External Periclinal Wall Research Articles

F-Actin Organization and Epidermal Cell Morphogenesis in the Brown Alga Sargassum vulgare.

The ordinary epidermal cells of various vascular plants are characterized by wavy anticlinal wall contours. This feature has not yet been reported in multicellular algal species. Here, we found that, in the leaf-like blades of the brown alga Sargassum vulgare, epidermal cells exhibit prominent waviness. Initially, the small meristodermal cells exhibit straight anticlinal contour, which during their growth becomes wavy, in a pattern highly reminiscent of that found in land plants. Waviness is restricted close to the external periclinal wall, while at inner levels the anticlinal walls become thick and even. The mechanism behind this shape relies on cortical F-actin organization. Bundles of actin filaments are organized, extending under the external periclinal wall and connecting its junctions with the anticlinal walls, constituting an interconnected network. These bundles define the sites of local thickening deposition at the anticlinal/periclinal wall junctions. These thickenings are interconnected by cellulose microfibril extensions under the external periclinal wall. Apart from the wavy anticlinal contour, outward protrusions also arise on the external periclinal wall, thus the whole epidermis exhibits a quilted appearance. Apart from highlighting a new role for F-actin in cell shaping, the comparison of this morphogenetic mechanism to that of vascular plants reveals a case of evolutionary convergence among photosynthetic organisms.

Double Puzzle: Morphogenesis of the Bi-Layered Leaf Adaxial Epidermis of Magnolia grandiflora.

Anticlinal ordinary epidermal cell wall waviness is a widespread feature found in the leaves of a variety of land plant species. However, it has not yet been encountered in leaves with multiple epidermides. Surprisingly, in Magnolia grandiflora leaves, ordinary epidermal cells in both layers of the bi-layered adaxial epidermis exhibit wavy anticlinal contour. During the development of the above cells, cortical microtubules are organized in anticlinally oriented bundles under the anticlinal walls, and radial arrays extending from the bundles at the edges of anticlinal and external periclinal walls, under the external periclinal walls. This microtubule pattern is followed by cell wall reinforcement with local thickenings, the cellulose microfibrils of which are parallel to the underlying microtubules. This specialized microtubule organization and concomitant cell wall reinforcement is initiated in the external epidermal layer, while hypodermis follows. The waviness pattern of each epidermal layer is unrelated to that of the other. The above findings are discussed in terms of morphogenetic mechanism induction and any implications in the functional significance of ordinary epidermal cell waviness.

The short but useful life of Prepusa montana Mart. (Gentianaceae Juss.) leaf colleters-anatomical, micromorphological, and ultrastructural aspects.

Colleters are secretory structures involved in the protection of young and developing plant organs. Although the presence of colleters in Gentianales is described as a synapomorphy, studies on the morphofunctionality of colleters and the mechanisms underlying the synthesis and release of colleter secretion in Gentianaceae are scarce. Here, we described the ontogeny and the morphological and functional aspects of colleters of Prepusa montana, revealed the nature of the key compounds present in the secretion, and explored the cellular aspects of the synthesis and release of secretion and senescence of colleters. Samples of the stem apical meristem with leaf primordium and young leaves; adult and senescent leaves were observed using light and electron microscopy. The colleters, located in the axil of the leaf, have a protodermal origin and develop asynchronously. They are digitiform, possessing a short peduncle and a secretory head containing homogeneous cells with dense cytoplasm and abundant endoplasmic reticulum and Golgi bodies. The secretion, composed of polysaccharides and proteins, is accumulated in schizogenous spaces and released through the separation of peripheral secretory cells and loosening of the external periclinal wall. Presumably, senescence is caused by programmed cell death. The morphoanatomical characterization of P. montana leaf colleters described here is the first record for the genus and the peculiar accumulation of colleter secretion in schizogenous spaces expanding our knowledge on the diversity of these secretory structures. Our results also provide insights into programmed cell death as an eminent topic related to secretory structures.

Ontogenesis and secretion mechanism of Morinda citrifolia L. (Rubiaceae) colleters

Colleters are secretory structures present in more than 60 families of angiosperms, whose function is protecting the leaf primordium and meristem against biotic and abiotic damage. The colleters are developed from protoderm and ground meristem and the secretory process begins during cell differentiation. The secretion is a complex phenomenon of synthesis, separation and isolation of substances, as well as release or extracellular elimination. This research describes the ontogenesis of Morinda citrifolia L. colleters and the mechanism of exsudate externalization. For this purpose, various microscopy techniques, including scanning electron microscopy, light microscopy (including histochemical tests) and confocal scanning laser microscopy were used. Standard type colleters are attached on the stipule adaxial surface. During development, the colleters pass through four developmental stages defined by structural and anatomical changes: undifferentiated, pre-secretory, secretory and senescent. In the undifferentiated stage, the secretory structures are characterized by small protuberances. In the pre-secretory stage, the secretory epithelium begins its differentiation. In the following stages, the colleters present a parenchymatic central axis covered by palisade epidermal cells. Secretion occurs by the rupture of the cuticle. At the end of the secretory process, the colleters begin the senescent stage, characterized by deformation, color change and cuticle wrinkling. This work evidences the section passage mechanism by cuticle rupture, accumulating knowledge in the still poorly understood process of molecules passages by the external periclinal wall in Rubiaceae colleters.

Leaf morphoanatomy of the medicinal Maytenus imbricata (Celastraceae): an ecological approach

Background . The leaves of many species of Maytenus are used to prepare herbal drugs to treat stomach ulcers.
 Questions. In order to define key anatomical characters for the unambiguous species identification, the present study aimed to describe the leaf morphoanatomy of M. imbricata. 
 Species study . Maytenus imbricata Mart. ex Reissek (Celastraceae)
 Study site and dates. Collected in an area of ‘campo rupestre’ - one of the Brazilian Savannah vegetation (20º22’11.02”S, 43º30’22.81”W) in August 2015.
 Methods . The plant material was processed according to commonly used techniques in plant anatomy studies.
 Results. The major anatomical characters for several species of Maytenus identification also present in M. imbricata are marginal teeth, conspicuous epicuticular wax, ciclocytic stomata, thick external periclinal wall with large pits on epidermal cells and vascular system with a closed loop shape in cross-section. Strips on the anticlinal walls on epidermal cells and conspicuous gelatinous fibers sheath are diagnostic for M. imbricata .
 Conclusions. Strips on the anticlinal wall of the epidermal cell are reported for the first time for the genus. These xeromorphic traits help the species to survive in arid environments and may contribute to quality control of the raw material used in the production of herbal medicines.

Vegetation damage in the vicinity of an aluminum smelter in Brazil

A primary aluminum smelter, which is responsible for releasing fluoride and other pollutants to atmosphere, is located at the vicinities of rocky field ecosystem in Brazil. We aimed to evaluate the biological effects of the smelter emissions using Spondias dulcis as a bioindicator organism. Evaluations of rainwater quality, atmospheric oxidants and toxicity visual symptomatology were performed in 4 different sites. We also collected leaflets with and without visual toxicity symptoms for anatomical studies under light and scanning electron microscopes, histochemistry, X-ray microanalysis, and fluoride quantification. The fluoride detected on leaves was present in plants at all studied sites, principally at Site 1 (park entrance) and less detected at Site 3 (forest area). However, the fluoride quantity was not the main cause of damage, but the large amount of oxidants which was detected at the atmosphere. This amount of oxidants was increased with the distance from the emission source. It was noticed two types of visual symptoms on the leaflets: a darkening at the adaxial face and a wide brownish necrosis. The anatomical studies showed three damage patterns: superficial necrosis, reaching just the palisade and spongy parenchyma, deep necrosis, reaching the entire mesophyll and a punctual necrosis perceived only at the central veins. With scanning electron microscopy it was detected a turgor loss and a flattening of the cell's external periclinal wall. In the areas where the damage was more noticeable, there was an erosion of the epicuticular wax that lead to delayering, resulting on the epidermis rupture and internal tissue exposure. S. dulcis showed visual symptoms after few days of exposure, which culminated in structural alterations, thus indicating that these pollutants are impacting this important vegetation type from a rocky field ecosystem.

Morfología y anatomía de ejes caulinares, licofilos y esporangios de Phlegmariurus phylicifolius: un aporte a la sistemática de las Lycopodiaceae neotropicales

Phlegmariurus is the only genus of Lycopodiaceae with the species grouped in 22 informal groups. Species level relationships within Phlegmariurus are poorly understood and their circumscriptions require a thorough molecular and morphological review. A detailed study of morphology and anatomy of caulinar axes, lycophylls and sporangia of Phlegmariurus phylicifolius was carried out in order to contribute to the elucidation of species circumscription in the informal group Phlegmariurus phlegmaria. Small pieces of caulinar axes bearing trophophylls, sporophylls and sporangia were fixed, dehydrated, Histowax (paraffin) embedded, sectioned in a rotatory microtome, and stained using the common Safranin O-Fast Green technique; handmade cross sections were also made and stained with the same technique. P. phylicifolius includes slender, pendulous plants up to 40cm long. Shoots heterophyllous, in the basal divisions ca. 10-20(-25) mm in diameter including the trophophylls, then abruptly constricted to (1-) 1.5-2(-2.5) mm in diameter including the imbricate, reduced sporophylls. Trophophylls are borne in alternating whorls of three, or decussate, subdecussate, or alternate, widely spaced in alternate leaved caulinar axes portions, perpendicular to the caulinar axes to falcately ascending, lanceolate to linear-lanceolate, with flat to slightly revolute margins. Each lycophyll is supplied by a single central vascular bundle, connected to a protoxylem pole in the stele. At the site of leaf-trace departure, no leaf (lycophyll) gap is present. Caulinar axes excluding leaves 0.7-1.2 mm thick at the base, upward tapering to ca. 0.5 mm. Caulinar axes present unistratified epidermis and endodermis, the cortex is characterized by the presence of a trabecular structure of lisigenous origin formed in the parenchimatous tissue next to the endodermis. The vascular tissue occupies the central part of the caulinar axes, forming a plectostele ofsubradiate organization, with five poles ofprotoxylem. The epidermal cells present sinuous anticlinal walls; invaginations in the inner side of external periclinal wall of the epidermal cells could be probably adaptive morphological feature of a water deficient environment. Leaves of constricted terminal divi- sions are decussate, or subdecussate, continuously or discontinuously sporangiate, appressed, abaxially rounded to carinate, widely lanceolate to widely ovate or subcordate, acute to mucronate or cuspidate, shorter than the sporangia. Each sporangium originates from a group of epidermal cells, axilar to the sporophylls. The cell walls of epidermal cell of the sporangia are Huperzioideae type. The morphological studies of trophophylls contribute to confirm the differences between P. phylicifolius and P. subulatus.

Seed coat sculpture in Comanthera (Eriocaulaceae) and its implications on taxonomy and phylogenetics

Eriocaulaceae occurs primarily in the Neotropics, diversifying mostly in mountainous areas in southeastern Brazil. They are popularly known as everlasting plants, because once dried, they retain the appearance of living structures, being widely used as ornamentals. Most of the commercialized species belong to the genus Comanthera L.B.Sm., which was reestablished from Syngonanthus Ruhland. Comanthera groups 41 species, 26 in Comanthera subg. Comanthera and 15 in C. subg. Thysanocephalus, all restricted to South America. Phylogenetic analyses show Syngonanthus and Comanthera, as well as both Comanthera subgenera, as monophyletic and sister groups. Seed coat ornamentation proved to be useful and informative to help in determining taxonomic relationships in many plant groups. This study aims to characterize the external morphology of the seed coat of Comanthera and its subgenera using scanning electron microscopy, and discuss its taxonomic and phylogenetic implications. Seeds from nine species of Comanthera were analyzed, seven of which belong to C. subg. Comanthera and two to C. subg. Thysanocephalus. The results were compared with four species of Syngonanthus and one of Leiothrix. In Comanthera and Leiothrix the external periclinal walls remain intact, whereas they degenerate in the remaining genera. However, seed coat ornamentation in Leiothrix and Comanthera has distinct origins, as in the former, it comes from projections of the external layer of the outer integument, forming a striate pattern, and in the latter, from projections of the inner layer, conferring a rough pattern. Comanthera subg. Comanthera shows a rugose undulatory pattern, whilst C. subg. Thysanocephalus has a rugose micropapillate pattern. The newly reported features of the seed coat provide support for the Comanthera subgenera, thus presenting taxonomic and phylogenetic value.

The taxonomic value of floral characters in Rapateaceae (Poales-Monocotyledons)

The floral anatomy of Cephalostemon, Monotrema, Rapatea, Spathanthus, and Stegolepis was studied for taxonomic purposes. All species studied share colleters between the floral parts; sepals, petals, anthers, and style covered by an ornamented cuticle; short epidermal cells with sinuous walls on the abaxial surface of the petals; tetrasporangiate anthers with phenolic idioblasts in the epidermis; endothecium with spiral thickenings; incompletely septate ovary; and anatropous, bitegmic ovules. The floral anatomy is useful not only for characterizing the family, but also for delimiting the subfamilies and genera. Sepals with silica bodies in the epidermal cells; mature anther wall composed of epidermis, endothecium, and middle layer; absence of phenolic idioblasts in the sepals, filaments, and ovary; and stylar epidermal cells with thickened external periclinal wall support Rapateoideae. Cephalostemon and Rapatea show a great number of similarities, corroborating their close relationship indicated in the phylogenetic analyses of the family. Monotrema shares few characters with the genera of Rapateoideae, corroborating its placement in Monotremoideae. Stegolepis shows several distinctive characters, probably related to the greater diversity found in this genus.

The formation of the stigmatic surface in Passiflora elegans (Passifloraceae)

Abstract The stigma surface is a complex multicellular structure where the development of the pollen tube begins. This development is necessary for sucess in fertilization and depends on recognition processes that involve the anatomy of the stigma. Passiflora is an economically important genus because of its edible fruits. Many authors have described the stigma of Passiflora but nothing is known about the ontogenesis of this structure. This work aimed to describe the formation of the stigmatic surface of Passiflora elegans. Results showed that, in bud, the stigmatic surface of this species is flat with small cells. The cells in the subdermal layer have large vacuoles and the nucleus, near to the external periclinal walls. During its development the stigma surface becomes uneven due to the elongation of cells in the subdermal layer. Elongation results in an increase of external secretory surface area of the stigmas, and probably plays an important role in pollen recognition. The polysaccharide content found in the inner walls of these structures might be involved in the signal process for pollen tube growth during its early development. The morphological evidence presented here shows that, as the stigma of Passiflora is formed by dermal and subdermal cells, it should not be characterized as colleters or papillae and, therefore, it is defined here as stigma emergences.

Callose implication in stomatal opening and closure in the fern Asplenium nidus

The involvement of callose in the mechanism of stomatal pore opening and closing in the fern Asplenium nidus was investigated by examination of the pattern of callose deposition in open and closed stomata, and by examination of the effects of callose degradation and inhibition or induction of callose synthesis in stomatal movement. Callose was identified with aniline blue staining and a callose antibody and degraded via beta-1,3-D-glucanase. Callose synthesis was inhibited with 2-deoxy-D-glucose and induced by coumarin or dichlobenil. Stomatal pore opening and closing were assessed by estimation of the stomatal pore width. The open stomata entirely lacked callose, while the closed ones displayed distinct radial fibrillar callose arrays in the external periclinal walls. The latter displayed local bending at the region of callose deposition, a deformation that was absent in the open stomata. Both callose degradation and inhibition of callose synthesis reduced the stomatal ability to open in white light and close in darkness. By contrast, callose synthesis induction considerably improved stomatal pore opening and reduced stomatal closure in same conditions. The present data revealed that: during stomatal closure the external periclinal guard cell walls experience a strong mechanical stress, probably triggering callose synthesis; and that callose participates in stomatal movement.

Anatomia de espécies anfíbias de Cyperaceae de lagoas do semi-árido, BA, Brasil

Foi estudada a anatomia de raízes, rizomas, folhas e escapos de Cyperus odoratus L., Oxycaryum cubense (Poep. & Kunth) Lye e Pycreus macrostachyos (Lam.) Raynal (Cyperaceae-Poales) de lagoas do semi-árido da Bahia visando caracterizar anatomicamente as espécies e levantar estruturas adaptativas à forma de vida anfíbia. As espécies apresentam raízes com epiderme unisseriada, córtex com exoderme e lacunas de ar. Os rizomas apresentam feixes vasculares anfivasais ou colaterais no cilindro vascular. As folhas apresentam epiderme unisseriada, com células de parede periclinal externa mais espessada que a interna, estômatos somente na face abaxial, parênquima clorofiliano alternado com lacunas de ar e feixes vasculares colaterais. Os escapos apresentam epiderme unisseriada, feixes de fibras distribuídos perifericamente alternados com parênquima clorofiliano, lacunas de ar e feixes vasculares colaterais. Oxycaryum cubense difere de Cyperus odoratus e Pycreus macrostachyos por apresentar raízes com pêlos longos, rizomas e estolões com feixes vasculares colaterais, folhas com bordo agudo, e ausência de estrutura Kranz nas folhas e escapos. Características anatômicas como: lacunas de ar observadas principalmente nas raízes, células buliformes na face adaxial da epiderme foliar, hipoderme, reduzido número de elementos xilemáticos e pouca lignificação nas paredes celulares dos tecidos nos diferentes órgãos estudados são consideradas importantes na adaptação dessas plantas anfíbias às lagoas temporárias do semi-árido da Bahia.

Utilização de parâmetros morfoanatômicos na análise da fitotoxidez do flúor em folhas de Magnolia ovata (A. St.-Hil.) Spreng. (Magnoliaceae)

Com os objetivos de avaliar o grau de suscetibilidade e caracterizar as injúrias na morfoanatomia de folhas de Magnolia ovata, mudas foram submetidas à chuva simulada com flúor (10 µg.ml-1 de F-) por 10 dias consecutivos. No tratamento controle, utilizou-se apenas água deionizada. Folhas foram coletadas para quantificação de flúor na matéria seca e fixadas para análises em microscopia de luz e eletrônica de varredura. As folhas apicais apresentaram pequena porcentagem de necroses intervenais e marginais em uma ou ambas as faces e maior acúmulo de flúor, em relação ao controle, quando comparadas com as folhas da porção basal. A análise micromorfológica das folhas aparentemente sadias indicou alterações nas paredes periclinais externas da epiderme e formação de concavidades, além de cristas estomáticas danificadas, erosão de ceras epicuticulares e presença de esporos e hifas de fungos. A caracterização estrutural das injúrias evidenciou retração de protoplasto das células epidérmicas, colapso das células do mesofilo e da epiderme e acúmulo de compostos fenólicos em células das regiões necrosadas. As alterações micromorfológicas das folhas ocorreram antes que sintomas fossem observados, o que comprova a importância da micromorfologia na diagnose precoce da injúria. As plantas de M. ovata apresentaram poucos sintomas visuais em resposta ao flúor, entretanto as alterações morfoanatômicas indicam que essa espécie possui potencial para ser utilizada como bioindicadora.

Morfologia externa e interna das folhas vegetativas, esporofilos e esporângios de espécies de Huperzia Bernh. (Lycopodiaceae - Pteridophyta) do Brasil

Lycopodiaceae belongs to the Lycopsida, which autapomorphy is the presence of microphyllous leaves. It was studied 10 species, and seven are endemic to Brazil: the terrestrials Huperzia christii (Silveira) Holub, H. friburgensis (Nessel) B. Ollg., H. hemleri (Nessel) B. Ollg., H. intermedia Trevis., H. reflexa (Lam.) Trevis. and H. treitubensis (Silveira) B. Ollg.; the epiphytics H. fontinaloides (Spring) Trevis., H. heterocarpon (Fee) Holub, H. hexasticha B. Ollg. & P.G. Windisch and H. quadrifariata (Bory) Rothm. The anatomical features found that are probably adaptive to a water deficient environment are the presence of epidermal cells with sinuous anticlinal walls, invaginations in the inner side of external periclinal wall of the epidermal cells and amphiestomatic leaves. The analysed species were separated in two groups, corroborating existing classifications. The two groups were defined on the basis of the following characters: phyllotaxis helical or opposite, leaf position in relation to the stem, if reflexed or adpressed, and the number of sporangia cell layers, if three or four. An identification key was elaborated.

The morphogenesis of lobed plant cells in the mesophyll and epidermis: organization and distinct roles of cortical microtubules and actin filaments

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.

Probable involvement of cytoskeleton in stomatal-pore formation in Asplenium nidus L.

Stomatal-pore formation in the fernAsplenium nidus L. commences in postcytokinetic guard cells at the mid-region of the ventral wall, before the deposition of any cellulosic wall material on it, by the local movement of the adjacent plasmalemmata apart from each other. In this way a rudimentary “internal stomatal pore” is formed. At this stage the ventral wall exhibits an undulated appearance and gives a positive reaction to aniline blue. Detailed study of postcytokinetic guard cells by electron microscopy, as well as after tubulin immunolabeling and actin staining, shows that stomatal pore initiation coincides with the initiation of the organization of the anticlinal microtubule bundles along the middle of the ventral wall and the colocalization of actin filaments at the same sites. Afterwards, the stomatal pore broadens towards the periclinal walls, a phenomenon keeping pace with the further bundling of the cytoskeletal elements beneath the plasmalemmata lining the middle of the ventral wall. At this stage the anticlinal microtubule bundles lining the stomatal pore are very prominent. The above findings, as well as the fact that treatments with antimicrotubule drugs inhibit the “internal” stomatal-pore formation, denote that the cortical cytoskeleton lining the ventral wall and particularly the microtubules are involved in this process. Afterwards, distinct local wall thickenings are deposited at the sites of junction of the mid-region of the ventral wall with the periclinal walls as well as at the junctions of the polar ventral-wall ends with the external periclinal wall. Along the middle-lamella region of the former wall thickenings the fore- and rear-chambers of the stomatal pore are formed. The final stomatal-pore opening is achieved by disruption of the expanded thin median periclinal wall region inherited from the guard cell mother cell and of the overlying cuticle, which covers the stomatal pore externally and internally. At the same time the fore-chamber of the stomatal pore broadens by a schizogenous opening towards the polar ventral-wall ends. The observations show that the stomatal-pore formation inA. nidus is a unique process, which is probably restricted to ferns.

Microtubule and actin filament organization during stomatal morphogenesis in the fernAsplenium nidus

The newly-formed guard cell mother cells (GMCs) ofAsplenium 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 fernA. 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.

Sinuous ordinary epidermal cells: behind several patterns of waviness, a common morphogenetic mechanism.

Morphogenesis of sinuous epidermal cells in leaves of the fern Asplenium nidus and the monocotyledonous Cyperus papyrus, petals of the dicotyledonous Begonia lucerna. and in-vitro-grown leaves of the fern Adantum capillus-veneris is controlled by the local differentiation of their walls. In all these cases wall pads, including radial cellulose microfibrils, arc deposited at the junctions of the external periclinal wall with the anticlinal ones. Moreover, in Asplenium nidus, similar wall pads form at the junctions of the internal periclinal wall with the anticlinal ones. The wall pads are connected to anticlinal cellulose microfibril bundles running the whole depth of the anticlinal walls nr part of it. This wall differentiation imposes a highly controlled cell wall expansion, a consequence of which is the waviness of the epidermal cell anticlinal, walls. The pattern of wall reinforcement varies among different species, resulting in differences in the pattern of waviness. Cortical microtubule arrays mirror the orientated deposition of cellulose microfibrils in the epidermal Cells. These findings, derived from plants from different major groups, show a common epidermal cell morphogenetic mechanism depending on radial cellulose microfibrils and cellulose microfibril bundles. The facts that (a) epidermal cell morphogenesis in Adiantum copillus-veneris leaves grown in vitro differs considerably from that of typical leaves and (b) petal epidermal cells in Begonia lucerna are sinuous, while leaf epidermal cells are not, suggest that this mechanism may he affected by epigenetic factors.

Microtubule organization and cell morphogenesis in two semi-lobed cell types of Adiantum capillus-veneris L. leaflets.

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 arising under the microtubule bundles and including parallel cellulose microfibrils. The pattern of wall 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 is the organization of two different patterns of the cortical microtubule cytoskeleton in the same cell.

Microtubules and morphogenesis in ordinary epidermal cells ofVigna sinensis leaves

Undifferentiated ordinary epidermal cells (ECs) ofVigna 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.