Substructural morphogenesis of the spindle apparatus in meiotic basidia ofCoprinus micaceus (Agaricales)

The spindle apparatus ofCoprinus micaceus begins to develop from the diglobular polar body outside the nucleus. During both meiotic divisions it operates inside the nuclear envelope and consists of two amorphous poles, a central bundle of interpolar microtubules, and chromosomal microtubules. A metaphase plate cannot exist because the interpolar strand of fibers is persistent throughout the division process. Within the spindle axis more than 100 microtubules can be estimated. They are encircled by a ring of chromatic structures. During the telophase the former spindle pole is evaginated from the nuclear envelope and contacts the plasmalemma near the cell wall.     

The spermatozoa of ascidians: Acrosome and nuclear envelope

Summary The spermatozoon of Ascidia callosa has a head with a wedge-shaped tip. Between the nuclear envelope and the plasmalemma, at the tip of the head, there are one or two previously undescribed vesicles, 45 to 55 nm in diameter. These vesicles have the characteristics of an acrosome. Their role in the process of fertilization has not been determined. Ultrastructural studies of sperm activation are needed, but claims that the spermatozoa of ascidians do not have an acrosome should be reconsidered.Behind the tip of the sperm there are pores in the nuclear envelope. This part of the envelope also contains a dense band of amorphous material that may have a supportive function. A nearly identical structure, associated with pores has been found in the spermatozoon of Boltenia villosa. An analysis of the nuclear envelope of Ascidia callosa indicates that the same structure has previously been misinterpreted as an acrosome in the spermatozoon of Ascidia nigra.     

华东安蕨卵发生的超微结构观察

核心薄囊蕨是蕨类植物中的进化类群,但对受精作用具有显著影响的卵发生研究仍较少,该文利用超微技术对其中蹄盖蕨科的华东安蕨卵发生过程进行了研究,以进一步完善薄囊蕨植物卵发生的科学资料,为理解蕨类植物的有性生殖及演化机制奠定基础。超微结构观察显示:华东安蕨的幼卵和沟细胞在颈卵器中紧密联接;随后,在卵细胞上方出现了分离腔和临时细胞壁,但在卵细胞中间孔区处卵细胞和腹沟细胞始终联接在一起;分离腔中的无定形物质沉积在卵细胞的质膜外形成了1层加厚的卵膜,而在孔区处没有形成卵膜,该位置最后形成了受精孔。在进一步的卵发生过程中,卵细胞核变得高度不规则,形成了大量的核外突和核褶皱。     

ULTRASTRUCTURAL STUDY ON MICROSPORE WALL MORPHOGENESIS IN ISOETES JAPONICA (ISOETACEAE)

Spore wall morphogenesis of the microspore of Isoetes japonica was studied by transmission electron microscopy. The microspore wall consists of four layers: the perispore, outer exospore, inner exospore, and endospore. The perispore consists of electron-dense materials. The exospore is divided into outer and inner sections, with a large gap between the two. The outer exospore appears as an undulating plate consisting of tripartite lamellae with homogeneous sporopollenin. The inner exospore consists of an accumulation of tripartite lamellae on the microspore cell membrane. Immediately after meiosis, the tripartite lamellae of the outer exospore forms around the microspore. The lamellated inner exospore forms next, which adheres to the cell membrane of the microspore. The deposition of homogeneous sporopollenin material on the tripartite lamellae causes the plates of the outer exospore to thicken. Some homogeneous material may also be deposited on the inner exospore. Lastly, the electron-dense perispore is deposited on the outer exospore, and the electron-lucent endospore forms beneath the inner exospore. We conclude that the lamellae of the outer exospore, inner exospore, and endospore are formed and derived, in that order, from the gametophytic microspore cytoplasm. The homogeneous sporopollenin material of the outer exospore and perispore may be derived from the sporophytic tapetal cytoplasm.     

The development and ultrastructure of gum ducts inCitrus plants formed as a result of brown-rot gummosis

Summary Young stems ofCitrus plants were infected with the fungusPhytophthora citrophthora. The effect of the infection on gum duct development was studied. The following sequence of structural changes was observed in the cambial zone: 1. The middle lamellae between layers of xylem mother cells dissolve forming duct cavities. 2. The cells around the duct cavities differentiate into epithelial cells rich in cytoplasm. 3. The amount of Golgi bodies and associated vesicles increases. The vesicles and small vacuoles, some of which seem to originate from the fusion of Golgi vesicles, contain fibrillar material that stains for polysaccharides. Vesicles and vacuoles appear to fuse with the plasmalemma. Material staining positively for polysaccharides accumulates between the plasmalemma and cell wall, and penetrates the latter. 4. The protoplast shrinks and the space below the cell wall, which contains polysaccharides, increases in volume. 5. After a period of 10 days or more the gum ducts become embedded in the xylem, and the activity of the epithelial cells ceases. The cell walls of many of them break, and the gum still present in the cells is released.     

The neck constriction in plasmodesmata

Simple plasmodesmata between mesophyll and bundle sheath cells in actively expanding leaves of Salsola kali L. and roots of Epilobium hirsutum L. are shown to possess specialized structures, called sphincters, around their neck regions. The sphineters are made visible by the combined effects of tannic acid and heavy metal staining; they are localized just outside that area of the plasmalemma, which forms the collar around the entrance to each plasmodesmos. This localization corresponds to a very active area of the plasmodesmos/olasmalemma complex (i.e. enzyme activity and/or presence of strongly reducing substances).Evidence is presented that these ring structures are structural equivalents to hypothetical sphincters performing some valve function; i.e. participating in the control of rates and directions of symplastic transport of solutes through plasmodesmata. The middle layer of the plasmalemma in the neck region is composed of closely-packed, globular subunits appearing in negative contrast. Apparently, these subunits correspond to particle clusters observed at the plasmodesmatal entrance in freeze-fracture preparations. They appear similar to particle clusters in animal tight junctions, and their possible function in providing electrical coupling via low resistance junctions between plant cells is discussed.     

Observations on the postacrosomal region and the neck membranes of rabbit spermatozoa stained en bloc with uranyl acetate

Summary The postacrosomal region (PAC) of the head and the neck membranes of rabbit spermatozoa have been reinvestigated with the use of en bloc uranyl acetate staining. The fine structure of the PAC and neck membranes is visualized with great clarity and departs from that seen in rabbit sperm prepared by other methods. In cells so treated, the PAC contains a heavily enfolded nuclear envelope, a dense lamina attached to the plasmalemma by periodic connecting links and scattered dense material between the lamina and nuclear envelope. Evidence is presented that the dense lamina is a discrete structure, separated from the plasmalemma by the connecting links. The latter may be of a different composition from both the lamina and the plasmalemma. The lamina is a homogenous structure which resists degeneration under conditions which affect other components of the PAC. The membranes of the neck are a complex labyrinth of nuclear envelope, individual membranes, and membranes coursing through a matrical gound substance.This investigation was supported by Ford Foundation Grant 67–650.     

Physical properties of blue-green algae: Ultracentrifugation and electron microscope studies

Summary The Feulgen-positive and envelope-free nucleoplasm ofAnabaena andGloeocapsa contains DNA filaments. When ultracentrifuged it is displaced between the maze of photosynthetic lamellae to form a continuous, flattened layer in the centripetal half of the cell. The absence of a mesosome and lack of attachment of the nucleoplasm to the plasmalemma make the method of duplication and separation of the genome to the progeny an enigma. In the centripetal end of ultracentrifugedAnabaena, the photosynthetic lamellae are somewhat stretched and sometimes broken. This condition suggests that the cortical positioned photosynthetic lamellae are tightly connected in several places along their surfaces to an undisplaced cortical cytoplasmic layer. It is uncertain whether or not they are also directly attached to the plasmalemma. A vesicle is often observed in the centripetal end of the cell; it probably represents for the most part, the contents of distorted intralamellar spaces. In ultracentrifugedGloeocapsa, the photosynthetic lamellae show little displacement. They appear attached, probably at their ends to the plasmalemma and, likeAnabaena andNostoc, they possess phycobilisomes which are not greatly affected by ultracentrifugation. Cells usually survive a centrifugal force greater than required to separate most nonliving protein systems. When subcultured, a redistribution of the displaced components usually occurs and growth is resumed.     

FORMATION OF THE PROLAMELLAR BODY IN 8-DAY,DARK-GROWN SEEDLINGS

The development of the prolamellar body in etioplasts of dark-grown seedlings of Phaseolus vulgaris is followed through the 8th day. From 2 to 6 days there is an increase in plastid size and starch content and synthesis of a system of porous lamellae which appear to arise, as such, from the inner component of the plastid envelope. From 6 to 8 days much of the starch disappears accompanied by rapid membrane synthesis resulting in an extensive prolamellar body. A model of the prolamellar body is discussed in which the basic structural unit is a six-pointed star with four tubules joining at each node. Observation of face views of the porous peripheral lamellae at their juncture with the prolamellar body suggests the origin of the prolamellar body by the continued contraction of the porous lamellae and the formation of interconnecting tubules between adjacent lamellae. The pores of the peripheral lamellae appear to correspond to the areas of stroma within each star module. Short lengths of membranes of individual peripheral lamellae fuse, forming short overlaps which resemble small, two-compartmented grana. It is postulated that this is the initial step in grana formation.     

Fine structure of plant cuticles in relation to water permeability: The fine structure of the cuticle of Clivia miniata reg. leaves

The fine structure of the upper cuticular membrane (CM) of Clivia miniata leaves was investigated using electron microscopy. The CM is made up of a thin (130 nm) lamellated cuticle proper (CP) and a thick (up to 7 m over periclinal walls) cuticular layer (CL) of marbled appearance. Evidence is presented to show that the electron lucent lamellae of the CP do not simply represent layers of soluble cuticular lipids (SCL). Instead, the lamellation is probably due to layers of cutin differing in polarity. It is argued that the SCL in the Cp are the main barrier to water. Thickening of the CM during leaf development takes place by interposition of cutin between the CM and the cellin wall. The cutin of young, expanding leaves has a high affinity for KMnO₄ and is therefore relatively polar. As leaves mature, the external CL underneath the CP becomes non-polar, as only little contrast can be obtained with permanganate as the post fixative.Abbreviations CM cuticular membrane - CP cuticle proper - CL cuticular layer - SCL soluble cuticular lipids (cuticular waxes)     

The fine structure and development of the trabeculae and the trabecular ring in Selaginella kraussiana

In the shoot apex of Selaginella kraussiana A. Br., air spaces develop between the endodermal cells, isolating the two steles from the cortex. The endodermal cells elongate to form trabeculae connecting the two tissues. As each trabecular cell develops, cuticularization occurs on the external surface at a point mid-way along the cell and forms the trabecular ring. The plasmalemma of the trabecular cell becomes attached to the wall beneath the main concentration of the ring, resembling the connection between the plasmalemma and the Casparian strip of a primary endodermis. The trabeculae retain a functional cytoplasm throughout growth.     

Spermatogenesis of a marine snail,Littorina sitkana

Summary The fine structure of the spermatogonium, spermatocyte and spermatid of a marine snail, Littorina sitkana is described. The ring centriole (annulus) is formed from the distal centriole and it migrates to the base of the mitochondrial region where it lies in a joint-like structure which is formed by an area of invaginated plasma membrane. The distal and proximal centrioles are at first perpendicular to each other but the proximal centriole rotates to a position coaxial with the distal centriole and fuses with it. The peripheral doublet fibers are continuous between the two centrioles but the central fibers originate only in the distal centriole. The acrosome differentiates from the proacrosomal granule which is derived from a Golgi body. Microtubules, present at this stage, may assist acrosomal formation. Chromatin condensation begins with the formation of fibrous strands, then to lamellar plates which become folded and later twisted around the flagellar shaft. In the final stages the lamellae appear in cross section as concentric rings which eventually fuse to form a homogeneously dense nuclear tube.     

Periclinal penetration of potassium permanganate into mature cuticular membranes ofAgave andClivia leaves: new implications for plant cuticle development

Staining cuticular membranes ofAgave americana andClivia miniata en bloc with potassium permanganate results in a strong contrast in the interior cuticular layer while the exterior part remains unstained. This is not caused by a selective chemical reaction with the interior part but by the unidirectional penetration of the reagent from the interior side, the outside being protected by the cuticle proper. In transverse cryosections of the cuticular membrane, permanganate penetrates nearly as easily into the exterior cuticular layer as into the interior one giving the same contrast. However, compared with the periclinal penetration into the cuticle proper this penetration is accelerated five-to tenfold by the polysaccharide network within the cuticular layer which serves as a distribution-channel system. Periclinal penetration into the cuticle proper occurs independently in each cutin penetration unit included between two obvious lucent lamellae and further divided into subunits.     

阔鳞瘤蕨(水龙骨科)卵细胞发育超微结构观察

水龙骨科是蕨类植物中最进化的类群,该文采用超微技术对水龙骨科的阔鳞瘤蕨(Phymatosorus hainanensis)卵发育过程进行观察,以完善薄囊蕨植物卵发生的资料,为揭示蕨类植物的有性生殖及演化机制奠定基础。结果表明:(1)幼卵、颈沟细胞、腹沟细胞通过胞间连丝紧密连接。(2)发育过程中,卵与腹沟细胞之间细胞壁显著加厚,将卵细胞与腹沟细胞隔离。(3)在壁的下方产生分离腔,内含大量不定形物质,但卵细胞与腹沟细胞在中间处始终相连。(4)分离腔中的不定形物质沉积在卵细胞质膜外形成了一层加厚的卵膜,而在连接区(孔区)处不形成卵膜,该位置最终形成了受精孔。(5)卵细胞核变得高度不规则,近成熟时卵核产生了大量的核外突。     

Morphology and structural organization of gené's organ in Dermacentor reticulatus (Acari: Ixodidae)

Scanning and transmission electron microscopical investigations revealed that Gené's organ in unfed and ovipositing females of Dermacentor reticulatus is formed as a double-sac-structure consisting of an outer epithelial and an inner cuticular sac. In ovipositing ticks the latter emerges through the camerostomal aperture to the exterior. Gené's organ in unfed ticks consists of a corpus, two posterior horns and a pair of undeveloped glands at each side, which differentiate in ovipositing ticks to compound, branched tubular glands with a main efferent duct for each gland opening into the lumen between the epithelial and the cuticular sac. Gené's organ of egg-laying females corresponds basically in morphology and structural organization to that of unfed ticks. Compared with unfed ticks, however, in ovipositing ticks the corpus and horns are longer and broader, the glands are fully developed and the cuticular sac is evertable. The epithelial sac as the outermost part of Gené's organ is continuous with the hypodermis of the basis capituli and the scutum, arises at the camerostomal aperture, forms the corpus and the two blind-ending horns, passes into the epithelium of the main excretory ducts of the glands and envelops the cuticular sac. The cuticular sac passes into the cuticle of the basis capituli and the scutum, arises at the camerostomal aperture, is folded, expands into the horn tips and consists inwards of a smooth epicuticula and outwards of a fibrous endocuticula. Muscles originating from the scutum pass caudomedially through the epithelial sac and are inserted into the cuticular sac. The entire surface of the maximally everted cuticular sac is covered with an amorphous mass. In cleaned samples, ledge-like structures appear on the lateral surface. These ledges turn into balloon-like structures which extend over the medial and dorsal surface. The entire surface including the balloon-like structures and the ledges are provided with numerous cribrate pits.     

Is the nuclear envelope a ‘generator’ of membrane?

Summary Early diplotene oocytes from Necturus maculosus ranging from 0.2 to 0.5 mm in diameter were examined by electron microscopy. In the smallest oocytes of this range, the cytoplasm is largely devoid of membranes, but contains primarily ribosomes and mitochondria. In slightly larger oocytes, smooth-surfaced cytomembranes first appear in the perinuclear cytoplasm. At this time, the outer layer of the germinal vesicle nuclear envelope (GVNE) shows frequent connections with long membranous lamellae that extend for considerable, but variable distances into the juxtanuclear ooplasm. The number of smooth membranous lamellae increases tremendously as the oocytes increase in diameter. In such oocytes as well, frequent continuities are observed between the outer membrane of the GVNE and many of the cytoplasmic membranes. Eventually, as the ooplasm becomes populated with extensive numbers of membranous lamellae, instances of continuity between the membranous lamellae and nuclear envelope now become sparse and eventually non-existent. The frequent connections observed between membranous lamellae and the outer membrane of the GVNE during a circumscribed interval of diplotene strongly implicate the GVNE in the generation of extensive amounts of cytoplasmic membrane. The ooplasm of larger oocytes in the size range indicated contain numerous Golgi complexes and large quantities of annulate lamellae most of which are positioned in the peripheral or subcortical ooplasm, as well as extensive quantities of smooth membranes of the endoplasmic reticulum and lipid droplets.     

Formation and function of cytoplasmic annulate lamellae in the eggs ofPomatoceros triqueter L.

Summary During an ultrastructural study of the eggs of the serpulid wormPomatoceros triqueter L., annulate lamellae were frequently encountered in the cytoplasm. In particular, some observations indicated that they originate by successive outfoldings of the nuclear envelope. Consequently, annulate lamellae must consist of alternating layers of nuclear and cytoplasmic material, each layer being separated by part of the nuclear envelope. It was observed that there was a similarity between nuclear and inter-annulate lamellar material. Moreover tritiated thymidine was shown to be present in the stacks. It is inferred that this system might well function as an efficient means of transporting nuclear material into the cytoplasm. The authors wish to thank Messrs. P. C. Lloyd, P. Henley and D. Williams for technical assistance.     

Water permeability of plant cuticles: The effect of temperature on diffusion of water

The effect of temperature on water permeability of plant cuticles (astomatous Citrus leaf cuticles) has been investigated. The Arrhenius plot (logarithm of the permeability coefficient vs. 1/temperature) has two linear portions that intersect at 44° C. Evidence is presented to show that this intersection represents the solid/liquid phase transition of cuticular lipids. As the Arrhenius plot has only one phase transition in the temperature range of 5 to 80° C, it appears that all soluble cuticular lipids in the cuticle are present as a homogeneous mixture rather than as individual layers differing in composition. This view is supported by electron spin resonance evidence showing homogenous distribution of spin label fatty acids. The original distribution of soluble cuticular lipids is irreversibly altered by heating cuticular membranes above the transition temperature. This is accompanied by an irreversible increase in water peremeability, demonstrating the importance of the structure of cuticular lipids with regard to cuticular permeability.Abbreviations CM cuticular membranes - MX polymer matrix - SCL soluble cuticular lipids - MES morpholinoethane sulphonic acid - J flux - ESR electron spin resonance - THO tritiated water     

CYTOLOGY AND ULTRASTRUCTURE OF CHLORARACHNION REPTANS (CHLORARACHNIOPHYTA DIVISIO NOVA,CHLORARACHNIOPHYCEAE CLASSIS NOVA)1

The green amoeboid cells of Chlorarachnion reptans Geitler are completely naked and each contains a central nucleus, several bilobed chloroplasts each with a central projecting pyrenoid enveloped by a capping vesicle, several Golgi bodies, mitochondria with tubular cristae, extensive rough ER, and a distinct layer of peripheral vesicles. Complex extrusome-like organelles occur rarely in both the amoeboid and flagellate stages. The only organelles entering the reticulopodia are mitochondria, but microtubules are also present. The chloroplasts contain chlorophylls a and b, but histochemical tests suggest that the carbohydrate storage product probably is not a starch. The chloroplast lamellae are composed of one to three thylakoids or form deep stacks. A girdle lamella and interlamellar partitions are absent. Each chloroplast is bounded by either four separate membranes, a pair of membranes with vesicular profiles between them, or three membranes; all three arrangements may occur in the same chloroplast. A periplastidal compartment occurs near the base of the pyrenoid where there are always four surrounding membranes. The compartment has a relatively dense matrix and contains ribosome-like particles and small dense spheres; it extends over and into a deep invagination in the pyrenoid where its contents are enclosed in a double-membraned envelope which is penetrated by wide pores. The zoospores are ovoid and each bears a single laterally inserted flagellum which appears to be wrapped helically around the cell body during swimming. The flagellum lies in a groove in the cell surface and bears fine lateral hairs. Neither a second flagellum or vestige of one, nor an eyespot, is present. A single microtubular root and a larger homogeneous root run from the flagellar base parallel to the emerging flagellum, between the nuclear envelope and the plasmalemma. In the simple flagellar transition region, fine filaments connect adjacent axonemal doublets. A detailed comparison of C. reptans with all other algal taxa results in the conclusion that it must be segregated in the new class Chlorarachniophyceae, the only class in the new division Chlorarachniophyta. The possibility that C. reptans evolved from a symbiosis between a colorless amoeboid cell and a chlorophyll b- containing eukaryote is considered, but the possible affinities of the symbiont remain enigmatic. The implications of the unique chloroplast structure of C. reptans for current hypotheses concerning the origin of chloroplasts are discussed.     

Carapace repair in the green crab,Carcinus maenas (L.)

Formation of a circular hole 8–10 mm in diameter in the calcified layers of the carapace from crabs in stage C₄ of the molt cycle stimulates the tissue under and adjacent to the injury to deposit a unique calcified cuticular material below the intact membranous layer. Deposition was followed for 69 days using light microscopic histology, histochemistry, and scanning electron microscopy. Quantitative analyses of CaCO₃ were conducted using atomic absorption spectrophotometry and Gran titration. Spatial distribution of CaCO₃ was determined with X-radiography. A scab is formed by day two under the injury. At four days the epithelium changes from squamous to columnar and deposits a PAS-positive layer with an irregular lamellar fine structure, followed by highly organized lamellae structurally similar to normal exocuticle. Histochemically, however, these lamellae resemble normal endocuticle. CaCO₃ is evident external to the outermost lamellae by day eleven as a fused mass of aragonite granules. The lamellar region calcifies proximally from the outer surface and is amorphous CaCO₃. Repair cuticle is approximately 20%CaCO₃ by weight.