ANTHERIDIAL FORMATION IN ONOCLEA SENSIBILIS L.: GENESIS OF THE JACKET CELL WALLS

Antheridial initiation in Onoclea sensibilis L., an advanced leptosporangiate fern, begins with the production of a small, wedge-shaped cell within the anterior region of the vegetative cell. This is in contrast to previous reports claiming that the initials are formed by a localized protuberance in the cell wall of the vegetative cell (Campbell, 1886; Davie, 1951; Leung and Naf, 1979; Nayar and Kaur, 1971). The mature antheridium of Onoclea is composed of three uniquely shaped jacket cells surrounding spermatogenous cells. The two funnel-shaped jacket cell walls are shown to form in a lateral circular manner. Except for the production of the antheridial initial cell, jacket cell formation in Onoclea proceeds in accordance with the classical concept of antheridial development in advanced ferns accredited in part to Atkinson (1894), Campbell (1886), Kny (1869), and Strasburger (1869). The classical concept has been contested in more recent years by Davie (1951), Leung and Näf (1979), and Verma and Khullar (1966).     

SPERMATOGENESIS IN A HOMOSPOROUS FERN,ONOCLEA SENSIBILIS

A detailed study of spermatogenesis in a homosporous fern, Onoclea sensibilis L., is presented from the formation of the first spermatogenous cell to the release of the sperm. Two different walls are deposited around the developing spermatids at specific developmental stages as opposed to one wall reported for other species. Most ultrastructural changes that occur in Onoclea during spermatid differentiation resemble those described in previous studies on other fern species, with the following exceptions: 1) A previously undescribed structure appears during midspermatid stage. This dense layer of amorphous material with a row of evenly spaced light areas occurs between the anterior portion of the mitochondrion associated with the multilayered structure and the anterior plasmalemma of the spermatid. 2) An early stage in blepharoplast formation resembles that which occurs in the heterosporous fern Marsilea, in contrast to that which has been reported in Platyzoma, the only other homosporous fern studied at this stage. 3) The osmiophilic crest does not form as early as reported in other ferns. 4) The cap cell of Onoclea is removed intact, rather than collapsing or forming a pore during sperm release. Observations are reported on the number of sperm per antheridium, the time course of spermatogenous cell mitosis, and of differentiation of spermatids into sperm. In Onoclea, an antheridium may contain either 32 or 64 sperm. Regardless of the final number of sperm, each has approximately the same volume.     

葫芦藓精子发生过程中胞间连丝与胞质桥的超微结构

从超微结构水平上对葫芦藓(Funaria hygrometrica Hedw.)精子发生过程中胞间连接系统的结构及其变化动态进行了研究.结果表明,同一区中的相邻生精细胞由大量胞质桥相连,而不同区的细胞之间则不存在胞质桥.胞间连丝存在于套细胞之间以及套细胞与生精细胞之间,但它在生精细胞间不存在.在精子器发生的后期,当精子细胞壁开始降解时,同一个精子器中所有的精子细胞似乎都由扩大的胞质桥相互连接.胞质桥一直保持到精子分化的后期,最终精子细胞同步分化成精子.胞间连丝与胞质桥具有不同的内部结、分布以及生物发生机制,这表明它们在精子器的发育过程中可能扮演着不同的角色.     

葫芦藓精子发生过程中胞间连丝与胞质桥的超微结构

从超微结构水平上对葫芦藓(Funaria hygrometrica Hedw.)精子发生过程中胞间连接系统的结构及其变化动态进行了研究。结果表明,同一区中的相邻生精细胞由大量胞质桥相连,而不同区的细胞之间则不存在胞质桥。胞间连丝存在于套细胞之间以及套细胞与生精细胞之间, 但它在生精细胞间不存在。在精子器发生的后期,当精子细胞壁开始降解时,同一个精子器中所有的精子细胞似乎都由扩大的胞质桥相互连接。胞质桥一直保持到精子分化的后期,最终精子细胞同步分化成精子。胞间连丝与胞质桥具有不同的内部结、分布以及生物发生机制,这表明它们在精子器的发育过程中可能扮演着不同的角色。     

DEVELOPMENTAL FEATURES OF THE SPERMATOGENOUS CELL IN GINKGO BILOBA

A “double-blepharoplast” originates de novo in the spermatogenous cell of Ginkgo biloba L. Initially, the double-blepharoplast consists of two opposing hemispherical bodies comprised of densely staining material. The two blepharoplasts seemingly are pushed apart by the formation of densely packed fibrils which are oriented perpendicular to the distal, rounded edges of the two future blepharoplasts. As the latter move apart, each one develops lightly staining channels which are often organized in a hub and spoke configuration (procentrioles). Microtubules extend from the blepharoplasts as the latter move to their final position in the cell, and centrioles (probasal bodies) become organized at the periphery of each blepharoplast. Two large “osmiophilic globules,” conspicuous entities close to the nucleus of the mature spermatogenous cell, arise de novo. A fibrillogranular body in the cytoplasm, always closely associated with the nucleus, also arises de novo.     

THE ULTRASTRUCTURE OF THE STALK AND BASE OF THE ANTHERIDIUM OF POLYTRICHUM

The fluorescent boundary across the stalk of an antheridium of Polytrichum appears as a distinctive, secondary wall layer in electron micrographs. Lamellations of electron-dense and -lucent materials cause this layer to resemble the “suberized lamellae” of root endodermis and leaf bundle sheaths in grasses. The cells of the stalk below the boundary are especially rich in lipid droplets, whereas those in the base of the antheridium, above the boundary, have markedly fewer and smaller lipid droplets and abundant rough endoplasmic reticulum often in loosely parallel arrays. Cytological differences develop before the boundary appears, so that the distinctive wall layer is secreted by protoplasts that are already specialized morphologically. During maturation of an antheridium there is a secretion of a fluid into a space that forms at the bottom of the sperm chamber. However, the cells surrounding this fluid show no special morphological adaptations that would seem to relate to secretion.     

DIVISION OF THE GENERATIVE CELL AND LATE DEVELOPMENT IN THE MALE GAMETOPHYTE OF GINKGO BILOBA

Division of the generative cell in the male gametophyte of Ginkgo biloba to yield the sterile cell and spermatogenous cell was examined in vivo and in vitro. Evidence is presented in support of a new interpretation of development in which the sterile cell and spermatogenous cell arise from an unusual anticlinal ringlike division of the generative cell. This type of cell division is only known to occur during antheridial development in leptosporangiate ferns and stomatal development among certain ferns in the Schizaeaceae and Polypodiaceae. The strong similarities in development and cell arrangement within the male gametophytes of cycads and Ginkgo suggest that division of the generative cell in cycads may be the same as in Ginkgo. Although the ringlike (conically annular) divisions in the antheridia of leptosporangiate ferns and the male gametophytes of Ginkgo (and probably cycads) are remarkably similar and result in the production of a central spermatogenous cell, it is conjectural as to whether these patterns represent a striking convergence or evolutionary homology.     

FINE-STRUCTURAL STUDY ON THE FORMATION OF THE GENERATIVE CELL WALL AND INTINE-3 LAYER IN A GROWING POLLEN GRAIN OF LILIUM LONGIFLORUM

At the end of mitosis in the lily pollen microspore, the fan-shaped cell plate gives rise to a cell wall delineating a hemispherical cell. At first, the cell wall of the newly formed generative cell and the intine-3 layer of the pollen grain wall are inseparable. Gradually, the wall of the generative cell near the pollen grain wall becomes thicker and wall segments are formed between the thickened zones, and these make a network system by which the generative cell becomes suspended and separated from the pollen grain wall. After the separation, the intine-3 layer is formed inside the intine 2. The generative cell wall and the intine-3 layer are formed by coated vesicles, polysaccharide particles and rough ER.     

THE EFFECT OF AUXIN AND GUANINE ON CELL EXPANSION AND CELL DIVISION IN THE GAMETOPHYTE OF THE FERN,ONOCLEA SENSIBILIS

Miller , J. H. (Yale U., New Haven, Conn.) The effect of auxin and guanine on cell expansion and cell division in the gametophyte of the fern, Onoclea sensibilis. Amer. Jour. Bot. 48(9): 816–819. Illus. 1961.—Auxin and guanine promote cell expansion in 0. sensibilis gametophytes. The optimum concentration of auxin for total expansion is 10^−-5 M, but the optimum for elongation is 10^−-6 M. Above this concentration the cells expanded isodiametrically. Guanine is active at higher concentrations than auxin. Increasing concentrations of auxin progressively inhibit red light-induced cell division, while guanine has no effect on cell division. Neither kinetin nor adenine promotes cell expansion or cell division.     

SCANNING ELECTRON MICROSCOPY OF ANTHERIDIA AND ARCHEGONIA OF ANEMIA MEXICANA KLOTZSCH

Antheridia and archegonia of the fern Anemia mexicana were viewed with scanning electron microscopy (SEM). The mature antheridium is composed of a cap, ring, and basal cell with spermatozoids inside. The archegonium neck is composed of a neck canal cell surrounded by four rows of neck cells. The ventral canal cell and egg were not observed. The neck bends toward the notched meristem. The neck cells usually are uniform in shape and arrangement, but in some archegonia, shape and arrangement of neck cells was irregular. The apex of these archegonia often appeared swollen because of the random cell arrangement. In the presence of water, the antheridium cap is partially detached and the spermatozoids emerge. At this time, the neck cells open at the end of the archegonium in preparation for fertilization. The basic morphology of the antheridia and archegonia is similar to previous reports, although SEM provides more structural detail and a better three-dimensional visualization of these reproductive structures.     

THE FINE STRUCTURE OF THE GRASS GUARD CELL

Brown, W. V., and Sr. C. Johnson. (U. Texas, Austin.) The fine structure of the grass guard cell. Amer. Jour, Bot. 49 (2): 110–115. Illus. 1962.—An electron microscopic study of 16 species of grasses classified in 10 tribes and 5 subfamilies has revealed some hitherto unknown facts about guard-cell structure. In species of 3 subfamilies, but not in the Festucoideae, there are membranes on the guard cells overarching the stoma. In the Festucoideae, the membrane is rudimentary or absent and is associated with a different cross-sectional shape of the guard cell. The central canal through the thick-walled region of the guard cell is structurally quite complex. The wall between the central canal and the subsidiary cell is thin and lacks plasmodesmata. There are plastids but no developed chloroplasts in grass guard cells. Mitochondria are abundant, but vacuoles are undetectable. At the ends of the guard-cell pair, the wall between them is incomplete and the protoplasts are confluent.     

REGIONS OF CELL WALL EXPANSION IN THE PROTONEMA OF A FERN

Protonemata of Onoclea sensibilis were grown for 7 days in darkness and were then transferred into light on new media, either liquid or agar-solidified, which contained 0.15% colchicine. The growth of individual plants was observed on solid media in microchambers. Unequivocal evidence was obtained that cell wall expansion and an increase in cell diameter occurred in regions well behind the apex of the protonema. This finding is related to an hypothesis which proposes light-induced changes in microtubule orientation and cell wall structure as an explanation for certain changes in cell form in fern gametophytes.     

Behavior of chloroplasts and chloroplast nuclei during spermatogenesis in the fern,Pteris vittata L.

Summary The fate of the chloroplasts and chloroplast nuclei (cp-nuclei) was followed during spermatogenesis in the fernPteris vittata L. by epifluorescence microscopy after staining with 4-6-diamidino-2-phenylindole (DAPI) and by quantitation of chloroplast DNA (cp-DNA) by fluorimetry using a video intensified microscope photon counting system (VIMPICS). The spores were grown on solid medium that contained antheridiogen (An_ptd), and formed an antheridium initial on the protonema cell. The antheridium initial divided and produced 16 spermatocytes and 3 surrounding cells. The chloroplasts in the spermatocytes decreased in volume as cell division was repeated, until finally the volume of each chloroplast was 1/15 of that of the primary chloroplasts. The DNA content of the chloroplasts was also reduced to 1/5 of the original value and when the sperm matured, the fluorescence of cp-DNA disappeared. In the 16-cell spermatocyte, the recognition of the fluorescence of chlorophyll in the chloroplasts with a green excitation filter became difficult. But, the plastids could be observed until the final stage of the sperm. From these observations, it appears that there are two steps in the metamorphosis of chloroplasts during spermatogenesis in the fern. The first step involves the decrease in the volume of chloroplasts, accompanied by reduction of the DNA content, and the second step involves the change of the physical state of chloroplasts to amyloplasts and the disappearance of the cp-DNA from the amyloplasts.     

CELL DIVISION IN BULBOCHAETE. II. HAIR CELL FORMATION1

Most vegetative cells of Bulbochaete, and all those of Oedogonium, possess an apical, circular discontinuity in the structure of their secondary wall. Rupture of the wall at this precise site permits expansion of the ring during cell division and release of the zoospore following zoosporogenesis. Certain cells of Bulbochaete (always the apical daughter cell of a division pair) lack this type of discontinuity. Instead, the apical wall is thinned out on one side, so that the cell bulges asymmetrically. In the middle of the bulge is a wall discontinuity which extends only part way around the cell. The wall will rupture here, too, for zoospore release, but if a cell having such a wall, divides, it invariably does so asymmetrically, with one pole of the spindle located in the bulge. Cytokinesis then cuts off a small, colorless daughter cell. The wall ruptures at the discontinuity, and this daughter cell emerges through the slit and differentiates into a hair. The creation of hairs in such cells commences with the deposition of a pad of primary wall lining the bulge. Golgi bodies are involved in its secretion, but not in that of a secondary wall layer which forms next in the premitotic cell and covers the primary wall. The cell becomes polarized; the nucleus migrates toward this region as the chloroplast moves aside. After the asymmetric mitosis, a curved phycoplast cuts off the hair cell nucleus and prevents the chloroplast from moving back into the future hair, whose cytoplasm soon loses much of its affinity for heavy metal stains. Following rupture of the parental wall, the phycoplast moves some distance past the limits of the newly deposited secondary wall layer and then forms a cross wall under the hair. The secondary wall of the hair is not continuous with the secondary wall structure of the parental cell; the circular discontinuity that arises around the base of the bulging parental wall is then perpetuated and accentuated as the hair's secondary wall thickens. This wall weakening becomes the dislocation that will predetermine the site of the ring and consequently the direction of cell expansion in the next normal division of the cell subtending the hair. Abnormal ring formation and the creation of terminal twin hairs have also been examined. The lip of the growing hair contains a characteristic organization of membranes and other components which may be related to the organization of the hair's numerous longitudinally oriented microtubules. These results are discussed in terms of the morphology of the wall in the Oedogionales generally. The creation of the special wall morphology that leads to hair cell formation is considered to be ontogenetically related to a similar wall morphology that is involved in formation of the fertilization pore of the oogonium.     

THE ULTRASTRUCTURE OF SCENEDESMUS (CHLOROPHYCEAE). II. CELL DIVISION AND COLONY FORMATION1

Cell division in Scenedesmus is fairly typical of other chlorococcalean genera. The closed spindle has centrioles at polar fenestrae and apparently a series of nuclear divisions precedes cytokinesis. The phycoplast system of cytokinetic microtubules predicts the path of cleavage furrows whose mode of formation is obscure. Before and during cell division, the endoplasmic reticulum invariably accumulates granular material which later, during cytokinesis, appears to he secreted via the golgi bodies. Similar dense granular material then at accumulates outside the forming daughter cells but inside the parental wall, as the latter begins eroding away. By the end of colony formation, the cellulosic parental wall has disappeared, leaving its outer sheath and attached ornamentative features (spines, combs, reticulate or warty layer, etc.) intact as a “ghost.” The spines and combs of new colonies appear to condense out of the extracellular aggregate; their precise mode of formation is obscure. As they form, the daughter cells, having become rearranged within the parental wall, stick to one another apparently at specific sites on their outer surface. A trilaminar (sporopollenin-containing) layer arises first in each cell at these adhesive sites and immediately afterwards, dense material aggregates between the adjacent layers to give rise to the coenobial adhesive. Plaques of the trilaminar layer later appear over the rest of the cell's surface; they grow and fuse so that eventually each cell is enclosed by one continuous Trilaminar Sheath (TLS). While the plaques are forming, another dense layer materializes around the whole coenobium. Depending on the species, this layer turns into either the warty layer, in which instance it is applied directly on to the surface of the TLS except near the coenobial adhesive, or else it becomes the reticulate layer, in which instance it remains entirely separate from the TLS, soon acquiring the complex system of propping spikelets which suspend it from the coenobial surface. When fully farmed, the daughter coenobium is tightly compressed within the parental TLS, with its spines folded lengthwise along the daughter cells. Release of the colony follows a quite explosive rupturing of the parental TLS, and immediately upon release, the daughter colony flattens out and erects its spines.     

LIGHT MICROSCOPE AND ULTRASTRUCTURAL STUDIES OF THE MALE GAMETOPHYTE IN GINKGO BILOBA: THE SPERMATOGENOUS CELL

A light microscope and ultrastructural study was made of the pollen tube of Ginkgo biloba, with special emphasis given to the spermatogenous cell that gives rise to two motile sperms. Just prior to the mitotic division that results in the formation of two sperms, the spermatogenous cell consists of a large nucleus, two blepharoplasts, two large osmiophilic globules, and a conspicuous lipo-protein body. Other organelles in the cytoplasm include numerous electron-dense proplastids (with some lamellar development), mitochondria, small vacuoles, and lipid bodies. Ribosomes are present in abundance, but endoplasmic reticulum and dictyosomes are sparse. The nucleus, prior to mitosis, is relatively Feulgen-negative, due undoubtedly to the diffuse distribution of DNA. Each blepharoplast, the main organelle of interest, is nearly spherical, measures 3.5–4.5 μm in diam, and supports about 1,000 probasal bodies. The interior of a blepharoplast consists of an electron-dense matrix and of less dense regions which appear to be infiltrated by a network of microtubules. Each probasal body is composed of a cylinder of nine separate tubules (singlets) at the basal or proximal end. The cylinder becomes elaborated distally into nine pairs of subtubules (doublets) and then into nine sets of subtubules (triplets). A central tubule is present the entire length of the probasal body. Some of the subtubules, as well as microtubules from the interior of the blepharoplast, extend into the cytoplasm and probably constitute the “astral rays” as seen with the light microscope. Comparisons are made with other published accounts of the organization of blepharoplasts in plants and of centrosomes and centrioles in animals.     

VALVE AND BAND MORPHOLOGY OF SOME FRESHWATER DIATOMS. III. PRE- AND POST-AUXOSPORE FRUSTULES AND THE INITIAL CELL OF MELOSIRA ROESEANA1

Frustules of a clonal culture of Melosira roeseana Rabenh. were examined with light and scanning electron microscopy. Vegetative valves in the post-auxospore (full size) stage exhibit a larger width/length ratio than those in the pre-auxospore (size-reduced) stage. Cells form chains by linking spines of adjacent valves which occur at the periphery of the valve face-mantle junction. Three or jour large pores occur at the center of the valve face, with the diameter of each pore tapering from the inner to the outer valve surface; these pores are often occluded by siliceous processes. Features of M. roeseana, not shown previously for Melosira, include a “stepped” mantle, on only one of the two valves resulting from the same cell division, flattened processes attached to short siliceous stalks on the valve face, disk-like processes on the mantle, and an open girdle band with up to eight antiligulae. Siliceous scales on the surface of the initial cell are remnants of the auxospore wall. The epivalve of the initial cell is larger in diameter than the hypovalve, and both valves lack linking spines and a step on the valve surface. The initial, cell epicingulum consists of only two bands; the hypocingulum has up to seven. Initial cells with four or more hypocingular bands divide to form new post-auxospore filaments. Melosira roeseana should not be included in the genus Melosira as it is presently defined by the type species, M. nurnmuloides C. Ag. Major differences include irregular linking spines, a closed pseudoloculate valve construction, and labiate processes on the valve face and mantle of M. nummuloides, compared with well-defined linking spines, a valve constructed of a basal siliceous layer perforated by poroid areolae, and labiate processes lacking on the valve of M. roeseana.     

THE FORMATION OF BASAL BODIES (CENTRIOLES) IN THE RHESUS MONKEY OVIDUCT

Basal body replication during estrogen-driven ciliogenesis in the rhesus monkey (Macaca mulatta) oviduct has been studied by stereomicroscopy, rotation photography, and serial section analysis. Two pathways for basal body production are described: acentriolar basal body formation (major pathway) where procentrioles are generated from a spherical aggregate of fibers; and centriolar basal body formation, where procentrioles are generated by the diplosomal centrioles. In both pathways, the first step in procentriole formation is the arrangement of a fibrous granule precursor into an annulus. A cartwheel structure, present within the lumen of the annulus, is composed of a central cylinder with a core, spoke components, and anchor filaments. Tubule formation consists of an initiation and a growth phase. The A tubule of each triplet set first forms within the wall material of the annulus in juxtaposition to a spoke of the cartwheel. After all nine A tubules are initiated, B and C tubules begin to form. The initiation of all three tubules occurs sequentially around the procentriole. Simultaneous with tubule initiation is a nonsequential growth of each tubule. The tubules lengthen and the procentriole is complete when it is about 200 mµ long. The procentriole increases in length and diameter during its maturation into a basal body. The addition of a basal foot, nine alar sheets, and a rootlet completes the maturation process. Fibrous granules are also closely associated with the formation of these basal body accessory structures.     

LIGHT AND ELECTRON MICROSCOPE STUDIES OF THE CELL WALL STRUCTURE OF THE ROOT HAIRS OF RAPHANUS SATIVUS

Dawes , Clinton J., and Edwin Bowler . (U. of California, Los Angeles.) Light and electron microscope studies of the cell wall structure of the root hairs of Raphanus sativus. Amer. Jour. Bot. 46(8): 561–565. Illus. 1959.—The structure and development of the cell wall of the root hair of Raphanus sativus were studied under the light and electron microscopes. The outer layer of the root hair consists of mucilage which covers the entire hair and forms a thick cap at the tip. Beneath the mucilage a thin cuticle covers the inner layers of the cell wall. These layers consist of cellulose microfibrils, varying in pattern, in a granular matrix, presumably pectic in nature. The microfibrils of the outer layer, apparently laid down at the tip, are reticulate in arrangement. In mature regions of the root hair, the wall is thickened by an inner layer of parallel and longitudinally orientated microfibrils. Pores in the cellulose wall are evident and increase in number and size near the base of the hair.