Developmental, ultrastructural and cytochemical investigations of the female gametophyte in Sedum rupestre L. (Crassulaceae)

This article describes the development of female gametophyte in Sedum rupestre L. New embryological information about the processes of megasporogenesis and megagametogenesis provided in this paper expand the current knowledge about the embryology of the studied species. S. rupestre is characterized by monosporic megasporogenesis and the formation of Polygonum–type embryo sac. The process of megasporogenesis is initiated by one megaspore mother cell, resulting in the formation of a triad of cells after meiosis and cytokinesis. The functional megaspore, which is located chalazally, is a mononuclear cell present next to the megaspore in the centre of the triad. Only one of the two non-functional cells of the triad is binucleate, which occur at the micropylar pole. In this paper, we explain the functional ultrastructure of the female gametophytic cells in S. rupestre. Initially, the cytoplasm of the gametophytic cells does not differ from each other; however, during differentiation, the cells reveal different morphologies. The antipodals and the synergids gradually become organelle-rich and metabolically active. The antipodal cells participate in the absorption and transport of nutrients from the nucellar cells towards the megagametophyte. Their ultrastructure shows the presence of plasmodesmata with electron-dense material, which is characteristic of Crassulaceae, and wall ingrowths in the outer walls. The ultrastructure of synergid cells is characterized by the presence of filiform apparatus and cytoplasm with active dictyosomes, abundant profiles of endoplasmic reticulum and numerous vesicles, which agrees with their main function—the secretion of pollen tube attractants. Reported data can be used to resolve the current taxonomic problems within the genus Sedum ser. Rupestria.

Development of Embryo Suspensors for Five Genera of Crassulaceae with Special Emphasis on Plasmodesmata Distribution and Ultrastructure

The suspensor in the majority of angiosperms is an evolutionally conserved embryonic structure functioning as a conduit that connects ovule tissues with the embryo proper for nutrients and growth factors flux. This is the first study serving the purpose of investigating the correlation between suspensor types and plasmodesmata (PD), by the ultrastructure of this organ in respect of its full development. The special attention is paid to PD in representatives of Crassulaceae genera: Sedum, Aeonium, Monanthes, Aichryson and Echeveria. The contribution of the suspensor in transporting nutrients to the embryo was confirmed by the basal cell structure of the suspensor which produced, on the micropylar side of all genera investigated, a branched haustorium protruding into the surrounding ovular tissue and with wall ingrowths typically associated with cell transfer. The cytoplasm of the basal cell was rich in endoplasmic reticulum, mitochondria, dictyosomes, specialized plastids, microtubules, microbodies and lipid droplets. The basal cell sustained a symplasmic connection with endosperm and neighboring suspensor cells. Our results indicated the dependence of PD ultrastructure on the type of suspensor development: (i) simple PD are assigned to an uniseriate filamentous suspensor and (ii) PD with an electron-dense material are formed in a multiseriate suspensor. The occurrence of only one or both types of PD seems to be specific for the species but not for the genus. Indeed, in the two tested species of Sedum (with the distinct uniseriate/multiseriate suspensors), a diversity in the structure of PD depends on the developmental pattern of the suspensor. In all other genera (with the multiseriate type of development of the suspensor), the one type of electron-dense PD was observed.

Drosophila PLP forms centriolar-clouds that promote centriole stability, cohesion and MT nucleation

Pericentrin is a conserved centrosomal protein whose dysfunction has been linked to several human diseases. The precise function of Pericentrin, however, is controversial. Here, we examine Drosophila Pericentrin-like- protein (PLP) function in vivo, in tissues that form both centrosomes and cilia. PLP mutant centrioles exhibit four major defects: (1) They are too short and have subtle structural defects; (2) They separate prematurely, and so overduplicate; (3) They organise fewer MTs during interphase; (4) They fail to establish and/or maintain a proper connection to the plasma membrane— although, surprisingly, mutant centrioles can still form an axoneme and recruit transition zone (TZ) proteins. We show that PLP helps to form “ pericentriolar clouds” of electron-dense material that emanate from the central cartwheel spokes and spread outward to surround the mother centriole. The partial loss of these structures may explain the complex centriole, centrosome and cilium defects we observe in PLP mutant cells.

Chloroplast ultrastructure in leaves of Cucumis sativus chlorophyll mutant

The developing and young leaves of <em>Cucumis sativus</em> chlorophyll mutants are yellow, when mature they become green and do not differ in their colour from those of control plants. The mesophyll of yellow leaves contains a diversiform plastid population with a varying degree of defectiveness, which is mainly manifested in the reduction or disorganization of the typical thylakoid system. DNA areas, ribosome-like particles and aggregates of electron-dense material are preserved in the stroma of mutated plastids. Starch grains are deficient. Apart from mutated plastids, chloroplasts with a normal structure, as in control plants, were also observed.The leaf greening process is accompanied by a reconstruction and rearrangement of the inner chloroplast lamellar system and an ability to accumulate starch. However, in the mutant chloroplasts as compared with control-plant ones, an irregular arrangement of grana and reduced number of inter-grana thylakoids can be seen. An osmiophilic substance stored in the stroma of mutated plastids and the vesicles formed from an internal plastid membrane take part in restoration of the membrane system.

Self-organization of stabilized microtubules by both spindle and midzone mechanisms in Xenopus egg cytosol

Previous study of self-organization of Taxol-stabilized microtubules into asters in Xenopus meiotic extracts revealed motor-dependent organizational mechanisms in the spindle. We revisit this approach using clarified cytosol with glycogen added back to supply energy and reducing equivalents. We added probes for NUMA and Aurora B to reveal microtubule polarity. Taxol and dimethyl sulfoxide promote rapid polymerization of microtubules that slowly self-organize into assemblies with a characteristic morphology consisting of paired lines or open circles of parallel bundles. Minus ends align in NUMA-containing foci on the outside, and plus ends in Aurora B–containing foci on the inside. Assemblies have a well-defined width that depends on initial assembly conditions, but microtubules within them have a broad length distribution. Electron microscopy shows that plus-end foci are coated with electron-dense material and resemble similar foci in monopolar midzones in cells. Functional tests show that two key spindle assembly factors, dynein and kinesin-5, act during assembly as they do in spindles, whereas two key midzone assembly factors, Aurora B and Kif4, act as they do in midzones. These data reveal the richness of self-organizing mechanisms that operate on microtubules after they polymerize in meiotic cytoplasm and provide a biochemically tractable system for investigating plus-end organization in midzones.

Ultrastructure of the cirrus sac of the male strobila of Shipleya inermis (Fuhrmann, 1908) (Cestoda: Cyclophyllidea)

This study was designed to provide information on the ultrastructural traits of the cirrus sac of the male strobila of the dioecious cyclophyllidean tapeworm, Shipleya inermis Fuhrmann, 1908 from the small intestine of long-billed dowitchers, Limnodromus scolopaceus, in Chukotka, Russia. The cirrus sac is characterised by a thick muscular wall (comprising about 20 layers of longitudinal muscles) with the muscle cells being located outside the wall along the peripheral muscle layer and the presence of a thick, fibrillar septum inside the sac along the inner muscle layer of the wall. The epithelium of the intrabursal ducts is syncytial and has sunken perikarya. The ejaculatory duct is characterised by surface luminal microvilli and a large number of the sunken perikarya producing electron-dense secretory granules, which discharge into the duct lumen as an apocrine secretion. The cirrus is armed with two types of sclerotized structures formed by its epithelium, hooks of about 25 μm in length and microthrix-like structures on its luminal surface. The hooks are sigmoid in shape, have a blade circular in transverse section and about 3.5 μm in width, and taper at both extremities. The hook body consists of moderately electron-dense material mixed with a more electron-dense material and an electron-lucent core. The hook roots lie within the cirrus epithelium, where their lateral margins are composed of a thin covering of electrondense material with narrow lateral extensions. The usefulness of the ultrastructural characters of the cirrus sac as indicators of phylogenetic relationships within the Eucestoda is discussed.

Calcium-SANDOZ®-induced erythrocyte exovesiculation and internalization of hemichromic material into rat brown adipocytes

An ultramicroscopic study of brown adipose tissue (BAT) of rats treated with Ca-SANDOZ? (480 mg/l) for 3 days, revealed erythrocyte exovesiculation and migratory erythrocytic complexes from the capillaries to adipocyte cytoplasm and mitochondria. Two types of erythrocytic material transfer were observed: (i) numerous exocytic vesicles with electron dense material leaving the erythrocytes; (ii) furcated complexes with microholes, embedded in amorphous material. The content of red blood cell (RBC) complexes passed through the capillaries and transferred to the brown adipocytes where it was detectable in the cytoplasm and mitochondria. Light microscopy confirmed sphenoechinocytic transformation of the RBCs in the blood smears of the Ca-SANDOZ? treated rats.

Spermiogenesis and spermatozoon of the tapeworm Parabothriocephalus gracilis (Bothriocephalidea): Ultrastructural and cytochemical studies

Spermiogenesis and spermatozoon ultrastructure of the tapeworm Parabothriocephalus gracilis were described using transmission electron microscopy (TEM). Spermiogenesis is characterized by the formation of a zone of differentiation with two centrioles associated with striated rootlets, and an intercentriolar body between them. The two flagella undergo a rotation of 90° until they become parallel to the median cytoplasmic extension with which they fuse. Electron-dense material is present in the apical region of the zone of differentiation in the early stages of spermiogenesis. This electron-dense material is characteristic for the orders Bothriocephalidea and Diphyllobothriidea. The mature spermatozoon contains two axonemes of the 9 + ‘1’ trepaxonematan pattern, nucleus, parallel cortical microtubules and electron-dense granules of glycogen. The anterior extremity of the spermatozoon exhibits a single helical electron-dense crested body 130 nm thick. One of the most interesting features is the presence of a ring of cortical microtubules surrounding the axoneme. This character has been reported only for species of the order Bothriocephalidea and may be unique in this cestode group.

Ultrastructure of the mesonotal mycangium of Xylosandrus mutilatus (Coleoptera: Curculionidae)

Mycangial structures of female Xylosandrus mutilatus (Blandford, 1894), an Asian ambrosia beetle recently introduced and now established in the southeastern United States, were examined. In addition to the glandular (secretory) mesonotal mycangium located below the scutellum, nonglandular pit mycangia containing fungal propagules were discovered to occur externally on the scutellum. The ultrastructure of the glandular mesonotal mycangium, which consisted of an outer secretory layer covering an inner paired cuticular sac, is described and illustrated. Both secretory and cuticular layers of the mesonotal mycangium were highly tracheolated. Tracheae and tracheoles in association with a Xyleborine mycangium are reported here for the first time. Type 1 secretory cells were identified and observed passing electron-dense material into the glandular mycangium via efferent cuticular ductules, although type 2 secretory cells were not observed. Secretory cells were not observed in association with the nonglandular pit mycangia.