Internal valves in populations of Meridion circulare from the A'er Mountain region of northeastern China: Implications for taxonomy and systematics

A population of Meridion circulare var.circulare (Greville) C.A.Agardh from Inner Mongolia was found to produce Innenschalen or internal spores.Examination of this population with light and scanning electron microscopy showed morphological differentiation between vegetative and spore morphologies.Vegetative valves typically bear costae and one rimoportula at the headpole.Spores lack costae and have two rimoportulae,one at the headpole and the other at the footpole.There is plasticity in the production of valve morphologies,and a variety of vegetative valve and spore combinations are evident.This population of M.circulare var.circulare has initial valves of over 90μm in length,and all of the initial cells encountered are acostate and bear two rimoportulae.These observations suggest that either spores are the product of sexual reproduction,or that initial valves may be produced parthenogenetically in Meridion.Spores as products of the sexual process have not been reported in diatoms previously,and parthenogenesis in Meridion was reported previously but discounted in other published reports.The plasticity of valve morphologies expressed in M.circulare var.ciculare,between vegetative valves and spores (and back) across a short temporal period suggests that diatoms can alter their cell wall structure dramatically and quickly in response to external variables.     

PUNCTICULATA VERSIFORMIS SP. NOV. AND CYCLOTELLA KATHMANDUENSIS SP. NOV. (BACILLARIOPHYTA), NEW FOSSIL SPECIES FROM MIDDLE PLEISTOCENE LACUSTRINE SEDIMENTS,KATHMANDU, NEPAL HIMALAYA1

New fossil species, Puncticulata versiformis sp. nov. and Cyclotella kathmanduensis sp. nov., are described from lacustrine sediments in the Kathmandu Basin on the southern slope of the Nepal Himalaya. They were dominant in the Middle Pleistocene. Both LM and SEM observations reveal their unique morphological features. Puncticulata versiformis is characterized by (1) various valve outlines (circular, elliptical, or oval), (2) a tangentially undulate central area, (3) a complex alveolar structure composed of three kinds of costae (thick costae, thin costae, and thin and short costae), (4) well‐developed spines (Y‐shaped and tapering) located on one side of the valve face/mantle area junction, and (5) a valvocopula with an extremely undulate margin. The species‐specific feature of C. kathmanduensis is the presence of two kinds of alveolate zones in a single valve: type‐1 zone composed only of normal costae, and type‐2 zone composed of both normal costae and recessed costae bearing fultoportulae. Changes in valve ornamentation occur in these two species from initial valves to vegetative valves. In P. versiformis, the arrangement of areolae with internal domed cribra and fultoportulae in the central area changes from radial rows in the initial valve to groups in the vegetative valve. In the initial valve of C. kathmanduensis, the type‐1 alveolate zone is generally absent.     

Resting spore formation in the antarctic diatoms Coscinodiscus furcatus Karsten and Thalassiosira australis Peragallo

Summary The resting spore morphology of the antarctic diatoms Coscinodiscus furcatus Karsten and Thalassiosira australis Peragallo are described. Both species form endogenous resting spores. The spore valve of C. furcatus differ from those of the vegetative cells primarily by (i) a greater convexity and (ii) a coarser and more distinctly fasciculated areolation. This resting spore is identical to the diatom traditionally identified as C. stellaris var. symbolophorus (Grunow) Jørgensen in the Antarctic. The resting spore of T. australis differs from the vegetative cells by (i) a lack of clusters of strutted processes in a modified ring on valve face, (ii) a coarser areolation and tangential rows of areolae and (iii) a narrower and more simply structured girdle. The resting spore valve of T. australis has been described as belonging to a separate species, Actinocyclus excentricus Peragallo.     

Germination and physiological properties of Frankia spores

Spores from four Frankia strains were isolated and purified to homogeneity. The purified spores were biochemically and physiologically characterized and compared to vegetative cells. Frankia spores exhibited low levels of endogenous respiration that were at least ten-fold lower than the endogenous respiration rate of vegetative cells. The macromolecular content of purified spores and vegetative cells differed. One striking difference among the Frankia spores was their total DNA content. From DAPI staining experiments, only 9% of strain ACN1^AG spore population contained DNA. With strains DC12 and EuI1c, 92% and 67% of their spore population contained DNA. The efficiency of spore germination was correlated to the percentage of the spore population containing DNA. These results suggest that the majority of strain ACN1^AG spores were immature or nonviable. The presence of a solidifying agent inhibited the initial stages of spore germination, but had no effect once the process had been initiated. The optimal incubation temperature for spore germination was 25°C and 30°C for strains DC12 and EuI1c, respectively. A mild heat shock increased the efficiency of spore germination, while root extracts also stimulated spore germination. These results suggest that strains DC12 and EuI1c may be suitable strains for further germination and genetic studies.     

OBSERVATIONS ON CHAETOCEROS BUCEROS (BACILLARIOPHYCEAE), A RARE TROPICAL PLANKTONIC SPECIES COLLECTED FROM THE MEXICAN PACIFIC1

Examination of net plankton samples from the Gulf of Tehuantepec (Mexican Pacific) yielded a rare tropical species of the genus Chaetoceros, C. buceros Karsten. This species is conspicuous because of its relatively large size, type of chain formation, and shape of the terminal setae. Electron microscopic study revealed other interesting characteristics: the intercalary values are more lightly silicified than the terminal valves and show a pattern of costae radiating form the center with various annuli (“central hyaline fields”) in the center of the valve face; both kind of valves are perforated by small poroids. Terminal valves possess several (21–30) slitlike and randomly oriented rimoportulae. Important morphological differences exist between the intercalary and the terminal setae. Morphological characters, comparision with related species, and the systematic position are discussed. A new section of the subgenus Hyalochaete, Conspicua, is proposed to include C. buceros.     

FURTHER OBSERVATIONS AND SOME COMMENTS ON THE FINE STRUCTURE OF THE CENTRIC DIATOM AULACOSEIRA ISLANDICA (BACILLARIOPHYCEAE)1

Using light and electron microscopy, the diatom species Aulacoseira islandica (O. Müll.) Sim. was examined with special emphasis on the following characteristics: structure of the valve areolae, heterovalvy, and distribution of the rimoportulae. The mantle and valve face areolae were pores containing volate occlusions. However, observations only using transmission electron microscopy may result in an incomplete interpretation because of the fragility of the dissected system of volae. Relief valves with a stepped mantle and intaglio valves with a plain mantle occurred. Another form of heterovalvy resulted from the formation of separation valves. Linking valves had spatulate spines while separation valves bore tapering spines. In Aulacoseira, the rimoportulae usually occurred near the “Ringleiste.” The presence of several rimoportulae on the mantle was one of the most striking features in Aulacoseira islandica.     

Thalassiosira antarctica (Bacillariophyceae): Vegetative and resting stage ultrastructure of an ice-related marine diatom

Summary The ultrastructure of T. antarctica var. antarctica vegetative and resting stages are compared using light and transmission electron microscopy. Resting spores contain noticeably more lipid reserves than do vegetative cells. Numerous mitochondria and generally fewer numbers of other organelles are eliminated from spores into an abortive daughter cell when the spore formation division sequence is terminated. The remaining spore contents are a compact arrangement of organelles with lipid bodies predominating. These two stages are thus ultrastructurally distinct, and differences in their chemical composition can be manifested as cytological modifications.     

Germination and outgrowth of Bacillus subtilis and Bacillus licheniformis spores in the gastrointestinal tract of pigs

Aims: To determine if orally ingested Bacillus spores used as probiotics or direct‐fed microbial feed additives germinate and the vegetative cells grow in the gastrointestinal (GI) tract. Methods and Results: Three independent experiments were done to determine if spores of Bacillus licheniformis and Bacillus subtilis germinate and grow in the GI tract of pigs. After a 2 weeks spore‐feeding period, spores were detected in all segments of the GI tract. The lowest number of spores was found in the stomach, increasing in the small intestine to approx. 55% of the dietary inclusion. When spores were withdrawn from the feed, faecal excretion of spores reflected the dietary inclusion, but decreased gradually to the background level after 1 week. By containing spores in short, sealed pieces of dialysis membrane that were orally administered to the pigs, both the number of spores and vegetative cells could be determined by flow cytometry. Spores accounted for 72% of the total counts after 4–6 h in the stomach and proximal part of the small intestine. After 24 h, spores constituted only 12% of the total counts in the stomach, caecum, and mid‐colon. Less spores and more vegetative cells were detected after 24 h, but total counts increased only 2·14‐fold compared to time zero. Conclusions: The experiments showed that 70–90% of dietary‐supplemented Bacillus spores germinate in the proximal part of the pig GI tract, and that only limited outgrowth of the vegetative cell population occurs. The two Bacillus strains can temporarily remain in the GI system, but will be unable to permanently colonize the GI tract. Significance and Impact of the Study: A substantial population of growing vegetative cells in the GI tract is not a prerequisite for the mode of action of Bacillus feed additives and probiotics.     

Ultrastructure of Minchinia Sp. Spores from Shipworms (Teredo Spp.) in the Western North Atlantic, with a Discussion of Taxonomy of the Haplosporidiidae

Electron microscopy of haplosporidan spores from Teredo navalis and T. furcifera revealed 4 distinct membrane-bound extensions, 1 apical extension opposite the opercular hinge, 1 terminal and 2 opposing lateral extensions. These extensions were not continuous with the spore wall, but contained microtubule-like structures and degrading epispore cytoplasm. No other known species in the family Haplosporidiidae is characterized by spores possessing four epispore extensions. There are currently two genera in this family, Minchinia and Haplosporidium. The genus Minchinia includes spores such as those of M. chitonis which bear two epispore cytoplasm extensions. Spores of the genus Haplosporidium have been characterized by spore wall derived filaments. A 3rd group of haplosporidan species with spores ornamented by wrappings have traditionally also been assigned to the genus Haplosporidium. Based on the presence of epispore cytoplasm extensions rather than spore wall filaments, the haplosporidan of Teredo spp. can be placed in the genus Minchinia.     

Germination of Schizosaccharomyces pombe spores separated by zonal centrifugation

Spores from the fission yeast Schizosaccharomyces pombe (H90 strain) were separated from residual vegetative cells into distinct size classes by zonal density centrifugation. Spores were sized photographically and with a Coulter counter. The kinetics of germination were followed by time-lapse photomicrography. The duration of the pre-germination interval was size dependent. Large spores (˜50 μm³) germinated as early as 5 h after resuspension in nutrient media, smaller ones (˜20 μm³) did so at 11 h. The first cell division occurred 4–5 h later regardless of spore size. The large spores divided more synchronously as shown by the occurrence of peaks in the cell plate index at approximately one doubling time intervals.     

Sensitivity of spores and growing cells ofBacillus thuringiensis varisraeliensis andBacillus sphaericus to osmotic variations

EntomopathogenicBacillus thuringiensis var.israelensis (Bti) andBacillus sphaericus (Bf) strains species were studied in relation to their capacity to resist osmotic and nutritional shifts. Their behavior was compared with other bacilli,B. subtilis (Bs) andB. megaterium (Bm). In contrast to these reference strains, vegetative cultures of both species presented a dramatic sensitivity to hyperosmotic shock, independent of the growth period assayed. Subjected to an osmotic and nutritional shift-down (one hundredth dilution in water), Bti cultures resisted it, divided, and sporulated, as did Bm strains, whereas Bf and Bs cultures lysed or died. Spores from these toxic species were of less quality regarding resistance to heat or osmotic strength; but a nontoxic Bti derivative produced spores of better quality. Spore germination was also followed in these strains. The poor spore quality of these species correlated well with their poor survival in field experiments.     

“INTERNAL THECAE” OF EUNOTIA SOLEIROLII (BACILLARIOPHYCEAE): DEVELOPMENT,STRUCTURE AND FUNCTION AS RESTING SPORES1

The “double thecae” or “internal septa” of Eunotia soleirolii (Kütz.) Rabenh, are shown to represent the thecae of resting spores, as characterized by their physiology, as well as morphology. They differ from all resting spores of centric diatoms by the formation of both their valves as a result of unequal cell divisions; and, from the majority of centric spores by the presence of several girdle bands in both their thecae. Spore formation can be induced by high or low pH, high temperature (24 C), and iron, silica, phosphate or nitrate deficiencies, whereas low temperatures defer it. Spores do not germinate directly, but dormancy can be removed by dark treatments (–2 to 15 C) for a minimum of 4–5 wk. Longer dark treatments result in higher germination rates. At 15 C, a minimum of 2 mo is required and 4 mo is better. Heat treatments (27–42 C) are ineffective, but may shorten the dormancy-breaking subsequent cold period. Instances of secondary dormancy, as well as relative dormancy, were observed. Germination usually occurs in the light between 2 and 21 C. An equal division of the spore is followed by unequal divisions of both new cells with only the two resulting large cells being viable. The experiences in the laboratory aided the discovery of stages of spore germination in nature.     

SPORE MORPHOLOGY IN THE DICKSONIACEAE. I. THE GENERA CYSTODIUM,THYRSOPTERIS, AND CULCITA

The most mature spores available in herbarium specimens of the dicksoniaceous genera Cystodium, Thyrsopteris, and Culcita were studied by scanning electron microscopy and light microscopy, and representative specimens were analyzed to determine the number of spores produced per sporangium. Thyrsopteris and Culcita feature 64-spored sporangia, but Cystodium is consistently 32-spored. Spores were analyzed both in their native state as found on the specimens and in a perine-free state achieved by treatment with sodium hydroxide or acetolysis mixture. The sodium hydroxide assay demonstrated the presence of a perine in Cystodium, Thyrsopteris, and Culcita subgenus Culcita, but no evidence of a perine so defined was found in Culcita subgenus Calochlaena. Spores of Cystodium feature a nearly psilate exine overlain by a striate inner perine and a granular outer perine and are in several respects similar to those of Metaxya in the cyatheoid-dicksonioid complex and to those of Saccoloma in the dennstaedtioids. The most mature Thyrsopteris spores available may not have been fully mature. They feature a sparsely distributed, granular perinous layer over a microverrucate sculptine. The latter topography is taken as largely perinous since treatment with sodium hydroxide left a nearly psilate exine. The spore morphologies of Cystodium and Thyrsopteris reinforce the taxonomic distinctness of these monotypic genera indicated by their other characters. The two subgenera of Culcita are very dissimilar in their spore morphologies. The exine in subgenus Culcita ranges from psilate to slightly microverrucate proximally and distally, with varying margo development. Spores of subgenus Calochlaena are strongly differentiated from those of subgenus Culcita by their exine of broad spinules which vary in their degree of lateral fusion to each other and in the granular appearance of their distal surfaces. Spore morphology in Culcita strongly supports the argument of those who would raise its subgenera to generic rank.     

Sporulation and regeneration efficiency of phosphobacteria (<Emphasis Type="Italic">Bacillus megaterium</Emphasis> var <Emphasis Type="Italic">phosphaticum</Emphasis>)

Sporulation in Bacillus megaterium var phosphaticum (PB — 1) was induced using modified nutrient media. This modified medium induced sporulation within 36 h. After spore induction the spores were kept under refrigerated (5°C) and room temperature (32°C) for five months and survival of spores was studied at 15 days intervals by plating them in nutrient agar medium. It was observed that there was not much variation in the storage temperature (5°C & 32°C). The spore cells of Bacillus megaterium var phosphaticum (PB — 1) were observed up to five months of storage under refrigerated (5°C) and room temperature (32°C). Regeneration of spore cells into vegetative cells was studied in tap water, rice gruel, nutrient broth, sterile lignite and sterile water at different concentrations of spore inoculum. The multiplication of sporulated Bacillus megaterium var phosphaticum culture was fast and reached its maximum (29.5 × 10⁸ cfu ml⁻¹) in nutrient broth containing 5 per cent inoculum level.     

Spore morphology of the north Asian members of Cystopteridaceae

Spores of Cystopteridaceae from northern Asia were examined using scanning electron microscopy. To evaluate the utility of spore morphology in the taxonomy of each genus, we examined spores of 14 species: seven species each of Gymnocarpium and Cystopteris. Among these are 12 species occurring in northern Asia and two species from other regions for comparative studies. The study focused particularly on perispore characters and spore size. Spores of all species examined are monolete, bean-shaped, with a range in spore size of 26–56 × 18–37 μm for Cystopteris and 25–48 × 16–34 μm for Gymnocarpium. The perispore is morphologically diverse within Cystopteris, but less so within Gymnocarpium. The perispore of the Cystopteris spores is characterised by folds and spines that are separate or form complex sculptural elements. Sacci, ridges and flanges, sometimes on the same spore, are characteristic of the perispore of Gymnocarpium. Spores have straight laesura over which the perispore forms a crest. The crest represents a high and flat fold, which is entire, foveolate or reticulate.     

INTERACTIVE EFFECTS OF COPPER AND SILICIC ACID ON RESTING SPORE FORMATION AND VIABILITY IN A MARINE DIATOM1

The toxic effects of copper on resting spore formation and viability in the marine diatom Chaetoceros protuberans Lauder were determined both with and without silicic acid added to the medium. With silicic acid available, partial inhibition of resting spore formation occurred only at the highest cupric ion activity (pCu 8.6), while the percentage of cells forming spores at pCu's 10.2 and 11.3 was nearly the same as in the controls. Without silicic acid added to the medium, sporulation was completely inhibited at pCu 8.6 and greatly inhibited, at pCu 10.2. At pCu 11.3 and in the controls, the rate of spore formation was less than 50%. The results indicate that the inhibition of resting spore formation by copper is related to the concentration of silicic acid available to cells of C protuberans. This is consistent with previous studies which show that copper toxicity during vegetative growth involves interference with silicification in diatoms and is a Junction of the silicic acid concentration of the medium. Viable resting spores of C. protuberans were still present in cultures following exposure to elevated copper concentrations during a 100-day incubation period. This indicates that resting spores can serve to enhance diatom survival in areas polluted by heavy metals.     

TIBETIELLA PULCHRA GEN. NOV. ET SP. NOV., A NEW FRESHWATER EPILITHIC DIATOM (BACILLARIOPHYTA) FROM RIVER NUJIANG IN TIBET,CHINA1

Tibetiella pulchra Y. L. Li, D. M. Williams et Metzeltin is described from River Nujiang. Its main features are heteropolar valves, which are linear with capitate ends; narrow sternum, expanding at its center; 2–5 rimoportulae at each apex; uniseriate striae; two short projections arising on the surface above each apical pore plate; and an ocellulimbus, extending from the edge of the valve margin to the edge of the valve surface. Of these characters, it is defined by the 2–5 rimoportulae at each apex. T. pulchra was common to abundant on rocks in the samples examined herein.     

Morphological investigations of the frustule, perizonium and initial valves of the freshwater diatom Achnanthes crenulata Grunow (Bacillariophyceae)

The present study clarifies the fine structure of the vegetative frustules, initial valves and perizonium of Achnanthes crenulata Grunow. The valves of the vegetative cell are distinctly linear‐lanceolate with an undulate margin. The valve face is quite flat and in girdle view is smoothly curved as in species of Gephyria (Bacillariophyceae). However, the valve face of the initial cells is slightly rounded and does not have an undulate margin. Furthermore, the rapheless sternum is centrally positioned along the apical axis of the araphid initial valve. As this taxon develops from auxospore to initial valve, it forms only longitudinal perizonial bands; no transverse bands arise. The perizonium consists of three silicified bands: one large, central longitudinal plate and two bands that underlie this plate; these two bands are either open or closed. This taxon has several conspicuous structures compared to other marine species of Achnanthes, but the structure of the perizonium supports the position of A. crenulata within Achnanthes sensu stricto.     

Cyclotella orientalis sp. nov. (Bacillariophyceae) from South Korea

Cyclotella ortentalis sp. nov, is described from an epilithic sample taken in Lake Imha, located in Kyungsangbuk-do. South Korea. The species is characterized by a conspicuous and short costa regularly extending from each marginal fultoportula to the valve margin. It can be included in the Cyclotella stelligeroid group. The new species can be separated from the most similar species C. stelligera Cleve et Grunov var. stelligera by the more distant position of marginal fultoportulae from the valve margin, the external long tubes of fultoportulae and having short costae. It differs from C. stelligera var. robusta Must, and var. hyalina Hust., in having much denser marginal striae; from C. glomerata H. Bachm., C. pseudostelligera Hust., C. stelligeroides Must, and C. woltereckii Hust., in its much larger valve, coarser marginal striae and short costae with fultoportulae.