLC确实为同一基因。以上结果表明,SLC/AGO1所介导的转录后基因沉默对控制植物器官和细胞形状决定均起重要作用。     

细胞不对称分裂

细胞不对称分裂是多细胞生物发育的基础。细胞不对称分裂的重要特征是细胞命运决定子在细胞分裂期间的不对称分离。细胞不对称分裂一般要经历4个步骤：在细胞中建立一个极性轴;沿此轴定向并形成纺锤体;细胞命运决定子沿极性轴作极性分布;细胞分裂后,不同的细胞命运决定子指导决定细胞的不同命运。     

曼陀罗叶水浸液对大豆幼根生长及细胞分裂的影响

以曼陀罗叶干粉为供体,大豆种子为受体,用室内培养皿法研究了曼陀罗叶水浸液化感胁迫对大豆种子萌发、幼根生长、根毛发育和根尖细胞分裂的影响。结果表明:各试验浓度的曼陀罗叶干粉水浸提液均抑制了大豆种子的萌发以及幼根和侧根的生长,且幼根生长随胁迫浓度的增加呈现逐渐缩短变粗变褐的趋势;化感胁迫还使根尖分生区细胞的染色体畸变和微核高频率发生。根毛发生和根尖细胞的分裂对化感胁迫都表现出"低促高抑"的响应,即轻度胁迫能显著促进根毛的生长并提高根尖细胞的分裂指数,而高度胁迫对根毛的生长有极显著的抑制作用,且使根尖细胞的分裂指数显著下降。     

The Bacterial Cell Cycle: DNA Replication,Nucleoid Segregation,and Cell Division

Data on the bacterial cell cycle published in the last 10–15 years are considered, with a special stress on studies of nucleoid segregation between dividing cells. The degree of similarity between the eukaryotic mitotic apparatus and the apparatus performing nucleoid separation is discussed.__________Translated from Mikrobiologiya, Vol. 74, No. 4, 2005, pp. 437–451.Original Russian Text Copyright © 2005 by Prozorov.     

生长素对拟南芥叶片发育调控的研究进展

叶片（包括子叶）是茎端分生组织产生的第一类侧生器官,在植物发育中具有重要地位。早期叶片发育包括三个主要过程：叶原基的起始,叶片腹背性的建立和叶片的延展。大量证据表明叶片发育受到体内遗传机制和体外环境因子的双重调节。植物激素,尤其是生长素在协调体内外调节机制中起着不可或缺的作用。生长素的稳态调控、极性运输和信号转导影响叶片发育的全过程。本文着重介绍生长素在叶片生长发育和形态建成中的调控作用,试图了解复杂叶片发育调控网络。     

B细胞不对称分裂

细胞的不对称分裂对于细胞多样性产生的重要性已经被大部分人所认识。B细胞的不对称分裂首先是在抗体类别转换的研究中发现的。最近,美国5科学家对B细胞在免疫发生中心中不对称分裂的原因进行了探索。结果发表在2012年1月20日出版的《Science》中。B细胞的不对称分裂参与体液免疫的抗体类别转换和抗体亲和力成熟过程。对于其机制仍不清楚,但目前研究初步提示细胞内分子的不对称分布是其发生的上游因素。并且B细胞的不对称分裂可能与不对称抗原分离可能在抗体亲和力成熟过程中具有独立协同作用。     

Targeted manipulation of leaf form via local growth repression

A classical view is that leaf shape is the result of local promotion of growth linked to cell proliferation. However, an alternative hypothesis is that leaf form is the result of local repression of growth in an otherwise growing system. Here we show that leaf form can indeed be manipulated in a directed fashion by local repression of growth. We show that targeting expression of an inhibitor of a cyclin-dependent kinase (KRP1) to the sinus area of developing leaves of Arabidopsis leads to local growth repression and the formation of organs with extreme lobing, including generation of leaflet-like organs. Directing KRP1 expression to other regions of the leaf using an miRNA target sequence tagging approach also leads to predictable novel leaf forms, and repression of growth in the leaf margin blocks the outgrowth of lobes, leading to a smoother perimeter. In addition, we show that decreased growth around the perimeter and across the leaf abaxial surface leads to a change in 3D form, as predicted by mechanical models of leaf growth. Our analysis provides experimental evidence that local repression of growth influences leaf shape, suggesting that it could be part of the mechanism of morphogenesis in plants in the context of an otherwise growing system.     

Cortical and Nuclear Events During Cell Division and Resting Cyst Formation in Colpoda inflata

Nuclear and cortical phenomena during dividing and resting cyst formation of Colpoda inflata are described. Cell division forms a cyst and produces two or four tomites. In each tomite, the right oral field results from the proliferation of the anterior extreme of a single kinety, and the left oral field results from the proliferation of four, five, or six somatic kineties. After macronuclear division, each macronuclear mass undergoes a chromatinic extrusion process. During resting cyst formation, the oral infraciliature of the vegetative cell is resorbed. The somatic kineties dispose in a radial way and some pairs of kinetosomes disappear. As in cell division, there is an extrusion process. From these results we conclude that the resting cysts of Colpoda inflata cannot be included in any group of the previous classifications for hypotrich resting cysts. Thus, we propose a new additional group to Walker and Maugel's classification called PKR (partial-kinetosome-resorbing) cysts.     

Cytokinin-Regulated Mesophyll Cell Division and Expansion during Development of Cucurbita pepo Leaves

The role of cytokinins in the development of mesophyll structure was studied in developing pumpkin Cucurbita pepo L. leaves. Leaves were treated with cytokinins at different stages of growth: when they reached 25 or 50% of their final size (S _max), immediately after leaf growth ceased, and during senescence. At the early stages of leaf development, treatment with exogenous benzyladenine accelerated division of mesophyll cells. At the later stages of development, BA treatment activated expansion of growing cells and those, which have just accomplished their growth. The exogenous cytokinin did not affect the senescent leaf cells. The content of endogenous cytokinins changed during mesophyll development. The juvenile leaves (25% of S _max) were characterized by low level of these phytohormones. In the expanding leaves (50% of S _max), the content of phytohormones increased and decreased when leaf growth ceased. In the senescent leaves, the cytokinin content decreased markedly. It was concluded that the response of mesophyll cells to cytokinin depended on the cell growth phase at the moment of hormone action. Furthermore, in the young leaves, lower cytokinin concentrations were required for division of mesophyll cells in vivo than for cell expansion at the final stage of leaf development.     

Rho of Plants GTPases and Cytoskeletal Elements Control Nuclear Positioning and Asymmetric Cell Division during Physcomitrella patens Branching

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Cell Division and Expansion in the Growth of the Leaf

Volumes and numbers of cells were determined at different stagesof development of the fifth leaf of Lupinus albus, and eachof the second pair and the tenth leaf of Helianthus annuus.In the case of the second pair of sunflower leaves the valuescover the whole life of the leaf from initiation to senescence. During both primordial development and the ensuing ‘grandperiod of growth’ division is the determinant of growth.About 10 per cent. of the cells in the fully grown leaf arelaid down before leaf-emergence; the remaining 90 per cent.are formed during unfolding. Division does not cease in thelupin leaf or the second pair of sunflower leaves until theyhave reached half their maximum area. The tenth leaf, on theother hand, is as much as three-quarters fully grown beforedivision ceases. Cell expansion commences soon after leaf initiation and continuesthroughout the life of the leaf. With lupin and the second pairof sunflower leaves there is a fourfold increase in the averagevolume of the cells before emergence from the apical region.During unfolding, there is a further tenfold increase in theaverage volume of the cells of the lupin leaf, and a twentyfoldincrease with the second pair of sunflower leaves. Expansioncontinues after the cessation of division but this further increasein volume is comparatively small. The data are discussed in relation to the ‘two phase’hypothesis of leaf development.     

The Roles of Cell Division and Cell Expansion in the Growth of Alfalfa Leaf Mesophyll

Leaf mesophyll of Medicago sativa (L.) was investigated to determinethe roles of cell division and cell expansion in tissue growth.Samples of leaf tissue were macerated, stained, and squashed.The slides were studied under a phase microscope to determinethe percentage of recently divided cells and the average celldiameter for leaflets of varying lengths. Cell division wasgreatest in young leaflets and virtually ceased as a leaf lengthof 12 mm was attained. For leaflets less than 12 mm in length,the rate of increase in cell size appeared to be inversely associatedto the degree of cell division. For alfalfa leaflets greaterthan 12 mm in length, the mean cell size increased in proportionto leaf length since cell division had virtually ceased.     

Unconventional Cell Division Cycles from Marine-Derived Yeasts

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Host-Polarized Cell Growth in Animal Symbionts

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CPPU对瓠瓜单性结实的诱导作用及对细胞分裂和内源激素水平的影响

NAA和GA3处理未经授粉的瓠瓜子房不能显著促进其细胞分裂和膨大而产生单性结实果,而CP-PU处理未经授粉的瓠瓜子房则使其细胞数目和中果皮单个细胞横切面积以及单果重都显著高于未授粉和人工授粉果.经CPPU诱导座果而产生的单性结实果中IAA、ABA和t-zeatin的浓度均不同程度地低于人工授粉和不授粉果实.     

Ectopic BASL Reveals Tissue Cell Polarity throughout Leaf Development in Arabidopsis thaliana

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丛藓科（Pottiaceae）植物叶细胞形态特征及其系统学意义

通过光学显微镜（LM）和扫描电镜（SEM）观察了17属国产丛藓科（Pottiaceae）植物叶中上部细胞的形态特征,结果表明：丛藓科植物的叶中上部细胞的形状、大小及表面形态等特征上具较大相似性;据细胞表面特征,叶细胞可分为无疣或具乳突、具圆疣以及具分枝的马蹄形疣3种类型,且该特征在丛藓科不同属、种间有较大的区别。因此,叶细胞形态特征可为丛藓科植物属级和亚科级的划分提供细胞形态学依据。