Flagellar apparatus ultrastructure inMesostigma viride (Prasinophyceae)

The ultrastructure of the flagellar apparatus ofMesostigma viride Lauterborn (Prasinophyceae) has been studied in detail with particular reference to absolute configurations, numbering of basal bodies, basal body triplets and flagellar roots. The two basal bodies are interconnected by three connecting fibers (one distal fiber = synistosome, and two proximal fibers). The flagellar apparatus shows 180° rotational symmetry; four microtubular flagellar roots and two system II fibers are present. The microtubular roots represent a 4-6-4-6-system. The left roots (1s, 2s) consist of 4 microtubules, each with the usual 3 over 1 root tubule pattern. Each right root (1d, 2d) is proximally associated with a small, but typical multi-layered structure (MLS). The latter displays several layers corresponding to the S₁ (the spline microtubules: 5–7), and presumably the S₂—S₄ (the lamellate layers) of the MLS of theCharophyceae. At its proximal origin (near the basal bodies) each right root originates with only two microtubules, the other spline microtubules being added more distally. The structural and positional information obtained in this study strongly suggest that one of the right roots (1d) ofMesostigma is homologous to the MLS-root of theCharophyceae and sperm cells of archegoniate land plants. Thus the typical cruciate flagellar root system of the green algae and the unilateral flagellar root system of theCharophyceae and archegoniates share a common ancestry. Some functional and phylogenetic aspects of MLS-roots are discussed.Dedicated to Prof. DrLothar Geitler on the occasion of his 90th birthday.     

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.     

COMPARATIVE ULTRASTRUCTURAL STUDIES OF SPERMATOGENESIS IN THE METZGERIALES (HEPATOPHYTA) II. THE BLEPHAROPLAST OF BLASIA PUSILLA

As in other hepatics, the young spermatid of Blasia pusilla contains a well-developed blepharoplast comprising a four-layered multilayered structure (MLS) and two overlying dimorphic basal bodies. The asymmetrical spline (S₁ or upper stratum of the MLS) numbers 20 or 21 microtubules (MTs) at its anterior tip and reduces to eight at the posterior limit of the lamellar strip (LS). Behind this the shank of the spline is five or six tubules in width over most of its length, approximately one revolution of the circumference of the gamete. The three-microtubule spline aperture underlies the anterior basal body and like those of most hepatics, it is closed at its anterior end. The asymmetrical LS (approx. 2.0 μm in length) is characterized by a right-hand posterior notch which lies below the spline aperture at the region of the cartwheel configuration of the anterior basal body (ABB). The staggered dimorphic basal bodies overlap for approximately one third of their lengths. Both lie parallel to the long axis of the spline. As in other hepatics, the ABB (1.2 μm in length) is subapical and comprises an anterior hub extension with progressive rearward additions of lateral, dorsal and ventral triplets. Over most of its length (2.1 μm) the longer posterior basal body (PBB) consists of a distinct central hub and three ventral triplets. Transition zones of both basal bodies contain stellate configurations into which the two central axonemal MTs frequently extend. The blepharoplast of Blasia shows several features in common with leafy, simple thalloid and complex thalloid liverworts. Compared with the few Metzgeriales observed thus far, the LS is less elongate and the basal bodies less staggered. Dimensions of basal body components and spline dimensions, however, are comparable to those of most leafy and thalloid hepatics. Striking similarities with the complex thalloid liverworts include a posterior notch in the LS and a spline aperture three MTs wide.     

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.     

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.     

Immunofluorescent localization of cytoskeletal tubulin and actin during spermatogenesis inPteridium aquilinum (L.) Kuhn

Summary Details concerning the appearance and behaviour of blepharoplasts during spermatogenesis, and the assembly of the cytoskeletal motile apparatus of spermatids were elucidated by immunofluorescence microscopy using antibodies to tubulin and actin, applied to material prepared from antheridia of the fernPteridium aquilinum (L.) Kuhn. Blepharoplast immunofluorescence with antitubulin first appears as spheres at the future spindle poles prior to the last spermatogenous division. Developing spermatids each have one blepharoplast, which gives rise to a triangular layer corresponding to the incipient microtubule ribbon. Compared to the ribbon, immunoreactivity of the multilayered structure is relatively weak. Intensely fluorescing basal bodies appear, increase in number, and become arranged in rows along two edges of the microtubule ribbon as it widens and elongates. Along the dorsal edge is a dense file of basal bodies spaced at about 0.3 m intervals, parallel to each other and oriented at 145° to the multilayered structure. This spacing and orientation is maintained throughout spermatid development. Basal bodies at the opposite edge are initially oriented at 115° to the multilayered structure but become rearranged into small groups that rotate so that the angle is reduced to 55–70° by the time the assembly of flagella commences on both sets of basal bodies. By this stage the microtubule ribbon has encircled about 2/3 of the nuclear circumference and the nucleus is assuming a crescent shape. In fully developed spermatozoids the groups of basal bodies are oriented at 25° to the multilayered structure, parallel to the long body of the now helical nucleus. Immunofluorescence using antiactin showed that towards the completion of nuclear shaping, actin forms a strip along the helical multilayered structure. Detergent-extraction of mature spermatozoids revealed that actin is associated also with the flagellar band, particularly with basal bodies.Abbreviations MLS multilayered structure - MT microtubule     

Fine structure of the flagellar apparatus of gametesin situ and motile zygotes of the green algaUlothrix flacca var.Roscoffensis (Ulotrichales) (Chlorophyta)

Summary This fine structural study ofUlothrix flacca (Dillw.) ThuretRoscoffensis variety (Berger-Perrot), a marineUlothrix, describes in detail the flagellar apparatus configuration of gametesin situ in the gametangia and in motile zygotes. The gametes's flagellar apparatus shows two basal bodies overlapping at their proximal end at a 30° angle, in an 11/5 o'clock configuration or with a counterclockwise absolute orientation. The basal bodies are interconnected by a non-striated band or capping plate. They are wrapped in their proximal part by an electron-dense sheath and obtured by a bilobed terminal cap. A cruciate microtubular root system having a 4-2-4-2 alternation pattern is present. A striated microtubule associated component (S.M.A.C.) or system I fibres accompany the two membered root R₂. The system II fibres or rhizoplasts along with striated bands associated to the microtubular roots, were not observed and are presumed to be absent.In the motile zygotes, the basal bodies are paired in a cruciate pattern. During the fusion process, two basal bodies, one of each pair, slide in a face to face position with a slight displacement into the 11/5 o'clock direction; the other two make a 30° counterclockwise rotation, thus making a 60° angle between the two basal bodies of each pair instead of 30° in the gamete.After comparison with the flagellar apparatus of other green alga gametes, it is concluded that the taxonomic affinities ofUlothrix flacca var.Roscoffensis, lie with theUlvophyceae sensuStewart andMattox 1978.Abbreviations CP capping plate - ER endoplasmic reticulum - G Golgi body - LG lipid globule - M mitochondria - MS presumed mating structure - N nucleus - R ₂,R ₄ microtubular roots - SH sheath - SMAC striated microtubule associated component - TC terminal cap - V vacuole - Ve vesicles in the anterior papilla - 1, 2, 1, 2 basal bodies numerotation     

Dynamics of spermiogenesis in Drosophila melanogaster

Summary A morphogenetic process that transforms spermatids from a syncytial state to a state in which each spermatid is invested in its own membrane, is initiated at the head region of the spermatid bundle and traverses through the entire length of the bundle in the testis of Drosophila melanogaster. This process not only eliminates the syncytial bridges between spermatids but also removes unneeded organelles and the excess parts of the nuclear membrane, nucleoplasm and cytoplasm. It also brings about structural modifications to flagellar elements. The propagation of this process is seen as the caudal movement of a fusiform swelling of the spermatid bundle, 100 or more in length. Spermatids are individualized in the basal half of the swelling, whereas they remain syncytial in the apical half. The swelling increases its volume as it accumulates cytoplasmic debris while traversing the sperm bundle, from about 15 in maximum diameter in the basal testicular region to as large as 30 at the apical end where it becomes a bag of wastes. A variation of the process in a mutant stock which is known to inactivate up to half of the products of meiosis is briefly described. The morphological change of interspermatid bridges prior to the individualization is also reported.This work was supported by grants from the National Institutes of Health (USPHS-HD 03015 and GM-15971) and a contract from the Atomic Energy Commission, AT(04-3)-34, P.A. 150.Graduate training grant USPHS GM 00702.     

Comparative cytology and taxonomy of theUlvaphyceae II. Ulvalean characteristics of the stephanokont flagellar apparatus ofDerbesia tenuissima

Summary The stephanokont flagellar apparatus of the zoospores ofDerbesia tenuissima (De Not.) Crouan is examined and compared to the flagellar apparatuses of other green algae. The flagella ofDerbesia are attached to two of three bands which lie at the junction of the body and papilla. Serial longitudinal and cross sections reveal that the basal bodies are attached to the bands along their sides and at their proximal ends. The bands are not striated in any plane. The lack of striation in the bands and the partial covering of the proximal end of the basal bodies by one of the bands closely resemble the type of flagellar connection system described as the Bryopsis-type byMelkonian (1980). Zoospores of ulvalean green algae also possess these features, suggesting that green siphons are phylogenetically related to theUlvales. It is proposed that green siphons be tentatively classified in theUlvaphyceae rather than in theChlorophyceae orCharophyceae.This work supported by NSF Grant DEB 78-03554.     

Transformation and development of the flagellar apparatus ofCryptomonas ovata (Cryptophyceae) during cell division

Summary InCryptomonas ovata, long, dorsal flagella are produced which transform during the following cell division into short, ventral flagella. At division there is a reorientation in cell polarity, and the parental basal apparatus, which comprises the basal bodies and associated roots, is distributed to the daughter cells via a complex sequence of events. Flagellar apparatus development includes the transformation of a four-stranded microtubular root into a mature root of different structure and function. Each newly formed basal body nucleates new microtubular roots, but receives a striated fibrous root from a parental basal body. The striated roots are originally produced on the transforming basal body and are transferred to the new basal bodies at each successive division. The development of the asymmetric flagellar apparatus throughout the cell cycle is described.     

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.     

The arrangement of chromosomes in nuclei of sperm from plethodontid salamanders

Plethodontid salamanders have n = 13 or 14 large metacentric or sub-metacentric chromosomes. Sperm nuclei from Plethodon cinereus measure 72×1 m. The nucleoprotein of spermatids is at first finely granular. In elongate spermatids it clumps into larger granules, which then fuse to form the compact nucleoprotein of the mature sperm. The nuclei of mature sperm are negatively birefringent with respect to their length. — ³H RNA complementary to high-density satellite DNA of centromeric heterochromatin in P. cinereus has been hybridized in-situ to spermatids and sperm, and its site of binding to these cells has been examined by autoradiography. Labelling of round spermatid nuclei is localized in a single patch. Elongate spermatid nuclei are labelled only over the rear quarter of the nucleus. Label over the nuclei of mature sperm is localized in a region extending 10–20 m forwards from the rear of the nucleus. — In P. cinereus the ribosomal genes are located near the centromere on the short arm of chromosome 7. ³H ribosomal RNA hybridizes to a single patch in round spermatid nuclei. Elongate spermatid nuclei show label over a short segment of the rear half of the nucleus. In spermatids nearing maturity the labelled region is never more than 20 m long. — These results indicate that in P. cinereus each chromosome is arranged in a U formation with its centromere at the base of the sperm nucleus, and its arms extended forwards along the length of the nucleus. — Among plethodontids, increase in C value and corresponding increase in chromosome size is accompanied by increase in the length rather than the width of the sperm nucleus. — ³H ribosomal RNA hybridizes to a short segment in spermatid and sperm nuclei from Xenopus and Triturus. In these animals, the position of the labelled segment varies from sperm to sperm.     

The effect of sex hormones on the proximal tubules in the rat kidney

Summary The three segments (S₁, S₂, S₃) of the proximal tubule of the rat kidney were investigated, with special reference to lysosomes, after castration, estradiol application, and at the end of pregnancy. Especially in S₁ and S₂ castration induces an increase of cellular autophagy. The nuclei become smaller; endoplasmic reticulum (ER), ribosomes, and Golgi apparatus are reduced; catabolism predominates. In S₁ more giant lysosomes occur; the total number of lysosomes increases whereas acid phosphatase activity decreases at the same time. Sex differences which exist in untreated animals disappear. Substitution with estradiol causes an activation of the proximal tubule cells: Heterophagy predominates, and cellular autophagy is reduced. Nuclear size is unchanged; ER, ribosomes and Golgi apparatus show a clear increase. Giant lysosomes are absent in S₁. On the whole lysosomes are larger, but less numerous than after castration. Acid phosphatase is highly active. All changes are most evident in S₃. At the end of pregnancy the proximal tubule cells are stressed considerably: Pinocytotic activity increases, and large numbers of cell organelles and many lipid vacuoles can be observed. The basal lamina in S₁ and S₂ becomes thicker. Lysosomes enlarge and increase in number in all segments; giant lysosomes are absent in S₁; acid phosphatase activity is extremely high. The results indicate that sex hormones directly influence the regulation of the proximal tubule cell; moreover, they are indirectly important for the functioning of the kidney via changes in the whole organism.Supported by the Deutsche Forschungsgemeinschaft (SFB 105)Dedicated to Prof. Dr. O. Bucher, Head of the Institute of Histology and Embryology of the University of Lausanne/Switzerland, on the occasion of his 65th birthday     

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.     

Changes in endoplasmic reticulum during spermiogenesis in the mouse

Summary Changes in the endoplasmic reticulum of mouse spermatids during spermiogenesis were examined by scanning electron microscopy, applying the OsO₄-DMSO-OsO₄ method, which permits 3-dimensional observation of cell organelles. At the same time, the endoplasmic reticulum was stained selectively by the Ur-Pb-Cu method, and 0.5 m-thick sections were prepared for observation by transmission electron microscopy. The results demonstrated stereoscopically the mode of disappearance of the endoplasmic reticulum. In spermatids of the early maturation phase, the endoplasmic reticulum was of uniform diameter, branched and anastomosed, forming a complicated three-dimensional network throughout the cytoplasm. A two-dimensional net was also noted to have formed just beneath the plasma membrane and about Sertoli cell processes invaginating the spermatid cytoplasm. As spermiogenesis progressed, the spread-out endoplasmic reticulum gradually aggregated to form a condensed, glomerulus-like structure consisting of a very thin endoplasmic reticulum connected to the surrounding endoplasmic reticulum. This structure corresponds to the so-called radial body. Thus, the endoplasmic reticulum may aggregate, condense, be transformed into a radial body, and be removed from the cytoplasm. The two-dimensional endoplasmic reticulum-net, just beneath the plasma membrane and surrounding processes of Sertoli cells, disappeared in spaces where the three-dimensional endoplasmic reticulum network was scarce. Both the two-dimensional endoplasmic reticulum-net structure and the three-dimensional endoplasmic reticulum network disappeared at the same time, indicating that they may be closely related.     

THE BASAL APPARATUS OF THE QUADRIFLAGELLATE SPERMATOZOPSIS EXSULTANS(CHLOROPHYCEAE):NUMBERING OF BASAL BODY TRIPLETS REVEALS TRIPLET INDIVIDUALITY AND DEVELOPMENTAL MODIFICATIONS1

Though there are no detectable structural differences between each of the axonemal doublets of Spermatozopsis exsultans Korshikov, basal body triplets do show structural peculiarities: one triplet consistently has an electron-dense patch appressed to its proximal part. This triplet is labeled No. 1, and all triplets are numbered in accordance to the numbering system used for other flagellate green algae. We present a detailed analysis of the basal apparatus (basal bodies and attached cytoskeletal elements) of S. exsultans and describe how basal apparatus elements are attached, very specifically, to particular basal body triplets. The analysis includes immunogold detection of centrin-containing structures and characterization of their sites of attachment to basal bodies. The sequence of basal body development in S. exsultans is deduced from what we know of other green algae. With this, we describe how the cytoskeletal structures associated with the separate basal bodies, particularly those attached to the right side of a basal body, undergo apparent morphological modifications from cell generation to generation. The data indicate that basal body triplets are truly different from one another and that this subsequent basal body asymmetry, combined with the developmental differences between basal bodies themselves, presumably accounts for the heterogeneity in the basal apparatus and any asymmetry in the cell as a whole.     

Localization of gamma-tubulin to the basal foot associated with the basal body extending a cilium

The human oviduct epithelium primarily consists of ciliated cells and secretory cells. Solitary cilia usually extend from the apical surface of the secretory cells. We investigated the localization of -tubulin in the ciliary basal apparatus of both cell types by fluorescence immunohistochemistry and immunoelectron microscopy. In addition to basal bodies, -tubulin was identified in the lateral basal foot, especially the basal foot cap. This observation is consistent with previous observations that microtubules radiate from the basal foot and the basal foot serves as the microtubule organizing centre.     

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.     

Some observations on the development of dictyosome-like structures in guinea pig testes

Summary Structures superficially resembling dictyosomes (DLS) are present in guinea pig spermatocytes. They are first visible in late stages of spermatogonial development as single, irregularly shaped saccules. DLS saccules continue to form, at what appears to be a much accelerated rate, during the first stages of spermatocyte development. After formation, the saccules mature and aggregate into a stacked, or dictyosomal, configuration. DLS reach their maximum numbers in spermatocytes just prior to the formation of proacrosomal granules and, at this time, constitute more membrane than Golgi apparatus and as much as 25% of the total endomembrane of the spermatocyte. The DLS then decline in numbers and only a few remain in spermatids. DLS reappear just prior to spermiation and become conspicuous features of the residual body and cytoplasmic droplet. DLS membranes have structural and cytochemical similarities to the membranes of the mature (trans) faces of the Golgi apparatus, and especially the thick cisternae of the spermatid Golgi apparatus. They are similar, also, to the membranes of the acrosome, the cell surface, multivesicular bodies (MVB), and a class of vesicles whose membranes appear thin following fixation in tannic acid. Both the thin membrane vesicles (i.e., the tannic acid asymmetrical vesicles-TAAV) and the MVB may act as membrane pools for the generation and/or dissipation of DLS.Mention of a commercial or proprietary product in this paper does not constitute an endorsement of this product by the USDA. Supported in part by a grant from the National Institute of Health HD 11508.     

An electron microscopical study of cell contacts in the seminiferous tubules of some mammals

Summary Different types of cell contacts in the seminiferous tubules have been studied electron microscopically in some laboratory and domestic mammals. Specialized inter-Sertoli cell contacts are always present. Most of them show a narrow — partly perhaps closed — intercellular space at some distance from the basement membrane, above the spermatogonia but below the spermatocytes. Fibrillar material is present in the cytoplasm near the junction as well as subsurface cisterns of the endoplasmic reticulum. Two main types of narrow junctions and one wide junction are described. These junctions are interpreted as devices for adhesion and perhaps intercommunication between the basal parts of the Sertoli cells. The narrow junctions are also considered to impede the intercellular transport of substances to spermatocytes and spermatides and into the luminal fluid. This interpretation emphasizes the importance of the Sertoli cells as nurse cells for the spermatocytes and spermatids.Numerous fine branches of the Sertoli cells surround spermatocytes, spherical spermatids, and true residual bodies, and others protrude deeply into the postnuclear cytoplasm of elongated spermatids. The plasma membrane of developing spermatids turns thicker and becomes a distinct unit membrane. Dense, fibrillar material and long, narrow subsurface cisterns are always present in the Sertoli cells along their border to the acrosomal area of the elongated spermatids. This arrangement is interpreted as an attachment device of hemidesmosomal character.Intercellular bridges are considered to interconnect as many as four primary spermatocytes or sixteen spermatids.