COMPARATIVE ULTRASTRUCTURAL STUDIES OF SPERMATOGENESIS IN THE METZGERIALES (HEPATICAE). I. THE BLEPHAROPLAST OF PALLAVICINIA LYELLII

The blepharoplast in the young spermatid of Pallavicinia is similar to that of other hepatics in that it comprises a four-layered multilayered structure (MLS) and two staggered, dimorphic basal bodies. The spline, approximately 40 μm in length and extending through nearly two full gyres, comprises 20 parallel microtubules at its anterior end and narrows to 17 at the posterior limit of the subjacent lamellar strip (LS). Behind this, the spline shank, approximately 32 μm in length, is reduced to six tubules. The LS curves around the spermatid, following the anterior one-third of the first gyre of the spine, and is approximately 7.5 μm in length, the longest yet recorded for the bryophytes. It is spatulate in outline, equaling the width of the spline anteriorly but tapering steeply from the right-hand side behind the anterior basal body (ABB). It then extends posteriorly as a narrow strip beneath the left-hand margin of the spline. The basal bodies of the greatly staggered flagella are nonoverlapping and separated by a distance of about 4.4 μm. The subapical ABB and PBB measure (including the ventral triplet extensions and transition zones) 1.2 μm and 2.4 μm in length, respectively. A short, narrow aperture equaling one tubule-diameter in width is located in the spline directly beneath the ABB. The anterior mitochondrion is about 7 μm long and follows the outline of the overlying LS, while a cupshaped posterior mitochondrion is appressed to the plastid. Comparisons with other taxa indicate that major distinguishing features of metzgerialian blepharoplasts are highly staggered, nonoverlapping basal bodies, greatly elongate anterior mitochondria, and six-tubule shanks. Great differences between the spermatids suggest wide phylogenetic discontinuities between the genera of the Metzgeriales.     

STUDIES OF SPERMATOGENESIS IN THE HEPATICAE : II. Blepharoplast Structure in the Spermatid of Marchantia

The blepharoplast in a young, developing spermatid of Marchantia polymorpha, is a composite structure consisting of two basal bodies and a subjacent narrow band of axonemal-type tubules that we have termed the "spline." For most of its length, the spline consists of six long parallel tubules that nearly encircle the cell. The spline anterior is asymmetrically widened for about 2 µ by shorter tubules of the same kind. The lateral displacement of three long, adjacent marginal tubules by three short intervening tubules at the spline tip produces a long narrow aperture. Distally, the aperture is closed by the convergence of the displaced tubules with another trio of long tubules. Together, these form the six-membered cell-encircling portion. The expanded spline anterior has, at this stage of development, the four-layered (Vierergruppe) structure, of which the aforementioned tubules constitute the uppermost layer. The lower three strata consist of diagonal fins, elongated chambers, and fine tubules, respectively. The two flagellar bases lie close above the spline tip—one slightly anterior to the other—and diverge unequally from the spline axis. A few triplets extend proximally from the basal bodies, but do not connect with the spline. The anterior basal body is longer than the posterior one.     

Edmund Fredric Warburg; 1908–1966

Abstract

Ultrastructural analyses of mid-stage spermatids of Hypnum jutlandicum and H. mammillatum reveal a maximally structured blepharoplast closely similar in most respects to the other moss taxa previously investigated. The multilayered structure is four-layered and the dimorphic basal bodies highy staggered. The latter are inserted into the gamete in a slightly staggered subapical position. Both are longer than those reported for the majority of mosses and hepatics. Like other true mosses, the posterior basal body diverges from the longitudinal axis of the spermatid and is associated with a solitary microtubule which is equally divergent from the main body of the spline. In contrast to previous reports on other mosses, the stray microtubule of Hypnum is here interpreted as remaining separate from the spline, i.e., it does not converge posteriorly with the body of the spline.

The lamellar strip of Hypnum is roughly oblong in outline with an acute anterior tip which extends beyond the spline microtubules both anteriorly and on the righthand side. The posterior margin of the lamellar strip rapidly tapers from right to left. Like most mosses, the lamellar strip is approximately the same length as the anterior basal body and terminates at the level of the anterior basal body transition zone. In hepatics, in contrast, the lamellar strip subtends the posterior basal body over most of its length.     

Ultrastructural studies of spermatogenesis inAnthocerotophyta V. Nuclear metamorphosis and the posterior mitochondrion ofNotothylas orbicularis andPhaeoceros laevis

Summary Ultrastructural observations reveal that the spermatozoids of the hornwortsNotothylas andPhaeoceros contain two mitochondria and not one as described previously. Mitochondrial ontogeny and nuclear metamorphosis during spermiogenesis in these plants differ from all other archegoniates. The discovery that the posterior region of the coiled nucleus (when viewed from the anterior aspect) lies to the left of the anterior, in striking contrast to the dextral coiling of the nucleus of spermatozoids of other embryophytes, underlines the isolated nature of the hornworts among land plants. As the blepharoplast develops, the numerous ovoid mitochondria initially present in the nascent spermatid fuse to form a single elongated organelle which is positioned subjacent to the MLS and extends down between the nucleus and plastid. At the onset of nuclear metamorphosis, the solitary mitochondrion has separated into a larger anterior mitochondrion (AM) associated with the MLS and a much smaller posterior mitochondrion (PM) adjacent to the plastid. The PM retains its association with the plastid and both organelles migrate around the periphery of the cell as the spline MTs elongate. By contrast, in moss spermatids, where mitochondria undergo similar fusion and division, the AM is approximately the same size as the PM and the latter is never associated with the spline. As in other archegoniates, except mosses, spline elongation precedes nuclear metamorphosis in hornworts. Irregular strands of condensed chromatin compact basipetally to produce an elongated cylindrical nucleus which is narrower in its mid-region. During this process excess nucleoplasm moves rearward. It eventually overarches the inner surface of the plastid and entirely covers the PM.Abbreviations ABB anterior basal body - AM anterior mitochondrion - LS lamellar strip - MLS multilayered structure - MT microtubule - PBB posterior basal body - PM posterior mitochondrion     

Comparative spermatogenesis in the Jungermanniales (Hepaticae) I. Observations on the structure of the young spermatids of Cephalozia lunulifolia and Chiloscyphus pallescens

Abstract

A comparative analysis of the young spermatids of Cephalozia and Chiloscyphus reveals the organisation of the Jungermannialian blepharoplast to be basically the same as in other hepatics and mosses. Common features include the four-layered multilayered structure, the spatulate, asymmetrical anterior portion of the spline, and the staggered subapical insertion of the basal bodies, each with proximal triplet extensions. The range of spline widths in the Jungermanniales appears to be as great as in other groups of bryophytes and of no major taxonomic significance, but the position of the spline aperture may be more variable in hepatics than mosses. The lengths of the basal bodies are intermediate between those from unrelated taxa in other orders of hepatics.

However, the data also suggest the Jungermannialian spermatids exhibit many taxonomic variations and novel features. Whereas the left-lateral expansion of the spline in Cephalozia is common to most other bryophytes, a right-lateral expansion is peculiar to Marsupella. Chiloscyphus manifests an intermediate condition: its spline is unequally bilateral, the left-lateral expansion wider than the right. Lateral extensions of the lamellar strip beyond the spline in Cephalozia, Chiloscyphus and Marsupella have been previously recorded only in Anthocerotae. A posterior notch on the right hand side of the lamellar strip in Marchantiales is absent in Chiloscyphus and Cephalozia and has not been observed in the Metzgeriales.     

SPERMATOGENESIS IN COLEOCHAETE PULVINATA (CHAROPHYCEAE): EARLY BLEPHAROPLAST DEVELOPMENT

Transmission electron microscopy of serial thin sections was used to reconstruct several early developmental stages of the blepharoplast in Coleochaete pulvinata spermatids. These were compared to published studies of blepharoplast development in Charales and the closest relatives of charophycean green algae among embryophytes, i.e., hornworts and liverworts. Bicentriolar centrosomes such as occur in bryophytes and fern allies were not observed in Coleochaete. Centriole replication in C. pulvinata was orthogonal as in Charales. The resulting two daughter centrioles were oriented perpendicularly and joined proximally by electron-dense material. Their orthogonal relationship was maintained throughout blepharoplast development by a massive, banded connective which appeared early. In spermatids of hornworts and liverworts, a multilayered structure (MLS) develops in association with two centrioles destined to become flagellar basal bodies. When the MLS of these lower land plants is sectioned at right angles to the long axis of the microtubular layer, the MLS is observed to lie beneath cross sections of both centrioles. In contrast, when developing MLSs of C. pulvinata and Charales are similarly sectioned, they occur beside a cross section of just one of the two centrioles. In C. pulvinata (as in other charophytes), MLS lamellae are oriented at a 90-degree angle to the long axis of the S₁ microtubules from the beginning. This contrasts with the 40–45 degree angle between the MLS lamellae and S₁ microtubules universally reported for archegoniates. In early C. pulvinata spermatids, spline microtubules are closely associated with an anterior mitochondrion having a low stromal density and few cristae. An anterior mitochondrion is typically associated with blepharoplast development in hornworts and liverworts, but has not previously been reported to occur in Coleochaete or any other charophycean alga. In Coleochaete, as in hornworts and liverworts, but unlike Charales, structure of mature blepharoplasts reflects early blepharoplast ontogeny. Very little change in positional relationships among blepharoplast components (flagella, connective, MLS) occurs during development. These character-state differences are of importance in cladistic analyses of charophycean algae and lower land plants.     

Structural and immunocytochemical characterization of microtubule organizing centers in pteridophyte spermatogenous cells

Summary During the development of the spermatogenous cells, the pteridophyteCeratopteris richardii produces three structurally well-defined microtubule organizing centers (MTOCs). The blepharoplast, a spherical body that occurs during the last two spermatogenous divisions, organizes two microtubule (MT) arrays, one associated with a nuclear indentation and the other that organizes the spindle apparatus for the final divisions. After the last spermatogenous division, the blepharoplast reorganizes to produce two new putative MTOCs: the lamellar strip (LS) of the multilayered structure (MLS), which apparently organizes the spline microtubule array, and an amorphous zone (AM), that connects the basal bodies. Thin and semi-thin sections of this tissue were probed with antisera which recognize MTOCs in lower eukaryotes and animals to determine if any of these structures contain MTOC-associated proteins or epitopes recognized by monoclonal antisera. Gamma tubulin antibodies, which recognizeonly the minus ends of MTs in mammalian cells, label along the MT in all arrays found in the pteridophyte spermatogenous cells. Kinetochore MTs are unlabelled near the kinetochore, however. The monoclonal antibodies MPM-2 and C-9, that recognize centrosomal and nuclear epitopes in mammalian cells, label the interphase nucleus, the cytoplasm of mitotic cells, and the blepharoplast during both nuclear indentation and spindle formation. Double labelling of the blepharoplast-containing cells with anti-tubulin and either MPM-2 or C-9 reveals that the blepharoplast-associated fluorescence is the focus of the tubulin arrays. Centrin labels the reorganizing blepharoplast, the MLS, the AM, and a stellate pattern in the transition region of the flagella. These data indicate the usefulness of the structurally well-recognized MTOCs in pteridophyte spermatogenous cells in investigation of land plant MTOCs.     

STUDIES OF SPERMATOGENESIS IN THE HEPATICAE V. BLEPHAROPLAST DEVELOPMENT IN MARCHANTIA POLYMORPHA

Coaxial centrioles and a microtubule organizing center (MTOC) constitute each centrosome in spermatid mother cells of Marchantia polymorpha. During cell division the centrosome separates at its midregion and the two centrioles undergo a planar rotation that brings them to lie somewhat staggered and nearly parallel with their proximal ends embedded in osmiophilic granular material similar in appearance to that of the MTOC. Microtubules of the multilayered structure (MLS) arise in this material below the posterior centriole and parallel to its long axis. The rotation of centrioles and the initiation of S₁ tubules below the posterior centriole determine polarity of the incipient blepharoplast. Lower MLS strata are formed under the anterior centriole by the compaction of granular, osmiophilic matrix. Formation and growth of S₂ vertical lamellae occur at the left front edge of the MLS in association with MTOC-like matrix localized near the cell membrane. The MLS enlarges to about 0.4 μm wide by 0.6 μm long and is ovoid in outline except for a short distal projection underlying the posterior centriole. Subsequently the lamellae are transformed into homogenous, osmiophilic matrix that contributes directly to the expansion of all MLS strata including microtubules. The stratum of lamellae is interpreted as a planar MTOC subject to morphogenetic control. Each of the four strata grows proximally while the tapering distal projection lengthens beneath the posterior basal body. Dense matrix above the MLS, apparently elaborated by the S₂ layer, is organized into cartwheel and triplet components of the basal bodies’ proximal extensions. Organization of triplet tubules proceeds from proximal to distal toward preexisting triplets. Osmiophilic matrix contributes to the formation of microtubule keels and osmiophilic crests and may serve as a cementing material that stabilizes the spatial relationships of blepharoplast components. After full expansion of the MLS’ lower strata, the S₂ layer is reorganized into lamellae. Flagellar growth in Marchantia is postulated to involve a process whereby subunits or their precursors are elaborated by the MLS, translocated to the distal end of the flagellum and incorporated into the axonemal tubules. When MLS microtubules elongate to form a long, narrow band, the distal half of the S₂ layer is again in the osmiophilic matrix state.     

Ultrastructure of the spermatozoid of Lycopodium obscurum (Lycopodiaceae)

Ultrastructural observations reveal that the spermatozoid of Lycopodium obscurum is crescent shaped and contains two posteriorly directed flagella that are inserted at the front of the cell. The nucleus is broad and elongated with a narrow posterior projection or nuclear diverticulum. Spline microtubules (MTs) number 180 at their maximum and provide the framework for the cell. These MTs extend from the anterior of the locomotory apparatus and along the outermost surface of the nucleus, with a central shank of 14–17 MTs encircling the cell for at least one-third gyre beyond the nucleus. The two basal bodies are slightly staggered and positioned at the front of the cell over a highly elongated multilayered structure (MLS). The MLS extends laterally around the cell anterior and curves posteriorly over the nucleus. One large anterior mitochondrion is situated subjacent to the MLS, while numerous small mitochondria are scattered near or among the lobes of the single plastid. The plastid rests on the inner nuclear surface and contains numerous large starch grains. This cell differs from that of L. cernuum, the only other species of Lycopodium examined to date, in that it is more elongated and has an anterior-posterior orientation of the nucleus, basal bodies, MLS, and spline. Comparisons with coiled gametes of bryophytes and Selaginella suggest that some degree of coiling and cell streamlining may be ancestral in archegoniate spermatozoids.     

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.     

Phylogenetic Relationships of the Liverworts (Hepaticae), a Basal Embryophyte Lineage, Inferred from Nucleotide Sequence Data of the Chloroplast GenerbcL

Sequence data from the chloroplast-encoded generbcL were obtained for 24 liverworts, a basal group of embryophytes. Maximum likelihood and parsimony analyses of these data, along with data from other major green plant lineages, confirm hypotheses based on morphological data, such as the paraphyly of bryophytes, and the basal position of liverworts. Molecular data corroborate the deep separation between the complex thalloid and leafy/simple thalloid liverworts implied by morphological data, but the monophyly of liverworts could not be rejected. The effects of accounting for site-to-site rate heterogeneity in these data were examined using maximum likelihood methods. Comparison of trees obtained with and without rate heterogeneity showed that simply allowing for heterogeneity had a greater improvement on likelihood score than optimization of transition/transversion bias. Incorporation of site-to-site rate heterogeneity in the larger analysis, however, did not necessarily change which topology was favored. Properties ofrbcL sequences from the two liverwort groups were compared. Significantly different substitution rates were found between leafy/simple thalloid and complex thalloid liverwort taxa, with rates ofrbcL sequence evolution in leafy/simple thalloid taxa being higher and more indicative of those of vascular plants, and with those of complex thalloid taxa (such asMarchantia) being slower. Codon usage inrbcL in complex thalloid liverworts was biased toward NNU and NNA, compared to the leafy/simple thalloid liverworts. Although base composition and relative substitution rates differed between the two groups, no significant differences were detected within each of the two groups of liverworts. The signal present in first and second codon sites versus third codon sites was compared. While the third codon positions inrbcL across this taxon sampling are highly variable (with only 15 constant sites of 439), the trees obtained were in general agreement with trees from the entire data set and with trees obtained from independent sources of data. The presence of signal in third codon positions across greater than 400 MY of plant evolution means that definitions of saturation based on pair-wise comparisons of sequences inadequately assess phylogenetic signal.     

ULTRASTRUCTURAL STUDIES OF SPERMATOGENESIS IN THE ANTHOCEROTALES. I. THE BLEPHAROPLAST AND ANTERIOR MITOCHONDRION IN PHAEOCEROS LAEVIS: EARLY DEVELOPMENT

Electron microscopic examination of thin sections showed that the blepharoplast of a young spermatid of Phaeoceros consists of two side-by-side centrioles and an accumulation of osmiophilic, granular matrix at their proximal ends. Lying between these nearly parallel organelles is a dark-staining body that will later disappear at the onset of flagellogenesis. For a brief period the centrioles are oriented perpendicular to the nuclear surface so that the granular matrix at their proximal ends is confluent with the nuclear envelope; furthermore, the nucleoplasm immediately in front of the centrioles becomes densely staining. The multilayered structure (MLS) develops directly under the centrioles. It comprises a band of 12 microtubules (the S₁ stratum) and three lower strata (S_2–4) whose constitutent lamellae are oriented at an oblique angle to the S₁ axis. While the S₁ tubules grow rearward over the nucleus which forms a beak adjacent to the posterior end of the lamellar strata, the centrioles are transformed into basal bodies with the distal growth of the axonemes and the proximal growth of the central cartwheels and lowermost triplets. The proximal ends of the basal bodies and the S₁ tubules overlying the lamellar strata are invested with osmiophilic matrix that extends down to the S₂ layer and may temporarily occlude the lamellar plates. At the onset of nuclear elongation an anterior mitochondrion becomes situated close beneath the lamellar strata which extend laterally beyond the S₁ tubules.     

蕨类植物精细胞运动器和细胞骨架的研究

介绍了近年来蕨类植物游动精子运动器和细胞骨架的研究进展。游动精子由配子体精子器中的非运动细胞发育形成,其分化过程包括了运动器官和细胞骨架的合成和组装。精子发生过程中形成的运动器的各部分结构包括鞭毛、基体、多层结构及附属结构;基体是细胞中新形成的结构,在不同类群的蕨类植物中分别由双中心粒、分支生毛体和生毛体产生。鞭毛、基体和多层结构中的微管带形成了游动精子三个独特的微管列阵,由于微管蛋白的后修饰作用这些微管列阵十分稳定;centrin是运动器中的重要成分, 但功能尚不清楚,可能和细胞骨架及运动器的构建有关。     

Recovery of microtubules on the blepharoplast of Ceratopteris spermatogenous cells after oryzalin treatment

Most land plants have ill-defined microtubule-organizing centers (MTOCs), consisting of sites on the nuclear envelope or even along microtubules (MTs). In contrast, the spermatogenous cells of the pteridophyte Ceratopteris richardii have a well-defined MTOC, the blepharoplast, which organizes MTs through the last two division cycles. This allows a rare opportunity to study the organization and workings of a structurally well-defined plant MTOC. In this study, antheridial plants were treated with levels of oryzalin that cause complete MT loss from the cells containing blepharoplasts. The oryzalin was then washed out and plants were allowed to recover for varying amounts of time. If the spermatogenous cells were fixed prior to washing out, the blepharoplasts had an unusual appearance. In the matrix (pericentriolar) material where MT ends are normally found, clear areas of about the diameter of MTs were seen embedded in a much deeper matrix, made more obvious in stereo pairs. Occasionally, the matrix material was highly distended, although the basal body template cylinder morphology appeared to be unaltered. The blepharoplasts often occurred as clusters of 2 or 4, indicating that blepharoplast reproduction is not affected by the lack of MTs, but that their movement to the poles is. Gamma (gamma) tubulin antibodies labeled the edge of the blepharoplast in areas where the pits are located, indicating that these might be sites for MT nucleation. After wash out, the new MTs always re-appeared on the blepharoplast and the recovery occurred within an hour of washout. MT lengths increased with increasing washout time and were indistinguishable from untreated blepharoplasts after 24 h of recovery. After washout, arrays formed in new sperm cells such as the spline and basal bodies were often malformed or present in multiple copies, as were the blepharoplasts in these cells prior to wash out. These data indicate that the blepharoplast serves as the site of MT nucleation and organization even after complete MT de-polymerization.     

蕨类植物分株紫萁精子发生过程中生毛体和多层结构的超微结构

应用电镜技术对蕨类植物分株紫萁(Osmunda cinnamomea L. var.asiatica Fernald)精子发育过程中的生毛体和多层结构的超微结构进行了研究.生毛体在幼精子细胞中出现,正在分化的生毛体略呈球状,球状体的中央由一团染色深的颗粒状物质构成,外围分化出若干柱状体.已分化的生毛体由柱状体分散或辐射状排列构成,呈球状,球体中心不含染色深的物质.多层结构位于精子细胞内的基体和巨大线粒体之间,刚形成时仅由片层构成,片层相互平行排列形成片层带.多层结构在分化中期由微管带、片层带和蚀斑三层构成.多层结构在分化末期又形成附属微管带、嗜锇冠和嗜锇层.微管带从多层结构长出,沿细胞核的表面伸展,并与核膜之间形成复合结构.基体由柱状体转变而成,它向两端生长,在远端产生鞭毛的轴丝,在近轴端形成楔状结构.本文首次详细阐明了原始薄囊蕨分株紫萁生毛体和多层结构发育的超微结构特点,并与其他蕨类进行了比较,发现其片层带出现在微管带形成之前.     

SPERMATOGENESIS IN LYCOPODIUM: THE MATURE SPERMATOZOID

The mature spermatozoid of Lycopodium cernuum is a blunt ended, fusiform cell, 8–10 μm long by 4–5 μm wide. A multilayered structure (MLS) and a subtending anterior mitochondrion are located at the anterior of the cell. The MLS is coiled through 1–1.5 gyres in a shallow sinistral helix around the periphery of the cell. The MLS would be triangular in outline if unwound and laid flat, about 1.4 μm wide, 7.5–8 μm long, and 80 nm thick. The MLS comprises four layers, S₁–S₄. The S₁ forms the spline, a supportive sheet of microtubules; the S₂, lamellate in younger stages, is an homogeneous, darkly staining layer in the mature sperm; the S₃ and S₄ retain their lamellate appearance and are delimited by lateral connections. Approximately 200 S₁ microtubules extend posteriorly from the MLS at about 45° to the MLS long axis and form a partial sheath around the nucleus. The two basal bodies are located on opposite sides of the cell external to the MLS. Each is tangential to the curve of the MLS and surrounded by a globular matrix. At their attachment, the axonemes are oriented laterally and are antiparallel to each other. Distally, the flagella, each about 38 μm long, trail behind the cell as it swims. The nucleus is roughly ovoid, about 4 μm diam, and centrally or sometimes laterally located. The greater volume of the nucleus is occupied by condensed, amorphic chromatin. Cavities within the chromatin are often seen to contain spheroidal inclusions that have two differently staining regions. The inclusions are also located at the periphery of the chromatin. The posterior of the cell is occupied by several small mitochondria and an amyloplast, about 2 μm diam containing numerous starch grains.     

蕨类植物分株紫萁精子发生过程中生毛体和多层结构的超微结构

应用电镜技术对蕨类植物分株紫萁(Osmunda cinnamomea L. var．asiatica Fernald)精子发育过程中的生毛体和多层结构的超微结构进行了研究。牛毛体在幼精了细胞中出现,正在分化的生毛体略呈球状,球状体的中央由一团染色深的颗粒状物质构成,外围分化出若干柱状体。已分化的生毛体由柱状体分散或辐射状排列构成,呈球状,球体中心不含染色深的物质。多层结构位于精子细胞内的基体和巨大线粒体之间,刚形成时仅由片层构成,片层相互平行排列形成片层带。多层结构在分化中期由微管带、片层带和蚀斑三层构成。多层结构在分化末期又形成附属微管带、嗜锇冠和嗜锇层。微管带从多层结构长出,沿细胞核的表面伸展,并与核膜之间形成复合结构。基体由柱状体转变而成,它向两端生长,在远端产生鞭毛的轴丝,在近轴端形成楔状结构。本文首次详细阐明了原始薄囊蕨分株紫其生毛体和多层结构发育的超微结构特点,并与其他蕨类进行了比较,发现其片层带出现在微管带形成之前。     

Some ultrastructural aspects of spermatogenesis inLycopodium complanatum

Summary Analysis of thin sections shows that the blepharoplast in an early spermatid ofLycopodium consists of two basal bodies and the subtending spline apparatus. The latter has a 4-layered or Vierergruppe organization much like that reported for certain bryophytes and vascular plants. During the course of spermatid maturation the vertically lamellate S₂ stratum of the spline apparatus is transformed into a thinner layer of dense osmiophilic material, although the vertical lamellae of the S_3,4 strata persist. Rarely there occurred double Vierergruppen, presumably anomalous structures in which a single layer of spline microtubules is flanked on each side by two separate sets of S_2–4 strata. Longitudinal sections show that the basal bodies in an early spermatid lie parallel and close together with their microtubular triplets imbricating in the same direction. In late spermatids these basal bodies lie antiparallel and widely separated, their triplets now imbricating in opposite directions. This change is intrepreted to result from the relocation of one of the basal bodies to a position halfway around the cell by moving distal end first over the subtending spline. The basal bodies become invested by a globular-textured material not previously observed in plant spermatids. The role of this investing material is tentatively thought to be related to anchorage of the basal bodies.     

Three‐dimensional organization of flagellar basal apparatus in Ectocarpus gametes

The flagellar basal apparatus of the brown alga Ectocarpus siliculosus was re‐investigated in details using transmission electron microscopy and electron tomography. As a result, three‐dimensional structures with spatial arrangement of bands and microtubular flagellar rootlets were observed. Fibrous structures linking the anterior flagellar basal body to the major anterior rootlet (R3) or the bypassing rootlet was newly discovered in this study. A direct attachment from the minor anterior rootlet (R4) to the anterior and posterior basal bodies was also discovered, as were attachments from the minor posterior rootlet (R1) to the deltoid striated band and from the major posterior rootlet (R2) to the posterior fibrous band. The microtubular flagellar rootlets were connected to the bands and to the anterior or posterior basal body. These bands may have a role in maintaining the spatial arrangement of the anterior and posterior flagellar basal bodies and the microtubular flagellar rootlets. A numbering system of the basal body triplets was established by tracing axonemal doublets in the serial sections. From these observations, the precise position of two flagellar basal bodies, bands, and flagellar rootlets was determined.     

蕨类植物精细胞运动器和细胞骨架的研究

介绍了近年来蕨类植物游动精子运动器和细胞骨架的研究进展.游动精子由配子体精子器中的非运动细胞发育形成,其分化过程包括了运动器官和细胞骨架的合成和组装.精子发生过程中形成的运动器的各部分结构包括鞭毛、基体、多层结构及附属结构;基体是细胞中新形成的结构,在不同类群的蕨类植物中分别由双中心粒、分支生毛体和生毛体产生.鞭毛、基体和多层结构中的微管带形成了游动精子三个独特的微管列阵,由于微管蛋白的后修饰作用这些微管列阵十分稳定;centrin是运动器中的重要成分,但功能尚不清楚,可能和细胞骨架及运动器的构建有关.