The structure of the intrapigmented aesthetes and the properiostracum layer in Callochiton achatinus (Mollusca: Polyplacophora)

The ultrastructure of the intrapigmented aesthetes which occur in specific areas of the different valves of Callochiton achatinus are described. The possible functions of the aesthete and the pigmented body are discussed in the light of their ultrastructure and the ecological requirements of the animal. The properiostracum in C. achatinus is unusually thick and has a structure very similar in appearance to that of collagen.     

The valve morphology of Cullochhiton uchutinus (Mollusca: Polyplacophora: Ischnochitonidae)

The valves of Callochiton achatinus comprise four layers which are penetrated by channels carrying extensions of the mantle epithelium known as aesthetes. Three patterns of dorsal sculpturing within defined areas of the various valves are described and these are related to the different types of aesthete channel which perforate the respective areas. The processes involved in valve growth are described and related to the arrangement of the many holes penetrating the eave tissue.     

Die Ästheten vonAcanthochiton fascicularis (Mollusca,Polyplacophora)

Zusammenfassung Im Gegensatz zu allen anderen bisher untersuchten Polyplacophorenarten hatAcanthochiton fascicularis L. zwei Typen von Ästheten in den Schalenplatten. Im medianen Trakt gleichen sie den bisher bekannten Formen, in den lateralen Feldern sind sie extrem klein. Hier hat der stark entwickelte Gürtel das Tegmentum zurückgedrängt; dieses bildet in diesem Bereich um jeden Ästheten eine säulenstumpfartige Erhebung. Die beiden Ästhetentypen sind in ihrem Aufbau ähnlich: keulenförmige Sekretzellen und dünne Zentralzellen nehmen den meisten Raum in diesen Organen ein. Meist zweigen seitlich einige wenige Mikrästheten nach oben hin ab. Diese unterscheiden sich bei den beiden Ästhetentypen stark in ihrer Feinstruktur. Vor allem differieren die zwei Typen in ihren Sehzellen, die seitlich im Ästheten liegen. Median sind es rhabdomere Sehzellen, wie sie alle anderen bisher untersuchten Arten aufweisen, lateral hingegen ciliäre Lamellenzellen.

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The aesthetes ofAcanthochiton fascicularis (mollusca, polyplacophora)

Summary In contrast to all other investigated species the polyplacophoranAcanthochiton fascicularis L. has two types of aesthetes in their shell plates. Those which are situated in the median part of the shells are of a normal size and shape, whereas the aesthetes in the lateral fields are the smallest hitherto known. Here the tegmentum is repressed by the exuberantly developed girdle and forms trunklike structures around every aesthete. On the whole both aesthete types are similar: clubshaped secretory cells and thin central cells fill most of the organ. Up to a few micraesthetes may branch from the main part towards the shell surface. But there are also marked differences. In the median aesthetes rhabdomeric visual cells are present; in the lateral ones they have become ciliary lamellate cells which are probably also active photoreceptors.

     

Die Mantelpapillen und Stacheln vonAcanthochiton fascicularis L. (Mollusca,Polyplacophora)

Zusammenfassung Struktur und Ultrastruktur der Papillen im Mantelepithel der PolyplacophoreAcanthochiton fascicularis werden beschrieben. Sie bestehen zu einem gro\en Teil aus Sekretzellen. In vielen Papillen sind Sehzellen vorhanden. Die Papillen bilden einen bis mehrere Stacheln aus. Ein organischer Becher verbindet den Kalkstachel mit einer Stachelzelle, hÄufig noch mit einer zweiten Zelle, die distal eine Cilie trÄgt. Sie sind Tastrezeptoren. Andere Stacheln dienen lediglich der Abwehr; sie können durch Muskeln bewegt werden. Diese Stacheln wachsen stÄndig basal nach, wÄhrend die Taststacheln nach einiger Zeit abgesto\en und durch neu von der Papille gebildete ersetzt werden. Ästheten und Mantelpapillen sind homologe Orgame.

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The mantle papillae and the spines inAcanthochiton fascicularis L. (Mollusca, Polyplacophora)

Summary Structure and ultrastructure of the papillae in the mantle epithelium of the polyplacophoranAcanthochiton fascicularis are described. They consist to a major part of various secretory cells. Visual cells occur frequently in the papillae. Each of these organs form up to a few spines which have basally a cup of organic material. This connects the calcareous spine with the spine cell and often with a second cell which has distally one cilium. They are tactile receptors. Other spines are only for the defense and can be moved by muscles. They continue to grow basally in contrast to the tactile spines which are pushed off after some time and replaced by new ones formed in the papillae. The aesthetes and the mantle papillae are homologous organs.

     

Light and electron microscopical investigations on shell pores (caeca) of fissurellid limpets (Mollusca: Archaeogastropoda)

The organic content (caecum) of the shell pores of five species of fissurellid (key-hole) limpets was investigated by means of light and electron microscopy. Fissurellid caeca are unbranched, polycellular extensions of the mantle epithelium, which penetrate the whole shell and contact the periostracum via organic fibres called 'brush'. They are built up by two cell-types, which enclose a central lumen, and are formed concurrently with the shell itself. Because of fundamental structural and developmental differences, the superficially similar shell pores of bivalves (caeca) and polyplacophorans (aesthetes) are considered as analogous rather than homologous organs. Similarities are found with brachiopod caeca, probably owing to similar functions.     

Die Feinstruktur der Ästheten vonChiton olivaceus (Mollusca,Polyplacophora)

The aesthete organs in the shell of the polyplacophoranChiton olivaceus (Spengler) were studied by scanning and transmission electron microscopy. Compared to previously described species they reveal marked differences. In the upper third of the aesthete, photoreceptor cells have been found. The granula of the club-shaped cells, which fill most of the aesthete, are formed in the proximal part of young aesthetes. The secretory cells located in this part increase in size and become gradually club-shaped. The central cells, hitherto the only known sensory cells in this organ, are very variable in their appearence. The apical as well as the subsidiary caps have pores which penetrate the whole cap in the former, whereas the subsidiary caps are proximally and distally covered by a continous envelope. In contrast, an exchange of substances with the surrounding environment cannot be excluded in the apical cap: there are some indications of secretory processes occurring through the shell surface.     

Age-related alterations of mitochondria from muscle tissue

The ultrastructure of mitochondria of cross-striated muscles during aging was studied by electron microscopy. Mitochondrial ultrastructure was analyzed in the flight muscle of D. melanogaster (1- and 36-day-old) and in the cardiomyocytes and skeletal muscle of young and senile Wistar and OXYS rats (3- and 25-month-old). The mitochondria in the flight muscle samples of senile D. melanogaster flies were shown to have several types of peculiar age-related mitochondrial abnormalities corresponding to those described previously. Previously unknown changes were revealed in the ultrastructure of cardiomyocyte mitochondria in senile rats (both Wistar and OXYS). Substantial changes in the ultrastructure of subsarcolemmal mitochondria were found in the fibers of red skeletal muscle of senile OXYS rats. It has been shown that the subsarcolemmal mitochondria of red muscle fibers are a peculiar population of mitochondria with atypical ultrastructure. Initial changes in the ultrastructure of subsarcolemmal mitochondria were revealed even in 3-month-old OXYS rats. At the same time, the skeletal muscle mitochondria of senile Wistar rats maintain their morphological characteristics, and their ultrastructure corresponds to that of skeletal muscle mitochondria in 3-month-old Wistar rats.     

Ultrastructure and composition of pigments of Sagittaria sagittifolia L. Leaves

A comparative analysis of the cellular ultrastructure and pigment content of both underwater and above-water Sagittaria sagittifolia leaves was conducted by means of the method of transmission electron microscopy and spectrophotometric analysis. Considerable distinctions of the S. sagittifolia ultrastructure, photosynthesizing cells of underwater leaves in comparison to the ultrastructure of above-water leaves, are examined as adaptation reactions of this plant to submerging.     

Ultrastructure and identification of giant muscular cells in certain proboscis worms of the family Polymorphidae

The results of ultrastructure study of the giant muscular cells located at the base of proboscis receptacle are given. Peculiarities of cell ultrastructure suggest the presence of the "nuclear secretion" in these cells. By their location and morphological features they are identical to the retinacular cells formerly described by some authors.     

Ultrastructure of Hendra virus and Nipah virus within cultured cells and host animals

The ultrastructure of Hendra and Nipah viruses is described in cultured cells, pigs, horses and humans. Differences in ultrastructure between the viruses are evident within infected cell cultures and lungs from infected amplifier hosts. These differences are important in viral identification and differentiation and understanding the pathogenesis of disease.     

达坂山蚤缀和裸茎金腰叶绿体超微结构的研究

对高山植物达坂山蚤缀和裸茎金腰叶绿体超微结构的研究表明,叶绿体和线粒体镶嵌很紧密;基粒和基质类囊体膨大,膨大的类囊体呈梭形或圆形,没有发现脂质小球的存在;基粒叠垛程度很低,平均每个基粒类囊体的片层数为5．4。这2种高山植物叶绿体超微结构上的特征是青藏高原特殊的生态条件,包括低温、低气压、强辐射影响的结果。     

Seasonal changes of the ultrastructure of the pars tuberalis of the hypophysis of Rana temporaria

Summary In the pars tuberalis of the hypophysis of Rana temporaria, which shows the ultrastructural characteristics of a polypeptide hormone secreting endocrine gland, seasonal changes of the ultrastructure are described. In accordance with the literature, these seasonal changes of ultrastructure are interpreted as the morphological expression of seasonal changes of endocrine activity of the pars tuberalis.     

Exine ultrastructure of in situ peltasperm pollen from the Rhaetian of Germany and its implications

Morphology and exine ultrastructure of pollen grains of Triassic peltasperms have been studied for the first time. Pollen grains of Antevsia zeilleri from the Rhaetian of Germany are of the Cycadopites-type and monosulcate; the sculpturing is the same in the apertural and non-apertural areas. The proximal exine includes a row of lacunae covered by a solid, thick tectum and underlined by a foot layer. Pillars are hanging from the tectum between the lacunae. The exine is thinning to a homogeneous layer in the apertural region. The latter is bordered by thicker alveolate areas of the exine, in places resembling a saccus-like ultrastructure. The endexine includes white-line-centred lamellae. The exine ultrastructure is compared with that of pollen of Permian peltasperms. Although pollen types ascribed to Permian peltasperms are completely different in their general morphology, a transformation can be hypothesized by ultrastructural data from Permian Vesicaspora into Triassic Cycadopites extracted from pollen sacs of Antevsia. Comparison with Cycadopites of non-peltaspermalean (Ginkgoalean, Cycadophyte) and unknown affinities has been accomplished. The exine ultrastructure is distinctive enough to differentiate among peltaspermalean, cycadalean and bennettitalean Cycadopites; some ultrastructural features are shared with pollen of modern Ginkgo biloba. More ultrastructural data are needed as well as numerous sections of pollen grains are necessary to reveal original unchanged ultrastructure.     

Ultrastructure of wheat coleoptile mitochondria at short-term anoxia and post-anoxia

Abstract. Mitochondrial ultrastructure in the cells of coleoptiles of 4 d seedlings was investigated under conditions of a 1.5, 3, and 36 h anoxia and with subsequent transfer of the seedlings, after a 1.5 h anoxia, from the anaerobic into an aerobic medium. Even with short-term anoxia (1.5 h) destructive changes take place in the ultrastructure of mitochondria, which are reversible not only following the transfer of these seedlings from the anaerobic into aerobic conditions, but also with their continued maintenance under strict anoxia. Irreversible changes in the ultrastructure of mitochondria were seen only with a more prologed (36 h and longer) anoxia. The observed phenomena are discussed from the viewpoint of energy provision of the seedling cells in anoxia and post-anoxia.     

Changes in the ultrastructure of the chloride cells of sturgeon during adaptation to a hypertonic medium]

Alterations in the ultrastructure of chloride cells of young sturgeons Acipenser guldenstadti Brandt in the process of adaptation to hypertonic medium (S=105%) were under study. In the process of this adaptation thread-shaped long mitochondria became shorter, their random position was substituted by orientation in parallel to the axis of the cell. The amount of mitochrondria increased. A great number of vacuoles appeared in the cytoplasm. The character of the endoplasmic reticulum changed. The obtained data on the ultrastructure of chloride cells of the sturgeon confirm and supplement earlier light microscopy investigations of chloride cells of the sturgeon. The changes of the ultrastructure of chloride cells are interpreted as functional and adaptational ones.     

Scanning electron microscopy of spherules of Physarum polycephalum

The ultrastructure of starvation-induced sclerotic and mannitol-induced spherules was studied by a scanning electron microscope (SEM). Each spherule in the berry-like sclerotium is not rounded and has lobe-like forms, whereas the separate spherules are significantly bigger and rounded. Bead-like granules were observed inside and on the spherules. Broken spherules observed in the SEM show ultrastructure of cell wall, cytoplasm, vacuoles and granules, nuclei and nucleoli.     

The Ultrastructure of the Spores of the Devonian Plant Parka decipiens

The ultrastructure of the spores of Parka decipiens Flemingwas investigated by SEM and TEM. The spores are shown to havea structured wall consisting of two distinct layers, one ofwhich exhibits a lamellate organization. The deposition of thespore wall by a tapetum is suggested to account for these lamellae.Comparison is made between the spore ultrastructure of Parkaand that of algae and bryophytes. It is suggested that the sporewall of Parka bears some similarities with the lamellate exinefound in the Hepaticae. Parka decipiens, Devonian, fossil, spore wall, ultrastructure, lamellae, tapetum     

MEGASPORE WALL ULTRASTRUCTURE IN ISOETES

In Selaginella, megaspore wall ultrastructure (unit morphology and arrangement) is correlated with taxonomic position. In some Pennsylvanian lycopods there is a correlation with dispersal strategy. This study was designed to assess any correlation between habitat preference and wall ultrastructure in Isoetes. Except for a few minor structural correlations, wall ultrastructure appears to be constant in terrestrial, amphibious, and aquatic species of Isoetes. Several distinct sizes of megaspores occur in some megasporangia and correspond to 1) full-size megaspores with siliceous coatings, 2) small megaspores with siliceous coatings, and 3) full-size megaspores without siliceous coatings. The uniformity in wall ultrastructure within modem Isoetes together with the lack of uniformity of fossil isoetalean megaspore wall ultrastructure suggest that the modem species of Isoetes are closely related.     

Morphology and wall ultrastructure of leiosphaeric and acanthomorphic acritarchs from the Ediacaran of Australia

Acritarchs are a group of organic-walled microfossils with unknown biological affinities. The wall ultrastructure of the unornamented, smooth Leiosphaeridia sp. and the acanthomorphic Gyalosphaeridium pulchrum from the Ediacaran Dey Dey Mudstone in the Officer Basin, South Australia, was studied by use of transmission and scanning electron microscopy, and transmitted light microscopy. The study of the ultrastructure reveals a complexity in the cell wall not seen in prokaryotes. Wall ultrastructures range from single-layered to three- or four-layered and from homogeneous to porous. Acritarchs with different wall ultrastructures may be different organisms, but may also reflect different stages in a life cycle. In this paper I review previous ultrastructure studies and discuss possible algal and metazoan affinities for the specimens studied herein.     

Devonian Spores of <Emphasis Type="Italic">Kryshtofovichia africani</Emphasis> Nikitin (Tracheophyta): Morphology and Ultrastructure

The morphology and ultrastructure of spores of the Devonian plant Kryshtofovichia africani Nikitin are examined. The structure of ultrathin exine megaspores of K. africani is established. The exine consists of two layers: granular ectexine and lamellate endexine. Microspores have a lamellate ultrastructure with a trend toward loosening and formation of the granular structure towards the ectexine outer part. Heterospory of K. africani is apparent in both morphological characters and sporoderm ultrastructure of micro- and megaspores.