Periclinal Divisions Research Articles

Development of the successive cambia in Sesuvium verrucosum Raf (Aizoaceae)

The structure and development of successive cambia and its products were studied in the stems of the halophyte Sesuvium verrucosum Raf. The young stem has several collateral vascular bundles arranged in a circle and separated by interfascicular zones. The secondary thickening begins with the differentiation of fascicular and interfascicular cambia which give rise to secondary xylem, phloem and lignified cells. This normal cambium ceases to divide after a limited period of activity. A new segment of anomalous cambium was developed from the phloem parenchyma cells outside the normal previous cambium. These cells are served as a site for the origin of the anomalous cambium and subjected to repeated periclinal divisions. This cambium has fusiform cells with semi-storied appearance. The activity of this anomalous cambium produces secondary xylem, phloem, fibers and soft parenchyma as conjunctive tissues. The formation of subsequent cambia followed a similar pattern of development and causes vascular increments in the old stem. So, the old stem of S. verrucosum is constructed of concentric fibrovascular bands separated from each other by cylinders of conjunctive parenchyma tissue. This internal structure has a great adaptive potential to the halophyte S. verrucosum. This can be detected by the following points: (1) Production of large number of vessels and sieve tubes elements increases the conductive activity; (2) Occurrence of fibers alongside the vessels increases the mechanical strength that helps and protects water columns from embolism and ensures this water to store and transport in the succulent leaves; and (3) Thin walled parenchyma conjunctive tissue offers flexibility to the plant stem which forms a mat like and able to bend toward the ground without harm. Perhaps these features matched well with the S. verrucosum plant habitat.

The parenchymo-vascular cambium and its derivative tissues in stems and roots of Bougainvillaea glabra Choisy (Nyctaginaceae)

In the shoots and roots of <i>Bougainmllaea</i>, the parenchymo-vascular cambium produces thinwalled secondary parenchyma to one side and the secondary vascular bundles embedded in the "conjunctive tissue" to the other. Periclinal division of a single cambial cell in one radial row brings about periclinal divisions of the adjacent cells of the neighbouring rows. Anticlinal division of a single cambial cell at one level, on the other hand, causes anticlinal. divisions of the adjacent cells of the overlying and underlying tiers.

Organization of the root apical meristem in Linum usitatissimum L. grown at 25°C and 7°C

In the first days of intensive growth of the Linum usitatissimum root, the central part of the apical meristem exhibits usually a 4-tier organization. When growth ceases reorganization of the cell arrangement occurs. It starts by periclinal division of the subprotodermal initials, whose derivatives are forming the secondary columella in the central part of the root cap.

Anther ontogeny in Brachypodium distachyon.

Brachypodium distachyon has emerged as a model plant for the improvement of grain crops such as wheat, barley and oats and for understanding basic biological processes to facilitate the development of grasses as superior energy crops. Brachypodium is also the first species of the grass subfamily Pooideae with a sequenced genome. For obtaining a better understanding of the mechanisms controlling male gametophyte development in B. distachyon, here we report the cellular changes during the stages of anther development, with special reference to the development of the anther wall. Brachypodium anthers are tetrasporangiate and follow the typical monocotyledonous-type anther wall formation pattern. Anther differentiation starts with the appearance of archesporial cells, which divide to generate primary parietal and primary sporogenous cells. The primary parietal cells form two secondary parietal layers. Later, the outer secondary parietal layer directly develops into the endothecium and the inner secondary parietal layer forms an outer middle layer and inner tapetum by periclinal division. The anther wall comprises an epidermis, endothecium, middle layer and the secretory-type tapetum. Major documented events of anther development include the degradation of a secretory-type tapetum and middle layer during the course of development and the rapid formation of U-shaped endothecial thickenings in the mature pollen grain stage. The tapetum undergoes degeneration at the tetrad stage and disintegrates completely at the bicellular stage of pollen development. The distribution of insoluble polysaccharides in the anther layers and connective tissue through progressive developmental stages suggests their role in the development of male gametophytes. Until sporogenous cell stage, the amount of insoluble polysaccharides in the anther wall was negligible. However, abundant levels of insoluble polysaccharides were observed during microspore mother cell and tetrad stages and gradually declined during the free microspore and vacuolated microspore stages to undetectable level at the mature stage. Thus, the cellular features in the development of anthers in B. distachyon share similarities with anther and pollen development of other members of Poaceae.

Unresolved issues in pre-meiotic anther development.

Compared to the diversity of other floral organs, the steps in anther ontogeny, final cell types, and overall organ shape are remarkably conserved among Angiosperms. Defects in pre-meiotic anthers that alter cellular composition or function typically result in male-sterility. Given the ease of identifying male-sterile mutants, dozens of genes with key roles in early anther development have been identified and cloned in model species, ordered by time of action and spatiotemporal expression, and used to propose explanatory models for critical steps in cell fate specification. Despite rapid progress, fundamental issues in anther development remain unresolved, and it is unclear if insights from one species can be applied to others. Here we construct a comparison of Arabidopsis, rice, and maize immature anthers to pinpoint distinctions in developmental pace. We analyze the mechanisms by which archesporial (pre-meiotic) cells are specified distinct from the soma, discuss what constitutes meiotic preparation, and review what is known about the secondary parietal layer and its terminal periclinal division that generates the tapetal and middle layers. Finally, roles for small RNAs are examined, focusing on the grass-specific phasiRNAs.

Cellular events during interfascicular cambium ontogenesis in inflorescence stems of Arabidopsis

Development of cambium and its activity is important for our knowledge of the mechanism of secondary growth. Arabidopsis thaliana emerges as a good model plant for such a kind of study. Thus, this paper reports on cellular events taking place in the interfascicular regions of inflorescence stems of A. thaliana, leading to the development of interfascicular cambium from differentiated interfascicular parenchyma cells(IPC). These events are as follows: appearance of auxin accumulation, PIN1 gene expression, polar PIN1 protein localization in the basal plasma membrane and periclinal divisions. Distribution of auxin was observed to be higher in differentiating into cambium parenchyma cells compared to cells within the pith and cortex. Expression of PIN1 in IPC was always preceded by auxin accumulation. Basal localization of PIN1 was already established in the cells prior to their periclinal division. These cellular events initiated within parenchyma cells adjacent to the vascular bundles and successively extended from that point towards the middle region of the interfascicular area, located between neighboring vascular bundles. The final consequence of which was the closure of the cambial ring within the stem. Changes in the chemical composition of IPC walls were also detected and included changes of pectic epitopes, xyloglucans (XG) and extensins rich in hydroxyproline (HRGPs). In summary, results presented in this paper describe interfascicular cambium ontogenesis in terms of successive cellular events in the interfascicular regions of inflorescence stems of Arabidopsis.

In vitro Embryo Morphogenesis and Micropropagation of Dendrobium aggregatum Roxb.

In vitro embryo morphogenesis and micropropagation of Dendrobium aggregatum Roxb. were described. The gradual developmental stages of embryos to seedlings were traced out. Within two weeks of culture the cells of undifferented embryos underwent repeated aniclinal and periclinal division producing a compact, green parenchymatous cell mass called spherule that emerged out by rupturing the testa. The spherules subsequently differentiated into greenish protocorms were considered as typical seed germination. Germination occurred on both (MS and Phytamax (PM) medium but MS medium proved to be more efficient. The primary protocorms underwent profuse proliferation through production of secondary (2º) protocorms when transferred to different plant growth regulators (PGRs) supplemented MS; the medium fortified with 2.0 mg/l BAP and 1.0 mg/l NAA proved to be most effective for induction of 2º protocorms and seedling development. Multiple shoot buds (MSBs) were induced in pseudobulb segments of the in vitro grown seedlings when cultured on different PGRs supplemented media; and the maximum number of MSBs were obtained MS + 2.0 mg/l BAP + 0.5 mg/l picloram. The MSBs underwent elongation and then they rooted when they were transferred to half strength of MS + 0.5 mg/l IAA. The well rooted plantlets were finally transferred to outside natural environment with 80% survival. D. O. I. http://dx.doi.org/10.3329/ptcb.v23i2.17525 Plant Tissue Cult. & Biotech. 23(2): 241-249, 2013 (December)

Nonparallelism of cambium cells in neighboring rows

The periclinal walls of cambial cells in neighboring lineages (rows) may not be parallel when viewed in their radial aspect. This lack of longitudinal parallelism may be so extensive that in active cambium pairs of cells from neighboring rows may be in contact only along restricted segments. This means that the initial cells, rather than farming a continuous layer, may be arranged in an irregular network pattern from which some parts project inward or outward from the layer of their mutual cantacts. The longitudinal nonparallelism of cambial cells becomes more pronounced during symplasitic radial growth. Unequal periclinal divisions counteract this, and in initial cells abscission of the parts projecting from the layer of mutual contact occurs. When the cambium passes from a period of activity to a Period of rest a continuous layer of initials is reestabhshed. This involves elongation by intrusive growth of those cells previously shortened as the result of irregular periclinal divisions. The division walls in cambial cells may be warped, that is they change their orientation along the longitudinal direction perhaps even similar to an aircraft propeller. A division wall may thus be periclinal in one part of the cell and anticlinal in another.

Phyllotaxis of vegetative shoots of Anagallis arvensis L. treated in vitro with 6-benzylaminopurine

Application of 6-benzylaminopurine (BA), a synthetic cytokinin, to the growth medium in vitro stimulates the formation of adventitious shoots on stem explants of <em>Anagallis arvensis</em>. They regenerate from dedifferentiating epidermal cells of stem internodes. The process starts from periclinal and anticlinal divisions in a few of neighbouring cells. The amount of adven-titious shoots increases with an increasing BA concentration. The BA treatment also affects phyllotaxis, but only of adventitious shoots, and not of normal lateral shoots developing in leaf axils. Leaf arrangement on adventitious shoots is always variable, even on the control medium. Generally, patterns observed in case of in vitro shoots do not differ from those reported earlier for intact <em>A. arvensis</em> plants. BA treatment also leads to the teratologic development, i.e. fasciation and the formation of abnormally shaped leaves, but again in adventitious rather than in normally developing shoots. We postulate that the variability of phyllotaxis characteristic for adventitious shoots and their responce to BA treatment, result from the fact that their apical meristems develop de novo from initially unorganised meristematic centres, whereas meristems of normally developing lateral shoots are well organised from the time of their initiation.

Development of the pericarp, septa and zone of dehiscence in the fruit of Cassia tora L.

The pod of <em>Cassia tora</em> is the product of a single carpel consisting of 20-30 seeds enclosed one in each compartment formed by the ingrowth of the endocarpic tissue. There are three distinct histological zones of the pericarp Epicarp (a), Mesocarp (b) and Endocarp (c). The paracytic stomata and uniseriate multicellular trichomes are found only in the outermost layer of the epicarp. The epicarp is single layered. The outer mesocarp in later stages of its development has many collenchyma, particularly at dorsal and ventral margins. The mesocarp develops from the homogenous mesodermal tissue of the ovary wall. The middle mesocarpic tissue becomes sclerenchymatous above the :main bundles providing rigidity at the two sutures where the zones of dehiscence develop inbetween them. The endocarp develops from the inner epidermis and 2-3 hypodermal layers. Due to frequent periclinal and anticlinal divisions and enlargement of the cells in the inner hypodermal layers, the septa are formed which never fuse; thus the so called compartment of the seed is not completely closed and the seeds slide off on separation of the valves. The inner hypodermal layers form the band of sclerenchyma above the septal cells. The inner margins without septa and sclerenchyma provide easy opening of the two valves from the chamber side.

The intrusive growth of initial cells in re-arangement of cells in cambium of Tilia cordata Mill.

In the cambium of linden producing wood with short period of grain inclination change (2-4 years), the intensive reorientation of cells takes place. This is possible mainly through an intrusive growth of cell ends from one radial file entering space between tangential walls of neighboring file and through unequal periclinal divisions that occur in the "initial surface". The intrusive growth is located on the longitudinal edge of a fusiform cell close to the end, and causes deviation of cell ends in a neighbouring file from the initial surface. Unequal periclinal division divides a cell with a deviated end into two derivatives, unequal in size. The one of them, which inherits the deviated end, leaves the initial surface becoming a xylem or phloem mother cell. This means that the old end is eliminated. The intensity of intrusive growth and unequal periclinal divisions is decisive for the velocity of cambial cell reorientation. The oriented intrusive growth occurs only in the initial cells. For that reason, changes in cell-ends position do not occur within one packet of cells but are distinct between neighbouring packets.

The sequence of cell divisions in the I tunic layer of Actinidia arguta Planch in light of the development of twin cell complexes

In <em>Actinidia arguta</em>, the I tunc layer is formed by four cell complexes which descend from single initials. These initials are positioned in a corner of their complex, around the meristem axis. The meristematic activity of the I tunic layer depends on the formative divisions of the initials; the entire I tunic layer above the youngest leaf primordia is formed during the time the initials undergo only 4-8 divisions. In light of the development of the twin cell complexes. it is impossible for cells to be displaced from the I tunic layer into the meristem. The supposition is set forth that the impermanent. mericlinal sectors on variegated perinclinal chimeras develop due to periclinal cleavages within the subcomplexes which derive from tissue mother cells. Whereas. the cell initials do not undergo periclinal divisions and are not displaced.

Growth and development of shoot apex in barley I. Morphology and histology of shoot apex in vegetative phase

The vegetative phase of development of the main shoot apex lasts over 5 plastochrons after germination. The endosperm has a sufficient store of nutrition for this period. At the beginning of this phase the apex has a one-layer tunica. The cells of the latter divide above the level of bulge formation for leaf primordia, exclusively anticlinally, although somewhat lower within the leaf bulge periclinal divisions may occur. The cells immediately under the first tunica layer in the apical part grow tangentially to the surface. These cells divide only anticlinally forming gradually the second tunica layer. In the course of the entire phase the shape of the meristeanatic caulis from the tip to the 4th frustum remains unchanged.

A Callixylon (Archaeopteridales, Progymnospermopsida) trunk with preserved secondary phloem from the Late Devonian of Morocco

During the Devonian, the evolution of secondary phloem produced by a bifacial vascular cambium was a key innovation that increased the ability of plants within the lignophyte clade to redistribute photosynthates and other organic compounds throughout their body. Unraveling the secondary phloem anatomy of the first arborescent lignophytes is crucial to understand the evolution of this tissue and the physiology of early trees. A 10 cm wide stem of Callixylon with preserved secondary phloem from the Famennian of Morocco is described using thin-sections. The secondary phloem of this Callixylon zalesskyi-type of stem is composed of fibers, sclereids, rays, axial parenchyma, and putative sieve cells. Fibers differentiate early and are relatively abundant in the inner phloem. In the older phloem, fibers are arranged in tangential bands alternating with extensive layers of axial parenchyma. Changes between the young and old phloem involve the periclinal division and radial elongation of the axial parenchyma cells. The presence of fibers in the inner, presumably functional phloem, combined with evidence for rhythmicity in the production of different phloem cell types are documented for the first time in detail in an archaeopteridalean progymnosperm. No periderm was observed within the preserved seven millimeters of bark tissues. The secondary phloem anatomy supports a close affinity of archaeopteridalean progymnosperms with both aneurophytalean progymnosperms and seed plants. The production of secondary phloem might have provided an advantage to these first arborescent lignophytes over other types of Devonian early trees, especially in dry conditions.

Regulation of cell divisions and differentiation by MALE STERILITY32 is required for anther development in maize

Male fertility in flowering plants relies on proper division and differentiation of cells in the anther, a process that gives rise to four somatic layers surrounding central germinal cells. The maize gene male sterility32 (ms32) encodes a basic helix-loop-helix (bHLH) transcription factor, which functions as an important regulator of both division and differentiation during anther development. After the four somatic cell layers are generated properly through successive periclinal divisions, in the ms32 mutant, tapetal precursor cells fail to differentiate, and, instead, undergo additional periclinal divisions to form extra layers of cells. These cells become vacuolated and expand, and lead to failure in pollen mother cell development. ms32 expression is specific to the pre-meiotic anthers and is distributed initially broadly in the four lobes, but as the anther develops, its expression becomes restricted to the innermost somatic layer, the tapetum. The ms32-ref mac1-1 double mutant is unable to form tapetal precursors and also exhibits excessive somatic proliferation leading to numerous, disorganized cell layers, suggesting a synergistic interaction between ms32 and mac1. Altogether, our results show that MS32 is a major regulator in maize anther development that promotes tapetum differentiation and inhibits periclinal division once a tapetal cell is specified.

Anatomy of vegetative organs with an emphasis on the secretory structures of two species of Aldama (Asteraceae–Heliantheae)

Aldama arenaria (Baker) E.E.Schill. & Panero and Aldama robusta (Gardner) E.E.Schill. & Panero are aromatic plants, morphologically very similar and usually confused on the analysis of exsiccates. The present study aimed to identify the secretory structures present in vegetative organs and to survey for anatomical features with diagnostic value between A. arenaria and A. robusta based on an examination of these organs. Aldama arenaria and A. robusta exhibit hydathodes in the dentate ornamentations of the leaf margins and apices in addition to glandular trichomes, secretory cavities and ducts, all of which vary with respect to type and location in each species. Xylopodia and adventitious roots constitute the underground system. The xylopodium is covered by epidermis or by suberised cells resulting from periclinal divisions of parenchyma cells. The tuberisation process of adventitious roots results mainly from hypertrophy and hyperplasia of medullary cells, especially in A. arenaria. Through anatomical analysis, useful features for distinction between A. arenaria and A. robusta in exsiccates and fresh materials were identified, and these features were related mainly to the position and frequency of secretory structures.

A bHLH Complex Controls Embryonic Vascular Tissue Establishment and Indeterminate Growth in Arabidopsis

Plants have a remarkable potential for sustained (indeterminate) postembryonic growth. Following their specification in the early embryo, tissue-specific precursor cells first establish tissues and later maintain them postembryonically. The mechanisms underlying these processes are largely unknown. Here we define local control of oriented, periclinal cell division as the mechanism underlying both the establishment and maintenance of vascular tissue. We identify an auxin-regulated basic helix-loop-helix (bHLH) transcription factor dimer as a critical regulator of vascular development. Due to a loss of periclinal divisions, vascular tissue gradually disappears in bHLH-deficient mutants; conversely, ectopic expression is sufficient for triggering periclinal divisions. We show that this dimer operates independently of tissue identity but is restricted to a small vascular domain by integrating overlapping transcription patterns of the interacting bHLH proteins. Our work reveals a common mechanism for tissue establishment and indeterminate vascular development and provides a conceptual framework for developmental control of local cell divisions.

Anther ontogeny in Campsis radicans (L.) Seem. (Bignoniaceae)

In this study anther ontogeny of Campsis radicans (L.) Seem. was investigated by transmission electron microscopy and light microscopy with special reference to the development of the anther wall. The anther wall formation follows the dicotyledonous type. The differentiation in anther starts with the appearance of archesporial cells which undergo periclinal divisions to give primary parietal layer to the epidermal site and the primary sporogenous cells to the inside. The primary parietal layer also divides to form two secondary parietal layers. Later, the outer secondary parietal layer (spl1) forms the endothecium and the middle layer by periclinal division whereas the inner one (spl2) directly develops into the outer tapetum forming the inner most layer of the anther wall. The sporogenous tissue is generally organized in two rows of cells with a horseshoe-shaped outline. The remainder of the tapetum lining the sporogenous mass is derived from the connective tissue. The tapetum thus has dual origin and dimorphic. Anthers are tetrasporangiate. The wall of the anther consists of an epidermis, endothecium, middle layer, and the secretory type tapetum. Tapetal cells are usually binucleated. Epidermis and Endothecium layers of anther wall remain intact until the end of anther and pollen development; however, middle layer and tapetum disappear during development.

MKRN expression pattern during embryonic and post-embryonic organogenesis in rice (Oryza sativa L. var. Nipponbare)

Rice MKRN is a member of the makorin RING finger protein gene (MKRN) family, which encodes a protein with a characteristic array of zinc-finger motifs conserved in various eukaryotes. Using non-radioactive in situ hybridization, we investigated the spatio-temporal gene expression pattern of rice MKRN during embryogenesis, imbibition, seminal and lateral root development of Oryza sativa L. var. Nipponbare. MKRN expression was ubiquitous during early organogenesis in the embryo along the apical-basal and radial axes. The expression of MKRN decreased during embryonic organ elongation and maturation compared to early embryogenesis, but increased again during imbibition. Tissue-specific and position-dependent MKRN expression was found during embryonic and post-embryonic root and shoot development. Meristematic cells ubiquitously expressed MKRN transcripts, while differentiating cells showed a gradual reduction and termination of MKRN expression. Interestingly, during post-germination MKRN expression was prominent and continued in the metabolically active, differentiated companion cells of the phloem. The differential expression pattern was observed both in the differentiating and differentiated cells. Also, MKRN was expressed in the various developmental stages of the lateral root primordia and the cells surrounding them. Expression of MKRN was also observed after periclinal division of the presumptive pericycle founder cells. The MKRN expression pattern during development of various growth stages suggests an important role of makorin RING finger protein gene (MKRN) in embryonic and post-embryonic organogenesis in both apical-basal and radial developmental axes of rice.

Developmental synchronization of male and female gametophytes in Ginkgo biloba and its neck mother cell division prior to fertilization

This study investigated male and female gametophytes in Ginkgo biloba, while a droplet of fluid was present in the fertilization chamber and found that the central cell, the generative cell and the neck mother cell divided simultaneously prior to fertilization. In male gametophytes, the generative cell divided to yield two sperm cells. Concomitantly, the two neck mother cells of the archegonium increased in size then divided asymmetrically resulting in two big cover cells and two small base cells. Each cell had a fixed end in direct contact with an adjacent jacket cell and a free end overlapping its counterpart. This unique arrangement could allow for their free ends to swing into the fertilization chamber as a result of the force from the interior of the archegonium where a polar periclinal division had occurred to produce a canal cell and an egg. The subsequent withdrawal of the content of the archegonium may facilitate the entry of sperm into the archegonium. The neck apparatus closed after the fertilization occurred. The concurrence oftheabove divisions and the delicate structure of neck apparatus suggest that the gametophytes undergo a synchronization process to become receptive at the time of fertilization. However, the formation of neck cells and the opening time of neck apparatus of the archegonia within the same ovule were slightly different, which could lead to the formation of zygotes at a temporally distinct interval. The earlier formed zygote may progress as the only mature embryo in the ovule.