Preprophase Band Of Microtubules Research Articles

The evolution, structure and functioning of stomata

Summary The anatomy and ultrastructure of guard cells from a range of species varying from the primitive types, such as mosses, to the advanced grasses and orchids are described. An attempt is made to trace the lines along which stomata developed and to define what might be considered advanced stomata. Additionally, the differentiation of guard cells from guard mother cells is discussed. Of particular note is the preprophase band of microtubules which marks the zone where the future cell wall will form and the movement of the spindle and developing cell plate through 45 degrees. The structure and function of guard cells are intimately linked. Stomata are turgor regulated valves; the osmotica for absorbing water during opening are K+, Cl- and malate anions which accumulate in the guard cell vacuoles. Upon stomatal closure, K+ and Cl- exit from the guard cells while at least some of the carbon from malate is channelled into starch and there is a resultant loss of guard cell turgor. The Calvin cycle may be a...

Microtubule and F-actin dynamics at the division site in living Tradescantia stamen hair cells

ABSTRACT We have visualised F-actin and microtubules in living Tradescantia virginiana stamen hair cells by confocal laser scanning microscopy after microinjecting rhodamine-phalloidin or carboxyfluorescein-labelled brain tubulin. We monitored these components of the cytoskeleton as the cells prepared for division at preprophase and progressed through mitosis to cytokinesis. Reorganisation of the interphase cortical cytoskeleton results in preprophase bands of both F-actin and microtubules that coexist in the cell cortex, centred on the site at which the future cell plate will fuse with the parent cell wall. The preprophase band of microtubules is formed from microtubules that polymerise and incorporate tubulin during prophase. The preprophase band of actin may form either by reorganisation of pre-existing filaments or by de novo polymerisation. Both cytoskeletal components disappear from the future division site approximately five minutes prior to the breakdown of the nuclear envelope. Cortical microtubules are undetectable throughout mitosis and cytokinesis, whereas cortical F-actin remains abundant, although it is notably excluded from the division site. The phragmoplast, containing both F-actin and microtubules, expands towards the cortical actin exclusion-zone through a region that has no detectable microtubules or F-actin. The phragmoplast comes to rest in the predefined region of the cortex that is devoid of F-actin. It is proposed that cortical F-actin may act as a “negative” template which could position the phragmoplast and cell plate correctly. This is the first in vivo documentation of F-actin dynamics at the division site in living plant cells.

Pollen development in orchids 4. Cytoskeleton and ultrastructure of the unequal pollen mitosis inPhalaenopsis

The unequal first mitosis in pollen ofPhalaenopsis results in a small generative cell cut off at the distal surface of the microspore and a large vegetative cell. No preprophase band of microtubules is present, but polarization of the microspore prior to this critical division is well marked. A generative pole microtubule system (GPMS) marks the path of nuclear migration to the distal surface, and the organelles become unequally distributed. Mitochondria, plastids and dictyosomes are concentrated around the vegetative pole in the center of the microspore and are almost totally excluded from the generative pole. The prophase spindle is multipolar with a dominant convergence center at the GPMS site. The metaphase spindle is disc-shaped with numerous “minipoles” terminating in broad polar regions. In anaphase, the spindle becomes cone-shaped as the spindle elongates and the vegetative pole narrows. These changes in spindle architecture are reflected in the initial shaping of the telophase chromosome groups. F-actin is coaligned with microtubules in the spindle and is also seen as a network in the cytoplasm. An outstanding feature of orchid pollen mitosis is the abundance of endoplasmic reticulum (ER) associated with the spindle. ER extends along the kinetochore fibers, and the numerous foci of spindle fibers at the broad poles terminate in a complex of ER.

Ameiotic, a gene that controls meiotic chromosome and cytoskeletal behavior in maize

Microtubule organization during the novel cell division of ameiotic microsporocytes was examined using indirect immunofluorescence microscopy. A recessive mutation of the maize gene Ameiotic causes the replacement of meiosis I with a synchronized mitotic division ( Palmer, R. G. (1971). Chromosoma 35, 233–246). All identifiable cytological features of this division, including chromosome behavior and microtubule organization, were typical of somatic cell division. Significantly, a cortical microtubule band was observed during prophase in ameiotic cells. In most somatic plant cells, a preprophase band of microtubules (PPB) predicts the cortical site where the future cell plate will join the sidewall. Similar structures, however, are absent in all meiotic and postmeiotic reproductive cells examined to date. These disruptions are consistent with a model where the wild-type Ameiotic gene encodes a product which acts during or before G2 and is necessary for initiating several independent meiotic processes, including both meiotic chromosome behavior and microtubule organization. The ameiotic mutation provides additional evidence that aspects of cytoskeletal organization unique to meiosis are genetically controlled. Finally, the presence of a PPB during the ameiotic division supports a model whereby multiple mechanisms are used to determine and maintain division plane polarity during normal meiosis.

Inhibition by kinase inhibitors of the development and the disappearance of the preprophase band of microtubules in tobacco BY-2 cells

ABSTRACT The effects of two kinase inhibitors, staurosporine and K-252a, on the development and the disappearance of the preprophase band of microtubules (PPB) were studied in tobacco BY-2 cells, the cell cycle of which had been synchronized. Treatment of cells at late G2 phase or at prophase with 20 M staurosporine or 2 M K-252a for 2 or 3 h caused a decrease in the rate of development of PPBs and inhibited the disappearance of PPBs once they had developed, with the resultant accumulation of cells with a PPB. Cortical microtubules (MTs) or PPBs on protoplast ghosts, which were prepared from BY-2 cells in late G2 phase or at prophase, disappeared on treatment of the ghosts with ATP or ATP S but not on treatment with AMP-PNP. The effect of ATP on the disappearance of MTs on the ghosts was suppressed by 20 M staurosporine. Although 2 M K-252a applied to the culture medium suppressed the anticipated disappearance of PPBs, it did not suppress the disappearance of MTs on the ghosts that was caused by ATP. We propose tentatively that a kinase sensitive to staurosporine but not to K-252a is directly involved in the disappearance of MTs and that a kinase that is sensitive to K-252a is indirectly involved in this process. The disappearance of MTs on protoplast ghost that was induced by ATP did not occur in the presence of 20 μM taxol.

Cell cycle-specific disruption of the preprophase band of microtubules in fern protonemata: effects of displacement of the endoplasm by centrifugation

ABSTRACT The preprophase band (PPB) of microtubules (MTs), which appears at the future site of cytokinesis prior to cell division in higher plant cells, disappears by metaphase. Recent studies have shown that displacement of the endoplasm from the PPB region by centrifugation delays the disappearance of the PPB. To study the role of the endoplasm in the cell cycle-specific disruption of the PPB, the filamentous protonemal cells of the fern Adiantum capiUus-veneris L. were centrifuged twice so that the first centrifugation displaced the endoplasm from the site of the PPB and the second returned it to its original location. The endoplasm, including the nucleus of various stages of mitosis, could be returned by the second centrifugation to the original region of the PPB, which persists during mitosis in the centrifuged cells. When endoplasm with a prophase nucleus was returned to its original location, the PPB was not disrupted. When endoplasm with a prometaphase-telophase nucleus was similarly returned, the PPB was disrupted within 10 min of termination of centrifugation. In protonemal cells of Adiantum, a second PPB is often formed near the displaced nucleus after the first centrifugation. In cells in which the endoplasm was considered to have been returned to its original location at the prophase/prometaphase transition, the second PPB did not disappear even though the initial PPB was disrupted by the endoplasm. These results suggest that cell cycle-specific disruption of the PPB is regulated by some factor(s) in the endoplasm, which appears at prometaphase, i.e. the stage at which the PPB is disrupted in non-centrifuged cells.

Establishment of division plane and mitosis in monoplastidic guard mother cells of Selaginella

AbstractStomatogenesis, the determinate developmental pathway leading to formation of a pair of specialized guard cells, was studied in monoplastidic cells ofSelaginella. Observations of living cells followed by immunofluorescence microscopy of the same cells made it possible to correlate changes in cytoskeletal organization with developmental events. The guard mother cell divides in a plane perpendicular to previous divisions and this shift in polarity is marked by morphogenetic plastid migration, as well as by extensive reorganization of cytoskeletal arrays. The single plastid divides and daughter plastids move to a position opposite each other (incipient spindle poles). The axis defined by the opposing plastids rotates in the cell before becoming fixed in position with polar plastids adjacent to the lateral anticlinal walls. Plastid polarity predicts spindle orientation and the plane of division. Once division polarity is defined by plastid position, which will remain unchanged throughout mitosis and cytokinesis, cortical microtubules become reorganized from radial to longitudinal (relative to the long axis of the leaf). The initially random cortical F‐actin also becomes aligned longitudinally. A wide preprophase band of microtubules and F‐actin is formed at right angles to the spindle axis. Plastid‐based microtubules establish the preprophase spindle and also connect to the preprophase band. The mitotic spindle remains anchored at the polar plastids. After mitosis, a phragmoplast that forms among microtubules emanating from plastids and nuclei develops in the plane marked previously by the preprophase band. Mitosis is completed in 1 h 15 min ± 3 min (mean ± S.E.). © 1992 Wiley‐Liss, Inc.

Pollen development in orchids. 5. A generative cell domain involved in spatial control of the hemispherical cell plate

ABSTRACT The unequal first pollen mitosis in moth orchids (Phalaenopsis) is followed by an unusual form of cytokinesis that isolates a small lens-shaped generative cell from a large vegetative cell. No preprophase band of microtubules predicts the division plane and the new cell plate grows completely around the generative cell rather than fusing with the parental wall. Development of the phragmoplast cytoskeleton consisting of fusiform bundles of microtubules and F-actin occurs in three major stages: (1) the initial asymmetrical phragmoplast conforming to the shape of the interzonal region, which tapers from the broad mass of chromosomes at the generative pole to the rounded mass at the vegetative pole; (2) the symmetrical plate-like phragmoplast; and (3) the hemispherical phragmoplast, which curves around the generative nucleus. Microtubules of the generative half of the hemispherical phragmoplast are nuclearbased, while those on the vegetative side terminate in endoplasmic reticulum. The path of the phragmoplast appears to outline a cytoplasmic domain defined by a radial system of microtubules emanating from the generative nucleus.

Presence and absence of the preprophase band of microtubules in moss protonemata: a clue to understanding its function?

InFunaria protonemata, preprophase bands (PPBs) of microtubules do not develop when the tip cell divides, when side branches are initiated or in intercalary regeneration divisions. We report here that PPBs do, however, develop when a tmema cell is formed. In the former cases, cell division is not coupled with an expansion of the mother cell wall at the site where the cell plate will attach. In the latter case, the mother cell wall ruptures at that site and the tmema cell elongates. This observation and the findings on presence and absence of the PPB in other cell types indicate a connection between PPB occurrence and mother cell wall expansion. They support the idea that the PPB might be involved in the local secretion of cell wall material. We extend this notion, suggesting that the microtubules of the PPB control the oriented deposition of a thin layer of cellulose microfibrils at the mother cell wall which supports the firm attachment of the cell plate when the mother cell wall expands.

P 34cdc2 kinase homologue in the preprophase band

Immunofluorescence microscopy with a monoclonal antibody raised against the PSTAIR sequence, which corresponds to a peptide conserved in the p 34cdc2 protein kinase throughout the phylogenetic scale including higher plants, was used to study the intracellular localization of p 34cdc2 during the cell cycle in onion root tip cells. Although p 34cdc2 was evenly distributed in the cytoplasm throughout the cell cycle, a more intense staining was observed in the cortical region, where the preprophase band of microtubules (MTs) was located. Double staining with the PSTAIR and plant tubulin antibodies showed that the width of p 34cdc2 band was narrower than that of MT band. These data raise the interesting question regarding the possible role of p 34cdc2 protein kinase in determining the division site in plant cells.

The microtubular cytoskeleton during development of the zygote, proembryo and free-nuclear endosperm in Arabidopsis thaliana (L.) Heynh

The microtubular cytoskeleton has been studied during development of the zygote, proembryo and free-nuclear endosperm in A. thaliana using immunofluorescence localization of tubulin in enzymatically isolated material. Abundant micro tubules (MTs) are found throughout proembryogenesis. Microtubules in the coenocytic endosperm are mainly internal. By contrast, there is a re-orientation of MTs to a transverse cortical distribution during zygote development, predominantly in a subapical band which accompanies a phase of apical extension. The presence of these cortical arrays coincides with the elongation of the zygote. Cortical arrays also accompany elongation of the cylindrical suspensor. Extensive networks of MTs ramify throughout the cytoplasm of cells in the proembryo proper. Perinuclear arrays are detected in a number of cell types and MTs contribute to typical mitotic configurations during nuclear divisions. Preprophase bands of MTs are absent throughout megasporogenesis and embryo-sac development and do not occur in endosperm cell divisions. We have observed MTs throughout the first division cycle of the zygote. By placing the observed stages in a most probable sequence, we have identified this cell cycle as the point during embryogenesis at which a preprophase band is reinstated as a regular feature of cell division. Preprophase bands were observed to predict planes of cytokinesis in cell divisions up to the octant stage.

Patterns of cortical and perinuclear microtubule organization in meristematic root cells ofAdiantum capillus veneris

The interphase meristematic root cells ofAdiantum capillus venerispossess a well developed cytoskeleton of cortical microtubules (Mts), which disappear at prophase. The preprophase-prophase cells display a well organized preprophase microtubule band (PMB) and a perinuclear Mt system. The observations favour the suggestion that the cell edges included in the PMB cortical zone possess a Mt organizing capacity and thus play an important role in PMB formation. The perinuclear Mts are probably organized on the nuclear surface. The preprophase-prophase nuclei often form protrusions towards the PMB cortical zone and the spindle poles, assuming a conical or rhomboid shape. Mts may be involved in this nuclear shaping.

Microtubule organization and morphogenesis of stomata in caffeine-affected seedlings ofZea mays

Treatment ofZea mays seedlings with a 5 mM caffeine solution inhibits cytokinesis in guard cell mother cells (GMCs), producing unicellular, binucleate aberrant stomata (a-stomata). Ventral wall (VW) strips of limited length, which usually meet the wall portions of GMCs adjoining the cortical zone of the preprophase microtubule band (PMB), are laid down in many a-stomata.

Pollen development in orchids 1. Cytoskeleton and the control of division plane in irregular patterns of cytokinesis

The cytokinetic apparatus in microsporogenesis lacks a preprophase band of microtubules and the selection of cytokinetic planes is dependent upon disposition of nuclei which define cytoplasmic domains via post-meiotic radial systems of microtubules. Meiotic cytokinesis was investigated in hybrid moth orchids (Phalaenopsis) exhibiting irregular patterns of cytokinesis. In these polliniate orchids, spindle orientation is imprecise, and the tetrad nuclei (therefore the microspores) may be in rhomboidal, tetrahedral or linear arrangement. The hybrid “Sabine Queen” (section Phalaenopsis) regularly undergoes simultaneous cytokinesis, as is common in orchids. The hybrid “Vista Rainbow” (section Amboinenses) produces either a complete dyad wall, a partial wall, or no wall after first nuclear division. In all cases, a first division phragmoplast is initiated in the interzonal region and expands centrifugally into the peripheral cytoplasm. Fluorescence microscopy shows that the phragmoplast consists of fusiform bundles of microtubules and Factin bisected by a non-fluorescent zone. If a cell plate fails to form, a band of organelles polarized in the equatorial region effectively divides the cell into two domains. The organelles disperse when a dyad wall is complete, but tend to remain polarized around an incomplete wall. In four-nucleate coenocytes, the usual interzonal microtubules between sister nuclei (primary) form slightly in advance of secondary arrays between non-sister nuclei. Phragmoplasts are initiated in sites defined by the post-meiotic microtubule arrays.

The microtubular cytoskeleton during development of the zygote, proembryo and free-nuclear endosperm inArabidopsis thaliana (L.) Heynh

The microtubular cytoskeleton has been studied during development of the zygote, proembryo and free-nuclear endosperm inA. thaliana using immunofluorescence localization of tubulin in enzymatically isolated material. Abundant micro tubules (MTs) are found throughout proembryogenesis. Microtubules in the coenocytic endosperm are mainly internal. By contrast, there is a re-orientation of MTs to a transverse cortical distribution during zygote development, predominantly in a subapical band which accompanies a phase of apical extension. The presence of these cortical arrays coincides with the elongation of the zygote. Cortical arrays also accompany elongation of the cylindrical suspensor. Extensive networks of MTs ramify throughout the cytoplasm of cells in the proembryo proper. Perinuclear arrays are detected in a number of cell types and MTs contribute to typical mitotic configurations during nuclear divisions. Preprophase bands of MTs are absent throughout megasporogenesis and embryo-sac development and do not occur in endosperm cell divisions. We have observed MTs throughout the first division cycle of the zygote. By placing the observed stages in a most probable sequence, we have identified this cell cycle as the point during embryogenesis at which a preprophase band is reinstated as a regular feature of cell division. Preprophase bands were observed to predict planes of cytokinesis in cell divisions up to the octant stage.

A role for preprophase bands of microtubules in maturation of new cell walls, and a general proposal on the function of preprophase band sites in cell division in higher plants

ABSTRACT Time-lapse video microscopy of dividing Tradescantia stamen hair cells that are undergoing cytokinesis has revealed that the maturation of the new cell wall is aided by factors at the site where the preprophase band of microtubules forms before mitosis. The wall changes from being fluid and wrinkled before it is inserted into the parental wall at the end of cytokinesis, to being stiff and flat by about 20 min after the time of attachment. This change occurs only if the new wall is inserted at the site formerly occupied by the preprophase band. The cell plate does not flatten when it is caused to insert elsewhere by drug treatments or by centrifugal displacement. If insertion at the correct site is delayed locally by centrifugation against the direction of expansion of the cell plate, then flattening is delayed at the same locality. In combination with a number of points from the literature of plant cell division, some of them very long-standing, our observations lead to a general proposal regarding the nature of the preprophase band site, its mode of action and timing of its operations, and how its role in spatial regulation of histogenesis is achieved.

Tubulin conformation in microtubule-free cells ofVigna sinensis

The primary leaf, epicotyl, and root cells ofVigna sinensis seedlings grown continuously in a 0.08% colchicine solution, become microtubule-free and polyploid. In meristematic root cells a tubulin transformation is detected 1–3 h after the treatment had begun. Tubulin strands are organized at the positions of the pre-existing microtubules. Frequently, the strands converge on or are organized in the cortical cytoplasmic zone where in normal cells the preprophase microtubule band (PMB) is assembled. In meristematic root cells subjected to a 6–12 h colchicine treatment, the tubulin strands become perinuclear, entering the cortical cytoplasm at regions close to the nucleus. One day after the onset of the treatment, tubulin generally forms a continuous reticulum of interconnected strands in all the organs examined. In most cells this reticulum surrounds the nucleus partly or totally or lies close to it, exhibiting variable configurations in different cells. After prolonged treatments, the organization of the tubulin reticulum changes further. Now this consists of crystal-like structures interconnected by thin strands.

MONOPLASTIDIC CELL DIVISION IN LOWER LAND PLANTS.

In many bryophytes and vascular cryptogams mitosis and/or meiosis takes place in cells containing a single plastid. In monoplastidic cell division plastid polarity assures that nuclear and plastid division are infallibly coordinated. The two major components of plastid polarity are morphogenetic plastid migration and microtubule organization at the plastids. Before nuclear division the plastid migrates to a position intersecting the future division plane. This morphogenetic migration is a reliable marker of division polarity in cells with and without a preprophase band of microtubules (PPB). The PPB, which predicts the future division plane before mitosis, is a characteristic feature of land plants and its insertion into the cytokinetic apparatus marks the evolution of a cortical microtubule system and a commitment to meristematic growth. Microtubule systems associated with plastid division, the axial microtubule system (AMS) in mitosis and the quadripolar microtubule system (QMS) in meiosis, contribute to predictive positioning of plastids and participate directly in spindle ontogeny. Division polarity in monoplastidic sporocytes is remarkable in that division sites are selected prior to the two successive nuclear divisions of meiosis. Plastid arrangement prior to meiosis determines the future spore domains in monoplastidic sporocytes, whereas in polyplastidic sporocytes the spore nuclei play a major role in claiming cytoplasmic domains. It is hypothesized that predivision microtubule systems associated with monoplastidic cell division are early forming components of the mitotic apparatus that serve to orient the spindle and insure equal apportionment of nucleus and plastids. "Can it be supposed that cytoplasm would be intrusted with so important a task as the preparation of a chloroplast for each of the four nuclei that are later to preside over the spores before there is any indication that such nuclear division is to take place?" Bradley Moore Davis, 1899.

The role of the cytoskeleton in positioning of the nucleus in premitotic tobacco BY-2 cells

ABSTRACT In premitotic tobacco BY-2 cells, the nucleus moves from the periphery to the central region of the cell and settles there. This premitotic migration of the nucleus occurs in the presence of aphidicolin, an inhibitor of DNA polymerase α, which suppresses the formation of the preprophase band of microtubules (PPB). Thus, the formation of the PPB is not a prerequisite for this premitotic nuclear migration. Tethered by transvacuolar cytoplasmic strands, which contain both microtubules and actin filaments, the nucleus migrates to the site of future division. This migration is not prevented by disruption of actin filaments caused by treatment with cytochalasin, suggesting that microtubules play an important role in the premitotic migration of the nucleus. In the preprophase cell, microtubules were present in the PPB and in cytoplasmic strands, which extended from the nucleus to the periphery of the cell near the PPB and near the poles, and which were associated with actin filaments. At the end of prophase, microtubules in the cytoplasmic strands and the PPB disappeared, leaving actin filaments in the transvacuolar cytoplasmic strands. Thereafter, the position of the mitotic apparatus (or that of the cytokinetic phragmoplast) was maintained by cytoplasmic strands that contained only actin filaments. The disruption of microtubules by treatment with propyzamide prevented the formation of the PPB-like band of actin filaments, as well as that of the PPB itself. From these results, we propose the following hypothesis. In premitotic tobacco BY-2 cells, microtubules change their arrangement irrespective of the presence of actin filaments. The resultant premitotic network of microtubules serves as a scaffold for building up the mitotic network of actin filaments, which plays an important role in maintaining the position of the mitotic apparatus and in controlling the direction of expansion of the phragmoplast.

Monoplastidic mitosis in the mossTimmiella barbuloides (Bryophyta)

Mitotic cell division of monoplastidic sporogones was investigated in the mossTimmiella barbuloides (Brid.) Moenk. (Pottiales, Bryophyta) by TEM. Division polarity of sporogones is established by the interphase position of the single oblong cup-shaped plastid, which is orientated with its long axis parallel to one of the cell walls. In preprophase the plastid elongates and its extremities bend at right angles. Plastid growth is directed by microtubules and accompanied by plastid tubules. The plastid begins the process of duplication by constricting centrally in the plane of the future cytokinetic septum. There is no preprophase band of microtubules at the division site. The large central nucleus becomes fusiform and aligned parallel to the main plastid axis. By the end of prophase the daughter plastids are positioned at the opposite poles of the nucleus where they probably function as nucleating or organizing centres for the spindle microtubules. Metaphase and anaphase spindles contain long sheets of ER. Cytokinesis involves the formation of a well developed phragmoplast.