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Taizo Motomura - One of the best experts on this subject based on the ideXlab platform.
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Is the life cycle of Derbesia (Chlorophyta) heterokaryotic? – Response to the commentary of Schnetter and Eckhardt (2000)
Phycologia, 2020Co-Authors: Taizo Motomura, Terunobu IchimuraAbstract:Abstract In response to a commentary on our previous work by Schnetter & Eckhardt [Phycologia 39: 355–357 (2000)], we reinvestigated the question of whether nuclear fusion takes place immediately after Plasmogamy in Derbesia. We also reexamined the first mitosis in the zygote that develops from the fusion of a male and a female gamete, As in our previous reports, we observed karyogamy to follow directly after Plasmogamy and normal mitosis of the single zygote nucleus. Our strain of D. tenuissima is therefore a diplohaplont and lacks a heterokaryotic phase in the life cycle, in contrast to what is claimed to occur in various species and strains of Derbesia by Schnetter and co-workers.
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Selective disappearance of maternal centrioles after fertilization in the anisogamous brown alga Cutleria cylindrica (Cutleriales, Phaeophyceae): Paternal inheritance of centrioles is universal in the brown algae
Phycological Research, 1998Co-Authors: Chikako Nagasato, Taizo Motomura, Terunobu IchrmuraAbstract:SUMMARY The behavior of centrioles in zygotes and female gametes developing parthenogenetically in the anisogamous brown alga Cutieria cyiindrica Okamura was studied using electron and immunofluorescence microscopy. Two pairs of centrioles, detected using anti-centrin antibody, were observed in the vicinity of the male and female nuclei, respectively, just after Plasmogamy. The fluorescence intensity of one of the two centrin foci became weak 6 h after Plasmogamy and finally disappeared. It was impossible to determine whether the male- or female-derived centrioles disappeared in zygotes, because there was nothing to detect morphological differences between the two centrioles. However, a prominent anti-centrin staining focus was located at the condensed male nucleus in zygotes in which karyogamy had not occurred yet. As a result, it was considered that the maternally inherited centrioles had selectively disappeared during development in C. cylindrica. The paternal inheritance of centrioles in zygotes was also confirmed by electron microscopy. Considering previous observations from oogamous and isogamous species of brown algae, we concluded that the paternal inheriance of centrioles could be universal in the brown algae.
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karyogamy follows Plasmogamy in the life cycle of derbesia tenuissima chlorophyta
Phycologia, 1998Co-Authors: Taizo Motomura, Terunobu IchimuraAbstract:AbstractFertilization in a multinucleate siphonous green alga, Derbesia tenuissima (Moris et De Notaris) Crouan, was studied using light, fluorescence, and electron microscopy. The male nucleus was...
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PREMATURE CHROMOSOME CONDENSATION OF THE KARYOGAMY-BLOCKED SPERM PRONUCLEUS IN THE FERTILIZATION OF FUCUS DISTICHUS (FUCALES, PHAEOPHYCEAE)1
Journal of Phycology, 1995Co-Authors: Taizo MotomuraAbstract:Mitosis of egg and sperm pronuclei of Fucus distichus subsp. evanescens (C. Agardh)Powell was examined by fluorescence and electron microscopy when migration of the sperm pronucleus and, as a result, karyogamy were blocked by colchicine treatment after Plasmogamy. Chromosome condensation was obsewed in both pronuclei Microspectrophotometric studies after staining the nuclei with mithramycin A clearly showed that DNA synthesis ocurred in the egg pronucleus but not in the sperm pronucleus. This means that chromosomes condensed prematurely in the sperm pronucleus (premature chromosome condensation). In some cases, the egg chromosomes became arranged on a metaphase plate, whereas the sperm chromosomes lay scattered near the egg pronucleus. Immuno fluorescence microscopy using anti-β-tubulin antibody confirmed that a normal spindle was formed at the egg pronucleus. A pair of centrioles existed at the two poles of this spindle. The sperm nuclear membrane disappeared, and microtubules radiated to the sperm chromosomes from one pole of the egg spindle.
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Electron and immunofluorescence microscopy on the fertilization of Fucus distichus (Fucales, Phaeophyceae)
Protoplasma, 1994Co-Authors: Taizo MotomuraAbstract:Processes of fertilization and zygote development inFucus distichus were studied by indirect immunofluorescence microscopy using anti-β tubulin antibody and electron microscopy. Just after Plasmogamy, sperm aster formation occurs during migration of a sperm nucleus toward an egg nucleus at the center of cytoplasm. Only sparse microtubules (MTs) exist around the egg nucleus. The sperm aster can be observed till karyogamy, but afterwards vanishes. Accompanying sperm aster formation, cortical MTs which are reticulately arranged develop further in the zygotes. In 4 h-old zygotes, characteristic structures which are composed of fine granular masses and consist of intermixed dense and lighter staining areas appear around the nucleus. These structures cannot be detected with anti-β tubulin immunofluorescence microscopy. The two centrioles derived from the sperm separate and migrate to both poles. In 4 h-and 8 h-old zygotes, there are no defined MT foci around the zygote nucleus and MTs radiate from the circumference of it. In 12 h-old zygotes, each centriole has migrated to the poles and derivative centrioles are generated. The fine granular masses also migrate to both poles and finally disappear accompanying the appearance of numerous MTs radiating from the poles. Therefore, two distinct MT foci appear from 12 h onwards. Progressive stages of nuclear division were also examined with electron and immunofluorescence microscopy in 16 h-old zygotes. The sperm chloroplast with an eyespot and the sperm mitochondria with an intercristal tubular structure, which are distinctive from those of egg, can be detected after Plasmogamy and karyogamy. The sperm chloroplast is still present in 16 h-old zygotes.
John A. West - One of the best experts on this subject based on the ideXlab platform.
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MECHANISMS CONTROLLING NUCLEAR MIGRATION ALONG THE TRICHOGYNE IN THE RED ALGA, BOSTRYCHIA MORITZIANA (RHODOMELACEAE, RHODOPHYTA)
Journal of Phycology, 2020Co-Authors: Sarah M. Wilson, Jeremy D. Pickett-heaps, John A. WestAbstract:Sexual reproduction in red algae has been studied for over a century primarily for taxonomic purposes. Despite this interest, only recently have the critical events of fertilisation been revealed. Time-lapse video microscopy techniques have been used to document the stages in the fertilization process within Bostrychia moritziana. Once Plasmogamy between a trichogyne and spermatium is achieved, two differentiated male nuclei may enter the trichogyne. One of the two migrates to the carpogonium while the other travels in the opposite direction towards the trichogyne tip and plays no further role in fertilisation. The precise mechanism governing this bidirectional movement of male nuclei is unknown, but the cytoskeleton is believed to be involved. Fluorescent staining and confocal microscopy shows an extensive arrangement of actin filaments in spermatia and along trichogynes yet microtubules are only evident in dividing spermatia. Actin filaments appear to be involved in Plasmogamy and ensheath male nuclei as they migrate from the spermatium and as they travel along the trichogyne in either direction. Drug-inhibition studies and UV-microbeam irradiation indicate nuclear migration along trichogynes is actin/myosin dependent
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Time-lapse videomicroscopy of fertilization and the actin cytoskeleton in Murrayella periclados (Rhodomelaceae, Rhodophyta)
Phycologia, 2020Co-Authors: Sarah M. Wilson, John A. West, Jeremy D. Pickett-heapsAbstract:Abstract Fertilization in Murrayella periclados was followed, using time-lapse videomicroscopy, from spermatial release to nuclear migration along the trichogyne. The localization of actin filaments in male and female gametes is shown during stages of fertilization using fluorescence microscopy techniques. These observations are compared to fertilization and actin localization in another red alga, Bostrychia moritziana. The results suggest that the fertilization events are generally the same in both species and that the actin cytoskeleton partly governs sexual Plasmogamy and nuclear migration.
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time lapse video observations on sexual Plasmogamy in the red alga bostrychia
European Journal of Phycology, 1998Co-Authors: J D Pickettheaps, John A. WestAbstract:In the red alga Bostrychia moritziana, release of spermatia is triggered by slight osmotic shock; they emerge under pressure apparently generated by swelling of the mucilaginous sheath. Spermatia adhere tenaciously to trichogynes of the carpogonium. Adhesion triggers spermatial mitosis, which is complete in about 30–45 min; there is no cytokinesis and the binucleate spermatium becomes vacuolated. The delicate, dynamic trichogyne cytoplasm contains complex membranous components and vacuoles. At the contact zone, the trichogyne and spermatial wall erode, forming a pore, and cytoplasmic continuity (Plasmogamy) is achieved after about 50–70 min. Many trichogynes rupture during these events because of inadequate structural connection with the spermatia. Normally, both spermatial nuclei enter the trichogyne in sequence; rarely, both nuclei enter together. Entrance is rapid, and the nuclei often become thin and greatly elongated as each squeezes through the narrow pore into the trichogyne. Once inside, each nucl...
T. Motomura - One of the best experts on this subject based on the ideXlab platform.
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Electron and immunofluorescence microscopy on the fertilization ofFucus distichus (Fucales, Phaeophyceae)
Protoplasma, 1994Co-Authors: T. MotomuraAbstract:Processes of fertilization and zygote development in Fucus distichus were studied by indirect immunofluorescence microscopy using anti-β tubulin antibody and electron microscopy. Just after Plasmogamy, sperm aster formation occurs during migration of a sperm nucleus toward an egg nucleus at the center of cytoplasm. Only sparse microtubules (MTs) exist around the egg nucleus. The sperm aster can be observed till karyogamy, but afterwards vanishes. Accompanying sperm aster formation, cortical MTs which are reticulately arranged develop further in the zygotes. In 4 h-old zygotes, characteristic structures which are composed of fine granular masses and consist of intermixed dense and lighter staining areas appear around the nucleus. These structures cannot be detected with anti-β tubulin immunofluorescence microscopy. The two centrioles derived from the sperm separate and migrate to both poles. In 4 h-and 8 h-old zygotes, there are no defined MT foci around the zygote nucleus and MTs radiate from the circumference of it. In 12 h-old zygotes, each centriole has migrated to the poles and derivative centrioles are generated. The fine granular masses also migrate to both poles and finally disappear accompanying the appearance of numerous MTs radiating from the poles. Therefore, two distinct MT foci appear from 12 h onwards. Progressive stages of nuclear division were also examined with electron and immunofluorescence microscopy in 16 h-old zygotes. The sperm chloroplast with an eyespot and the sperm mitochondria with an intercristal tubular structure, which are distinctive from those of egg, can be detected after Plasmogamy and karyogamy. The sperm chloroplast is still present in 16 h-old zygotes.
David G Mann - One of the best experts on this subject based on the ideXlab platform.
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Sperm ultrastructure in the diatoms Melosira and Thalassiosira and the significance of the 9 + 0 configuration
Protoplasma, 2013Co-Authors: Masahiko Idei, Keigo Osada, Shinya Sato, Takeshi Nakayama, Tamotsu Nagumo, David G MannAbstract:The most complete account to date of the ultrastructure of flagellate cells in diatoms is given for the sperm of Thalassiosira lacustris and Melosira moniliformis var. octogona , based on serial sections. The sperm are uniflagellate, with no trace of a second basal body, and possess a 9 + 0 axoneme. The significance of the 9 + 0 configuration is discussed: lack of the central pair microtubules and radial spokes does not compromise the mastigoneme-bearing flagellum’s capacity to perform planar beats and thrust reversal and may perhaps be related to sensory/secretory function of the sperm flagellum during Plasmogamy. The basal bodies of diatoms are confirmed to contain doublets rather than triplets, which may correlate with the absence of some centriolar proteins found in most cells producing active flagella. Whereas Melosira possesses a normal cartwheel structure in the long basal body, no such structure is present in Thalassiosira , which instead possesses ‘intercalary fibres’ linking the basal body doublets. No transitional helices or transitional plates are present in either species studied. Cones of microtubules are associated with the basal body and partially enclose the nucleus in M. moniliformis and T. lacustris . They do not appear to be true microtubular roots and may arise through transformation of the meiosis II spindle. A close association between cone microtubules and tubules containing mastigonemes may indicate a function in intracellular mastigoneme transport. No correlation can yet be detected between methods of spermatogenesis and phylogeny in diatoms, contrary to previous suggestions.
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Congruence of morphological, reproductive and ITS rDNA sequence data in some Australasian Eunotia bilunaris (Bacillariophyta)
European Journal of Phycology, 2007Co-Authors: Pieter Vanormelingen, David G Mann, Victor A. Chepurnov, Sylvie Cousin, Wim VyvermanAbstract:Clones identified as Eunotia bilunaris were isolated from two freshwater habitats in New Zealand and one in Tasmania. Experimental studies of sexual reproduction showed that the mating system was strictly heterothallic. All clones were morphologically similar and, in mixtures of compatible clones, were able to produce a viable F1, regardless of geographical origin. There was nevertheless some geographically related variation in ITS rDNA sequences, suggesting that dispersal and concerted evolution are unable to prevent allopatric divergence. Isolates from two of the three localities also showed significant ITS polymorphisms. Auxosporulation followed a similar pattern to that in other Eunotia species, being isogamous with a single functional gamete per gametangium; Plasmogamy was effected via two fusing papillae. Details of auxospore structure, initial cell size, and vegetative valve metrics (width, striation densities) show that conspecificity with a recently studied European E. bilunaris is doubtful. The ...
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Auxosporulation of Licmophora communis (Bacillariophyta) and a review of mating systems and sexual reproduction in araphid pennate diatoms
Phycological Research, 2004Co-Authors: Victor A. Chepurnov, David G MannAbstract:SUMMARY The auxosporulation of Licmophora communis is allogamous and dioecious. Pairing between sessile, shortstalked cells of compatible clones is followed by meiosis and gametogenesis, to form two gametes in each gametangium. The behavior of the gametes differs between the gametangia. In the male gametangium, the gametes detach from the frustule, round up, and migrate out of the gametangium after its dehiscence at the broader, unattached pole. In the female gametangium, both gametes remain attached to the adjacent theca over almost their whole length and do not move. Plasmogamy therefore occurs within the female gametangium and this is where the zygotes are formed and remain. After fertilization, the zygotes detach from the thecae of the female gametangia, contract, and become ellipsoidal, before expanding parallel to the apical axis of the gametangium. We review the types of auxosporulation in other pennate diatoms and the systems used for classifying these. Dioecy and cis-type anisogamy (in which one gametangium produces active gametes and the other produces passive gametes), as in L. communis, are probably primitive within the pennate group (although there is no information on the AsterionellopsisRhaphoneis clade). However, size can also be restored in various araphid pennates by allogamous sexual reproduction involving the formation of only one gamete per gametangium, or in rare cases by automixis or (apparently) vegetative enlargement.
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MATING SYSTEM, SEXUAL REPRODUCTION, AND AUXOSPORULATION IN THE ANOMALOUS RAPHID DIATOM EUNOTIA (BACILLARIOPHYTA)1
Journal of Phycology, 2003Co-Authors: David G Mann, Victor A. Chepurnov, Masahiko IdeiAbstract:The diatom genus Eunotia is unusual among raphid diatoms in having a raphe system consisting of two short slits that are not integrated into the primary pattern center. This and other characteristics, particularly the presence of rimoportulae, are consistent with the hypothesis that Eunotia is a basal lineage within the raphid group. We studied auxosporulation in E. bilunaris (Ehrenberg) Mills and E. tropica Hustedt for comparison with other raphid pennate diatoms and with araphid pennates; E. bilunaris was studied in parental and F1 generations. Like araphid pennates, E. bilunaris and E. tropica are heterothallic. Clones of the same mating type did not interact sexually, and intraclonal sexual reproduction was absent or very rare. Clones retained the same sex throughout the life cycle, as shown by experiments using abrupt size reduction to produce clones of similar age but different size and using subclones derived from a single initial cell within six mitotic generations. Unlike in araphid pennate diatoms, in the Eunotia species the gametes are not visibly or behaviorally differentiated. Gametogenesis is merogenous, because the gametangium formed a supernumerary cell as well as a single gametic cell, both undergoing meiosis II to form a surviving functional nucleus and a nucleus that quickly degenerated. Plasmogamy is via papillae that grew out toward each other from the ends of the gametangia to create a copulation canal. After Plasmogamy, the gametes moves bodily into the copulation canal, producing an elongate zygote, which expands to form a curved sausage-like auxospore.
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Sexual reproduction and systematics of Placoneis (Bacillariophyta)
Phycologia, 1995Co-Authors: David G Mann, Alan J. StickleAbstract:Abstract Sexual reproduction and protoplast structure are used to check the classification of the naviculoid genus Placoneis Mereschkowsky (Bacillariophyta). The gametangia are closely associated within a robust mucilage capsule throughout auxosporulation, and pairing is ± random with respect to asymmetries of the frustule and protoplast. Two gametes are produced per gametangium, which are morphologically identical but differentiated into active and passive (physiological anisogamy). The supernumerary nuclei from meiosis II begin to degenerate soon after telophase II, but can still be detected in the initial cells. The gametes become rearranged within the gametangia after meiosis II and Plasmogamy takes place via a single, simple aperture. The auxospores expand parallel to the apical axes of the gametangia. The classification of Placoneis in the Cymbellales, as the sister group to the cymbelloid and gomphonemoid diatoms, is supported by valve and protoplast structure, the method ofchloroplast division, an...
J D Pickettheaps - One of the best experts on this subject based on the ideXlab platform.
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time lapse video observations on sexual Plasmogamy in the red alga bostrychia
European Journal of Phycology, 1998Co-Authors: J D Pickettheaps, John A. WestAbstract:In the red alga Bostrychia moritziana, release of spermatia is triggered by slight osmotic shock; they emerge under pressure apparently generated by swelling of the mucilaginous sheath. Spermatia adhere tenaciously to trichogynes of the carpogonium. Adhesion triggers spermatial mitosis, which is complete in about 30–45 min; there is no cytokinesis and the binucleate spermatium becomes vacuolated. The delicate, dynamic trichogyne cytoplasm contains complex membranous components and vacuoles. At the contact zone, the trichogyne and spermatial wall erode, forming a pore, and cytoplasmic continuity (Plasmogamy) is achieved after about 50–70 min. Many trichogynes rupture during these events because of inadequate structural connection with the spermatia. Normally, both spermatial nuclei enter the trichogyne in sequence; rarely, both nuclei enter together. Entrance is rapid, and the nuclei often become thin and greatly elongated as each squeezes through the narrow pore into the trichogyne. Once inside, each nucl...