Development and histochemistry of the cells,cell walls,and cuticle of the dermal system of fruit of the grape,Vitis vinifera L.

Summary The dermal system comprises the outer epidermis of the pericarp, its covering of wax and cuticle and the collenchymatous hypodermal cells. During the first of the two post-anthesis phases of fruit growth, differentiation occurred with respect to cell and nuclear volume, content of polyphenolic substances, and wall thickening. Walls of the presumptive dermal system cells developed massive primary thickenings which stained intensely with fluorescent brightener dyes. In the second phase of fruit growth these cells were redifferentiated, their walls becoming thinner as they enlarged to accommodate fruit expansion. Binding of the fluorescent brightener dye was reduced and confined to the outer edges of the walls. At maturity, the walls of the cortical cells adjacent to the dermal system underwent autolysis.The cuticle was evident during the first 16 days after anthesis as a thin layer which reacted positively with neutral lipid dyes and which contained periodate sensitive vinyl groups. Differentiation of a secondary cuticle followed, and a number of distinct layers were detected by autofluorescence, and staining with auramine 0, Nile blue, and PAS. Cuticle thickness and complexity was maintained throughout the second growth phase.     

Developmental pattern formation of somatic embryos induced in cell suspension cultures of cowpea [Vigna unguiculata (L.) Walp]

The sequence of events in the functional body pattern formation during the somatic embryo development in cowpea suspensions is described under three heads. Early stages of somatic embryogenesis were characterized by both periclinal and anticlinal cell divisions. Differentiation of the protoderm cell layer by periclinal divisions marked the commencement of somatic embryogenesis. The most critical events appear to be the formation of apical meristems, establishment of apical-basal patterns of symmetry, and cellular organization in oblong-stage somatic embryo for the transition to torpedo and cotyledonary-stage somatic embryos. Two different stages of mature embryos showing distinct morphology, classified based on the number of cotyledons and their ability to convert into plantlets, were visualized. Repeated mitotic divisions of the sub-epidermal cell layers marked the induction of proembryogenic mass (PEM) in the embryogenic calli. The first division plane was periclinally-oriented, the second anticlinally-oriented, and the subsequent division planes appeared in any direction, leading to clusters of proembryogenic clumps. Differentiation of the protoderm layer marks the beginning of the structural differentiation in globular stage. Incipient procambium formation is the first sign of somatic embryo transition. Axial elongation of inner isodiametric cells of the globular somatic embryo followed by the change in the growth axis of the procambium is an important event in oblong-stage somatic embryo. Vacuolation in the ground meristem of torpedo-stage embryo begins the process of histodifferentiation. Three major embryonic tissue systems; shoot apical meristem, root apical meristem, and the differentiation of procambial strands, are visible in torpedo-stage somatic embryo. Monocotyledonary-stage somatic embryo induced both the shoot apical meristem and two leaf primordia compared to the ansiocotyledonary somatic embryo.     

Differential growth resulting in the specification of different types of cellular architecture in root meristems

Symplastic growth of plant organs may be described by a continuous growth tensor field. In tensorial analysis of meristems, the trajectories of periclinal and anticlinal cell walls represent trajectories of the principal directions of growth (PDGs); this follows from the maintenance of mutual orthogonality between periclinal and anticlinal wall trajectories during growth. Periclinal and anticlinal cell divisions are also oriented in the principal planes of growth. The growth tensor for the root apex is specified in such a way that the principal directions of the tensor fit the pattern of periclinal and anticlinal walls in the apex, and that the grid formed by material particles aligned along PDG trajectories preserve this alignment during growth. Two growth tensors are formulated--one giving a maximum and the other giving a minimum of the volumetric relative elemental growth rate at the region of the initial cell(s). Temporal sequences of deformation of a grid formed by lines coinciding with the principal directions of growth are shown. The formation of cellular patterns in root apices is simulated. Two types of patterns are obtained: one with an apical cell and merophytes, and another with files of cells converging towards a quiescent centre.     

ANATOMY AND ASPECTS OF DEVELOPMENT OF THE STAMINATE INFLORESCENCES AND FLORETS OF SEVEN SPECIES OF ALLOCASUARINA (CASUARINACEAE)

The morphology, ontogeny, and vascular anatomy of the staminate inflorescences and florets of seven species of Allocasuarina are described. The generally terminal but open-ended inflorescences occur on monoecious or staminate dioecious trees and consist of whorls of bracts, each subtending a sessile axillary floret. Each floret consists of one terminal stamen with a bilobed, tetrasporangiate anther enclosed typically by cuculliform appendages, commonly considered bracteoles, an inner median pair and an outer lateral pair. The mature stamen is exerted, the anther is basifixed and is extrorsely dehiscent. In early development of a male inflorescence very little internodal elongation occurs and enclosing cataphylls appear. The inflorescence apex is a low dome with a uniseriate tunica and a small group of central corpus cells. Bract primordia are initiated by periclinal divisions of C₁ followed by further divisions of the corpus and anticlinal divisions in the tunica. The bracts are epinastic and become gamophyllous except apically by cell divisions in both sides of each primordium. Stomata are restricted to the axis furrows and the abaxial tips of the bracts. The axillary florets arise in acropetal succession initiated by periclinal divisions in C₁ accompanied by anticlinal divisions in the tunica. The lateral floral appendages are also initiated by C₁ followed by anticlinal divisions in the tunica. They become adnate basally later with the subtending bract. The median sterile appendages are initiated in a manner similar to the initiation of the outer appendages. The stamen is initiated by divisions in the outer layers of the corpus and in the tunica, and then develops first by apical growth followed by intercalary growth. The vascular system of the inflorescence is identical to that of the vegetative stem. Each floret is supplied by a single bundle that has its source in a branch from each of the two traces supplying a bract. Six bundles arise from the floral bundle; four of these terminate in the base of the stamen and two form an amphicribal bundle that supplies the anther. Pollen is binucleate, 3- to 7-porate. The exine is tegillate.     

Lateral Root Initiation or the Birth of a New Meristem

Root branching happens through the formation of new meristems out of a limited number of pericycle cells inside the parent root. As opposed to shoot branching, the study of lateral root formation has been complicated due to its internal nature, and a lot of questions remain unanswered. However, due to the availability of new molecular tools and more complete genomic data in the model species Arabidopsis, the probability to find new and crucial elements in the lateral root formation pathway has increased. Increasingly more data are supporting the idea that lateral root founder cells become specified in young root parts before differentiation is accomplished. Next, pericycle founder cells undergo anticlinal asymmetric, divisions followed by an organized cell division pattern resulting in the formation of a new organ. The whole process of cell cycle progression and stimulation of the molecular pathway towards lateral root initiation is triggered by the plant hormone auxin. In this review, we aim to give an overview on the developmental events taking place from the very early specification of founder cells in the pericycle until the first anticlinal divisions by combining the knowledge originating from classical physiology studies with new insights from genetic-molecular analyses. Based on the current knowledge derived from recent genetic and developmental studies, we propose here a hypothetical model for LRI.     

DEVELOPMENTAL CHANGES IN THE VASCULAR CAMBIUM IN LEITNERIA FLORIDANA

Developmental changes in the vascular cambium of Leitneria floridana, a shrub, were determined primarily by an analysis of the secondary xylem. During the production of the first growth ring of secondary xylem, 37% of the anticlinal divisions in the fusiform initials were lateral, the remaining were oblique. The oblique partition averaged ½ of the length of the dividing initials during this period of growth. Following their origin in anticlinal division, daughter cells elongated at a rapid rate until they were about as long as the mean for all cells, and then most cells elongated at a slow rate. Almost all initials survived during the formation of the inner secondary xylem (growth rings 1–10), and few new rays were formed from fusiform initials. During the production of the outer secondary xylem (growth rings 22–26), lateral divisions accounted for less than 5% of all anticlinal divisions. The oblique partition averaged only ¼ of the length of the dividing cells during this period, although the mean length of dividing initials was relatively constant throughout secondary growth. About 20% of the initials studied during the deposition of the outer secondary xylem disappeared from the cambium, and many others were transformed into ray initials. The findings are discussed in relation to the developmental changes in the vascular cambium in plants of different habits.     

Division and differentiation during normal and liguleless-1 maize leaf development

The maize leaf is composed of a blade and a sheath, which are separated at the ligular region by a ligule and an auricle. Mutants homozygous for the recessive liguleless-1 (lg1) allele exhibit loss of normal ligule and auricle. The cellular events associated with development of these structures in both normal and liguleless plants are investigated with respect to the timing of cell division and differentiation. A new method is used to assess orientation of anticlinal division planes during development and to determine a division index based on recent epidermal cross-wall deposition. A normal leaf follows three stages of development: first is a preligule stage, in which the primordium is undifferentiated and dividing throughout its length. This stage ends when a row of cells in the preligule region divides more rapidly in both transverse and longitudinal anticlinal planes. During the second stage, ligule and auricle form, blade grows more rapidly than sheath, divisions in the blade become exclusively transverse in orientation, and differentiation begins. The third stage is marked by rapid increase in sheath length. The leaf does not have a distinct basal meristem. Instead, cell divisions are gradually restricted to the base of the leaf with localized sites of increased division at the preligule region. Divisions are not localized to the base of the sheath until near the end of development. The liguleless-1 homozygote shows no alteration in this overall pattern of growth, but does show distinct alteration in the anticlinal division pattern in the preligule region. Two abnormal patterns are observed: either the increase in division rate at the preligule site is absent or it exhibits loss of all longitudinal divisions so that only transverse (or cell-file producing) divisions are present. This pattern is particularly apparent in developing adult leaves on older lg1 plants, in which sporadic ligule vestiges form. From these and results previously published (Becraft et al. (1990) Devl Biol. 14), we conclude that the information carried by the Lg1+ gene product acts earlier in development than formation of the ligule proper. We hypothesize that Lg1+ may be effective at the stage when the blade-sheath boundary is first determined.     

Formative and proliferative cell divisions,cell differentiation,and developmental changes in the meristem of Azolla roots

The root of the water fern Azolla is a compact higher-plant organ, advantageous for studies of cell division, cell differentiation, and morphogenesis. The cell complement of A. filiculoides Lam. and A. pinnata R.Br. roots is described, and the lineages of the cell types, all derived ultimately from a tetrahedral apical cell, are characterised in terms of sites and planes of cell division within the formative zone, where the initial cells of the cell files are generated. Subsequent proliferation of the initial cells is highly specific, each cell type having its own programme of divisions prior to terminal differentiation. Both formative and proliferative divisions (but especially the former) occur in regular sequences. Two enantiomorphic forms of root develop, with the dispositions of certain types of cell correlating with the direction, dextrorse or sinistrorse, of the cell-division sequence in the apical cells. Root growth is determinate, the apical cell dividing about 55 times, and its cell-cycle duration decreasing from an initial 10 h to about 4 h during the major phase of root development. Sites of proliferation progress acropetally during aging, but do not penetrate into the zone of formative divisions. The detailed portrait of root development that was obtained is discussed with respect to genetic and epigenetic influences; quantal and non-quantal cell cycles; variation in cell-cycle durations; relationships between cell expansion and cell division: the role of the apical cell; and the limitation of the total number of mitotic cycles during root formation.     

Microtubular configurations during the cellularization of coenocytic endosperm in Ranunculus sceleratus L.

Summary Endosperm cellularization in Ranunculus sceleratus was studied in terms of the initiation of cell-wall formation in the coenocytic endosperm. The first endosperm cell walls were in an anticlinal position relative to the cell wall of the embryo sac and originated from the cell plates and not from wall ingrowths from the embryo-sac wall itself. Alveolar endosperm was formed 3 days after pollination. Microtubules were associated with the freely growing wall ends of the anticlinal walls and were observed in various orientations that generally ranged from angles of 45 ° to 90 ° to the plane of the wall. They were absent in the regions where vesicles had already fused. These microtubules may function in maintaining the growth and the direction of growth of the anticlinal wall until cellularization is completed. At the site where three neighbouring alveoli share their freely growing wall ends, remarkable configurations of microtubules were observed: in each alveolus, microtubules ran predominantly parallel to the bisector of the angle formed by the common walls. These microtubules may form a physically stable framework and maintain the direction of growth of the wall edges. It is concluded that the growing edge of the anticlinal endosperm wall and its associated microtubules are a special continuum of the original phragmoplast that gave rise to the anticlinal wall.     

Peltate Leaf Development in Brasenta schreberi Gruel

The present investigation is a report with a detailed account of peltate leaf development in Brasenia schreberi. The preliminary indication of leaf initiation is seen in periclinal divisions of the subepidrmal cells on the flank of the shoot apex. By the time a leaf primordium becomes 73 μm high, the apical growth is present, and it has undergone repeated periclinal and anticlinal divisions and introduces aew cells into the body of the primordium. The procambial strand is evident very early in ontogeny. Vacuolation of cells proceeds acropetally along the primordium. At 109 μm longitudinal sections reveal a ventral outgrowth. This ventral growth, termed a lateral zone or Querzone, is initiated by subepidermal cells on the ventral (adaxial) side of primordium. The Querzone is considered to represent the congenital fused laminar margins of the leaf. Transection analysis of a primordium of 160 μm indicates that the Querzone growth is initiated on the midbasal portion of primordium. Below the midbasal portion of primordittm which later forms the petiole of the leaf. The marginal 'growth occurs at a time when the primordinm is approximately 160 μm high. Initiation of marginal growth takes place in 42 μm from the base of a primordium. Marginal growth at first can be seen while the primordium exhibits unilateral. By anticlinal divisions, the marginal initials produce the upper and lower protoderm, which give rise to the upper and lower epidermis respectively, and submarginal initiates divide in anticlinal plane, giving rise to the adaxial and abaxial layers. Subsequent divisions of the adaxial layer are anticlinal only so that it forms a single layer which later develops as the palisade parenchyma. The cells of the abaxial layer, by divisions in all planes, form the tissues of the spongy parenchyma and all of the lateral venation system. At maturity, the mesophyll is much less compact and there are mumerous large intercellular spaces in the spongy region and between the palisade cells. The veins are collateral: There is a reduction in the amount of xylem and the ultimate veinlets terminate as single spiral tracheids. The glandular bairs are mumerous on the lower epidermis and are epidermal in origin, each consisting two basel cells and one termined cell. On the basis of morphological examination we suggest that the peltate leaf of Brasenia schreberi is clearly distinct from the foliage leaf in the development of adaxial meristem and marginal growth. We found the primordimn of Brasenia schreberi as an erect organ and arises.by monopodial growth. In the development of leaf and the form of venation the Brasenia schreberi shows marked resemblance and relationship to the Nelumbo nucifera.     

First divisions of somatic embryogenic cells inCichorium hybrid “474”

Summary First divisions of embryogenic cells were studied in leaves of plantlets of aCichorium hybrid (C. intybus L. ×C. endivia L.) cultured in vitro in a liquid agitated medium, at 35 °C in the dark. Stages of reactivation of competent cells were characterized by increase of nucleus and nucleolus diameter, migration of the nucleus in the centre of the cell and thickening of the cell wall. The first division of reactivated embryogenic cells was symmetrical and anticlinal in regard to the xylem vessels orientation. Embryogenic structures consisted in I-type tetrads or in rows of 4–8 cells. Then the divisions occurred in thickness at one end, without polarization or formation of a suspensor-like structure.Abbreviations EC embryogenic cell - ES embryogenic structure     

Xcl1 causes delayed oblique periclinal cell divisions in developing maize leaves, leading to cellular differentiation by lineage instead of position

Differentiation of plant cells is regulated by position-dependent mechanisms rather than lineage. The maize Extra cell layers1 (Xcl1) mutation causes oblique, periclinal divisions to occur in the protoderm layer. These protodermal periclinal divisions occur at the expense of normal anticlinal divisions and cause the production of extra cell layers with epidermal characteristics, indicating that cells are differentiating according to lineage instead of position. Mutant kernels have several aleurone layers instead of one, indicating that Xcl1 alters cell division orientation in cells that divide predominantly in the anticlinal plane. Dosage analysis of Xcl1 reveals that the mutant phenotype is caused by overproduction of a normal gene product. This allows cells that have already received differentiation signals to continue to divide in aberrant planes and suggests that the timing of cell division determines differentiation. Cells that divide early and in the absence of differentiation signals use positional information, while cells that divide late after perceiving differentiation signals use lineage information instead of position.     

STRUCTURE AND DEVELOPMENT OF THE SECRETORY CELLS AND DUCT SYSTEM IN MACROCYSTIS PYRIFERA (L.) C. A. AGARDH1

Sporophytes of Macrocystis pyrifera (L.) C. A. Agardh of various stages of growth were studied by light microscopy to determine the initiation and ontogeny of secretory cells and the accompanying duct system. Secretory cells are initiated by asymmetric, periclinal divisions of meristoderm cells; subsequent mitoses increase the number of secretory cells associated with each duct. Duct formation occurs by schizogeny of anticlinal cell walls adjacent to the site of secretory cell initiation. Differences in distribution and structure of the duct system occur in various parts of the sporophyte. The duct system does not have openings directly to the sporophyte surface. Histochemical techniques showed that the duct contents are mostly sulfated polysaccharides with perhaps some lipid.     

The specific overexpression of a cyclin-dependent kinase inhibitor in tomato fruit mesocarp cells uncouples endoreduplication and cell growth

The size of tomato fruit results from the combination of cell number and cell size, which are respectively determined by the cell division and cell expansion processes. As fruit growth is mainly sustained by cell expansion, the development of fleshy pericarp tissue is characterized by numerous rounds of endoreduplication inducing a spectacular increase in DNA ploidy and mean cell size. Although a clear relationship exists between endoreduplication and cell growth in plants, the exact role of endoreduplication has not been clearly elucidated. To decipher the molecular basis of endoreduplication-associated cell growth in fruit, we investigated the putative involvement of the tomato cyclin-dependent kinase inhibitor SlKRP1. We studied the kinetics of pericarp development in tomato fruit at the morphological and cytological levels, and demonstrated that endoreduplication is directly proportional to cell and fruit diameter. We established a mathematical model for tissue growth according to the number of divisions and endocycles. This model was tested in fruits where we managed to decrease the extent of endoreduplication by over-expressing SlKRP1 under the control of a fruit-specific promoter expressed during early development. Despite the fact that endoreduplication was affected, we could not observe any morphological, cytological or metabolic phenotypes, indicating that determination of cell and fruit size can be, at least conditionally, uncoupled from endoreduplication.     

Reproduction and differentiation of the cells in enchondral osteogenesis

Light and electron-microscopical 3H-thymidine autoradiography was used to study the dynamics of cell populations in the zones of enchondral osteogenesis in a tubular bone. In the early postnatal ontogenesis little differentiated perivascular cells are characterized by the highest proliferative activity in this region; they are considered as a population containing initial forms of the histogenetic sequence (differon) of the stromal fibroblast-like cells including osteoblasts. Differentiation of osteogenic cells from the initial forms to the mature osteoblasts proceeds through a number of successive divisions (1-3 divisions) and is accompanied by a decrease in the proliferative activity due to the increase in the generation time and decrease in the cell proliferative pool. The major part of osteoblasts is outside the mitotic cycle. At the later stages of ontogenesis the intensity of growth processes in the bone is provided for by changes in the proliferative pool of the committed precursor cells (preosteoblasts) which make a part of endosteum, vascular channels and bone marrow stroma.     

Sucrose-Caused Changes in the Frequency and Localization of Anticlinal Divisions in the Cambial Zone of Silver Birch

This study continues our previous experiments intended to elucidate the role of sucrose in a figured wood formation in silver birch (Betula pendula Roth var. carelica). The purpose of the study was the investigation of the role of sucrose in the regulation of cell division in the cambial zone. Using an earlier-developed technique, sucrose solutions of different concentrations have been delivered into trunk tissues of silver birch. A microscopic analysis of samples collected 28 days after the beginning of the experiment has shown that an increased sucrose concentration in an exogenous solution causes an increase in the frequency of anticlinal cell divisions in the cambial zone. In the case of high sucrose concentrations (10 or 20%), the zone of anticlinal divisions is significantly wider than in variants with low sucrose concentrations, since anticlinal divisions are observed on both phloem and xylem sides and at a larger distance from rays. A comparison of the obtained results with the previous experiments shows that the increased frequency of anticlinal divisions in cambial cells observed in the case of application of 10 or 20% sucrose solutions coincides with an increased parenchymatization of tissues. A revealed localization of anticlinal divisions within the cambial zone indicates that, in the case of the exogenous sucrose uptake, the morphogenesis of conductive tissues in silver birch (Betula pendula Roth var. pendula) occurs in the same way as in Karelian birch (Betula pendula Roth var. carelica). Data presented in this paper agree with the earlier hypothesis that the formation of figured wood similar to that of Karelian birch occurs due to increased sucrose content in trunk tissues.     

Estimation of directional division frequencies in vascular cambium and in marginal meristematic cells of plants

Using simple arithmetical formulae, it is shown that, when the meristematic initial cells of a growing plant organ are arranged in a ring, the cellular dimensions predict the relative frequencies of anticlinal and periclinal divisions which these cells undergo. The pattern of cell file branching which appears during the course of development, and which is predicted by this mathematical model, is validated using data pertaining to the numbers and dimensions of initial cells within the secondary vascular cambium of hybrid aspen trees. Data pertaining to a second, simpler set of initial cells which comprises the outer cellular ring of the thallus of the alga Coleochaete orbicularis, and from which all the radial cell files of the circular disc-like thallus are descended, have also been used for model validation. Combining the mathematical approach to division frequencies with data of actual cell sizes permits inferences about the course of the increase of the number of cell files (generated by the anticlinal divisions) and the number of cells within each file (generated by the periclinal divisions) during the earlier stages of secondary tissue or thallus development, and also about how they will develop at future stages. The question whether or not cell division patterns conform to the geometry of the system in which the cells are embedded is also discussed.     

A model for an early stage of tomato fruit development: cell multiplication and cessation of the cell proliferative activity

Changes in cell number during the early period of tomato fruit development were analysed by means of a deterministic model of cell multiplication. The period commenced at the seed stage with one theoretical cell undergoing intensive cell division, and ended when the cell number became nearly constant. The model takes into consideration the proliferative activity of the fruit cell population which, a few days before flower anthesis, begins to decrease progressively after each mitotic cycle. Model parameters, namely the time at which proliferative activity diminishes, its rate of decrease and the length of the cell cycle, were estimated by fitting the model to observed cell population dynamics in tomato fruits growing in three different positions on the truss. It is hypothesized that the molecular mechanism responsible for the cessation of mitosis in growing fruits is associated with shortening of telomeric ends of nuclear DNA, as suggested previously for other growing cell populations.