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Shinya Sato - One of the best experts on this subject based on the ideXlab platform.
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spermatogenesis and Auxospore structure in the multipolar centric diatom hydrosera
Journal of Phycology, 2015Co-Authors: Masahiko Idei, Shinya Sato, Tamotsu Nagumo, Kensuke Toyoda, Chikako Nagasato, Taizo Motomura, David G. MannAbstract:Spermatogenesis and Auxospore development were studied in the freshwater centric diatom Hydrosera triquetra. Spermatogenesis was unusual, lacking depauperating cell divisions within the spermatogonangium. Instead, a series of mitoses occurred within an undivided cell to produce a multinucleate plasmodium with peripheral nuclei, which then underwent meiosis. 32 or 64 sperm budded off from the plasmodium leaving a large residual cell containing all the chloroplasts. Similar development apparently occurs in Pleurosira, Aulacodiscus, and Guinardia, these being so distantly related that independent evolution of plasmodial spermatogenesis seems likely. After presumed fertilization, the Hydrosera egg cell expanded distally to form a triangular end part. However, unlike in other triangular diatoms (Lithodesmium, Triceratium), the development of triradiate symmetry was not controlled by the "canonical" method of a perizonium that constrains expansion to small terminal areas of the Auxospore wall. Instead, the Auxospore wall lacked a perizonium and possessed only scales and a dense mat of thin, apparently entangled strips of imperforate silica. No such structures have been reported from any other centric diatoms, the closest analogs being instead the incunabular strips of some raphid diatoms (Nitzschia and Pinnularia). Whether these silica structures are formed by the normal method (intracellular deposition within a silica deposition vesicle) is unknown. As well as being more rounded than vegetative cells, the initial cell is aberrant in its structure, since it has a less polarized distribution of the "triptych" pores characteristic of the species.
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Repeated evolution of uniparental reproduction in Sellaphora (Bacillariophyceae)
European Journal of Phycology, 2014Co-Authors: Aloisie Poulíčková, Victor A. Chepurnov, Shinya Sato, Katharine M Evans, David G. MannAbstract:Diatoms possess a remarkable life cycle in which cell size decreases slowly during vegetative cell division and then increases rapidly via special expanding cells called ‘Auxospores’, which are usually formed as a result of biparental sexual reproduction. However, Auxospores are sometimes produced by single unpaired cells, i.e. uniparentally. We examined the nature of uniparental auxosporulation in Sellaphora and used a two-gene dataset to study phylogenetic relationships between uniparental and biparental Sellaphora demes and species; we tested whether uniparental reproduction has evolved once or repeatedly in the genus. In at least two of the uniparental demes auxosporulation occurred through autogamy (i.e. intra-tetrad mating within an undivided cell). Maximum likelihood phylogenies indicated four lineages of uniparental Sellaphora and significance tests of alternative topologies, in which combinations of uniparental Sellaphora were constrained to be monophyletic, coupled with likelihood reconstruction...
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sexual reproduction and Auxospore structure in diploneis papula bacillariophyta
Phycologia, 2013Co-Authors: Masahiko Idei, Tamotsu Nagumo, Shinya Sato, Tsuyoshi Watanabe, David G. MannAbstract:We give a detailed account of sexual reproduction and Auxospore development in the diatom genus Diploneis, principally from clonal cultures of the marine benthic Diploneis papula. Sexual reproduction of D. papula was apparently homothallic. After pairing side to side, cells entered meiosis, and each gametangium produced two gametes. Fertilization was physiologically anisogamous, and both gametes of one gametangium were active and those of the other gametangium passive so that the two zygotes were formed within or close to the ‘passive’ gametangium. Each gamete contained a single chloroplast. The zygote became surrounded by delicate incunabula that contained circular or elliptical scales; this confirmed recent observations that scales (or apparently homologous strips or plates) are quite commonly formed by the zygotes of raphid diatoms. Subsequently, a robust transverse perizonium was built up as the Auxospore expanded, and the perizonium was comprised of a closed primary band at the centre and open secondary bands towards each pole. The ends of the secondary bands, which met along one side of the Auxospore to form a suture as in other pennate diatoms, were curved inwards towards the centre of the Auxospore. Novel features were the extension of the transverse perizonium to cover the tips of the Auxospores (in other diatoms it stopped short of the poles, leaving an apical dome covered only by the incunabula) and a differentiation of the ends of the transverse bands into truncated and prolonged variants, which alternated along the suture. The longitudinal perizonium possessed the same highly conserved configuration as in other pennate diatoms, with a wide bifacial central band flanked by two other bands, which here differed in shape and structure. All the perizonial bands were fimbriate. The possible homology of the longitudinal perizonium to the thecae of vegetative cells was discussed. During formation of the initial cell, the protoplast contracted away from the perizonium, but the latter nevertheless moulded the outline shape of the initial valves, which were more strongly constricted than preAuxospore cells and gametangia. Other Diploneis species produced either one or two gametes per gametangium.
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Heterothallic sexual reproduction in the model diatom Cylindrotheca
European Journal of Phycology, 2013Co-Authors: Pieter Vanormelingen, Koen Sabbe, Shinya Sato, Rosa Trobajo, Bart Vanelslander, Jeroen Gillard, Wim VyvermanAbstract:Cylindrotheca is one of the main model diatoms for ecophysiological and silicification research and is among the few diatoms for which a transformation protocol is available. Knowledge of its life cycle is not available, however, although sexual reproduction has been described for several related genera. In this study, 16 Cylindrotheca closterium strains from a single rbcL lineage were used to describe the life cycle of this marine diatom, including the sexual process and mating system. Similar to other Bacillariaceae, sexual reproduction was induced by the presence of a suitable mating partner, with two gametes produced per gametangium, resulting in two Auxospores per gametangial pair. Differences with other Bacillariaceae include details of cell pairing, gamete behaviour, Auxospore orientation and chloroplast configuration, and perizonium structure. The mating system is heterothallic, since strains fell into two mating type groups, with several strains of one mating type occasionally displaying intraclo...
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gametogenesis and Auxospore development in actinocyclus bacillariophyta
PLOS ONE, 2012Co-Authors: Masahiko Idei, Shinya Sato, Tamotsu Nagumo, Kensuke Toyoda, Keigo Osada, David G. MannAbstract:cGametogenesis and Auxospore development have been studied in detail in surprisingly few centric diatoms. We studied the development of sperm, eggs and Auxospores in Actinocyclus sp., a radially symmetrical freshwater diatom collected from Japan, using LM and electron microscopy of living cultures and thin sections. Actinocyclus represents a deep branch of the ‘radial centric’ diatoms and should therefore contribute useful insights into the evolution of sexual reproduction in diatoms. Spermatogenesis was examined by LM and SEM and involved the formation of two spermatogonia (sperm mother-cells) in each spermatogonangium through an equal mitotic division. The spermatogonia produced a reduced ‘lid’ valve, resembling a large flat scale with irregular radial thickenings. Sperm formation was merogenous, producing four sperm per spermatogonium, which were released by dehiscence of the ‘lid’ valve. The sperm were spindle-shaped with numerous surface globules and, as usual for diatoms, the single anterior flagellum bore mastigonemes. One egg cell was produced per oogonium. Immature eggs produced a thin layer of circular silica scales before fertilization, while the eggs were still contained within the oogonium. Sperm were attracted in large numbers to each egg and were apparently able to contact the egg surface via a gap formed between the long hypotheca and shorter epitheca of the oogonium and a small underlying hole in the scale-case. Auxospores expanded isodiametrically and many new scales were added to its envelope during expansion. Finally, new slightly-domed initial valves were produced at right angles to the oogonium axis, after a strong contraction of the cell away from the Auxospore wall. At different stages, Golgi bodies were associated with chloroplasts or mitochondria, contrasting with the constancy of Golgi–ER–mitochondrion (G-ER-M) units in some other centric diatoms, which has been suggested to have phylogenetic significance. Electron-dense bodies in the vacuole of Actinocyclus are probably acidocalcisomes containing polyphosphate.
Marina Montresor - One of the best experts on this subject based on the ideXlab platform.
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Genetic and microscopic evidence for sexual reproduction in the centric diatom Skeletonema marinoi.
Protist, 2014Co-Authors: Anna Godhe, Anke Kremp, Marina MontresorAbstract:This study provides microscopic and molecular evidence for sexual reproduction in the homothallic centric diatom Skeletonema marinoi isolated from the Baltic Sea. The species is capable of restoring cell size asexually through an Auxospore-like stage. However, cells were sexualized after shifting strains from low (6 PSU) to high (16 PSU) salinity. We observed flagellate male gametes and oogonia, with diameters of 3-4 and 3.2-6.3 μm, respectively. Fertilization took place followed by the formation of round Auxospores surrounded by thin siliceous incunabular scales. Auxosporulation was synchronized, and a maximum of Auxospores was detected on day three following the salinity shift. The proportion of Auxospores to vegetative cells ranged from 0.02 to 0.18. There was a significant correlation between auxosporulation success and inoculum cell density. At lower cell concentration (5,000 cells ml-1), proportionally fewer Auxospores were formed. Auxospores were formed in single strains and in crosses of strains. The proportion of Auxospores differed significantly among strains and crosses of strains. Additionally, we isolated single Auxospores, obtained F1 strains and performed microsatellite based pedigree analysis of parental generations and their offspring. We proved that the Auxospores were formed sexually, either by inter- or by intra-strain fertilization.
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Plastid Inheritance in the Planktonic Raphid Pennate Diatom Pseudo-nitzschia delicatissima (Bacillariophyceae)
Protist, 2007Co-Authors: Jung Hee Levialdi Ghiron, Marina Montresor, Alberto Amato, Wiebe H. C. F. KooistraAbstract:Plastid inheritance was followed during sexual reproduction in the raphid pennate diatom Pseudo-nitzschia delicatissima , using rbc L haplotypes as plastid identification tools. Pseudo-nitzschia species are dioecious and show functional anisogamy with ‘male’ mating type+(PNd + ) cells and ‘female’ PNd − cells. Vegetative cells possess two plastids. In P. delicatissima , meiosis results in two gametes that both contribute two plastids to the zygote. The latter initially contains four plastids, but during Auxospore development two of these four seem to disappear, and the initial cell emerging from the Auxospore appears to contain only two. Here we assessed if the plastids are inherited strictly unipaternally, strictly biparentally, or randomly. We traced the source of the plastids in the F 1 generation by using PNd + and PNd − parental strains with different rbc L genotypes, here denoted AA (homoplastidial, with two plastids of rbc L haplotype A) and BB (homoplastidial; two plastids of haplotype B). Results showed that 16 out of 96 strains raised each from single F 1 cells had retained two paternal (PNd + ) plastids, 20 had two maternal (PNd − ) plastids and the remaining 60 had one maternal and one paternal plastid. This pattern is in accordance with the hypothesis that either two of the four plastids are eliminated during Auxospore formation, or that all plastids are retained in the Auxospore and segregate in pairs joining at random during the first mitotic division of the initial cell. Heteroplastidic F 1 -strains retained the AB genotype throughout the vegetative phase of their life cycle. The finding that 60 out of 96 F 1 strains were heteroplastidial contrasts with an absence of such genotypes in our strains raised from single cells sampled in the Gulf of Naples.
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Auxospore formation by the silica sinking oceanic diatom fragilariopsis kerguelensis bacillariophyceae 1
Journal of Phycology, 2006Co-Authors: Philipp Assmy, Joachim Henjes, Victor Smetacek, Marina MontresorAbstract:Size restoration by the Auxospore that develops from the zygote is a crucial stage in diatom life cycles. However, information on sexual events in pelagic diatom species is very limited. We report for the first time Auxospore formation by the pennate diatom Fragilariopsis kerguelensis (O'Hara) Hustedt during an iron-induced bloom in the Southern Ocean (EIFEX, European Iron Fertilization EXperiment). Auxospores of F. kerguelensis resembled those described for Pseudo-nitzschia species. The Auxospore was characterized by an outer coating, the perizonium; two caps, one at each distal end; and four chloroplasts, one at each end and two in the central part. Different stages of Auxospore elongation were recorded, with a length of 24–91 μm, but only the largest Auxospores contained the initial cell, whose apical axis ranged between 76 and 90 μm. Gametangial cell walls were often attached to the Auxospores and ranged from 10 to 31 μm in length. Auxospore abundances were consistently higher in the fertilized patch, where an increase in the F. kerguelensis population was observed, as compared with surrounding waters.
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Auxospore FORMATION BY THE SILICA‐SINKING, OCEANIC DIATOM FRAGILARIOPSIS KERGUELENSIS (BACILLARIOPHYCEAE)1
Journal of Phycology, 2006Co-Authors: Philipp Assmy, Joachim Henjes, Victor Smetacek, Marina MontresorAbstract:Size restoration by the Auxospore that develops from the zygote is a crucial stage in diatom life cycles. However, information on sexual events in pelagic diatom species is very limited. We report for the first time Auxospore formation by the pennate diatom Fragilariopsis kerguelensis (O'Hara) Hustedt during an iron-induced bloom in the Southern Ocean (EIFEX, European Iron Fertilization EXperiment). Auxospores of F. kerguelensis resembled those described for Pseudo-nitzschia species. The Auxospore was characterized by an outer coating, the perizonium; two caps, one at each distal end; and four chloroplasts, one at each end and two in the central part. Different stages of Auxospore elongation were recorded, with a length of 24–91 μm, but only the largest Auxospores contained the initial cell, whose apical axis ranged between 76 and 90 μm. Gametangial cell walls were often attached to the Auxospores and ranged from 10 to 31 μm in length. Auxospore abundances were consistently higher in the fertilized patch, where an increase in the F. kerguelensis population was observed, as compared with surrounding waters.
David G. Mann - One of the best experts on this subject based on the ideXlab platform.
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The phylogeny of the diatoms.
Progress in molecular and subcellular biology, 2020Co-Authors: Wiebe H. C. F. Kooistra, David G. Mann, Mario De Stefano, K. MedlinAbstract:Diatoms are among the most diverse groups of eukaryotic microorganisms and there are probably well in excess of 100,000 species (Mann and Droop 1996).The beauty and unbelievable variation of their intricately shaped and ornamented silica cell wall, called the frustule, have attracted taxonomists and naturalists alike (Round et al. 1990). More recently, ultrastructure, sexual reproduction, and the development of their unique type of zygote, called the Auxospore, have also become the focus of research.
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Mating system, auxosporulation, species taxonomy and evidence for homoploid evolution in Amphora (Bacillariophyta)
Phycologia, 2020Co-Authors: David G. Mann, Aloisie PoulíčkováAbstract:Abstract Mann D.G. and PoulIckova A. 2010. Mating system, auxosporulation, species taxonomy and evidence for homoploid evolution in Amphora (Bacillariophyta). Phycologia 49: 183–201. DOI: 10.2216/09-08.1 Cytological characteristics of the mitotic cycle, sexual reproduction and Auxospore formation are described for three members of the type group of Amphora: A. ovalis, A. copulata and A. minutissima. All have a single lobed ventral chloroplast, nuclei with granular heterochromatin and a single nucleolus (unusually large in A. ovalis). Amphora copulata is heterothallic, with two mating types that do not differ in gamete behaviour. All three species reproduce allogamously via fusion of two rearranged gametes per gametangium to produce elongate zygotes enclosed within the volume delimited by the gametangial thecae. Pairing is strictly via the ventral sides of the cells, with tight apposition of the cells, and expansion of the Auxospores is strictly perpendicular to the gametangium long axes. Comparisons are m...
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spermatogenesis and Auxospore structure in the multipolar centric diatom hydrosera
Journal of Phycology, 2015Co-Authors: Masahiko Idei, Shinya Sato, Tamotsu Nagumo, Kensuke Toyoda, Chikako Nagasato, Taizo Motomura, David G. MannAbstract:Spermatogenesis and Auxospore development were studied in the freshwater centric diatom Hydrosera triquetra. Spermatogenesis was unusual, lacking depauperating cell divisions within the spermatogonangium. Instead, a series of mitoses occurred within an undivided cell to produce a multinucleate plasmodium with peripheral nuclei, which then underwent meiosis. 32 or 64 sperm budded off from the plasmodium leaving a large residual cell containing all the chloroplasts. Similar development apparently occurs in Pleurosira, Aulacodiscus, and Guinardia, these being so distantly related that independent evolution of plasmodial spermatogenesis seems likely. After presumed fertilization, the Hydrosera egg cell expanded distally to form a triangular end part. However, unlike in other triangular diatoms (Lithodesmium, Triceratium), the development of triradiate symmetry was not controlled by the "canonical" method of a perizonium that constrains expansion to small terminal areas of the Auxospore wall. Instead, the Auxospore wall lacked a perizonium and possessed only scales and a dense mat of thin, apparently entangled strips of imperforate silica. No such structures have been reported from any other centric diatoms, the closest analogs being instead the incunabular strips of some raphid diatoms (Nitzschia and Pinnularia). Whether these silica structures are formed by the normal method (intracellular deposition within a silica deposition vesicle) is unknown. As well as being more rounded than vegetative cells, the initial cell is aberrant in its structure, since it has a less polarized distribution of the "triptych" pores characteristic of the species.
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Repeated evolution of uniparental reproduction in Sellaphora (Bacillariophyceae)
European Journal of Phycology, 2014Co-Authors: Aloisie Poulíčková, Victor A. Chepurnov, Shinya Sato, Katharine M Evans, David G. MannAbstract:Diatoms possess a remarkable life cycle in which cell size decreases slowly during vegetative cell division and then increases rapidly via special expanding cells called ‘Auxospores’, which are usually formed as a result of biparental sexual reproduction. However, Auxospores are sometimes produced by single unpaired cells, i.e. uniparentally. We examined the nature of uniparental auxosporulation in Sellaphora and used a two-gene dataset to study phylogenetic relationships between uniparental and biparental Sellaphora demes and species; we tested whether uniparental reproduction has evolved once or repeatedly in the genus. In at least two of the uniparental demes auxosporulation occurred through autogamy (i.e. intra-tetrad mating within an undivided cell). Maximum likelihood phylogenies indicated four lineages of uniparental Sellaphora and significance tests of alternative topologies, in which combinations of uniparental Sellaphora were constrained to be monophyletic, coupled with likelihood reconstruction...
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sexual reproduction and Auxospore structure in diploneis papula bacillariophyta
Phycologia, 2013Co-Authors: Masahiko Idei, Tamotsu Nagumo, Shinya Sato, Tsuyoshi Watanabe, David G. MannAbstract:We give a detailed account of sexual reproduction and Auxospore development in the diatom genus Diploneis, principally from clonal cultures of the marine benthic Diploneis papula. Sexual reproduction of D. papula was apparently homothallic. After pairing side to side, cells entered meiosis, and each gametangium produced two gametes. Fertilization was physiologically anisogamous, and both gametes of one gametangium were active and those of the other gametangium passive so that the two zygotes were formed within or close to the ‘passive’ gametangium. Each gamete contained a single chloroplast. The zygote became surrounded by delicate incunabula that contained circular or elliptical scales; this confirmed recent observations that scales (or apparently homologous strips or plates) are quite commonly formed by the zygotes of raphid diatoms. Subsequently, a robust transverse perizonium was built up as the Auxospore expanded, and the perizonium was comprised of a closed primary band at the centre and open secondary bands towards each pole. The ends of the secondary bands, which met along one side of the Auxospore to form a suture as in other pennate diatoms, were curved inwards towards the centre of the Auxospore. Novel features were the extension of the transverse perizonium to cover the tips of the Auxospores (in other diatoms it stopped short of the poles, leaving an apical dome covered only by the incunabula) and a differentiation of the ends of the transverse bands into truncated and prolonged variants, which alternated along the suture. The longitudinal perizonium possessed the same highly conserved configuration as in other pennate diatoms, with a wide bifacial central band flanked by two other bands, which here differed in shape and structure. All the perizonial bands were fimbriate. The possible homology of the longitudinal perizonium to the thecae of vegetative cells was discussed. During formation of the initial cell, the protoplast contracted away from the perizonium, but the latter nevertheless moulded the outline shape of the initial valves, which were more strongly constricted than preAuxospore cells and gametangia. Other Diploneis species produced either one or two gametes per gametangium.
Irena Kaczmarska - One of the best experts on this subject based on the ideXlab platform.
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Effect of light: dark cycles and cell apical length on the sexual reproduction of the pennate diatom Pseudo-nitzschia multiseries (Bacillariophyceae) in culture
Phycologia, 2020Co-Authors: Margot Hiltz, Stephen S. Bates, Irena KaczmarskaAbstract:Abstract Sexual reproduction in the domoic acid–producing pennate diatom Pseudo-nitzschia multiseries (Hasle) Hasle is dioecious and involves pairing of two morphologically isogamous parent cells (gametangia) and the production of two gametes per gametangium. Gamete fusion leads to the formation of zygotes, which elongate into Auxospores. Within each Auxospore, a long initial cell is formed, thereby restoring the longer cell sizes in the population. Mating experiments were performed by mixing active “male” and passive “female” cells from pairs of clones and growing them under different light : dark (L : D) cycle regimes. Two pairs of clones were studied: one pair was ontogenetically older and therefore shorter than the other. After mating, the relative abundance of gametes, zygotes, Auxospores, and initial cells was determined for a minimum of four consecutive days. Cell size, which reflects population age, influences sexualization. The short-celled clones had a lower maximum proportion of gametes per veg...
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Evolution of the Diatoms: V. Morphological and Cytological Support for the Major Clades and a Taxonomic Revision.
Phycologia, 2020Co-Authors: Linda K Medlin, Irena KaczmarskaAbstract:Abstract Phylogenetic reconstructions of the diatoms have been inferred with the 18S and 16S ribosomal RNA genes. Previous studies have shown that the group is divided into two major clades, with support coming initially from the arrangement of the Golgi bodies inside the cells in extant taxa. Features of extinct taxa that also support these clades can be found in the earliest fossil record of the diatoms and include the presence or absence of a central structure in the valve wall and the type of peripheral linking mechanisms between cells. Here we demonstrate that the general pattern of the Auxospore expansion and the structure of their walls, the structure of the pyrenoid and the ultrastructure of the spermatozoid further support the molecular clades. Given the combined molecular and morphological support, we propose two new subdivisions (Coscinodiscophytina and Bacillariophytina), emend the classes Coscinodiscophyceae and Bacillariophyceae and propose a new class, the Mediophyceae for the bipolar centr...
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Auxosporulation in Biddulphia tridens (Ehrenberg) Ehrenberg (Mediophyceae, Bacillariophyta)
European Journal of Phycology, 2020Co-Authors: Brajogopal Samanta, Irena Kaczmarska, James M. EhrmanAbstract:ABSTRACTWe documented male and female gametogenesis, Auxospore structure and development of the biddulphioid diatom species Biddulphia tridens (Ehrenberg) Ehrenberg, a close relative of the generit...
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Auxospore wall structure and postsexual valve morphology in Rhabdonema minutum Kützing
Plant and Fungal Systematics, 2019Co-Authors: Irena Kaczmarska, James M. EhrmanAbstract:AbstractSeveral decades ago, three members of the araphid pennate genus Rhabdonema (R. adriaticum, R. arcuatum, R. minutum) were the first araphid diatoms studied using cultures and electron microscopical methods to determine Auxospore structure and development. Of these, R. minutum was the least documented at that time. None have been reinvestigated until now. Here we present the structural elements of the mature Auxospore and the initial and postsexual valve characteristics of R. minutum. Although in general the Auxospore wall of this diatom is similar to that of the two other species examined (to the extent that they were documented), there are intriguing differences. Most unanticipated is the structure of the primary band of the longitudinal perizonium, which shows remarkable similarities to the raphid pennate diatom valve. The evolutionary implications of such a similarity are considered.
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Auxosporulation in Chaetoceros acadianus sp. nov. (Bacillariophyceae), a new member of the Section Compressa
European Journal of Phycology, 2019Co-Authors: Irena Kaczmarska, James M. Ehrman, Brajogopal Samanta, Ellen M. A. PorcherAbstract:We document the fine structure of Auxospores in a Chaetoceros species isolated from the Acadian coast of New Brunswick, Canada. Auxospore development in this species occurs in a terminal rather than lateral position, a characteristic never before observed in this genus. Our observations suggest that auxosporulation was uniparental, probably an extreme form of autogamy with sister nuclei fusing following meiosis II. Mature Auxospores were adze-shaped to sub-globular and contained both scales and transverse perizonia in their walls. The transverse perizonial band structure was similar to longitudinal perizonial bands found in other species of Chaetoceros and differed from the pinnate bands of pennate transverse perizonia, which consisted of a central rib and bilateral fimbria. Instead, the band structure in C. acadianus was more similar to unilateral fimbriate bands in cymatosiroids. We also propose that our diatom represents a species new to science and is a member of the Chaetoceros Section Compressa. We provide its morphological, molecular and reproductive characterization.
Philipp Assmy - One of the best experts on this subject based on the ideXlab platform.
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Auxospore formation by the silica sinking oceanic diatom fragilariopsis kerguelensis bacillariophyceae 1
Journal of Phycology, 2006Co-Authors: Philipp Assmy, Joachim Henjes, Victor Smetacek, Marina MontresorAbstract:Size restoration by the Auxospore that develops from the zygote is a crucial stage in diatom life cycles. However, information on sexual events in pelagic diatom species is very limited. We report for the first time Auxospore formation by the pennate diatom Fragilariopsis kerguelensis (O'Hara) Hustedt during an iron-induced bloom in the Southern Ocean (EIFEX, European Iron Fertilization EXperiment). Auxospores of F. kerguelensis resembled those described for Pseudo-nitzschia species. The Auxospore was characterized by an outer coating, the perizonium; two caps, one at each distal end; and four chloroplasts, one at each end and two in the central part. Different stages of Auxospore elongation were recorded, with a length of 24–91 μm, but only the largest Auxospores contained the initial cell, whose apical axis ranged between 76 and 90 μm. Gametangial cell walls were often attached to the Auxospores and ranged from 10 to 31 μm in length. Auxospore abundances were consistently higher in the fertilized patch, where an increase in the F. kerguelensis population was observed, as compared with surrounding waters.
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Auxospore FORMATION BY THE SILICA‐SINKING, OCEANIC DIATOM FRAGILARIOPSIS KERGUELENSIS (BACILLARIOPHYCEAE)1
Journal of Phycology, 2006Co-Authors: Philipp Assmy, Joachim Henjes, Victor Smetacek, Marina MontresorAbstract:Size restoration by the Auxospore that develops from the zygote is a crucial stage in diatom life cycles. However, information on sexual events in pelagic diatom species is very limited. We report for the first time Auxospore formation by the pennate diatom Fragilariopsis kerguelensis (O'Hara) Hustedt during an iron-induced bloom in the Southern Ocean (EIFEX, European Iron Fertilization EXperiment). Auxospores of F. kerguelensis resembled those described for Pseudo-nitzschia species. The Auxospore was characterized by an outer coating, the perizonium; two caps, one at each distal end; and four chloroplasts, one at each end and two in the central part. Different stages of Auxospore elongation were recorded, with a length of 24–91 μm, but only the largest Auxospores contained the initial cell, whose apical axis ranged between 76 and 90 μm. Gametangial cell walls were often attached to the Auxospores and ranged from 10 to 31 μm in length. Auxospore abundances were consistently higher in the fertilized patch, where an increase in the F. kerguelensis population was observed, as compared with surrounding waters.