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Background and Aims: This work investigates the involvement of local differentiation of cell wall matrix polysaccharides and the role of microtubules in the morphogenesis of mesophyll cells (MCs) of three types (lobed, branched and palisade) in the dicotyledon Vigna sinensis and the fern Asplenium nidus., Methods: Homogalacturonan (HGA) epitopes recognized by the 2F4, JIM5 and JIM7 antibodies and callose were immunolocalized in hand-made leaf sections. Callose was also stained with aniline blue. We studied microtubule organization by tubulin immunofluorescence and transmission electron microscopy., Results: In both plants, the matrix cell wall polysaccharide distribution underwent definite changes during MC differentiation. Callose constantly defined the sites of MC contacts. The 2F4 HGA epitope in V. sinensis first appeared in MC contacts but gradually moved towards the cell wall regions facing the intercellular spaces, while in A. nidus it was initially localized at the cell walls delimiting the intercellular spaces, but finally shifted to MC contacts. In V. sinensis, the JIM5 and JIM7 HGA epitopes initially marked the cell walls delimiting the intercellular spaces and gradually shifted in MC contacts, while in A. nidus they constantly enriched MC contacts. In all MC types examined, the cortical microtubules played a crucial role in their morphogenesis. In particular, in palisade MCs, cortical microtubule helices, by controlling cellulose microfibril orientation, forced these MCs to acquire a truncated cone-like shape. Unexpectedly in V. sinensis, the differentiation of colchicine-affected MCs deviated completely, since they developed a cell wall ingrowth labyrinth, becoming transfer-like cells., Conclusions: The results of this work and previous studies on Zea mays (Giannoutsou et al., Annals of Botany 2013; 112: : 1067-1081) revealed highly controlled local cell wall matrix differentiation in MCs of species belonging to different plant groups. This, in coordination with microtubule-dependent cellulose microfibril alignment, spatially controlled cell wall expansion, allowing MCs to acquire their particular shape., (© The Author 2016. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

We investigated the organization of the cortical endoplasmic reticulum (ER) in prophase cells of the angiosperms Zea mays, Triticum turgidum, and Vigna sinensis. In both symmetrically and asymmetrically dividing protodermal leaf cells, cortical ER was enriched in the preprophase band and colocalized there with microtubules, forming a ring-like structure (ER ring). In contrast, ER ring was absent from prophase root-tip cells of the same plants, suggesting that ER ring formation in the preprophase band is organ specific. Immunolabeling of the protodermal leaf cells revealed the presence of acetylated microtubules, which are more stable than the nonacetylated ones. In contrast, neither this post-translational modification of tubulin nor an accumulation of ER in the preprophase band was detected in root-tip cells. Experimentally delaying the maturation/disassembly of the microtubule ring of the preprophase band by taxol or cyclopiazonic acid treatment led to the appearance of ER ring and acetylated microtubules in the preprophase band. Together, our data show that in dividing cells of angiosperms, an ER ring associated with acetylated microtubules forms in the preprophase band., (Copyright © 2012 Wiley Periodicals, Inc.)

Aniline blue staining and callose immunolabeling revealed the deposition of significant callose quantities, in the form of fibrils, in the periclinal walls of guard cells (GCs) of stomata of the fern Asplenium nidus. The stomata that were at an early stage of differentiation displayed short callose fibrils at the junctions of the periclinal walls with the dorsal ones, which converged on the site of the future stomatal pore. In stomata being at an advanced stage of differentiation, callose fibrils were radially arranged around the stomatal pore, while in mature closed ones they were focused on the margins of the wall thickenings lining the stomatal pore. The pattern of the callose fibril organization resembled that of cellulose microfibrils in the same walls. Like the cellulose microfibrils, callose fibrils appeared coaligned with the underlying radial arrays of cortical microtubules (MTs). Moreover, the stomata treated with cellulose synthesis inhibitors (coumarin or dichlobenil) and those recovering from treatments with callose synthesis inhibitors (2-deoxy-D-glucose or tunicamycin) exhibited distinct radial callose fibril arrays. Cytochalasin B did not affect the organization of the radial callose fibril arrays. In contrast, oryzalin completely disturbed the pattern of callose deposition in the affected GCs. Therefore, the fibrillar callose orientation in the periclinal GC walls is probably controlled by MTs but not by actin filaments. The MTs seem to orient callose synthases in the plasmalemma, thus determining the fibrillar nature of callose deposits and their radial mode of arrangement. The cellulose microfibrils are not involved in the callose fibril alignment.

In the present study, the involvement of phospholipase C and D (PLC and PLD) pathways in the asymmetric divisions that produce the stomatal complexes of Zea mays was investigated. In particular, the polar organization of microtubules (MTs) and actin filaments (AFs) and the process of asymmetric division were studied in subsidiary cell mother cells (SMCs) treated with PLC and PLD modulators. In SMCs treated with butanol-1 (but-1), which blocks phosphatidic acid (PA) production via PLDs, AF-patch formation laterally to the inducing guard cell mother cell (GMC) and the subsequent asymmetric division were inhibited. In these SMCs, cell division plane determination, as expressed by MT preprophase band (MT-PPB) formation, was not disturbed. Exogenously applied PA partially relieved the but-1 effects on SMCs. In contrast to SMCs, but-1 did not affect the symmetric GMC division. Inhibition of the PLC catalytic activity by neomycin or U73122 resulted in inhibition of asymmetric SMC division, while AF-patch and MT-PPB were organized as in control SMCs. These data show that the PLC and PLD signaling pathways are involved in the transduction and/or perception of the inductive stimulus that is emitted by the GMCs and induces the polar AF organization and asymmetric SMC division. In contrast, division plane determination in SMCs, as expressed by MT-PPB formation, does not depend on PLC and PLD signaling pathways., ((c) 2008 Wiley-Liss, Inc.)

Double labeling of microtubules and actin filaments revealed that in prophase subsidiary mother cells of Zea mays a monopolar prophase microtubule "half-spindle" is formed, which lines the nuclear hemisphere distal to the inducing guard mother cell. The nuclear hemisphere proximal to the guard mother cell is lined by an F-actin cap, consisting of a cortical F-actin patch and actin filaments originating from it. The microtubules of the "half-spindle" decline from the nuclear surface and terminate to the preprophase microtubule band. After disintegration of the latter, a bipolar metaphase spindle is organized. The polar F-actin cap persists during mitosis and early cytokinesis, extending to the chromosomes and the subsidiary cell daughter nucleus. In oryzalin treated subsidiary mother cells the prophase nuclei move away from the polar site. Cytochalasin B and latrunculin-B block the polar migration of subsidiary mother cell nuclei, but do not affect those already settled to the polar position. The prophase nuclei of latrunculin-B treated subsidiary mother cells are globally surrounded by microtubules, while the division plane of latrunculin-B treated subsidiary mother cells is misaligned. The prophase nuclei of brick 1 mutant Zea mays subsidiary mother cells without F-actin patch are also globally surrounded by microtubules. The presented data show that the prophase microtubule "half-spindle"-preprophase band complex anchors the subsidiary mother cell nucleus to the polar cell site, while the polar F-actin cap stabilizes the one metaphase spindle pole proximal to the inducing guard mother cell., ((c) 2006 Wiley-Liss, Inc.)

The morphogenesis of lobed plant cells has been considered to be controlled by microtubule (MT) and/or actin filament (AF) organization. In this article, a comprehensive mechanism is proposed, in which distinct roles are played by these cytoskeletal components. First, cortical MT bundles and, in the case of pavement cells, radial MT arrays combined with MT bundles determine the deposition of local cell wall thickenings, the cellulose microfibrils of which copy the orientation of underlying MTs. Cell growth is thus locally prevented and, consequently, lobes and constrictions are formed. Arch-like tangential expansion is locally imposed at the external periclinal wall of pavement cells by the radial arrangement of cellulose microfibrils at every wall thickening. Whenever further elongation of the original cell lobes occurs, AF patches assemble at the tips of growing lobes. Intercellular space formation is promoted or prevented by the opposite or alternate, respectively, arrangement of cortical MT arrays between neighboring cells. The genes that are possibly involved in the molecular regulation of the above morphogenetic procedure by MT and AF array organization are reviewed.

In dividing root-tip cells of Pinus brutia Ten., immunolocalization of the luminal endoplasmic reticulum (ER) proteins, which have the C-terminal HDEL sequence, reveals that the ER is reorganized during the preprophase/prophase stage. Portions of ER were arrayed into a ring-like structure at the site of the microtubule preprophase band (Mt-PPB). This preprophase ER band (ER-PPB) resembles that of the Mt-PPB. The former undergoes a maturation process closely similar to that of the latter. Our data show that the PPB region has a more complex organization than is currently believed. The probable function(s) of the ER-PPB is discussed.

Background and Aims The morphogenesis of lobed mesophyll cells (MCs) is highly controlled and coupled with intercellular space formation. Cortical microtubule rings define the number and the position of MC isthmi. This work investigated early events of MC morphogenesis, especially the mechanism defining the position of contacts between MCs. The distributions of plasmodesmata, the hemicelluloses callose and (1 → 3,1 → 4)-β-d-glucans (MLGs) and the pectin epitopes recognized by the 2F4, JIM5, JIM7 and LM6 antibodies were studied in the cell walls of Zea mays MCs. Methods Matrix cell wall polysaccharides were immunolocalized in hand-made sections and in sections of material embedded in LR White resin. Callose was also localized using aniline blue in hand-made sections. Plasmodesmata distribution was examined by transmission electron microscopy. Results Before reorganization of the dispersed cortical microtubules into microtubule rings, particular bands of the longitudinal MC walls, where the MC contacts will form, locally differentiate by selective (1) deposition of callose and the pectin epitopes recognized by the 2F4, LM6, JIM5 and JIM7 antibodies, (2) degradation of MLGs and (3) formation of secondary plasmodesmata clusterings. This cell wall matrix differentiation persists in cell contacts of mature MCs. Simultaneously, the wall bands between those of future cell contacts differentiate with (1) deposition of local cell wall thickenings including cellulose microfibrils, (2) preferential presence of MLGs, (3) absence of callose and (4) transient presence of the pectins identified by the JIM5 and JIM7 antibodies. The wall areas between cell contacts expand determinately to form the cell isthmi and the cell lobes. Conclusions The morphogenesis of lobed MCs is characterized by the early patterned differentiation of two distinct cell wall subdomains, defining the sites of the future MC contacts and of the future MC isthmi respectively. This patterned cell wall differentiation precedes cortical microtubule reorganization and may define microtubule ring disposition. [ABSTRACT FROM AUTHOR]

The effects of the aluminium (Al) on dividing root-tip cells of Triticum turgidum were investigated with tubulin immunolabelling and electron microscopy. Aluminium affects the mechanisms controlling the organization of microtubule (MT) cytoskeleton, as well as tubulin polymerization, and induces the following aberrations in mitotic cells. (1) It delays the MT disassembly during mitosis. resulting in the persistence of preprophase MT bands in the late prophase cells, the presence of prophase spindles in prometaphase cells, and a disturbance in this shortening of kinetochore MT bundles in anaphase cells. (2) It interferes with the self-organization process of MTs into bipolar systems, inhibiting the formation of prophase and metaphase spindles. (3) Aluminum induces the formation of atypical MT arrays, which in the immunofluorescent specimens specimens appear as ring-like tubulin aggregations in the cortical cytoplasm of the preprophase/prophase cells and as endoplasmic tubulin bundles in prophase and metaphase/anaphase cells; abnormal preprophase MT bands are assembled, consisting of atypical cortical and endoplasmic MT bundles, the latter clearly lining the nuclear envelope on the preprophase MT band plane. (4) It disorders the chromosome movements carried out by the mitotic spindle. In addition, after prolonged Al treatments chromatin condensation is inhibited. The outcome is greatly disturbed organization and function of the mitotic apparatus, as well as inhibition of cells from entering mitosis. This study shows that the MT cytoskeleton is a target site of Al toxicity in mitotic root-tip cells of T. turgidum. The possible mechanisms by which Al exerts its toxicity on MT organization and function are discussed. [ABSTRACT FROM AUTHOR]

The post-cytokinetic guard cells of Asplenium nidus display a prominent perinuclear microtubule system and a few microtubules under the periclinal walls. Afterwards, microtubules appear on the whole surface of the ventral wall, whereas those below the periclinal walls proliferate and tend to become parallel with the ventral wall. The perinuclear microtubules gradually diminish but persist in later stages of guard cell differentiation. In post- cytokinetic guard cells, actin is found in the perinuclear cytoplasm and in the cortical cytoplasm lining all the walls. In differentiating guard cells, the following cortical microtubules and actin filament 'systems' appear in succession: (a) radial microtubule and actin filament arrays beneath the periclinal walls converging on the stomatal pore region, (b) anticlinal microtubule bundles, which are co-localized with actin filaments, along the ventral wall outlining the region of the stomatal pore, (c) periclinal microtubules and actin filaments on the polar ventral wall ends. These cytoskeletal systems, except for the radial actin filaments, persist in advanced stages of guard cell differentiation. Instead of the radial actin filaments, a prominent actin filament reticulum is organized under the margins of the developing wall thickenings of the stomatal pore. In addition, an extensive endoplasmic actin filament reticulum develops around the plastids. It seems likely that the successive microtubule systems in guard cells are formed by putative microtubule organizing centres operating in a definite spatial arid temporal succession. Guard cell morphogenesis is the outcome of a definite process, in which the cortical microtubule cytoskeleton plays the primary role, implicated in the deposition of cellulose microfibrils and probably of the local wall thickenings. Callose or a callose-like glucan is deposited on the whole surface of the nascent ventral wall and in the wall regions where thickenings are deposited. Finally, the guard cells of Asplenium assume a kidney shape and display polar hypostomatic swellings. Particular structural features established in guard cell mother cells affect guard cell morphogenesis. [ABSTRACT FROM AUTHOR]

The typical scale cells (TSCs) of Marchantia paleacea Bert. contain a well-developed cortical microtubule (Mt) cytoskeleton, particularly below the anticlinal walls and also display complete but broad preprophase-prophase Mt bands (PMBs). In contrast, the cortical cytoskeleton of the inner thallus cells (ITCs) is less developed than that of TSCs and the PMBs are incomplete. The latter consist of one to four separate Mt bundles which lie on the cytokinetic plane, but do not form a complete Mt ring. In both cell types PMB formation precedes or keeps pace with the activation of the polar Mt-organizing centres (MTOCs) and nuclear shaping. The Mts in the PMBs are more numerous and densely packed at the cell edges than on the cell face. The polar MTOCs persist up to late prophase-prometaphase. Afterwards, the spindle Mts are focused on several minipoles, where endoplasmic reticulum is localized. In postcytokinetic cells the cortical Mts first reappear on the daughter wall surface. Our findings suggest that: (a) The formation of complete or incomplete PMBs in TSCs and ITCs of M. paleacea is related to differences in the development of the interphase cortical Mt arrays. (b) The cell edges are able to form or at least arrange the Mts of the PMB. (c) Tight mature PMBs like those found in flowering plant cells are not formed in the cells examined in the present study. (d) The final orientation of the cell plate is controlled by the PMB cortical zone. (e) The cytoplasm abutting on the postcytokinetic daughter wall has the ability to assemble cortical Mts. [ABSTRACT FROM AUTHOR]

Protodermal cells of Adiantum capillus-veneris leaflets are polyhedral, displaying regularly arranged cortical microtubules transverse to the main cell axis. The nascent epidermal cells partly detach from the underlying mesophyll cells by formation of intercellular spaces, containing PAS-positive material. In early differentiating upper epidermal cells discrete U-like bundles of cortical microtubules form on the internal periclinal and the anticlinal walls. In contrast, microtubules are randomly scattered along the external periclinal wall. Microtubule bundles of neighbouring anticlinal walls of epidermal cells exhibit an alternating disposition but are directly opposite to those of underlying mesophyll cells. Epidermal cell wall is locally reinforced by thickenings reflects that of the microtubule bundles. The internal periclinal epidermal cell region expands at the sectors free of wall thickenings, forming several lobes. Simultaneously, intercellular spaces open at the thickened regions of anticlinal walls, which finally become wavy. In contrast, the external periclinal wall does not form any lobes but remains smooth. As a result, epidermal cells become 'semi-lobed'. The lobes of lower epidermal cells are less prominent. Mesophyll cells surrounding the endodermis are also 'semi-lobed'. Their morphogenesis is achieved by the same mechanism. Colchicine treatment inhibits the 'semi-lobed' morphogenesis of epidermal cells and mesophyll cells surrounding the endodermis and the concomitant intercellular space opening. These observations reveal that the primary event of 'semi-lobed' cell morphogenesis in the organization of two different patterns of the cortical microtubule cytoskeleton in the same cell. [ABSTRACT FROM AUTHOR]

The cortical cytoplasm of the young guard cells of Adiantum capillus veneris is locally differentiated. At an early post-telophase stage, numerous microtubules diverge from the cytoplasm occupying the junctions of the midregion of the ventral wall with the periclinal ones, towards the periclinal and ventral wall faces as well as towards the inner cytoplasm. Microtubule-vesicle complexes (MVCs) are detected in these regions. Their appearance is accompanied by the initiation of local wall thickenings in the same areas. Afterwards, more distinct MVCs anchored to the plasmalemma were seen in the cortical cytoplasm of the periclinal walls, close to the growing thickenings, usually at a distance up to 3 μm from them. Sometimes, they seemed to contain an electron dense substance in which the microtubules were embedded. Cortical microtubules converging from more than one direction terminate at the MVCs. Besides, the microtubule population lining the periclinal walls radiate from the regions where the above cytoplasmic formations are localized. The overlying cellulose microfibrils exhibit the same orientation. The vesicles localized at the MVCs appear to be of dictyosomal origin, very electron dense and react positively to periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) test. Another population of microtubules fan out from the MVCs, entering deeper into the cytoplasm. They become associated with the nucleus and mitochondria, and traverse the peridictyosomal cytoplasm. In some instances the nucleus formed a protrusion towards an MVC and appeared associated with it via microtubules which radiate from the MVC and flank the nuclear envelope. The observations favour the hypothesis that prominent microtubule organizing centres (MTOCs) function in the cortical cytoplasm of the midregion of the periclinal walls surrounding the ventral one for a relatively long time. The MVCs and/or their adjacent plasmalemma sites may represent MTOCs or at least they specify the cortical cytoplasmic sites where microtubules are nucleated. [ABSTRACT FROM AUTHOR]

The newly-formed guard cell mother cells (GMCs) of Asplenium nidus are small, lens-shaped and are formed by one or two asymmetrical divisions. Their growth axis is parallel to the plane of their future division, a process during which the internal periclinal wall (IPW) is detached from the partner wall of the underlying cell(s). This oriented GMC expansion occurs transversely to a microfibril bundle, which is deposited externally to a U-like microtubule (Mt) bundle and a co-localized actin filament (Af) bundle. They line the IPW and the major part of the anticlinal walls. The deposition of the microfibril bundle is followed by the slight constriction of the internal part of the GMCs and the broadening of the substomatal cavity. The IPW forms a distinct bulging distal to the neighbouring leaf margin, as well as a less defined proximal one. During the IPW bulging, the Mts and Afs under the external periclinal wall (EPW) attain a radial organization. This is followed by thinning of the central EPW region, which becomes impregnated with a callose-like glucan. The rest of the EPW becomes unequally thickened. The disintegration of the U-like Mt bundle is succeeded by the organization of radial Mt and Af arrays under the IPW. The radial Mt systems, controlling the alignment of the newly-deposited microfibrils, allow the GMC to assume a round paradermal profile. The GMCs form a preprophase Mt band (PPB) perpendicular to the interphase U-like Mt bundle. The anticlinal PPB portions appear first and those lining the periclinal walls later. The cytoplasm adjacent to the latter walls retain the radial Mt systems during early preprophase, simultaneously with the anticlinal PPB portions. The observations suggest that the GMCs of the fern A. nidus obtain a unique form, as a result of a particular polarity established in the cortical cytoplasm of the periclinal walls, in which Mts and Afs appear involved. This polarity persists in cell division and is “inherited” to guard cells (GCs). It provides primary morphogenetic information not only to GMCs but also to GCs. [ABSTRACT FROM AUTHOR]

To examine whether preprophase microtubule band (PPB) organization occurs by rearrangement of pre-existing, or by assembly of new microtubules (Mts), we treated root cells of Triticum turgidum with taxol, which stabilizes pre-existing Mts by slowing their depolymerization. With taxol early preprophase cells failed to form a normal PPB and PPB narrowing was prevented in cells that had already formed a wide one. The PPB became persistent in prometaphase cells and the formation of multipolar prophase-prometaphase spindles was induced. These data favour the suggestion that PPB formation and narrowing, as well as prophase spindle development, are dynamic processes depending on continuous Mt assembly at the PPB site and in the perinuclear cytoplasm. [ABSTRACT FROM AUTHOR]

Undifferentiated ordinary epidermal cells (ECs) of Vigna sinensis leaves possess straight anticlinal walls and cortical microtubules (Mts) scattered along them. At an early stage of EC differentiation cortical Mts adjacent to the above walls form bundles normal to the leaf plane, loosely interconnected through the cortical cytoplasm of the internal periclinal wall. At the upper ends of the Mt bundles, Mts fan out towards the external periclinal wall and form radial arrays. Mt bundles and radial arrays exhibit strict alternate disposition between neighbouring ECs. An identical reticulum of cellulose microfibril (CM) bundles is deposited outside the Mt bundles. Local wall pads rise at the junctions of anticlinal walls with the external periclinal one, where the CM bundles terminate. They display radial CMs fanning towards the external periclinal wall. The CM bundles and radial CM systems prevent local cell bulging, but allow it in the intervening wall areas. In particular, the radial CM systems dictate the pattern of EC waviness by favouring local tangential expansion of external periclinal wall. As a result, ECs obtain an undulate appearance. 'Constrictions' in one EC correspond with protrusions of adjacent ECs. ECs affected by colchicine entirely lose their Mts and do not develop wavy walls, an observation substantiating the role of cortical Mts in EC morphogenesis. [ABSTRACT FROM AUTHOR]

Mesophyll cells (MCs) of Adiantum capillus veneris are elongated and highly asymmetric, bearing several lateral branches and forming a meshwork resembling aerenchyma. Young MCs are polyhedral and display oppositely arranged walls and transverse cortical microtubules (Mts). Their morphogenesis is accomplished in three stages. At first they become cylindrical. Intercellular space (IS) canals, containing PAS-positive material, open through their junctions and expand laterally. During the second stage the cortical Mts form a reticulum of bundles, externally of which an identical reticulum of wall thickenings, containing bundles of parallel cellulose microfibrils, emerges. MCs do not grow in girth in the regions of wall thickenings, where constrictions form and new ISs open. Thus, MCs obtain a multi-lobed form. At the third morphogenetic stage MCs display a multi-axial growth. During this process, additional Mt rings are assembled at the base of cell lobes accompanied by similarly organized wall thickenings-cellulose microfibrils. Consequently, cell lobes elongate to form lateral branches, where MCs attach one another, while the IS labyrinth broadens considerably. Colchicine treatment, destroying Mts, inhibits MC morphogenesis and the concomitant IS expansion, but does not affect IS canal formation. These observations show that: (a) MC morphogenesis in A. capillus veneris is an impressive phenomenon accurately controlled by highly organized cortical Mt systems. (b) The disposition of Mt bundles between neighbouring MCs is highly coordinated, (c) The perinuclear cytoplasm does not appear to be involved in cortical Mt formation. Cortical sites seem to participate in Mt bundling, (d) Although extensive IS canals open before Mt bundling, the Mtdependent MC morphogenesis contributes in IS formation. [ABSTRACT FROM AUTHOR]

Interphase cells of Dictyota dichotoma (Hudson) Lamour. lack cortical microtubules (Mts) but display an impressive network of cytoplasmic microtubules (c-Mts). These are focussed on two opposed perinuclear centriolar sites where centrin or a centrin-homologue is localized. Some of the Mts surround the nucleus, but the majority traverse the cytoplasm as bundles variously directed towards the plasmalemma. In apical cells, and to a lesser extent in the square or slightly elongated meristematic cells, Mts are more or less evenly arranged. In elongated cells they form thick bundles longitudinally traversing the cytoplasm; a pattern maintained in differentiated cells. In early prophase the non-perinuclear Mts disappear but by late prophase a bi-astral arrangement of short Mts is observed. They enter polar nuclear depressions and attach to differentiated regions of the nuclear envelope where polar gaps open. By metaphase the spindle Mts converge on the centrioles at the polar gaps. At anaphase, interzonal Mts are evident and the asters start to reassemble. After telophase disruption of the interzonal Mts, the daughter nuclei approach each other, but move apart again before cytokinesis. The latter movement keeps pace with the development of two interdigitating Mt systems, ensheathing both daughter nuclei. The partition membrane 'bisects' this Mt 'cage'. Between telophase and cytokinesis the centrosomes separate, finally occupying opposed perinuclear sites. New Mts arise at the new centrosomes, some terminating on the consolidating partition membrane. Our data show that D. dichotoma vegetative cells display a prominent cytoplasmic Mt cytoskeleton, which undergoes continual, but definite, change in organization during the cell cycle. [ABSTRACT FROM AUTHOR]

Treatment of Zea 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. In a-stomata with or without VW-strips, the periclinal walls are lined by numerous microtubules (Mts) converging on their mid-region, where local wall thickenings are deposited. When the VW-strips reach the mid-region of the periclinal walls, thickenings lined by numerous Mts rise at their free margins. In certain a-stomata an anticlinal wall column, surrounded by a dense Mt bundle, grows centripetally from either or both of the periclinal wall thickenings. In wall thickenings, the cellulose microfibrils are co-aligned with the adjacent Mts. Pore formation is initiated in all a-stomata. Deposition of an electron dense intra-wall material followed by lysis precedes 'pore' opening. This process is closely related to the a-stornata morphogenesis. These observations show that the primary morphogenetic phenomenon in a-stomata is the establishment of an intense and stable polarity in the cytoplasm abutting on the mid-region of the periclinal walls and/or the adjacent plasmalemma area. Prime morphogenetic factor(s), including microtubule organizing centres (MTOCs), seem to function in these sites. Morphogenesis in a-stomata is a Mt-dependent process that is carried out as in normal stomata but in the absence of a VW. [ABSTRACT FROM AUTHOR]