Ultrastructure and Cell Division of a Facultatively Parasitic Strain of Bdellovibrio bacteriovorus

Some aspects of cell development and division of Bdellovibrio bacteriovorus strain UKi2 were examined by use of electron microscopic techniques. Under saprophytic and parasitic conditions of growth, the comma-shaped cells enlarge, elongate, and form helical filaments. The mechanism of division appears to consist of an asymmetrical constriction of the filamentous cell by the cytoplasmic membrane, accompanied by a breakdown of the outer layers of the cell wall in the division region. During regeneration of the cell wall, the flagellum and flagellar sheath are formed. The development of the flagellum of the daughter cell is initiated prior to separation of the newly formed cells from the filament. Observations of B. bacteriovorus UKi2 grown under saprophytic and parasitic conditions indicate that development and ultrastructure are similar in both modes of growth.     

ANATOMICAL AND PHYSIOLOGICAL STUDIES OF FLORAL TUBE ELONGATION OF CROCUS VERNUS (IRIDACEAE)

Intact floral tubes of Crocus vernus grown under controlled conditions elongated 50 mm in 8 days. Mitoses of the epidermal cells did not occur during the growth of the intact tube; however, cells did elongate from 50 μm to 150 μm, a three-fold increase in cell length. When the floral buds were excised and maintained in distilled water, elongation of floral tubes was inhibited by 46%. The presence of the ovary or the addition of nutrients had no significant effect upon the elongation of the floral tubes of excised buds. When the excised floral buds were placed in 10^–6 m indoleacetic acid, the final tube lengths exceeded that of the water controls by 30% and achieved 91% of the elongation of the intact tubes. Gibberellic acid and kinetin had no effect on floral tube elongation. As with the intact floral tubes, mitoses of the epidermal cells did not occur during the elongation of the excised floral tubes.     

Granule cell induction of 9-O-acetyl gangliosides on cerebellar glia in microcultures

In previous studies we have shown that the expression of acetylated gangliosides recognized by the JONES monoclonal antibody is correlated with regions of cell migration in the developing rat nervous system. In this study we have investigated the expression of these gangliosides in two different types of cultures prepared from dissociated postnatal rat cerebella. In the first type, cells are plated after dissociation under conditions where most of the glial cells develop a stellate morphology that anchors neurons but does not support their migration. In the second type of culture, cells are plated in a ratio of four neurons to one glial cell and under these conditions the predominant form of astroglia is an elongate form that supports the migration of granule neurons. Granule neurons express JONES antigens in dissociated cell suspensions and in cultures in which cells are plated either after dissociation or in a 4:1 neuron:glia ratio. On the other hand, glial cells grown in the absence of neurons are JONES negative. In addition, the expression of JONES gangliosides by glial cells is different in the two types of culture. In cultures where the astroglial cells display the stellate morphology only a small proportion show JONES staining. Cultures in which the glial cells assume the elongate morphology have a significantly higher number of JONES-positive astroglia.     

Orientation and length of mammalian skeletal myocytes in response to a unidirectional stretch

Effects of mechanical forces exerted on mammalian skeletal muscle cells during development were studied using an in vitro model to unidirectionally stretch cultured C2C12 cells grown on silastic membrane. Previous models to date have not studied these responses of the mammalian system specifically. The silastic membrane upon which these cells were grown exhibited linear strain behavior over the range of 3.6-14.6% strain, with a Poisson's ratio of approximately 0.5. To mimic murine in utero long bone growth, cell substrates were stretched at an average strain rate of 2.36%/day for 4 days or 1.77%/day for 6 days with an overall membrane strain of 9.5% and 10.6%, respectively. Both control and stretched fibers stained positively for the contractile protein, alpha-actinin, demonstrating muscle fiber development. An effect of stretch on orientation and length of myofibers was observed. At both strain rates, stretched fibers aligned at a smaller angle relative to the direction of stretch and were significantly longer compared to randomly oriented control fibers. There was no effect of duration of stretch on orientation or length, suggesting the cellular responses are independent of strain rate for the range tested. These results demonstrate that, under conditions simulating mammalian long bone growth, cultured myocytes respond to mechanical forces by lengthening and orienting along the direction of stretch.     

Filament formation in Clostridium acidiurici under conditions of elevated temperatures

Terry, David R. (Brigham Young University, Provo, Utah), Abdul Gaffar, and Richard D. Sagers. Filament formation in Clostridium acidiurici under conditions of elevated temperatures. J. Bacteriol. 91:1625-1634. 1966.-Vegetative cells of Clostridium acidiurici, when grown at temperatures up to 42 C, are straight rods varying from 2.5 to 4 mu in length. When grown at 43 C, the cells show a definite tendency to elongate, and, when grown at 44 C, filaments are formed, often exceeding 500 mu in length. Only an occasional cross wall is apparent in the heat-induced long forms, but as the temperature is lowered they readily form cross walls and fragment into short, single cells. Chromatin material is distributed in evenly spaced clusters throughout the length of the filaments. The filaments grown at 44 C are gram-negative, whereas cells grown at 37 C are gram-positive. However, filament formation and gram-negativity apparently are not due to magnesium deficiency, since the gram-negative filaments are formed in concentrations of magnesium ranging from 10(-6) to 10(-2)m. The rapid transition from filaments to single cells upon lowering the temperature from 44 to 37 C suggests that the temperature-related repression of the cross wall-forming system is a phenotypic response rather than the selection of specific mutants which produce the observed phenomena.     

AN ANALYSIS OF STAMEN FILAMENT GROWTH OF NIGELLA HISPANICA

The post-meiotic stamen filament of Nigella hispanica L. under greenhouse conditions grows in length from 1 mm to approximately 10 mm at maturity in 16 days. Analysis of the filament epidermis suggests that the intercalary meristem is diffuse along the filament with a mid-point of activity near the center of the filament. The point of maximal activity, while initially central, is variable as cell division nears completion. Measurement of cell lengths along filaments suggests that an elongation gradient from base to tip is operative in filaments 1 mm and longer. Average cell lengths of epidermal cells increase faster than do those of terminal cells. Once average cell length begins to increase in any region of the epidermis it continues to do so until flower maturity. At maturity the longest epidermal cells are near the filament base and the shortest cells are at the tip. The differences between cell division and cell elongation patterns suggest that these two processes are controlled by different sites or substances. A comparison is made between the development of the Nigella filament and other determinate organs having intercalary meristems.     

The seminal root primordia in barley and the participation of their non-meristematic cells in root construction

In addition to the primary seminal primordium, the so-called secondary seminal root primordia are also initiated in a barley embryo. The primary root primordium is developmentally most advanced. It is formed by root meristem covered with the root cap, and by a histologically determined region with completed cell division. On germination, the restoration of growth processes begins in this non-meristematic region of root primordium by cell elongation, with the exception of the zone adjacent to the scutellar node, the cells of which do not elongate but continue differentiating. In the root primordia initiated later, the zone with completed cell division is relatively shorter, in the youngest primordia the non-meristematic cells may be lacking. The root meristem is reactivated after the primary root primordium has broken through the sheath-like coleorrhiza and emerges from the caryopsis as the primary root. The character of root meristem indicates a reduced water content at the embryonic development of root primordium. With progressing growth the root apex becomes thinner, the meristematic region becomes longer, and the differences in the extent of cell division between individual cell types increase. — The primary root base is formed of cells pre-existing in the seminal root primordium. Upon desiccation of caryopsis in maturation, and subsequent quiescent period, their development was temporarily broken, proceeding with the onset of germination. The length of this postembryonically non-dividing basal zone is different in individual cell types. The column of central metaxylem characteristic of the smallest number of cell cycles, has, under the given conditions, a mean length of about 22 mm, whereas the pericycle, as the tissue with most prolonged cell division, has a mean length of about 6 mm. In the seminal root primordia initiated later the non-dividing areas are relatively shorter. The basal region of seminal roots thus differs in its ontogenesis from the increase which is formed “de novo” by the action of root meristem upon seed germination.     

Cellular localization of oriC during the cell cycle of Escherichia coli as analyzed by fluorescent in situ hybridization

The origin of replication of Escherichia coli, oriC, has been labeled by fluorescent in situ hybridization (FISH). The E. coli K12 strain was grown under steady state conditions with a doubling time of 79 min at 28 degrees C. Under these growth conditions DNA replication starts in the previous cell cycle at -33 min. At birth cells possess two origins which are visible as two separated foci in fully labeled cells. The number of foci increased with cell length. The distance of foci from the nearest cell pole has been measured in various length classes. The data suggest: i) that the two most outwardly located foci keep a constant distance to the cell pole and they therefore move apart gradually in line with cell elongation; and ii) that at the initiation of DNA replication the labeled origins occur near the center of prospective daughter cells.     

Sucrose-mediated giant cell formation in the genus Neisseria.

Growth of Neisseria perflava, Neisseria cinerea, and Neisseria sicca strain Kirkland in media supplemented with sucrose (0.5 to 5.0% w/v) resulted in the formation of giant cells. Response to sucrose was specific in that a variety of other carbohydrates did not mediate giant cell formation. Giant cells appeared only under growth conditions and did not lyse upon transfer to medium lacking sucrose or upon resuspension in hypotonic media. Reversion of giant to normal cells occurred when giant cells were used as inocula and allowed to multiply in media lacking sucrose.     

Epidermal Growth Factor Signalling Controls Myosin II Planar Polarity to Orchestrate Convergent Extension Movements during Drosophila Tubulogenesis

Most epithelial tubes arise as small buds and elongate by regulated morphogenetic processes including oriented cell division, cell rearrangements, and changes in cell shape. Through live analysis of Drosophila renal tubule morphogenesis we show that tissue elongation results from polarised cell intercalations around the tubule circumference, producing convergent-extension tissue movements. Using genetic techniques, we demonstrate that the vector of cell movement is regulated by localised epidermal growth factor (EGF) signalling from the distally placed tip cell lineage, which sets up a distal-to-proximal gradient of pathway activation to planar polarise cells, without the involvement for PCP gene activity. Time-lapse imaging at subcellular resolution shows that the acquisition of planar polarity leads to asymmetric pulsatile Myosin II accumulation in the basal, proximal cortex of tubule cells, resulting in repeated, transient shortening of their circumferential length. This repeated bias in the polarity of cell contraction allows cells to move relative to each other, leading to a reduction in cell number around the lumen and an increase in tubule length. Physiological analysis demonstrates that animals whose tubules fail to elongate exhibit abnormal excretory function, defective osmoregulation, and lethality.     

Function of Trehalose and Glycogen in Cell Cycle Progression and Cell Viability in Saccharomyces cerevisiae

Trehalose and glycogen accumulate in Saccharomyces cerevisiae when growth conditions deteriorate. It has been suggested that aside from functioning as storage factors and stress protectants, these carbohydrates may be required for cell cycle progression at low growth rates under carbon limitation. By using a mutant unable to synthesize trehalose and glycogen, we have investigated this requirement of trehalose and glycogen under carbon-limited conditions in continuous cultures. Trehalose and glycogen levels increased with decreasing growth rates in the wild-type strain, whereas no trehalose or glycogen was detected in the mutant. However, the mutant was still able to grow and divide at low growth rates with doubling times similar to those for the wild-type strain, indicating that trehalose and glycogen are not essential for cell cycle progression. Nevertheless, upon a slight increase of extracellular carbohydrates, the wild-type strain degraded its reserve carbohydrates and was able to enter a cell division cycle faster than the mutant. In addition, wild-type cells survived much longer than the mutant cells when extracellular carbon was exhausted. Thus, trehalose and glycogen have a dual role under these conditions, serving as storage factors during carbon starvation and providing quickly a higher carbon and ATP flux when conditions improve. Interestingly, the CO₂ production rate and hence the ATP flux were higher in the mutant than in the wild-type strain at low growth rates. The possibility that the mutant strain requires this steady higher glycolytic flux at low growth rates for passage through Start is discussed.     

Gravitropism in Higher Plant Shoots : III. Cell Dimensions during Gravitropic Bending; Perception of Gravity

Cross and longitudinal sections were prepared for light microscopy from vertical control plants (Xanthium strumarium L. Chicago strain), free-bending horizontal stems, plants restrained 48 hours in a horizontal position, and plants restrained 48 hours and then released, bending immediately about 130°. Top cells of free-bending stems shrink or elongate little; bottom cells continue to elongate. In restrained stems, bottom cells elongate some and increase in diameter; top cells elongate about as much but decrease in diameter. Upon release, bottom cells elongate more and decrease in diameter, while top cells shorten and increase in diameter, accounting for the bend. During restraint, bottom cells take up water while tissue pressures increase; top cells fail to take up water although tissue pressures are decreasing.

Settling of amyloplasts was observed in cells of the starch sheath.

Removal of different amounts of stem (Xanthium; Lycopersicon esculentum Miller, cv Bonny Best; Ricinus communis L. cv Yolo Wonder) showed that perception of gravity occurs in the bending (elongation) zone, although bending of fourth and fifth internodes from the top was less than in uncut controls. Uniform application of 1% indoleacetic acid in lanolin to cut stem surfaces partially restored bending. Reversing the gradient in tension/compression in horizontal stems (top under compression, bottom under tension) did not affect gravitropic bending.

     

MUCILAGE PROCESSING AND SECRETION IN THE GREEN ALGA CLOSTERIUM. I. CYTOLOGY AND BIOCHEMISTRY1

Placoderm desmids (Conjugates, Chlorophyta) such as Closterium exhibit a gliding locomotory behavior. This results from the forceful extrusion of an acidic polysaccharide from one pole of the cell causing the cell to glide in the opposite direction. A biochemical and cytological analysis of gliding behavior was performed. The mucilage is a high molecular weight polysaccharide rich in glucuronic acid and fucose. Under normal growth conditions, 3 μg of mucilage is produced per cell in 30 days. Mucilage production increased 3–4 fold in cells challenged with low phosphate or nitrate conditions. A polyclonal antibody was raised against the mucilage and used in immunofluorescence studies. These results show that upon contact with another object Closterium aligns itself parallel to that object by a “jack-knife” motion. Subsequently, large amounts of mucilage are released to form elongate tubes enmeshing the cell with that object. In post-cytokinetic phases of the cell cycle, mucilage is extruded only through the pole of the developing semi-cell. Chlorotetracyclene-labeling of mucilage-secreting cells shows a correlation between calcium-rich loci on the cell surface and sites of mucilage release.     

Amber mutation affecting the length of Escherichia coli cells.

An amber mutation in a newly found gene (wee) of Escherichia coli has been isolated from strain OV-2, which harbors a temperature-sensitive suppressor. At 42 degrees C cells of the mutant, OV-25, increased in mass and deoxyribonucleic acid content and divided at normal rates, compared with the wild type under the same growth conditions. Total cell length increased under the restrictive conditions, although at a slightly lower rate. Values of mean cell length and cell volume, contrary to what would be expected from the increment in the rate of increase in particles, mass, and deoxyribonucleic acid, became at 42 degrees C smaller than those found in the wild type. A parallel increase in protein content per length and cell density and a loss of viability were found to occur after four generations at the restrictive temperature. The behavior of strain OV-25 in the absence of the wee gene product could be interpreted in terms of either a faulty regulation of the elongation processes or their abnormal coordination with the cell cycle. The genetic location of the wee gene has been found to be at 83.5 min on the E. coli genetic map.     

Neurite development in PC12 cells on flexible micro-textured substrates under cyclic stretch

We investigated the combined effect of micro-texture and mechanical strain on neuronal cell development such as neurite length and neurite density in a rat pheochromocytoma cell line (PC12 cells). Cells were seeded on flexible silicone substrates with micro-texture or no texture (smooth) and cultured under static and dynamic conditions. In the static condition substrates were not stretched and in the dynamic conditions substrates were subjected to cyclic uniaxial stretching at three different strain levels of 4%, 8%, and 16% with each at three different strain rates at 0.1, 0.5, and 1.0 Hz. Results showed that of all cell cultures there was no significant difference in neurite development between cells on smooth and textured substrates, except in the static and 4% at 0.1 Hz conditions, where micro-texture induced significantly longer neurites. With both types of substrates, a lower mechanical condition (4% at 1.0 Hz or 16% at 0.1 Hz) resulted in more and longer neurites and lower cell density, and a higher mechanical condition (16% at 1.0 Hz) resulted in fewer and shorter neurites and lower cell density as compared to the static condition. These findings suggest that the effect of the micro-texture on neurite development is more prominent in low mechanical conditions than in high mechanical conditions and that the strain level and strain rate have an interrelated effect on neurite development: a higher strain level at a lower strain rate has a similar effect as a lower strain level at a higher strain rate in terms of promoting neurite development.     

Comparative analysis of anoxic coleoptile elongation in rice varieties: relationship between coleoptile length and carbohydrate levels, fermentative metabolism and anaerobic gene expression

Rice ( Oryza sativa L.) seeds can germinate under anoxia and can show coleoptile elongation. The anoxic coleoptile is usually longer than aerobic coleoptiles. Although several hypotheses have been proposed to explain the ability of rice to elongate coleoptiles under anoxia, conclusive experimental evidence explaining this physiological trait is lacking. In order to investigate whether metabolic and molecular markers correlate with anoxic coleoptile length, we screened 141 Italian and 23 Sri Lankan rice cultivars for their ability to elongate coleoptiles under anoxia. Differences in anoxic coleoptile length were used to evaluate whether a correlation exists between coleoptile length and biochemical and molecular parameters. The expression of genes coding for glycolytic and fermentative enzymes showed a very low correlation with anoxic coleoptile length. Although differences were found in carbohydrate content between the varieties tested, this parameter also does not appear to be critical in terms of coleoptile elongation. Efficient ethanol fermentation does, however, correlate well with the elongation of coleoptiles under anoxic conditions.     

FGF-2 Inhibits Apoptosis in Human Teratocarcinoma Cells during Differentiation on Collagen Substratum

Tera-2 is a human teratocarcinoma cell line, which is induced to differentiate into neuronal direction by retinoic acid. Once differentiated, the cells form an almost nondividing population that can be maintained for weeks under conventional culture conditions. If differentiation by retinoic acid is induced while the cells are growing on type I collagen or if the already-differentiated cells are transferred onto collagen, they survive only a few days unless the cultures are repeatedly supplied with FGF-2. Lack of this growth factor induces programmed cell death (apoptosis) detectable after 24–48 h, as marked by DNA cleavage and nuclear fragmentation. The undifferentiated stem cells survive and proliferate readily on collagen without addition of FGF-2. Tera-2 cells express two members of the FGF family, FGF-2 and FGF-4. The expression of both FGFs is turned off during differentiation on collagen substratum, whereas when cultivated on plain tissue culture dish, the expression of only FGF-4 becomes undetectable. The results indicate that signaling through cell surface FGF receptors is vital for the cells, and differentiation on collagen substratum results in complete extinction of the autocrine stimulatory loop.In vivo,such induction of growth factor dependency upon differentiation would result in apoptotic death of those cells which fail to find adequate conditions for continuing FGF stimulation.     

Modulation of the Shape of Epithelial Lens Cells in vitro Directed by a Retinal Extract Factor

We have shown previously [1] that bovine epithelial lens cells can be stimulated to divide and elongate by a retinal extract (RE). In this report we show that the morphological response to the stimulatory factor is directly related to the target-cell shape, and we describe how the cell shape can be modulated into morphologically different types. If the cells are grown continuously from the explant in the presence of the RE factor, they keep a typical regular pavement-like epithelial shape (type I), even after serial passages. If the same cells are cultured in the absence of the factor, they become extremely irregular in shape and enlarge enormously (type II), and during serial passage elongate spontaneously to a fibroblast-like pattern. However, when type II cells are stimulated by RE, they elongate dramatically into type III cells as described in [1], provided they are stimulated at the optimal cell density. We show that the transformation of one type to another is directly under the control of RE, and we demonstrate that the changes in cell morphology are accompanied by alterations in cytoplasmic actin filaments. Type I cells contain few microfilaments, while type II cells display actin-tropomyosin polygonal fibre networks that reform during conversion to type III cells and then to elongated stress fibres. The change from type I to type II cells is also accompanied by massive accumulation of surface-associated fibronectin. We conclude that factors obtained directly from the eye have a direct ability to control morphology and proliferation of ocular cells like lens cells perhaps by modulation of cellular adhesiveness mediated by surface fibronectin and reorganization of cytoplasmic actin-based filaments.     

甘蔗茎尖原生分生组织区域化

甘蔗茎尖原生分生组织是甘蔗地上部分一切形态组织的发源中心,通过对6个不同茎径甘蔗品种4个不同营养发育时期的茎尖原生分生组织显微和超微结构观察研究发现:甘蔗茎尖原生分生组织呈半卵型结构,明显分为原套原始细胞区、原体原始细胞区、周缘分生细胞区、髓分生区,其区域化符合原套-原体学说。原套原始细胞区为最外一层细胞,原套细胞之间胞间连丝丰富,而原套与原体细胞之间胞间连丝极少,细胞以垂周分裂为主,扩大原生分生组织表面积;原体位于原套下的分生组织的中央区域,细胞可以进行各个方向的分裂,不断增加体积,原体原始细胞区呈一个球体;周缘分生区位于原套、原体下方两侧,细胞活跃产生叶原基和原形成层细胞;髓分生区细胞位于原体下方周缘分生区内侧,细胞横向分裂纵向排列,使甘蔗茎伸长。