ERECTA family genes regulate development of cotyledons during embryogenesis

Receptor-like kinases are important regulators of plant growth. Often a single receptor is involved in regulation of multiple developmental processes in a variety of tissues. ERECTA family (ERf) receptors have previously been linked with stomata development, above-ground organ elongation, shoot apical meristem function, flower differentiation and biotic/abiotic stresses. Here we explore the role of these genes during embryogenesis. ERfs are expressed in the developing embryo, where their expression is progressively limited to the upper half of the embryo. During embryogenesis ERfs redundantly stimulate the growth of cotyledons by promoting cell proliferation and inhibiting premature stomata differentiation.     

Intercellular Correlations: Relation between DNA Synthesis and Cell Division in Early Stages of in Vitro Bud Neoformation

As well as showing the existence, during the first stages of in vitro bud neoformation, of cell populations in a tissue composed of a single cell layer (stem epidermis of Torenia fournieri Lind), some new physiological characteristics of mitosis are defined. Most of the cells which divide during organogenesis synthesize their DNA between 20 and 48 hours of culture. On an epidermal strip (10 × 2.5 millimeters composed of about 5,500 cells) 20% of the original cells enter the S-phase. The first division takes place at the 20-hour stage after the entry into the S-phase of a cell population of about 25 cells. Almost none of the cells of this population divide. The greatest percentage of divisions occurs in cells which synthesize DNA near the 48-hour stage. The relation [Formula: see text] has a value of about 25 at the beginning of cell division (20 hours) and falls to a value of about 1.4 for cells which synthesize DNA near the 48-hour stage. A hypothesis of the existence of a mitotic stimulant in the epidermis is put forward; this stimulant, at first weak, increases progressively.     

An Equatorial Contractile Mechanism Drives Cell Elongation but not Cell Division

Cell shape changes and proliferation are two fundamental strategies for morphogenesis in animal development. During embryogenesis of the simple chordate Ciona intestinalis, elongation of individual notochord cells constitutes a crucial stage of notochord growth, which contributes to the establishment of the larval body plan. The mechanism of cell elongation is elusive. Here we show that although notochord cells do not divide, they use a cytokinesis-like actomyosin mechanism to drive cell elongation. The actomyosin network forming at the equator of each notochord cell includes phosphorylated myosin regulatory light chain, α-actinin, cofilin, tropomyosin, and talin. We demonstrate that cofilin and α-actinin are two crucial components for cell elongation. Cortical flow contributes to the assembly of the actomyosin ring. Similar to cytokinetic cells, membrane blebs that cause local contractions form at the basal cortex next to the equator and participate in force generation. We present a model in which the cooperation of equatorial actomyosin ring-based constriction and bleb-associated contractions at the basal cortex promotes cell elongation. Our results demonstrate that a cytokinesis-like contractile mechanism is co-opted in a completely different developmental scenario to achieve cell shape change instead of cell division. We discuss the occurrences of actomyosin rings aside from cell division, suggesting that circumferential contraction is an evolutionally conserved mechanism to drive cell or tissue elongation.     

Proliferation of Luteal Steroidogenic Cells in Cattle

The rapid growth of the corpus luteum (CL) after ovulation is believed to be mainly due to an increase in the size of luteal cells (hypertrophy) rather than an increase in their number. However, the relationship between luteal growth and the proliferation of luteal steroidogenic cells (LSCs) is not fully understood. One goal of the present study was to determine whether LSCs proliferate during CL growth. A second goal was to determine whether luteinizing hormone (LH), which is known have roles in the proliferation and differentiation of follicular cells, also affects the proliferation of LSCs. Ki-67 (a cell proliferation marker) was expressed during the early, developing and mid luteal stages and some Ki-67-positive cells co-expressed HSD3B (a steroidogenic marker). DNA content in LSCs isolated from the developing CL increased much more rapidly (indicating rapid growth) than did DNA content in LSCs isolated from the mid CL. The cell cycle-progressive genes CCND2 (cyclin D2) and CCNE1 (cyclin E1) mRNA were expressed more strongly in the small luteal cells than in the large luteal cells. LH decreased the rate of increase of DNA in LSCs isolated from the mid luteal stage but not in LSCs from the developing stage. LH suppressed CCND2 expression in LSCs from the mid luteal stage but not from the developing luteal stage. Furthermore, LH receptor (LHCGR) mRNA expression was higher at the mid luteal stage than at the developing luteal stage. The overall results suggest that the growth of the bovine CL is due to not only hypertrophy of LSCs but also an increase in their number, and that the proliferative ability of luteal steroidogenic cells decreases between the developing and mid luteal stages.     

Differentiation in Leaf Epidermis of Chlorophytum comosum Baker

The distribution of guard mother-cell formation has been studiedin developing abaxial epidermis in the basal meristem of theleaf of Chlorophytum comosum. It is concluded that, as tissueis displaced from the base of the leaf by growth, it passesthrough a proliferative zone in which only proliferative mitosesoccur, and then passes a boundary into a formative zone in whichformative mitoses occur, giving rise to guard mother cells,and proliferative mitoses are absent. Further distally, formativemitoses die out and in the next zone (the guard-cell zone) theonly mitoses which occur are those by which the guard mothercells give rise to the guard cells. Most distally there is azone with no mitotic activity. The probability of a cell undergoinga formative mitosis is highest at the proximal boundary of theformative zone. It is consequently suggested that the fate ofa cell on entering the formative zone depends partly on itsposition in the mitotic cycle; cells nearest to mitosis at entryare the most likely to undergo a formative mitosis during theirpassage through the formative zone. Similarly, guard mothercells which fail to undergo mitosis may be those which weremost distant from mitosis on entry into the guard cell zone.These suggestions may explain some of the elements of patternpreviously found in the mature epidermis. Chlorophytum comosum Baker, spider plant, leaf epidermis, stomata, pattern, development, formative mitosis, proliferative mitosis     

Distribution and Expression of Auxin Binding Protein 1 (ABP1) in the Thin Cell Layers of Tobacco

Tobacco （ Nicotiana tabacum L.） pedicel in the blooming period was used to study the distribution of auxin binding protein 1 (ABP1) in the tobacco tissue and cell at different time in the culture of thin cell layers (TCL). Using the immunofluorescence marker it was indicated that the main ABP1 was distributed in the epidermis and the 1st and 2nd layers of the subepidermis cells. A little ABP1 was distributed in the cortex. Tobacco ABP1 was induced to express in the protoplast of tobacco pedicel TCL cultured in MS culture medium containing IAA and BA. Expression of ABP1 in the protoplast was stronger in the active period of vegetative bud differentiation. ABP1 expression became weaker in later period of differentiation. The result of SDS-PAGE and Western blotting showed the molecular weight of tobacco ABP1 in TCL was 26 kD.     

Patterns of cell elongation in the determination of the final shape in galls of Baccharopelma dracunculifoliae (Psyllidae) on Baccharis dracunculifolia DC (Asteraceae)

Cell redifferentiation, division, and elongation are recurrent processes, which occur during gall development, and are dependent on the cellulose microfibrils reorientation. We hypothesized that changes in the microfibrils orientation from non-galled tissues to galled ones occur and determine the final gall shape. This determination is caused by a new tissue zonation, its hyperplasia, and relative cell hypertrophy. The impact of the insect’s activity on these patterns of cell development was herein tested in Baccharopelma dracunculifoliae—Baccharis dracunculifolia system. In this system, the microfibrils are oriented perpendicularly to the longest cell axis in elongated cells and randomly in isodiametric ones, either in non-galled or in galled tissues. The isodiametric cells of the abaxial epidermis in non-galled tissues divided and elongated periclinally, forming the outer gall epidermis. The anticlinally elongated cells of the abaxial palisade layer and the isodiametric cells of the spongy parenchyma originated the gall outer cortex with hypertrophied and periclinally elongated cells. The anticlinally elongated cells of the adaxial palisade layer originated the inner cortex with hypertrophied and periclinally elongated cells in young and mature galls and isodiametric cells in senescent galls. The isodiametric cells of the adaxial epidermis elongated periclinally in the inner gall epidermis. The current investigation demonstrates the role of cellulose microfibril reorientation for gall development. Once many factors other than this reorientation act on gall development, it should be interesting to check the possible relationship of the new cell elongation patterns with the pectic composition of the cell walls.     

烟草薄层培养生长素结合蛋白ABP1的定位和ABP1在细胞分化中的变化

以烟草（Nicotiana tabacum L.)盛花期花梗薄层为材料,研究营养芽分化的不同时期生长素结合蛋白（ABP1)在组织与细胞中的分布变化,免疫荧光标记结果表明,烟草花梗中ABP1主要分布于表皮及亚表皮1－2层细胞内。不同分化期ABP1在烟草花梗薄层原生质体中的表达不同,细胞分化旺盛期ABP1的表达最强,分化后期ABP1的表达有所减弱;Western blotting结果表明,ABP1多克隆抗血清与烟草花梗薄层细胞及分化过程中26kD蛋白有免疫交叉反应。     

The predominant role of the pith in the Growth and development of internodes in Liquidambar styraciflua (Hamamelidaceae). I. Histological basis of compressive and tensile stresses in developing primary tissues

Quantitative changes in cell pattern in the pith, cortex, cortical collenchyma, and epidermis were followed in developing internodes of Liquidambar to examine the cellular basis of compressive and tensile stresses in organized shoot growth. Initially, the highest rates of cell multiplication occur in the pith, followed successively by the epidermis, cortex, and cortical collenchyma. As internodes enter the phase of maximum elongation growth, mitotic activity begins to shift acropetally, accompanied by pronounced changes in cell pattern. The highest rates of cell multiplication now occur in the pith and cortex and continue until the cessation of internode growth. Concomitantly, reduced rates of cell division in peripheral tissues result in rapid increases in rates of cell elongation in the cortical collenchyma and epidermis. Attention is focused on the role of continued cell division in developing internodes with emphasis on differences in rates of cell multiplication between inner and outer tissues affecting patterns of tissue stress. For example, rapid and sustained increases in cell number in the pith, accompanied by growth of readily extensible pith cells, result in the development of compressive forces driving the growth of internodes. Conversely, continuing divisions in less extensible collenchyma and epidermal cells can relieve threshold tensile stresses resulting from the continuous stretching of these tissues by the developing pith. The concept that the passive extension of peripheral tissues, especially the epidermis, control the rate of internode elongation is viewed as an oversimplification of the interacting role of compressive and tensile forces in organized growth and development.     

STUDIES ON SARGASSUM. I. A LIGHT MICROSCOPIC EXAMINATION OF THE WOUND REGENERATION PROCESS IN MATURE STIPES OF S. FILIPENDULA

Regrowth from wounded stipe explants of Sargassum can be divided into four stages based on cytological changes. The first stage involves changes associated with the wound reactions and the formation of a wound epidermis. The second stage includes the formation of a well defined medullary pit with meristematically active cells around its periphery. Several “bud primordia” are also formed which begin to grow by cell division towards the wound surface. The third stage involves a period of internal tissue differentiation in the “bud primordia” such that mitotic activity is localized in the bud tip and the basal cells grow by cell elongation. The fourth stage marks a major change in the morphology of the regeneration branch from a tubular structure to that of a flattened blade. This change in morphology is preceded by the formation of an apical pit around which the flattened growth appears to be organized.     

Cell cycle regulation in the inner ear sensory epithelia: Role of cyclin D1 and cyclin-dependent kinase inhibitors

Sensory hair cells and supporting cells of the mammalian cochlea and vestibular (balance) organs exit the cell cycle during embryogenesis and do not proliferate thereafter. Here, we have studied the mechanisms underlying the maintenance of the postmitotic state and the proliferative capacity of these cells. We provide the first evidence of the role of cyclin D1 in cell cycle regulation in these cells. Cyclin D1 expression disappeared from embryonic hair cells as differentiation started. The expression was transiently upregulated in cochlear hair cells early postnatally, paralleling the spatiotemporal pattern of unscheduled cell cycle re-entry of cochlear hair cells from the p19^Ink4d/p21^Cip1 compound mutant mice. Cyclin D1 misexpression in vitro in neonatal vestibular HCs from these mutant mice triggered S-phase re-entry. Thus, cyclin D1 suppression is important for hair cell's quiescence, together with the maintained expression of cyclin-dependent kinase inhibitors. In contrast to hair cells, cyclin D1 expression was maintained in supporting cells when differentiation started. The expression continued during the neonatal period when supporting cells have been shown to re-enter the cell cycle upon stimulation with exogenous mitogens. Thereafter, the steep decline in supporting cell's proliferative activity paralleled with cyclin D1 downregulation. Thus, cyclin D1 critically contributes to the proliferative plasticity of supporting cells. These data suggest that targeted cyclin D1 induction in supporting cells might be an avenue for proliferative regeneration in the inner ear.     

G1 arrest and the division/conjugation decision in Tetrahymena.

The transformation from the asexual proliferative stage of Tetrahymena to the sexual stage, during which cells of complementary mating types pair and nuclear fertilization occurs, provides an opportunity to study the relationship between the division cycle and differentiation. Conjugation is induced in cells starved for at least 2 hr by mixing complementary mating types. To determine the effect of starvation on the cell cycle, dividing cells were selected from a log growth culture and stepped down to non-nutrient conditions. The G₁ stage is operationally divisible into two sectors, A and B. In the A stage, cells arrest in nutrient-free medium. In the B stage, they proceed through the division cycle. Arrested G₁A cells may conjugate directly when challenged with similar cells of a complementary mating type. It is thereby demonstrated that Tetrahymena cells in G₁A can be directed to divide (nutrient conditions) or can be directed to differentiate (non-nutrient conditions plus complementary mating type) without an intervening division cycle. This rules out a requirement for reprogramming via chromosomal replication or cell division and suggests that G₁A is a stage during which the division/differentiation decision is made in direct response to ambient conditions.     

Dianthus caryophyllus stems and Zantedeschia aethiopica petioles/pedicels show anatomical features indicating efficient photosynthesis

The fine structure of the green stem of Dianthus caryophyllus, the leaf petiole and the flower pedicel of Zantedeschia aethiopica were studied using light and scanning electron microscopy. It was revealed that these non-foliar plant parts of both species possess epidermis with numerous stomata. Stomatal density of D. caryophyllus stem was found to be relatively high (79 vs 100 per mm² found on leaf surface). Z. aethiopica petioles and pedicels also possess numerous stomata (17 per mm²), yet stomatal density was found to be about half of that of leaves. Anatomical differences observed between petioles and pedicels were only minor. Stems of D. caryophyllus as well as petioles and pedicels of Z. aethiopica have a chlorenchyma-type tissue whose fine structure is quite similar to the leaf palisade chlorenchyma. Yet, the palisade of Z. aethiopica petioles and pedicels shows a peculiar arrangement: palisade cells are arranged with their long axis parallel to the longitudinal organ axis. Palisade tissue found in the aforementioned non-foliar plant organs in both species shows strong red chlorophyll auto-fluorescence under epi-fluorescence optics, consists of cells with abundant chloroplasts, possesses high percentage of intercellular spaces (13 and 20%, respectively) and its cells expose considerable part of their surface to the intercellular air. The fine structure of this stem palisade tissue along with the abundance of functional stomata found on the epidermis may support efficient photosynthesis.     

Modification by ethylene of the cell growth pattern in different tissues of etiolated lupine hypocotyls

The influence of ethylene on growth in etiolated lupine (Lupinus albus L.) hypocotyls was studied in ethephon-treated plants. Ethephon reduced the length and increased the diameter of hypocotyls. At the end of the hypocotyl growth period (14 days), the fresh weight was reduced by 53%, and the dry weight was reduced by 16%. Thus, ethylene reduced water uptake in the tissues to a greater extent than the incorporation of new materials. Light microscopic measurements showed that the thickness of tissues was stimulated by ethylene, the vascular cylinder and cortex exhibiting greater increases (55 and 45%, respectively) than pith (26%) or epidermis (12%). Ethephon modified the cell growth pattern, stimulating lateral cell expansion and cell wall thickness, while reducing cell elongation. The response to ethylene varied in the different tissues and was higher in cortex and pith cells than in the epidermis cells. The ethylene-induced cell expansion in the cortex varied according to the localization of cells in the tissue: the central and subepidermal layers showed little change, whereas the innermost layers exhibited the greatest increase. Electron microscopy revealed that ethylene increased both the rough endoplasmic reticulum and dictyosomes, suggesting that ethylene stimulated the secretion of cell wall materials. In untreated seedlings, the pattern of cell growth was similar in cells from the epidermis, cortex, and pith. The final cell size varied along the hypocotyl, the cells becoming shorter and broader the closer to the basal zones of the organ.     

利用激光扫描共聚焦显微镜研究植物细胞发育形态学变化

通过激光扫描共聚焦显微镜,利用不同种类(波长)的激光研究植物细胞发育形态学变化。结果表明,利用紫外激光(351 nm)扫描可以清楚地观察到拟南芥叶片表皮细胞的形态及其变化,在已分化的叶片表皮上可观察到包括“铺垫”表皮细胞(epidermal pavement cells)、气孔保卫细胞(guard cell)、气孔伴胞(subsidiarycells)、表皮毛细胞(trichomes)和表皮毛的足细胞(socket cells)等多种形态不同的细胞种类;利用蓝光激光(488nm)辅助曙红浅染,可清晰地显示出拟南芥根生长区内部的各种原始细胞,包括静止区(quiescent center)细胞、皮层/内皮层原始细胞(cortex/endodermal initial cell)、表皮/根冠原始细胞(epidermal/root cap initial cell)和中柱/根冠原始细胞(columella/root cap initial cell)等。利用双光子激光(800 nm)连续扫描30 s可以诱发叶绿体产生自发荧光,并可观察到叶绿体在叶肉细胞中的运动轨迹。结果说明激光扫描共聚焦显微镜在植物细胞形态及发育研究上具有独特的功能。     

Analysis of Cell Division and Elongation Underlying the Developmental Acceleration of Root Growth in Arabidopsis thaliana

To investigate the relation between cell division and expansion in the regulation of organ growth rate, we used Arabidopsis thaliana primary roots grown vertically at 20°C with an elongation rate that increased steadily during the first 14 d after germination. We measured spatial profiles of longitudinal velocity and cell length and calculated parameters of cell expansion and division, including rates of local cell production (cells mm⁻¹ h⁻¹) and cell division (cells cell⁻¹ h⁻¹). Data were obtained for the root cortex and also for the two types of epidermal cell, trichoblasts and atrichoblasts. Accelerating root elongation was caused by an increasingly longer growth zone, while maximal strain rates remained unchanged. The enlargement of the growth zone and, hence, the accelerating root elongation rate, were accompanied by a nearly proportionally increased cell production. This increased production was caused by increasingly numerous dividing cells, whereas their rates of division remained approximately constant. Additionally, the spatial profile of cell division rate was essentially constant. The meristem was longer than generally assumed, extending well into the region where cells elongated rapidly. In the two epidermal cell types, meristem length and cell division rate were both very similar to that of cortical cells, and differences in cell length between the two epidermal cell types originated at the apex of the meristem. These results highlight the importance of controlling the number of dividing cells, both to generate tissues with different cell lengths and to regulate the rate of organ enlargement.