DICTYOSTELIUM AUREO-STIPES AND DICTYOSTELIUM TENUE: NEW SPECIES OF THE DICTYOSTELIACEAE

Three new cellular slime molds, Dictyostelium aureo-stipes sp. n., D. aureo-stipes var. helvetium var. n. and D. tenue sp. n., are described which possess characteristics heretofore unrecorded in the Dictyosteliaceae. The two species are unlike in dimensions and complexity of form, yet show a number of features in common, and may in fact be closely related. D. aureo-stipes var. helvetium is relatively large and robust, forming multiple-branched fruiting bodies without the regularity of form found in Polysphondylium, yet tending toward symmetry when well-developed. The golden-yellow stipe is a distinguishing feature of D. aureo-stipes and is even more pronounced in var. helvetium. D. tenue is smaller and simpler in form. The degree of branching is much reduced, and oftentimes a solitary sorus terminates a delicate stipe composed of a single tier of cells. Both species are quite sensitive to environmental conditions, particularly temperature, for optimum development occurs within relatively narrow ranges.     

The ultrastructure of the zygospore in Endogone flammicorona Trappe & Gerdemann

The ultrastructural organization of the spores of the sporocarp of Endogone flammicorona was studied. Two types of organization are described. Initially the spore possessed a vacuolate protoplasm and was bound by two cell wall layers. The spore was surrounded by a hyphal mantle formed of a sheet of vacuolized hyphae with uniformly thin walls. Secondly, although the ultrastructural features of the spore appeared the same, it was now surrounded by a hyphal mantle with unevenly thickened walls (i. e., the so-called flaming crown) due to the gradual and irregular deposition of granules and lamellae. This crown gives the spore its most commonly observed morphological feature and is the preminent character employed taxonomically to speciate Endogone flammicorona Trappe & Gerdemann.     

<Emphasis Type="Italic">Gynonectria intraspora</Emphasis> gen. et sp. nov. (Hypocreales), a perianthicolous phyllosphere fungus with a novel ascospore type

Gynonectria intraspora is described as a new monotypic genus of the Hypocreales (Ascomycetes). Relatively large perithecia form individually within the perianths of the hepatic Odontolejeunea sp. (Lejeuneaceae, Porellales), which grow in the phyllosphere of living vascular plants in the rainforests of Costa Rica and Panama. As in other hyperepiphyllous perianthicolous species, hyphae concentrate in the region of the sporophyte–gametophyte junction. They prevent sporophyte maturation, but do not visibly affect the leafy gametophyte. The most intriguing character of G. intraspora is exhibited by the ascospores. While they are still in the asci, each of them cleaves two new spores within its lumina leaving residual primary spore plasma around them. This novel spore type is comparable to the endoconidia of black meristematic fungi and is called an "intraspore". The formation of intraspores together with other features seem to indicate that the obligate hyperepiphyllous Hypocreales are undergoing an active evolutionary process of diversification, as are their epiphyllous lejeuneaceous hosts.     

Summer meeting 2013 – when the sleepers wake: the germination of spores of Bacillus species

Spores of Bacillus species can remain dormant and resistant for years, but can rapidly ‘come back to life’ in germination triggered by agents, such as specific nutrients, and non‐nutrients, such as CaDPA, dodecylamine and hydrostatic pressure. Major events in germination include release of spore core monovalent cations and CaDPA, hydrolysis of the spore cortex peptidoglycan (PG) and expansion of the spore core. This leads to a well‐hydrated spore protoplast in which metabolism and macromolecular synthesis begin. Proteins essential for germination include the GerP proteins that facilitate germinant access to spores' inner layers, germinant receptors (GRs) that recognize and respond to nutrient germinants, GerD important in rapid GR‐dependent germination, SpoVA proteins important in CaDPA release and cortex‐lytic enzymes that degrade cortex PG. Rates of germination of individuals in spore populations are heterogeneous, and methods have been developed recently to simultaneously analyse the germination of multiple individual spores. Spore germination heterogeneity is due primarily to large variations in GR levels among individual spores, with spores that germinate extremely slowly and termed superdormant having very low GR levels. These and other aspects of spore germination will be discussed in this review, and major unanswered questions will also be discussed.     

THE SIGNIFICANCE OF REPRODUCTIVE AND SPORE GERMINATION CHARACTERISTICS TO THE SYSTEMATIC OF THE CORALLINACEAE: NONARTICULATED CORALLINE ALGAE12

This paper deals with reproductive and spore germination characteristics to the systematics of the nonarticulated coralline algae. As can the articulated coralline algae, the nonarticulated coralline algae may also he divided into 2 groups on the basis of their yearly reproductive cycles, spore dimensions, and spore germination characteristics: the Lithophyllum group and the Lithothamnium group. These 2 groups are basically identical with the Amphiroa and Corallina groups of the articulated coralline algae, respectively, so far as these 3 characters are concerned. The grouping of these representatives of the Corallinaceae into 2 groups—Amphiroa—Lithophyllum and Corallina–Lithothamnium—coincides with a grouping based on the manner of connection between cells of adjacent filaments.     

THE “HYSTRICHOSPHAERID” RESTING SPORE OF THE DINOFLAGELLATE PYRODINIUM BAHAMENSE,PLATF, 19062

Germination experiments demonstrate that the “hystrichosphere” called Hemicystodinium zoharyi, which previously has been found only as a microfossil organism, is the resting spore stage in the life history of Pyrodinium bahamense, a modern bioluminescent, thecate dinoflagellate. The morphology of this spore, together with new details of the thecal structure and ontogeny of P. bahamense, is described, and it is concluded that Pyrodinium is closely related to Gonyaulax but worthy of retention as a discrete genus. The geological history of P. bahamense is traceable to the Eocene through fossil occurrences of its spore, and it is suggested that additional pyrodinioid dinoflagellates which now are extinct were represented in Lower Tertiary seas by another hystrichosphere genus, called Homotryblium. Selected aspects of the physiology and ecology of modern dinoflagellate resting spores are discussed briefly with special reference to Pyrodinium.     

THE SPORE-GERMINATION PATTERN OF THELYPTEROID FERNS

Cell division patterns in germinating spores of several Thelypteris species were studied using light microscopy of sectioned material and scanning electron microscopy. All species exhibited the same basic germination pattern, characterized by an asymmetric cell division of the spore parallel to the equatorial plane to delimit a proximal rhizoid, followed by a perpendicular division of the basal cell to form the protonemal cell. While spore-germination patterns appear to be a potentially useful taxonomic character in some groups of ferns, the homogeneity in this character exhibited by the thelypteroid group impairs its usefulness in the taxonomy of Thelypteris.     

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.     

STUDIES OF PALEOZOIC MARATTIALEANS: NEW SPECIES OF SCOLECOPTERIS (MARATTIALES) FROM THE PENNSYLVANIAN OF NORTH AMERICA

Two new species of the late Paleozoic fern Scolecopteris (Marattiales) are described and their relationships within the genus are discussed. Scolecopteris charma sp.n., from Steubenville, Ohio (Duquesne Coal, Upper Pennsylvanian), is similar to species in the Oliveri group, while S. gnoma sp.n. from Providence, Kentucky (Baker Coal, Middle Pennsylvanian), compares favorably with the Latifolia species group. Scolecopteris gnoma is most similar to S. fragilis but differs in its smaller synangia and spore type. S. charma appears generally similar to S. iowensis because of its large pedicel and histologically undifferentiated walls, but differs in a number of characters such as vasculature and spore type. Despite its occurrence late in the Pennsylvanian, S. charma is thought to possess a number of primitive character states (large trilete spores, vascularized pedicels, flat pinnules with downturned margins). Using the same criteria for the much older S. gnoma, we note a number of relatively apomorphic character states (small monolete spores, unvascularized pedicels, extended pinnule margins). An outgroup analysis of species-level characters of Scolecopteris gives a better concept of primitive versus derived traits in marattialean and other ferns. Genera in the Paleozoic fern orders Filicales (Ankyropteris) and Zygopteridales (Corynepteris, Musatea) were chosen as outgroups, and the comparisons support suggestions for the polarity of several important characters. Some of these agree with previously proposed evolutionary polarities based on the geological occurrence of marattialean ferns.     

Effects of modification of membrane lipid composition on Bacillus subtilis sporulation and spore properties

Aims: To determine effects of inner membrane lipid composition on Bacillus subtilis sporulation and spore properties. Methods and Results: The absence of genes encoding lipid biosynthetic enzymes had no effect on B. subtilis sporulation, although the expected lipids were absent from spores’ inner membrane. The rate of spore germination with nutrients was decreased c. 50% with mutants that lacked the major cardiolipin (CL) synthase and another enzyme for synthesis of a major phospholipid. Spores lacking the minor CL synthase or an enzyme essential for glycolipid synthesis exhibited 50–150% increases in rates of dodecylamine germination, while spores lacking enzymes for phosphatidylethanolamine (PE), phosphatidylserine (PS) and lysylphosphatidylglycerol (l‐PG) synthesis exhibited a 30–50% decrease. Spore sensitivity to H₂O₂ and tert‐butylhydroperoxide was increased 30–60% in the absence of the major CL synthase, but these spores’ sensitivity to NaOCl or Oxone^? was unaffected. Spores of lipid synthesis mutants were less resistant to wet heat, with spores lacking enzymes for PE, PS or l‐PG synthesis exhibiting a two to threefold decrease and spores of other strains exhibiting a four to 10‐fold decrease. The decrease in spore wet heat resistance correlated with an increase in core water content. Conclusions: Changing the lipid composition of the B. subtilis inner membrane did not affect sporulation, although modest effects on spore germination and wet heat and oxidizing agent sensitivity were observed, especially when multiple lipids were absent. The increases in rates of dodecylamine germination were likely due to increased ability of this compound to interact with the spore’s inner membrane in the absence of some CL and glycolipids. The effects on spore wet heat sensitivity are likely indirect, because they were correlated with changes in core water content. Significance and Impact of the Study: The results of this study provide insight into roles of inner membrane lipids in spore properties.     

SPORES OF BOTRYOPTERIS GLOBOSA AND BOTRYOPTERIS AMERICANA FROM THE PENNSYLVANIAN

A study of spores from fertile pinnae of Botryopteris from middle and upper Pennsylvanian coal balls from Iowa, Illinois, and Kansas indicates that there are two distinct species, Botryopteris globosa and B. americana. The organization and attachments of fertile pinnae and the sporangial morphology and dimorphism are identical in the two species. Data are given on fertile pinnae dimensions, attachments of six fertile pinnae, spore counts from individual sporangia, and spore morphology. The ornamentation of B. americana spores is verrucate to rugulate with verrucae fusing to a variable extent to form bars and convolute ridges; B. globosa spores are vermiculate or fossulate to densely rugulate with scattered verrucae. Comparisons are made with B. forensis and a re-interpretation of the spore forms of B. forensis is suggested.     

Osservazioni preliminari al microscopio elettronico a scansione sulle ornamentazioni delle spore di Russula

Abstract

Preliminary observations on spore ornementation of Russula, as seen in the scanning electron microscope. — The spores of 16 species of Russula have been examined in the scanning electron microscope, as a preliminary attempt to see if an accurate examination of the spore surface at the ultrastructural level could reveal details of ornamentation which might be useful for the classification of the many species of this genus. The examination, carried out both on fixed and unfixed specimens, has demonstrated that the spore shape is always round or slightly elliptic, and that the obnormal forms as previously described are probably artifacts. Five main types of ornamentation have been described: single wart-like and single finger-like Protrusion, wart- or finger-like protrusions interconnected by thin ridges, and thick, short « papillae » together with large ridges that run along large tracts of the spore circumference. The type of ornamentation was a constant character in each species.     

Structural analysis of Bacillus subtilis spore peptidoglycan during sporulation

A major structural element of bacterial endospores is a peptidoglycan (PG) wall. This wall is produced between the two opposed membranes surrounding the developing forespore and is composed of two layers. The inner layer is the germ cell wall, which appears to have a structure similar to that of the vegetative cell wall and which serves as the initial cell wall following spore germination. The outer layer, the cortex, has a modified structure, is required for maintenance of spore dehydration, and is degraded during spore germination. Theories suggest that the spore PG may also play a mechanical role in the attainment of spore dehydration. Inherent in one of these models is the production of a gradient of cross-linking across the span of the spore PG. We report analyses of the structure of PG found within immature, developing Bacillus subtilis forespores. The germ cell wall PG is synthesized first, followed by the cortex PG. The germ cell wall is relatively highly cross-linked. The degree of PG cross-linking drops rapidly during synthesis of the first layers of cortex PG and then increases two- to eightfold across the span of the outer 70% of the cortex. Analyses of forespore PG synthesis in mutant strains reveal that some strains that lack this gradient of cross-linking are able to achieve normal spore core dehydration. We conclude that spore PG with cross-linking within a broad range is able to maintain, and possibly to participate in, spore core dehydration. Our data indicate that the degree of spore PG cross-linking may have a more direct impact on the rate of spore germination and outgrowth.     

SPORE FORMATION IN THE LIFE CYCLES OF THE DIATOMS CHAETOCEROS DIADEMA AND LEPTOCYLINDRUS DANICUS1

A nitrogen limitation technique elicited the entire life cycle of the marine centric diatoms Chaetoceros diadema (Ehr.) Gran and Leptocylindrus danicus Cleve. In C. diadema the sexual cycle followed the same pattern as in the previously investigated C. didymus. Sexuality took place in narrow diameter cells, only at 2 and 5° C, and was seldom seen. Resting spore formation took place in cells of all sizes and at all temperatures at which the species grew vegetatively (2–15° C). The L. danicus life cycle is probably unique among diatoms. Nitrogen depletion induced sexuality in the entire culture at 10 and 15° C if the cell diameter was narrow (3–8 μm). Auxospore formation was followed by resting spore formation directly within the auxospore. In C. diadema, as in most centric diatoms, resting spores are not an obligate part of the life cycle, but they are in L. danicus. Resting spore formation is a versatile adaptive response in C. diadema, depending only on nitrogen depletion, although promoted by low temperatures. In L. danicus the linkage to the sexual process sharply limits conditions under which resting spores can form.     

The arachiform vacuolar body: an overlooked shared character in the ascospores of a large monophyletic group within Parmeliaceae (Xanthoparmelia clade, Lecanorales)

Sections of apothecia were used to study the internal morphology of ascospores in the largest monophyletic clade within Parmeliaceae composed of Xanthoparmelia and related genera. The results were compared with fertile representative species of most other parmelioid clades. All the Xanthoparmelia species had spores with a single smooth vacuole, which was peanut-shaped, with different degrees of constriction in the equatorial plane. This differs from the ellipsoid vacuole of other parmelioids. In the Xanthoparmelia clade, sexual reproduction seems much more common than in other parmelioids. Thus, we suggest that the presence of this unique spore morphology might contribute to the evolutionary success of this monophyletic group. Further, the discovery of this useful ascospore character demonstrates that detailed ascospore morphological studies significantly enhance molecular phylogenetic analyses. Ascospore features may be more taxonomically significant in Parmeliaceae than hitherto considered.     

Negative chemotaxis in Dictyostelium and Polysphondylium

A method has been described to measure negative chemotaxis in the cellular slime molds directly and to purify the repellents. Conclusive evidence is given that negative chemotaxis exists in the cellular slime molds and that it occurs generally in Dictyostelium and Polysphondylium. Amoebae respond shortly after their exposure to repellents, which are secreted by vegetative and not by preaggregative cells. The amoebae are sensitive to repellents in both development stages and contain enzyme(s) to inactivate them. Cross reactions of different species indicate that there is more than one repellent, although it cannot be excluded that the variability in response depends on the balancing effect of attractants and repellents.     

Spore types in Mexican and Mesoamerican species of Pteris L. (Pteridaceae)

Spore morphology of 25 Mexican and Central American species in Pteris were studied. This was accomplished using scanning electron and light microscopy. Spores are trilete, tetrahedral, with plane or slightly convex proximal faces, concave only occasionally, and convex or hemispherical distal faces. In addition to these general features and size, we also considered the following traits: (a) cingulum; (b) presence of a commissural flange; (c) types of macro-ornamentation; (d) ornamentation in distal and proximal faces. In general, distal and proximal faces of Pteris spores are divided by a circumfluent cingulum, lacking ornamentation, infrequently not well defined, or interrupted. The laesura have a commissural flange in almost half of the studied species. The most common macro-ornamentation is muriform, less frequently steliform or buliform. Ornamentation is usually different on both sides of the spore. In most of the studied species occasional to abundant globules are present on the spore surface. The combination of these traits allows us to recognise six spore types, which are described in detail. These spore types disagree with groups of species of Neotropical Pteris previously studied using other characteristics (mainly frond architecture and molecular data). Our results show that the use of spore characteristics can help clarify infrageneric taxonomy in Pteris.     

ULTRASTRUCTURE OF THE PSEUDOCAPILLITIUM AND SPORES OF THE MYXOMYCETE LYCOGALA EPIDENDRUM. LICEALES

The pseudocapillitium and spores of L. epidendrum were studied by transmission (TEM) and scanning electron microscopy (SEM). The SEM reveals that the pseudocapillitial surface is covered by bands of “wartlike” processes that alternate with non-ornamented regions. Otherwise, the pseudocapillitium is a hollow structure composed of three regions. The outer region is thin, electron dense and continuous with many irregular processes. Internal to this area is an amorphous region containing scattered electron dense material. The innermost region of the pseudocapillitium is thin, inconspicuous and usually electron dense. L. epidendrum possesses spores that are covered by a surface reticulum consisting of polygonal areas which are continuous with the outermost spore layer. The outer spore layer is thin and electron dense. The inner spore layer is an electron transparent region that contains granular or fibrillar components. Sections of spores showed a dense cytoplasm possessing most of the usual organelles along with microtubules and microbodies.