The ultrastructure of the ascus apical apparatus of some Dermateaceae (Helotiales)

The ascus apical apparatus ultrastructure of 12 species of the Dermateaceae (Helotiales, Ascomycota) was studied. Its development and details are described on the basis of transmission electron microscopy micrographs for all studied species. A majority of them, 8 species belonging to the genera Belonopsis, Mollisia, and Pyrenopeziza, show considerable similarity in the structure of their ascus apical apparatus. Two species, Mollisia melaleuca and Mollisia ramealis, show some deviations from this type, suggesting that the genus Mollisia is not fully homogeneous. Two other species, Podophacidium xanthomelum and Pezicula cinnamomea represent two ascus apical apparatus structure types of their own, which are remarkably different from the Mollisia type. The possible taxonomic implications arising from ascus apical apparatus diversity in the Dermateaceae are discussed.     

On the ascus types in thePhysciaceae (Lecanorales)

Comparative studies in thePhysciaceae revealed that characters of the apical apparatus of asci differ between the various genera. Two major ascus types are observable in this family. They are found to correspond with certain ascospore types.     

The 3D Structure of the Apical Complex and Association with the Flagellar Apparatus Revealed by Serial TEM Tomography in Psammosa pacifica,a Distant Relative of the Apicomplexa

The apical complex is one of the defining features of apicomplexan parasites, including the malaria parasite Plasmodium, where it mediates host penetration and invasion. The apical complex is also known in a few related lineages, including several non-parasitic heterotrophs, where it mediates feeding behaviour. The origin of the apical complex is unclear, and one reason for this is that in apicomplexans it exists in only part of the life cycle, and never simultaneously with other major cytoskeletal structures like flagella and basal bodies. Here, we used conventional TEM and serial TEM tomography to reconstruct the three dimensional structure of the apical complex in Psammosa pacifica, a predatory relative of apicomplexans and dinoflagellates that retains the archetype apical complex and the flagellar apparatus simultaneously. The P. pacifica apical complex is associated with the gullet and consists of the pseudoconoid, micronemes, and electron dense vesicles. The pseudoconoid is a convex sheet consisting of eight short microtubules, plus a band made up of microtubules that originate from the flagellar apparatus. The flagellar apparatus consists of three microtubular roots. One of the microtubular roots attached to the posterior basal body is connected to bypassing microtubular strands, which are themselves connected to the extension of the pseudoconoid. These complex connections where the apical complex is an extension of the flagellar apparatus, reflect the ancestral state of both, dating back to the common ancestor of apicaomplexans and dinoflagellates.     

ASCI OF THE PEZIZALES III: THE APICAL APPARATUS OF EUGYMNOHYMENIAL REPRESENTATIVES

Morphological, developmental and cytochemical examinations were made with light and electron microscopy on the apical apparatuses of four eugymnohymenial species, Pyronema domesticum, Ascodesmis sphaerospora, Coprotus winteri and C. lacteus. Ascal tips in all four species were notably thinner walled than the rest of the ascus. Ultrastructurally, demarcation of the opercula was enhanced after staining with silver methenamine. Wide zones of dehiscence are formed in the outer layer of A. sphaerospora and C. winteri. In P. domesticum the outer layer of the operculum is differentially stained from the rest of the ascal wall. Wall dimensions in the multispored asci of C. winteri are approximately three times greater than those in the eight-spored asci of C. lacteus. The shape of the apical apparatus of C. lateus is almost identical to that of C. winteri. Morphological and cytochemical similarities of the apical apparatuses in Ascodesmis, Pyronema and Coprotus help demonstrate greater relationship between these taxa and support the belief that these taxa are most closely related to members of the Otideaceae and Aleuriaceae.     

Six decades of Neurospora ascus biology at Stanford

Ascus is the largest cell in the entire life cycle of Neurospora; it is where the transient diploid nucleus undergoes meiosis and a postmeiotic mitosis. The eight haploid nuclei are then sequestered into eight linearly ordered ascospores. Dodge's pioneering work on Neurospora and its simple nutritional requirements inspired Beadle and Tatum of Stanford University to use N. crassa for their landmark demonstration that individual genes specify enzymes. McClintock visited Stanford in 1944, and showed that meiosis and chromosome behaviour in Neurospora are similar to those of higher eukaryotes. Most of the subsequent Neurospora ascus biology work was carried out in David Perkins' laboratory at Stanford from 1960–2007. Since 1974, I have extensively used an iron-haematoxylin staining procedure, the DNA-specific fluorochrome acriflavine, and GFP-tagged genes for visualizing meiotic chromosome behaviour and gene silencing during ascus and ascospore development. Our recent discovery of meiotic silencing, and the availability of genome sequence and GFP-tagged genes will no doubt pave the way for molecular analysis of complex processes during ascus development.     

The early development of the cement apparatus in the barnacle, Balanus balanoides (L.) (Crustacea: Cirripedia)

The development of the cement cells of Balanus balanoides (L.) has been followed over a 26-day post-settlement period. Cells of the cyprid cement glands de-differentiate to form part of the juvenile barnacle apparatus, but the majority of juvenile cement cells develop by differentiation of collecting duct cells. These latter cement cells are recognized by apical invaginations which are continuous with the collecting duct lumen. Collecting ducts are present in the cyprid. The cement duct system was not studied in detail, but preliminary observations of the arrangement in B. balanoides and Elminius modestus Darwin have shown them to differ, the system in E. modestus being simpler.     

Ultrastructure of asci,ascospores, and spore release inLophodermella sulcigena (Rostr.) v. Hohn.

Summary The croziers were formed from large multinucleate cells at the base of the hysterothecium. The diploid ascus had basal and apical vacuoles and there was prominant endoplasmic reticulum near the extending tip of the ascus. The spore delimiting membranes were continuous with the plasmalemma and possibly arose from it. The spore walls were formed between the two membranes. The ascus had a simple apical ring around a thinner region of the wall which became the pore through which the spores were released. Just before spore release the outer layer of the ascospore wall became vesiculated and eventually mucilagenous. The long clavate ascospores were released one at a time, stretching the neck of the ascus as they emerged.     

Ascospore formation and morphology in two species of the genusErysiphe remaining immature on the living host plant

Erysiphe cumminsiana andE. galeopsidis, which have immature asci in the current season, have been recorded from Japan, but the ascospores of both fungi have not been described. In the present experiments, some observations before and after overwintering were made on the cleistothecia ofE. cumminsiana on three species ofCacalia and two species ofLigularia, andE. galeopsidis onGeranium thunbergii. After overwintering, the former fungus developed six to eight, rarely four spores in an ascus and the latter fungus always four spores in an ascus. Their teleomorphic characteristics including those of ascospores are also described.     

Vertical trends in morphological variability of sea urchins of the genus Echinus from the Northeast Atlantic and Arctic

A study of the morphological variability of seven species of sea urchins of the genus Echinus from the Northeast Atlantic and Arctic with different depth preferences showed that in the group of species E. tenuispinus, E. esculentus, E. melo, E. acutus, E. elegans, E. affinis, and E. alexandri, arranged based on increasing depth of occurrence, the maximum test diameter decreases, the diameter of the apical system increases, the ratio of the number of interambulacral plates to the number of ambulacral plates increases, buccal and periproctal spines tend to disappear, and the number of ambulacral plates lacking a primary tubercle sharply decreases. At the same time, the test height decreases, while the number of secondary tubercles on coronal plates and number of lateral teeth on the valves of the globiferous pedicellariae increases. The change in the first six characters reflects the process of retention of juvenile features in deep-water Echinus. Similar trends in test height, apical system diameter and the ratio of the number of interambulacral plates to the number of ambulacral plates are recorded while comparing shallow-water and deep-sea populations of the eurybathic species E. acutus. This suggests that this species may currently be in the process of speciation.     

Caveolin Transfection Results in Caveolae Formation but Not Apical Sorting of Glycosylphosphatidylinositol (GPI)-anchored Proteins in Epithelial Cells

Most epithelial cells sort glycosylphosphatidylinositol (GPI)-anchored proteins to the apical surface. The “raft” hypothesis, based on data mainly obtained in the prototype cell line MDCK, postulates that apical sorting depends on the incorporation of apical proteins into cholesterol/glycosphingolipid (GSL) rafts, rich in the cholesterol binding protein caveolin/VIP21, in the Golgi apparatus. Fischer rat thyroid (FRT) cells constitute an ideal model to test this hypothesis, since they missort both endogenous and transfected GPI- anchored proteins to the basolateral plasma membrane and fail to incorporate them into cholesterol/glycosphingolipid clusters. Because FRT cells lack caveolin, a major component of the caveolar coat that has been proposed to have a role in apical sorting of GPI- anchored proteins (Zurzolo, C., W. Van't Hoff, G. van Meer, and E. Rodriguez-Boulan. 1994. EMBO [Eur. Mol. Biol. Organ.] J. 13:42–53.), we carried out experiments to determine whether the lack of caveolin accounted for the sorting/clustering defect of GPI- anchored proteins. We report here that FRT cells lack morphological caveolae, but, upon stable transfection of the caveolin1 gene (cav1), form typical flask-shaped caveolae. However, cav1 expression did not redistribute GPI-anchored proteins to the apical surface, nor promote their inclusion into cholesterol/GSL rafts. Our results demonstrate that the absence of caveolin1 and morphologically identifiable caveolae cannot explain the inability of FRT cells to sort GPI-anchored proteins to the apical domain. Thus, FRT cells may lack additional factors required for apical sorting or for the clustering with GSLs of GPI-anchored proteins, or express factors that inhibit these events. Alternatively, cav1 and caveolae may not be directly involved in these processes.     

Notes on the morphology of the robber flies (Diptera, Asilidae)

The position of antennae in the ventral part of head in the species of the genus Eremodromus Zimin is considered. It is different in the three species: the antennae are situated close to the mystacal bristles (E. noctivagus), distant from them (E. gracilis), and near the border between dorsal and ventral parts of head (E. zimini). All three species have reduced pulvilli. It is shown that both species of Theurgus Richter have a single straight apical anteroventral spur on the middle tibia.     

Krogia coralloides,a new lichen genus and species from Mauritius

Abstract:The new corticolous lichen genus Krogia and species K. coralloides are described from humid forest in Mauritius. The genus shows affinities with Phyllopsora, but differs in characters of the ascus, ascospores, and thallus anatomy. The ascal characters make its inclusion in the Bacidiaceae orPhyllopsoraceae problematic. The lichen contains boninic acid and an apparently related compound.     

A NEW SPECIES OFCATILLARIAFROM COASTAL MEDITERRANEAN REGIONS

A revision of several specimens ofCatillaria mediterraneaHafellner revealed that two species can be recognized:C. mediterraneas. str., which has 8–16 spores per ascus, grows on foliose and fruticose lichens, and has a Mediterranean-Macaronesian, montane distribution, andC. praedictaTretiach & Hafellner sp. nov., which has (16–)24–32(–48) spores per ascus, occurs on shrubs in coastal Mediterranean maquis, and has a Mediterranean, maritime distribution. The systematic affinities of the two species with the 8-sporedC. nigroclavata(Nyl.) Schuler are briefly discussed.     

PHYLOGENY OF THEPARMELIACEAE—DNA DATA VERSUS MORPHOLOGICAL DATA

In order to identify monophyletic groups within the familyParmeliaceae, eleven taxa (Bryoria capillaris,Cetraria islandica,Evernia pruniastri,Hypogymnia physodes,Parmelia saxatilis,Platismatia glauca,Pleurosticta acetabulum,Usnea florida,Vulpicida juniperina,V. pinastri, andXanthoparmelia conspersa) were studied using newly produced nuclear rDNA sequence data from the ITS and 5·8S regions. The resulting evolutionary hypothesis was compared with results from previous phylogenetic analyses based on anatomy, morphology, and chemistry. The outcome of this comparison does not support the earlier proposed phylogenies but is not stable enough for identifying monophyletic groups, with one exception. The results indicate a close relationship betweenCetrariaandVulpicida, which is contradictory to previous published analyses. The variation in ascus structures in theParmeliaceaeis discussed and it is questioned whether the earlier distinguished ‘ forms ’ of ascus types represent synapomorphies, if they are based on poorly supported analyses, or if they are exaggerations of relatively slight variation in shape. Further interpretations of the results are discussed and areas of future studies based on DNA-data are suggested.     

Division spindle and centrosomal plaques during mitosis and meiosis in some Ascomycetes

The behaviour of the division spindle and centrosomal plaques is described in four species of Ascomycetes (Ascobolus immersus, Ascobolus stercorarius, Podospora anserina and Podospora setosa) studied by light and electron microscopy. Two unique features of the kinetical apparatus were observed: presence of centrosomal plaques and intranuclear location of the spindle. In all types of mitoses (mycelium, crosier and postmeiotical mitosis) the apparatus is structurally identical to that found in meiosis. The centrosomal plaques, present in all divisions, are always contiguous with the nuclear envelope and never show centrioles similar to those commonly found in Metazoa and Protozoa. During metaphase and anaphase the plaque is constituted of two zones situated on each side of the nuclear envelope: an electron opaque outer zone and inner one less opaque in which most of the microtubules end. In Podospora the outer zone appears in sections as consisting of two dark layers separated by a clear one. Two dispositions of plaques are possible: either they are entirely contiguous with the nuclear envelope (Ascobolus) or only partially so, the remainder being perpendicular to the nuclear envelope (Podospora). — The localisation of the plaques in the ascus was determined by light and electron microscopy. The nuclear envelope was shown to remain intact during division. It was possible to observe that the sporal wall of each spore originated from the same unique double membrane formed in the ascus during the meiotic second division and postmeiotical mitosis. This fact is of genetical interest for the study of morphological and physiological characters of the spores.     

STUDIES IN THE GENUS NECTRIA. II. MORPHOLOGY OF N. GLIOCLADIOIDES

Hanlin , Richard T. (Georgia Experiment Station, Experiment.) Studies in the genus Nectria. II. Morphology of N. gliocladioides. Amer. Jour. Bot. 48(10): 900–908. Illus. 1961.—Swollen tips of vegetative hyphae develop into multicellular archicarps from which multinucleate ascogonia form. From basal cells of each archicarp arise hyphae which grow up into a prosenchymatous, true perithecial wall; around this wall is formed a thin pseudoparenchymatous stroma of compacted hyphae. The ascogonia give rise to ascogenous cells from which croziers and asci form directly. At the same time, an apical meristem forms cells that grow downward into the centrum. These are pseudoparaphyses. Asci grow up among the pseudoparaphyses, which deliquesce as the ascocarp matures. The ascus tip contains a thick ring with a pore and lateral thickening of the ascus wall. Ascospores are forcibly ejected. The chromosome number is 4. This species conforms to the Nectria Developmental Type of Luttrell.     

Euopsis and Harpidium,Genera of the Lichinaceae (Lichenes) with Rostrate Asci*

Based on corresponding ascocarp ontogeny and thallus structure, the genera Euopsis and Harpidium are included in the family Lichinaceae. In the two species of Euopsis, E. granatina and E. pulvinata, the apothecia develop from ascogonia in generative tissue, while in H. rutilans they are pycnoascocarps. In thallus anatomy, the species of Euopsis resemble Pyrenopsis haematopsis and allied species, while H. rutilans corresponds in structure and development of the thallus and apothecia to Pyrenopsis haemaleella (syn. P. sphinctotricha). H. rutilans is the first member of Lichinaceae known to have only a green algal symbiont. In E. granatina, two phycobionts are always present, a species of Gloeocapsa and a chlorococcalean alga. In Euopsis and Harpidium, the ascus wall is composed of an outer, non-expansible and an inner, expansible layer; the latter surrounds the protoplast as an amyloid collar, which expands during spore release into a long, tapering rostrum. In Euopsis, the outer wall layer is strongly amyloid and the upper part separated from the expanded amyloid rostrum by a non-amyloid zone, appearing like a slit in LM studies. The ultrastructure and function of the ascus in E. granatina has been studied in TEM and is interpreted as functionally unitunicate-rostrate. Unitunicate asci with short rostrum are described for P. haemaleella and P. haematopsis.