Ultrastructure of hyphae and ascospores in the genus Eremascus eidam

Hyphae and ascospores of Eremascus fertilis and E. albus were studied in ultrathin sections. The lateral wall of the hyphae had a thick electron-light inner layer and a thin dark outer layer. The septa had a simple central pore with or without a plug, and there were Woronin bodies in the vicinity. The wall of the ascospores of E. fertilis showed a thick light inner layer and a thin dark outer layer. In the wall of the spores of E. albus a dark fibrillar layer was present between the light inner layer and the dark outer layer. The spores of this species germinated with a tube the wall of which was continuous with a newly formed layer inside the spore wall.This investigation was supported by the Netherlands Organization for the Advancement of Pure Research (Z. W. O.)     

Ultrastructure of the ascospores of the new yeast genus Sporopachydermia Rodrigues de Miranda

Development of the ascospores of Sporopachydermia lactativora and S. cereana was studied in ultrathin sections. The spores have a very thick wall consisting of a thin dark outer layer and a double light inner layer the outer part of which is very wide and often irregular. During germination, this part disappears, the outer dark layer breaks up and the inner part of the light layer remains around the protoplast during development to a vegetative cell.This investigation was supported by the Netherlands Organization for the Advancement of Pure Research (Z.W.O.).     

Electron microscopy of germinating ascospores ofSaccharomyces cerevisiae

The wall of mature ascospores ofSaccharomyces cerevisiae showed in sections under the electron microscope a dark outer layer and a lighter inner layer. The latter was composed of a greyish inner part and a light outer part. During germination, the spore grew out at one side and the dark outer layer was broken. Of the light inner layer, the inner greyish part became the wall of the vegetative cell, but the extented part of the cell had a new wall.     

Electron microscopy of sporulation inSchwanniomyces alluvius

Sporulation inSchwanniomyces alluvius appeared to be preceded by fusion of a mother and a daughter cell. Meiosis probably occurred in the mother cell and one or two spores were formed in the latter. A study of thin sections showed that the spore wall developed from a prospore wall. The mature spore wall consisted of a broad light inner layer and a thinner dark outer layer including warts. An equatorial ledge was present. During germination in the ascus, a new light inner layer was formed and the old layers of the spore wall partly broke up. Ascospores in a strain ofS. persoonii had a different wall structure in that the dark layer had changed into light areas separated by dark material which formed bulges at the surface.     

Conjugation in the yeast Saccharomycopsis capsularis schiönning

Cells of the yeast Saccharomycopsis capsularis fused in pairs after dissolving of part of the cross wall between them near the lateral wall. After nuclear migrations through the opening, the cross wall was closed again and the cells at both sides became asci. The wall of the ascospores developed from a prospore wall. Between the two unit membranes a very thin dark layer broadened to the dark layer of the wall and after that, the light inner layer developed. Immature spores in the strain studied had a ledge which disappeared during maturation.     

A new genus: Sporopachydermia

In two species of the yeast genus Cryptococcus ascospores have been found. A genus is described to accommodate the two species, because the spore wall is extraordinarily thick and its ultrastructure differs from that found in all other yeast genera. The spores are easily liberated from the ascus at maturation. The name Sporopachydermia is proposed for the genus and the names S. lactativora and S. cereana are proposed for the species.     

Conjugation in the yeast Saccharomycopsis capsularis Schi?nning.

Cells of the yeast Saccharomycopsis capsularis fused in pairs after disolving of part of the cross wall between them near the lateral wall. After nuclear migrations through the opening, the cross wall was closed again and the cells at both sides became asci. The wall of the ascospores developed from a prospore wall. Between the two unit membranes a very thin dark layer broadened to the dark layer of the wall and after that, the light inner layer developed. Immature spores in the strain studied had a ledge which disappeared during maturation.     

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.     

ULTRASTRUCTURE OF DISPERSED AND IN SITU SPECIMENS OF THE DEVONIAN SPORE RHABDOSPORITES LANGII: EVIDENCE FOR THE EVOLUTIONARY RELATIONSHIPS OF PROGYMNOSPERMS

Abstract: The spore Rhabdosporites (Triletes) langii (Eisenack) Richardson, 1960 is abundant and well preserved in Middle Devonian (Eifelian) ‘Middle Old Red Sandstone’ deposits from the Orcadian Basin, Scotland. Here it occurs as dispersed individual spores and in situ in isolated sporangia. This paper reports on a detailed light microscope (LM), scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis of both dispersed and in situ spores. The dispersed spores are pseudosaccate with a thick walled inner body enclosed within an outer layer that was originally attached only over the proximal face. The inner body has lamellate/laminate ultrastructure consisting of fine lamellae that are continuous around the spore and parallel stacked. Towards the outer part of the inner body these group to form thicker laminate structures that are also continuous and parallel stacked. The outer layer has spongy ultrastructure. In situ spores preserved in the isolated sporangia are identical to the dispersed forms in terms of morphology, gross structure and wall ultrastructure. The sporangium wall is two‐layered. A thick coalified outer layer is cellular and represents the main sporangium wall. This layer is readily lost if oxidation is applied during processing. A thin inner layer is interpreted as a peritapetal membrane. This layer survives oxidation as a tightly adherent membranous covering of the spore mass. Ultrastructurally it consists of three layers, with the innermost layer composed of material similar to that comprising the outer layer of the spores. Based on the new LM, SEM and TEM information, consideration is given to spore wall formation. The inner body of the spores is interpreted as developing by centripetal accumulation of lamellae at the plasma membrane. The outer layer is interpreted as forming by accretion of sporopollenin units derived from a tapetum. The inner layer of the sporangium wall is considered to represent a peritapetal membrane formed from the remnants of this tapetum. The spore R. langii derives from aneurophytalean progymnosperms. In light of the new evidence on spore/sporangium characters, and hypotheses of spore wall development based on interpretation of these, the evolutionary relationships of the progymnosperms are considered in terms of their origins and relationship to the seed plants. It is concluded that there is a smooth evolutionary transition between Apiculiretusispora‐type spores of certain basal euphyllophytes, Rhabdosporites‐type spores of aneurophytalean progymnosperms and Geminospora‐/Contagisporites‐type spores of heterosporous archaeopteridalean progymnosperms. Prepollen of basal seed plants (hydrasperman, medullosan and callistophytalean pteridosperms) are easily derived from the spores of either homosporous or heterosporous progymnosperms. The proposed evolutionary transition was sequential with increasing complexity of the spore/pollen wall probably reflecting increasing sophistication of reproductive strategy. The pollen wall of crown group seed plants appears to incorporate a completely new developmental mechanism: tectum and infratectum initiation within a glycocalyx‐like Microspore Surface Coat. It is unclear when this feature evolved, but it appears likely that it was not present in the most basal stem group seed plants.     

Scanning electron microscopy of ascospores of Debaryomyces and Saccharomyces

Ascospores from species of Debaryomyces and the Torulaspora-group of Saccharomyces were examined by scanning electron microscopy. Ornamentation on ascospores of D. hansenii varied from short to long interconnected ridges or broad based, elongated conical protuberances. A spiral ridge system was detected on the ascospores of D. marama, but wart-like protuberances occurred on those of D. cantarellii, D. castellii, D. coudertii, D. formicarius, D. phaffii, D. vanriji and D. yarrowii. Ascospores of D. halotolerans did not have protuberances and the species appears to be identical with Pichia farinosa. Wart-like protuberances also were found on ascospores of S. delbrueckii, S. microellipsodes, S. rosei, S. inconspicuus, S. fermentati, S. montanus and S. vafer, but the ascospore surface of S. pretoriensis was covered by fine ridges. Short tapered ridges covered the ascospores of S. kloeckerianus.     

Cucullosporella mangrovei, ultrastructure of ascospores and their appendages

The ultrastructure ofCucullosporella mangrovei ascospores is described. Mature ascospores possess two wall layers, an outer electron-dense episporium and an innermost tripartite mesosporium. Episporial elaborations form electrondense spore wall ornamentations from which extend fibrils that may constitute a highly hydrated exosporium which was not visualised at either the scanning electron microscope or light microscope level. Ascospores possess a hamate appendage at each pole which unfolds in seawater to form a long thread. Ultrastructurally the polar appendage comprises folded fibro-granular electron-dense material and fine fibrils. The fibrils form a matrix around and within the fibro-granular appendage and around the entire unreleased ascospore. These fibrils have not been observed associated with the ascospore appendages in other species of the Halosphaeriales and are a discrete and new appendage component. The fibro-granular appendage and fibrils are bounded by the outer delimiting membrane which is absent around released ascospores. The nature of the spore appendage is compared with that of other marine and freshwater ascomycetes and the taxonomic assignment of the species is discussed.     

Geosiphon pyriforme,an Endosymbiotic Association of Fungus and Cyanobacteria: the Spore Structure Resembles that of Arbuscular Mycorrhizal (AM) Fungi

The zygomycete Geosiphon pyriforme is the only known endocyanosis of a fungus. The Nostoc spp. filaments are included in photosynthetically active and nitrogen fixing, multinucleated bladders, which grow on the soil surface. The spores of the fungus are white or slightly brownish. They are about 250 μm in diameter and develop singly on hyphal ends or, less frequently, intercalarly. The wall of the spores consists of a thin innermost layer, a laminated inner layer with a thickness of about 10–13 μm, and an evanescent outer layer. The laminated layer is composed of helicoidally arranged microfibrils, and is separated from the evanescent outer layer by a thin electron-dense sublayer. Polarisation microscopy indicates the occurrence of chitin. Shape and wall ultrastructure of the Geosiphon spores and their cytoplasm resemble that of Glomus spores, but are different from that of other genera of the Glomales and Endogonales. Germination occurs by a single thick hyphal outgrowth directly through the spore wall. Like various AM forming fungi, Geosiphon pyriforme contains endocytic bacteria-like organisms, which are not surrounded by a host membrane. Our observations indicate that Geosiphon is a potential AM fungus.     

CHANGES IN THE HEAT-RESISTANCE OF ASCOSPORES OF NEUROSPORA UPON GERMINATION

Lingappa , Yamuna , and A. S. Sussman . (U. Michigan, Ann Arbor.) Changes in the heat-resistance of ascospores of Neurospora upon germination. Amer. Jour. Bot. 46 (9): 671–678. Illus. 1959.—A rapid loss in heat-resistance accompanies activation of ascospores of Neurospora tetrasperma after incubation at 27°C. When activated spores are given a 5-min. “heat-flash” at 65°C. after only 5 min. at 27°C., fully % fail to germinate. Such treatment, if administered 25 min. after activation, results in the complete destruction of the spores. By contrast, when incubation at 27°C. is not interposed, more than ½ of the spores will germinate, even when they have been exposed to 65°C. for 30 min. Similar results were obtained with “heat-flashes” at 50 and 60°C., although exposures of longer duration were required to affect the spores. Conidia respond very differently to “heat-flashes” in that germination is stimulated if they are provided after an incubation period at 27°C. On the other hand, conidia are killed by short exposures to 60°C., so that they are far more susceptible to such treatment than are ascospores. A study of the cardinal temperatures of germination revealed that the maximum is about 44°C. for both conidia and ascospores. The maximum for the growth of two strains of N. tetrasperma and for one of N. crassa is between 40–45°C.; however, another strain of the latter species grows at 45°C. Dry heat was shown to be less effective than wet in activating ascospores. Removal of the exospore of ascospores results in the loss of considerable heat-resistance. In addition, the requirement for heat-activation is considerably mitigated in such spores, suggesting that the exospore, or an associated layer is the locus of the ascospore's heat-resistance.     

Torulaspora indica a novel yeast species isolated from coal mine soils

Four yeast strains (APSS 805, APSS 806, APSS 815 and AP-18) belonging to a novel Torulaspora species were isolated from coal mine soils of Singareni in Andhra Pradesh state, India. Another strain (PBA-22) was isolated from agricultural field soil from Gujarat state, India. The vegetative cells of all these strains were round, haploid and produced asci by conjugation between independent cells or mother cell and bud, with rough ascospores, suggesting their possible relation to ascomycetous yeast genus Torulaspora. Phylogenetic analysis of the D1/D2 domain of the large subunit (LSU) rRNA gene and Internal Transcribed Spacer (ITS) regions revealed that, among the five strains, three viz. APSS 805, APSS 806 and APSS 815 have identical sequences. The other two strains (AP-18 and PBA-22) differed from the other three strains in less than 1% nucleotide substitutions in the combined D1/D2 domain and ITS sequences, indicating that all of them (five strains) may belong to the same species. These five strains were closely related to Torulaspora globosa, but showed more than 3–7% sequence divergence from T. globosa and all other species in the genus Torulaspora in the combined sequence analysis of D1/D2 domain and ITS region of rRNA gene. In addition, these strains also showed distinct microsatellite finger-printing pattern from related species and differed in several physiological responses suggesting that these strains belong to a novel species of Torulaspora. We propose to name these strains as Torulaspora indica sp. nov., and designate APSS 805^T = MTCC 9772 ^T = CBS 12408 ^T as the type strain of this novel species. The Mycobank number of the novel species is MB 563738.     

Clavispora,a new yeast genus of the Saccharomycetales

In Candida lusitaniae van Uden et do Carmo-Sousa (1959), strains of opposite sex have been found. Cells of the opposite mating types conjugate and form asci with one to four clavate spores. These are easily liberated from the ascus. The type strain of Candida obtusa (Dietrichson) van Uden et do Carmo-Sousa ex van Uden et Buckley (1970) also produces ascospores after mating with one of the strains of Candida lusitaniae. As clavate ascospores are unknow in yeasts, a new genus, Clavispora, is proposed with Clavispora lusitaniae spec. nov. as type species.     

Acaulospora alpina, a new arbuscular mycorrhizal fungal species characteristic for high mountainous and alpine regions of the Swiss Alps

Acaulospora alpina sp. nov. forms small (65-85 microm diam), dark yellow to orange-brown spores laterally on the neck of hyaline to subhyaline sporiferous saccules. The spores have a three-layered outer spore wall, a bi-layered middle wall and a three-layered inner wall. The surface of the second layer of the outer spore wall is ornamented, having regular, circular pits (1.5-2 microm diam) that are as deep as wide and truncated conical. A "beaded" wall layer as found in most other Acaulospora spp. is lacking. The spore morphology of A. alpina resembles that of A. paulinae but can be differentiated easily by the unique ornamentation with the characteristic pits and by the spore color. A key is presented summarizing the morphological differences among Acaulospora species with an ornamented outer spore wall. Partial DNA sequences of the ITS1, 5.8S subunit and ITS2 regions of ribosomal DNA show that A. alpina and A. paulinae are not closely related. Acaulospora lacunosa, which has similar color but has generally bigger spores, also has distinct rDNA sequences. Acaulospora alpina is a characteristic member of the arbuscular mycorrhizal fungal communities in soils with pH 3.5-6.5 in grasslands of the Swiss Alps at altitudes between 1800 and 2700 m above sea level. It is less frequent at 1300-1800 m above sea level, and it so far has not been found in the Alps below 1300 m or in the lowlands of Switzerland.     

Ultrastructure of asci and ascospores of the mangrove ascomyceteDactylospora haliotrepha

Ultrastructure of the marine LoculoascomyceteDactylospora heliotrepha is presented and compared withMarinosphaera mangrovei, Swampomyces armeniacus and other marine species. Ascospores are bi-celled and ridged. The ridges are outgrowths of the outer mesosporial layer and formed later in ascosporogenesis. The exosporial layer fragments to release mucilaginous material present between the spore wall ridges. Asci and pseudoparaphyses are held together by a fibrillar mucilaginous network. The endoascus is thicker than the ectoascus. Comparisons are made of the diameter of ascomata, size of asci and ascospores ofD. heliotrepha collected from mangroves in Hong Kong, Malaysia, the Philippines and Taiwan.     

Airborne Ascomycotina on the island of Crete: Seasonal patternsbased on an 8-year volumetric survey

An 8-year study was conducted on the island of Crete in order to identify airborne ascospores and to determine their seasonal pattern. A Burkard 7-day, volumetric spore-trap was continuously operated in the city of Irakleion – located in the center of the island – from 1994 through 2001. Relatively „high” ascospore counts (20 – 48 spores/m ³) were obtained from mid-spring through summer, while the rest of the year exhibited lower activity (8–16 spores/m³). The predominant ascospores identified were those of Leptosphaeria and Chaetomium; their concentrations varied from 1 or 2 spores up to a few dozens of spores/m³. Other spores encountered sporadically were: Ascobolus, Endophragmiella, Didymella, Diatrypaceae, Leptosphaerulina, Massaria, Pleospora, Sporormiella, Xylaria. The mean daily concentration of all identified ascospores was 30/m³ for the entire study period, corresponding to 13.9% of the total fungal load. Ascospores have been recognized as important inhalant allergens and have been implicated as contributing to symptoms of both rhinitis and asthma.     

Amorphophallus: New insights into pollen morphology and the chemical nature of the pollen wall

In pollen characters, Amorphophallus is one of the most diverse genera in the Araceae. The present work is a critical survey of contradicting reports on the impact of acetolysis treatment on Amorphophallus pollen, on the chemical nature of the outer pollen wall layer and of electron-dense (dark) granules found within it. Furthermore, we wanted to clarify the pollen polarity and to test conclusions based on different preparation techniques. Pollen morphology of 25 species is investigated by light microscopy, scanning electron microscopy and transmission electron microscopy. Our results show that Amorphophallus pollen is not resistant to acetolysis treatment. The use of different transmission electron microscopy staining methods proved the polysaccharide nature of the outer pollen wall layer and of the granules within it. Moreover, an additional thin surface layer was found in all investigated species. Microspores in early and late tetrad stages show that the less convex side of the microspore is the proximal face and the more convex side the distal face. The extrusion of pollen in strands is illustrated for the first time by light microscopy and scanning electron microscopy. Furthermore, observations of pollen in water showed that in some of the investigated species the pollen wall is shed immediately before pollen tube formation.     

Wall formation in the saprolegniales

Summary The primary and secondary cysts of Saprolegnia ferax and the secondary cysts of Dictyuchus sterile have a two layered wall structure, the outer layer of which bears various types of spines. These spines, and the outer wall layer are derived from preformed structures (bars) found in the cytoplasm prior to encystment. Golgi derived vesicles appear to contribute to the inner layer of the primary cyst wall of S. ferax. The outer surface of the secondary cyst walls of this species has fibrils which are not embedded in matrix material.