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.     

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 MORPHOGENESIS OF BASAL BODIES AND ACCESSORY STRUCTURES OF THE CORTEX OF THE CILIATED PROTOZOAN TETRAHYMENA PYRIFORMIS

Dividing cells of Tetrahymena pyriformis were observed by transmission electron microscopy for signs of morphogenesis of cortical structures. The earliest stage of basal body development observed was of a short cylinder of nine single tubules connected by an internal cartwheel structure. This is set perpendicular to the mature basal body at its anterior proximal surface under the transverse microtubules and next to the basal microtubules. Sequential stages show that the single tubules become triplet tubules and that the "probasal bodies" then elongate and tilt toward the organism's surface while maintaining a constant distance of 75–100 mµ with the "parent." The new basal body after it is fully extended contacts the pellicle, and then assumes a parallel orientation with and moves anterior to the parent basal body. The electron-opaque core in the lumen of the basal body and accessory structures around its outer proximal surface appear after the developing basal body has elongated. These accessory structures associating with their counterparts from other basal bodies and with the longitudinal microtubules may play a role in the final positioning of basal bodies and thus in the maintenance of cortical patterns. Observations on a second sequence of basal body formation suggest that the oral anlage arises by multiple duplication of somatic basal bodies.     

On Flagellar Structure in Certain Flagellates

This paper describes the structure of the flagella, basal bodies, and some of the associated fibre systems in three genera of complex flagellates, Trichonympha, Pseudotrichonympha, and Holomastigotoides. Three groups of longitudinal fibres occur in a flagellum: two central and nine outer fibres such as have been repeatedly described in other material, and an additional set of nine smaller secondary fibres not previously identified as such. Each central fibre shows a helical substructure; the pair of them are enveloped in a common sheath. Each outer fibre is a doublet with one subfibre bearing projections—called arms—that extend toward the adjacent outer fibre. The basal body is formed by a cylinder of nine triplet outer fibres. Two subfibres of each triplet continue into the flagellum and constitute the doublets. The third subfibre terminates at the transition of basal body to flagellum, possibly giving rise to the nine radial transitional fibres that seem to attach the end of the basal body to the surface of the organism. The central and secondary flagellar fibres are not present in the lumen of the basal body, but other complex structures occur there. The form of these intraluminal structures differs from genus to genus. The flagellar unit is highly asymmetrical. All the flagella examined have possessed the same one of the two possible enantiomorphic forms. At least two systems of fibres are associated with the basal bodies of all three genera.     

STUDIES OF SPERMATOGENESIS IN THE HEPATICAE : I. Ultrastructure of the Vierergruppe in Marchantia

Spermatids of the liverwort Marchantia polymorpha were shown by analysis of thin-sections to contain a four-layered organelle, the Vierergruppe, lying between the flagellar bases above and a subjacent mitochondrial body. The uppermost layer consists of parallel tubules structurally similar to those of the axoneme. Some of the tubules extend beyond the four-layered region to form a long ribbon-like appendage. The second layer consists of low, vertical, membranous fins connected by numerous short links to the tubules above. The third layer, limited above and below by two horizontal membranes, consists of vertical partitions, apparently continuous with the fins. The fourth and lowermost layer consists of narrow parallel tubules aligned beneath alternate partitions. The long axes of the lower three layers are parallel to each other and lie at an angle of 48° to the tubule axis of the uppermost stratum. A graphic representation of a three-dimensional scale model interpreting organelle structure is given. The Vierergruppe supersedes Dreiergruppe interpretation in most if not all of the bryophytes studied to date.     

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.     

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.     

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.     

ULTRASTRUCTURE OF CEPHALEUROS VIRESCENS (CHROOLEPIDACEAE; CHLOROPHYTA). III. ZOOSPORES

Transmission electron microscopic examination of Cephaleuros virescens Kunze growing on leaves of Camellia spp. and Magnolia grandiflora L. indicates that unreleased zoospores in mature zoosporangia are similar to those produced by the related genus Phycopeltis epiphyton Millardet and unlike the quadriflagellate motile cells produced by taxa in other families of Chlorophyta. The zoospores bear four smooth isokont bilaterally “keeled” flagella containing typical “9 + 2” axonemes and lacking scales. Flagellar insertion is apical and the parallel basal bodies overlap laterally at two levels. A cross section through the four basal bodies shows a trapezoidal arrangement wherein the two upper (anterior) basal bodies are closer together than are the lower (posterior) two. Serial sections indicate that diagonally opposing upper and lower basal bodies anchor flagella which emerge from the same side of the apical papilla. Each of the four basal bodies is associated with a microtubular spline which extends beneath the plasmalemma to the posterior end of the zoospore. A distinct multilayered structure is associated with each of the lower basal bodies. A nucleus, mitochondria (two of which are closely associated with the nucleus and spline microtubules), a chloroplast, and cytoplasmic haematochrome droplets are present in each zoospore. Pyrenoids and eyespots are absent. Flagellar insertion is characterized by “reversed bilateral symmetry”; and zoospores with both right-handed and left-handed arrangements are produced. The ultrastructure of the zoospores clearly indicates that: 1) the mode of flagellar insertion: 2) morphology, number, and arrangement of multilayered structures, and 3) bilaterally keeled flagella are characteristic of the Chroolepidaceae.     

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.     

Food uptake and fine structure of Cryothecomonas longipes sp. nov., a marine nanoflagellate incertae sedis feeding phagotrophically on large diatoms

Cryothecomonas longipes Schnepf and Kühn sp. nov. is a colourless biflagellate organism, 9–14 μm long and 7–9 μm wide when not filled with food vacuoles. It was detected in the North Sea, feeding with pseudopodia on diatoms. It penetrates the host shell, while the main body of the flagellate remains outside the frustule. Cells are covered with a multilayered theca. The pseudopodium protrudes through a preformed slit in the theca. Each flagellum also emerges through a pit in which the theca forms a funnel of complex structure that girdles each flagellum. The anterior flagellum is 9–15 μm long and oriented forward; the ventral flagellum, posteriorly directed, is 20–24 μm long and bears fine hairs. The flagellar roots consist of microtubules that emerge at satellites around the basal bodies and run along the flagellar pits. In addition, the ventral flagellum is accompanied by a band of six microtubules. It is proximally attached to a small fibrillar band, which interconnects the basal bodies. Cryothecomonas longipes has two or three types of extrusomes which pierce the theca when discharged. Their mode of discharge is discussed. Microbody-like vesicles containing small tubules are closely associated with older digestion vacuoles. Cryothecomonas longipes is compared with other species of the genus and a diagnosis is given. Received: 4 March 1999 / Received in revised form: 28 July 1999 / Accepted: 30 August 1999     

Post-embryonic development of the Malpighian tubules in <Emphasis Type="Italic">Apis mellifera</Emphasis> (Hymenoptera) workers: morphology,remodeling, apoptosis,and cell proliferation

The honeybee Apis mellifera has ecological and economic importance; however, it experiences a population decline, perhaps due to exposure to toxic compounds, which are excreted by Malpighian tubules. During metamorphosis of A. mellifera, the Malpighian tubules degenerate and are formed de novo. The objective of this work was to verify the cellular events of the Malpighian tubule renewal in the metamorphosis, which are the gradual steps of cell remodeling, determining different cell types and their roles in the excretory activity in A. mellifera. Immunofluorescence and ultrastructural analyses showed that the cells of the larval Malpighian tubules degenerate by apoptosis and autophagy, and the new Malpighian tubules are formed by cell proliferation. The ultrastructure of the cells in the Malpighian tubules suggest that cellular remodeling only occurs from dark-brown-eyed pupae, indicating the onset of excretion activity in pupal Malpighian tubules. In adult forager workers, two cell types occur in the Malpighian tubules, one with ultrastructural features (abundance of mitochondria, vacuoles, microvilli, and narrow basal labyrinth) for primary urine production and another cell type with dilated basal labyrinth, long microvilli, and absence of spherocrystals, which suggest a role in primary urine re-absorpotion. This study suggests that during the metamorphosis, Malpighian tubules are non-functional until the light-brown-eyed pupae, indicating that A. mellifera may be more vulnerable to toxic compounds at early pupal stages. In addition, cell ultrastructure suggests that the Malpighian tubules may be functional from dark-brown-eyed pupae and acquire greater complexity in the forager worker bee.     

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.     

FINE STRUCTURE OF THE CILIA OF ROTIFERS

The fine structure of the coronal cilia of the rotifer Philodina citrina has been studied in detail. Specimens were fixed with OsO₄ and embedded in butyl—methyl methacrylate, Epon 812, or Vestopal and sectioned with a Porter-Blum microtome. The details of structure of the rootlets, basal bodies, basal plates, and free cilia are described. The general structure of the rotifer ciliary apparatus conforms well to that established for other species. One of the main observations is the difference in structure of the peripheral filaments in the opposing halves of a cross-section of the free cilium. Also, in longitudinal sections evidence is offered for the existence of a helical structure in the peripheral filaments.     

The flagellar root system inHeterosigma akashiwo (Raphidophyceae)

Summary The flagellar apparatus of 3 isolates ofHeterosigma akashiwo (Hada) Hada has been studied by serial sectioning. The two basal bodies lie at almost right angles to one another, but in a different plane, and are interconnected by an extensive root system. This consists of three roots (i) a massive cross-banded fibrous root (= rhizoplast) which extends from near the proximal ends of both basal bodies to the anterior surface of the nucleus, (ii) a compound microtubular root with a layered structure, associated with the hairy anterior flagellum and extending to the anterior surface and (iii) the rhizostyle which passes between the two basal bodies leading anteriorly to a vesicle in the flagellar groove region and following the nucleus posteriorly terminating deep in the cytoplasm. Both the characteristic arrangement of the basal bodies and the presence of the complex layered structure are characteristic of theRaphidophyceae. The broad microtubular root, however, to which the layered structure is attached, appears to be characteristic of nearly all heterokont algae, fungi and protozoa so far examined. Thus, our findings have important implications on phylogenetic relationships within the heterokonts and lead us to question whether some of the present classes such as theChrysophyceae andXanthophyceae are indeed natural groups.     

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.     

ULTRASTRUCTURE OF SWARMERS IN THE LAMINARIALES (PHAEOPHYCEAE). I. ZOOSPORES1

Zoospores of 17 species in 14 genera of Laminariales, collected in the northeast Pacific Ocean, were studied by electron microscopy. These zoospores are unique in the brown algae in lacking both an eyespot in the single chloroplast and any associated swelling at the base of the shorter, posterior flagellum. Spores of all species examined possess a distal whiplash portion on the longer, mastigoneme-bearing anterior flagellum. This appendage may sometimes be as long as the mastigoneme-bearing portion of the flagellum, but it is only seldom preserved in the preparations for electron microscopy. A microtubular cytoskeleton is probably responsible for maintaining the shape of the spore. It consists of a short band of about 10 microtubules between the two basal bodies, scattered tubules converging at the anterior of the spore, a band of 7–9 tubules directed anteriorly from the anterior basal body, and a band directed posteriorly from the posterior basal body. These anterior and posterior bands may form one continuous band looping around the periphery of the spore. Variation with possible taxonomic significance was found in the ultrastructure of vesicles which apparently contain adhesive material, and which are extruded through the plasmalemma when the zoospores settle.     

ENTOSIPHON SULCATUM (EUGLENOPHYCEAE): FLAGELLAR ROOTS OF THE BASAL BODY COMPLEX AND RESERVOIR REGION1,2

The flagellar root system of Entosiphon sulcatum (Dujardin) Stein (Euglenophyceae) is described and compared with kinetoplastid and other euglenoid systems. An asymmetric pattern of three microtubular roots, one between the two flagellar basal bodies and one on either side (here called the intermediate, dorsal, and ventral roots), is consistent within the euglenoid flagellates studied thus far. The dorsal root is associated with the basal body of the anterior flagellum (F₁) and lies on the left dorsal side of the basal body complex. Originating between the two flagellar basal bodies, and associated with the basal body of the trailing flagellum (F₂), the intermediate root is morphologically distinguished by fibrils interconnecting the individual microtubules to one another and to the over lying reservoir membrane. The intermediate root is often borne on a ridge projecting into the reservoir. The ventral root originates near the F₂ basal body and lies on the right ventral side of the cell. Fibrillar connections link the membrane of F₂ with the reservoir membrane at the reservoircanal transition level. A large cross-banded fiber joins the two flagellar basal bodies, and a series of smaller striated fibers links the anterior accessory and flagellar basal bodies. Large nonstriated fibers extend from the basal body complex posteriorly into the cytoplasm.     

Humble origins for a successful strategy: complete enrolment in early Cambrian olenellid trilobites

Trilobites are typified by the behavioural and morphological ability to enrol their bodies, most probably as a defence mechanism against adverse environmental conditions or predators. Although most trilobites could enrol at least partially, there is uncertainty about whether olenellids—among the most phylogenetically and stratigraphically basal representatives—could perform this behaviour because of their poorly caudalized trunk and scarcity of coaptative devices. Here, we report complete—but not encapsulating—enrolment for the olenellid genus Mummaspis from the early Cambrian Mural Formation in Alberta, the earliest direct evidence of this strategy in the fossil record of polymerid trilobites. Complete enrolment in olenellids was achieved through a combination of ancestral morphological features, and thus provides new information on the character polarity associated with this key trilobite adaptation.