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Auxospore

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Shinya Sato – 1st expert on this subject based on the ideXlab platform

  • spermatogenesis and Auxospore structure in the multipolar centric diatom hydrosera
    Journal of Phycology, 2015
    Co-Authors: Masahiko Idei, Shinya Sato, Tamotsu Nagumo, Kensuke Toyoda, Chikako Nagasato, Taizo Motomura, David G. Mann

    Abstract:

    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.

  • Repeated evolution of uniparental reproduction in Sellaphora (Bacillariophyceae)
    European Journal of Phycology, 2014
    Co-Authors: Aloisie Poulíčková, Victor A. Chepurnov, Katharine M Evans, Shinya Sato, David G. Mann

    Abstract:

    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…

  • sexual reproduction and Auxospore structure in diploneis papula bacillariophyta
    Phycologia, 2013
    Co-Authors: Masahiko Idei, Tamotsu Nagumo, Shinya Sato, Tsuyoshi Watanabe, David G. Mann

    Abstract:

    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.

Marina Montresor – 2nd expert on this subject based on the ideXlab platform

  • Genetic and microscopic evidence for sexual reproduction in the centric diatom Skeletonema marinoi.
    Protist, 2014
    Co-Authors: Anna Godhe, Anke Kremp, Marina Montresor

    Abstract:

    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.

  • Plastid Inheritance in the Planktonic Raphid Pennate Diatom Pseudo-nitzschia delicatissima (Bacillariophyceae)
    Protist, 2007
    Co-Authors: Jung Hee Levialdi Ghiron, Marina Montresor, Alberto Amato, Wiebe H. C. F. Kooistra

    Abstract:

    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.

  • Auxospore formation by the silica sinking oceanic diatom fragilariopsis kerguelensis bacillariophyceae 1
    Journal of Phycology, 2006
    Co-Authors: Philipp Assmy, Joachim Henjes, Victor Smetacek, Marina Montresor

    Abstract:

    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 – 3rd expert on this subject based on the ideXlab platform

  • The phylogeny of the diatoms.
    Progress in molecular and subcellular biology, 2020
    Co-Authors: Wiebe H. C. F. Kooistra, David G. Mann, Mario De Stefano, K. Medlin

    Abstract:

    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.

  • Mating system, auxosporulation, species taxonomy and evidence for homoploid evolution in Amphora (Bacillariophyta)
    Phycologia, 2020
    Co-Authors: David G. Mann, Aloisie Poulíčková

    Abstract:

    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…

  • spermatogenesis and Auxospore structure in the multipolar centric diatom hydrosera
    Journal of Phycology, 2015
    Co-Authors: Masahiko Idei, Shinya Sato, Tamotsu Nagumo, Kensuke Toyoda, Chikako Nagasato, Taizo Motomura, David G. Mann

    Abstract:

    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.