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Christos Katsaros - One of the best experts on this subject based on the ideXlab platform.
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Á-tubulin localization during the cell cycle in Sphacelaria rigidula (Phaeophyceae, Sphacelariales)
2005Co-Authors: D. Karyophyllis, Basil Galatis, Christos KatsarosAbstract:A-tubulin was localized by immunofluorescence for the first time in brown algae using a specific antibody raised against Dictyostelium discoideum A-tubulin. Its distribution during the cell cycle was studied in vegetative cells of Sphacelaria rigidula. A-tubulin was localized in the centrosome area during the whole cell cycle. During interphase, it appears as a weak fluorescent spot, while when the cell enters mitosis, the fluorescence increases, becoming broader and brighter at metaphase. The spot diameter and brightness decrease again by anaphase. The results show that A-tubulin is a permanent centrosomal component in brown algal cells and its accumulation depends on the microtubule nucleation activity of the centrosomes. The functional role of A-tubulin is discussed in comparison with other cell types.
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Cortical F -actin underlies cellulose microfibril patterning in brown algal cells
Phycologia, 2002Co-Authors: Christos Katsaros, D. Karyophyllis, Basil GalatisAbstract:The organization of actin filaments (AFs) was studied using rhodamine-phalloidin staining of F-actin in four different cell types of brown algae, namely: (I) differentiating cells of Sphacelaria rigidula; (2) the apical cells of Dictyota dichotoma; (3) the subapical cells of Choristocarpus tenellus; and (4) the meristematic epidermal cells of D. dichotoma. In all cases, it was revealed that, apart from the perinuclear and cytoplasmic AFs, intensely fluorescent AF bundles are present, forming a cortical system with a definite orientation in each cell type. In (1) and (4) the cortical AFs showed a transverse orientation, in (2) they were randomly distributed, and in (3) a principally axial orientation was combined with a reticulate one. Examination of thin sections under the transmission electron microscope revealed that cell wall microfibrils (MFs) of the innermost wall layer were always oriented parallel to the underlying cortical AFs. Cytochalasin B treatment of developing thalli of D. dichotoma for 24-36 h destroys cortical AFs and disturbs the cellulose MF orientation in the innermost wall layer of the meristematic cells near the apex. It is suggested that the mutual arrangement of cortical AFs and MFs is a phenomenon of general appearance in brown algal cells and that the AFs are probably involved in the orientation of the MFs. The differences observed in the orientation of both cortical AFs and MFs were in accordance with the growth pattern of the cells. This supports the hypothesis that, in brown algae, F-actin is involved in cell morphogenesis.
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The effect of taxol on centrosome function and microtubule organization in apical cells of Sphacelaria rigidula (Phaeophyceae)
Phycological Research, 2001Co-Authors: Ilias Dimitriadis, Christos Katsaros, Basil GalatisAbstract:SUMMARY Treatment of interphase apical cells of Sphacelaria rigidula Kutzing with 10 μmol L−1 taxol for 4 h induced drastic changes in microtubule (MT) organization. In normal cells these MTs converge on the centrosomes and are nucleated from the pericentriolar area. After treatment, the endoplasmic, perinuclear and centrosome-associated MT almost disappeared, and a massive assembly of cortical/subcortical, well-organized MT bundles was observed. The bundles tended to be axially oriented, usually following the cylindrical wall, although other orientations were not excluded. The MTs in the apical part of the cell seemed to reach the cortex of the apical dome, sometimes bending to follow its curvature, whereas those in the basal portion of the cell terminated close to the transverse wall. Mitotic cells were also highly affected. Typical metaphase stages were very rarely found, and typical anaphase arrangements of chromosomes were completely absent. The chromosomes usually appeared to be dispersed singly or in small groups. Different atypical mitotic configurations were observed, depending on the stage of the cell cycle when the treatment started. The position and the orientation of the atypical mitotic spindles was disturbed. The nuclear envelope was completely disintegrated. The separation of the duplicated centrioles, as well as their usual perinuclear position, was also disturbed. Cortical MT bundles similar to those found in interphase cells were not found in the affected mitotic cells. In contrast, numerous MTs, without definite focal points, were found in the pericentriolar areas. Cytokinesis was inhibited by taxol treatment. The perinuclear and centrosome-associated MTs found in mitotic cells were gradually replaced by a MT system similar to that of interphase cells. When the cytokinetic diaphragm had already been initiated when taxol treatment began, MTs were found on the cytokinetic plane, a phenomenon not observed in normal untreated cells. The results show clearly that: (i) in interphase cells the ability of centrosomes to nucleate MTs is intensely disturbed by taxol; (ii) centrosome dynamics in MT nucleation vary during the cell cycle; and (iii) taxol strongly affects mitosis and cytokinesis. In addition, it seems that the cortical/subcortical cytoplasm of interphase cells assumes the capacity to form numerous MT bundles.
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F-Actin organization during the cell cycle of Sphacelaria rigidula (Phaeophyceae)
European Journal of Phycology, 2000Co-Authors: D. Karyophyllis, Christos Katsaros, I. Dimitriadis, Basil GalatisAbstract:The organization of F-actin in vegetative cells of the brown alga Sphacelaria rigidula was studied after staining with a modified rhodaminephalloidin (Rh-Ph) protocol. The interphase vegetative cells display a well-organized F-actin cytoskeleton, consisting of cortical, endoplasmic and perinuclear arrays of actin filaments (AFs). The organization of these AFs changes slightly during mitosis, while they almost disappear at cytokinesis. The perinuclear AF population becomes more obvious during prophase, especially at the poles. At metaphase, an actin spindle is organized, co-localized with the microtubule spindle, while at anaphase an interzonal AF population appears, which persists at early telophase. At advanced telophase the image changes to a rather diffuse actin meshwork in the mid-area between the daughter nuclei. During post-telophase-early cytokinesis this AF system becomes gradually disassembled and a conspicuous actin plate is formed on the cytokinetic plane. This plate becomes more compact with t...
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F-actin involvement in apical cell morphogenesis of Sphacelaria rigidula (Phaeophyceae): mutual alignment between cortical actin filaments and cellulose microfibrils
European Journal of Phycology, 2000Co-Authors: D. Karyophyllis, Christos Katsaros, Basil GalatisAbstract:The polarized apical cells of Sphacelaria rigidula display a well-organized cortical F-actin cytoskeleton. This consists of bundles of actin filaments (AFs), assuming definite patterns of organization in different regions of the cell cortex. At the tip region of the apical dome the AFs appear randomly oriented, showing a diffuse fluorescence. Immediately below, at the base of the apical hemisphere, the AFs form a ring-like band around the plasmalemma transverse to the polar cell axis. The rest of the cell cortex is traversed by AFs showing an axial or slightly inclined or helical orientation. Examination of the apical cells of S. rigidula in appropriate thin sections revealed that the wall has a multi-layered structure. In the tip region of the apical dome the cell wall bears randomly oriented cellulose microfibrils (MFs), while in the basal part of the apical dome it is reinforced by a layer of densely arranged transverse MFs. As the cell grows at the apex, the transverse MFs are continuously displaced t...
Basil Galatis - One of the best experts on this subject based on the ideXlab platform.
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Á-tubulin localization during the cell cycle in Sphacelaria rigidula (Phaeophyceae, Sphacelariales)
2005Co-Authors: D. Karyophyllis, Basil Galatis, Christos KatsarosAbstract:A-tubulin was localized by immunofluorescence for the first time in brown algae using a specific antibody raised against Dictyostelium discoideum A-tubulin. Its distribution during the cell cycle was studied in vegetative cells of Sphacelaria rigidula. A-tubulin was localized in the centrosome area during the whole cell cycle. During interphase, it appears as a weak fluorescent spot, while when the cell enters mitosis, the fluorescence increases, becoming broader and brighter at metaphase. The spot diameter and brightness decrease again by anaphase. The results show that A-tubulin is a permanent centrosomal component in brown algal cells and its accumulation depends on the microtubule nucleation activity of the centrosomes. The functional role of A-tubulin is discussed in comparison with other cell types.
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Cortical F -actin underlies cellulose microfibril patterning in brown algal cells
Phycologia, 2002Co-Authors: Christos Katsaros, D. Karyophyllis, Basil GalatisAbstract:The organization of actin filaments (AFs) was studied using rhodamine-phalloidin staining of F-actin in four different cell types of brown algae, namely: (I) differentiating cells of Sphacelaria rigidula; (2) the apical cells of Dictyota dichotoma; (3) the subapical cells of Choristocarpus tenellus; and (4) the meristematic epidermal cells of D. dichotoma. In all cases, it was revealed that, apart from the perinuclear and cytoplasmic AFs, intensely fluorescent AF bundles are present, forming a cortical system with a definite orientation in each cell type. In (1) and (4) the cortical AFs showed a transverse orientation, in (2) they were randomly distributed, and in (3) a principally axial orientation was combined with a reticulate one. Examination of thin sections under the transmission electron microscope revealed that cell wall microfibrils (MFs) of the innermost wall layer were always oriented parallel to the underlying cortical AFs. Cytochalasin B treatment of developing thalli of D. dichotoma for 24-36 h destroys cortical AFs and disturbs the cellulose MF orientation in the innermost wall layer of the meristematic cells near the apex. It is suggested that the mutual arrangement of cortical AFs and MFs is a phenomenon of general appearance in brown algal cells and that the AFs are probably involved in the orientation of the MFs. The differences observed in the orientation of both cortical AFs and MFs were in accordance with the growth pattern of the cells. This supports the hypothesis that, in brown algae, F-actin is involved in cell morphogenesis.
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The effect of taxol on centrosome function and microtubule organization in apical cells of Sphacelaria rigidula (Phaeophyceae)
Phycological Research, 2001Co-Authors: Ilias Dimitriadis, Christos Katsaros, Basil GalatisAbstract:SUMMARY Treatment of interphase apical cells of Sphacelaria rigidula Kutzing with 10 μmol L−1 taxol for 4 h induced drastic changes in microtubule (MT) organization. In normal cells these MTs converge on the centrosomes and are nucleated from the pericentriolar area. After treatment, the endoplasmic, perinuclear and centrosome-associated MT almost disappeared, and a massive assembly of cortical/subcortical, well-organized MT bundles was observed. The bundles tended to be axially oriented, usually following the cylindrical wall, although other orientations were not excluded. The MTs in the apical part of the cell seemed to reach the cortex of the apical dome, sometimes bending to follow its curvature, whereas those in the basal portion of the cell terminated close to the transverse wall. Mitotic cells were also highly affected. Typical metaphase stages were very rarely found, and typical anaphase arrangements of chromosomes were completely absent. The chromosomes usually appeared to be dispersed singly or in small groups. Different atypical mitotic configurations were observed, depending on the stage of the cell cycle when the treatment started. The position and the orientation of the atypical mitotic spindles was disturbed. The nuclear envelope was completely disintegrated. The separation of the duplicated centrioles, as well as their usual perinuclear position, was also disturbed. Cortical MT bundles similar to those found in interphase cells were not found in the affected mitotic cells. In contrast, numerous MTs, without definite focal points, were found in the pericentriolar areas. Cytokinesis was inhibited by taxol treatment. The perinuclear and centrosome-associated MTs found in mitotic cells were gradually replaced by a MT system similar to that of interphase cells. When the cytokinetic diaphragm had already been initiated when taxol treatment began, MTs were found on the cytokinetic plane, a phenomenon not observed in normal untreated cells. The results show clearly that: (i) in interphase cells the ability of centrosomes to nucleate MTs is intensely disturbed by taxol; (ii) centrosome dynamics in MT nucleation vary during the cell cycle; and (iii) taxol strongly affects mitosis and cytokinesis. In addition, it seems that the cortical/subcortical cytoplasm of interphase cells assumes the capacity to form numerous MT bundles.
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F-Actin organization during the cell cycle of Sphacelaria rigidula (Phaeophyceae)
European Journal of Phycology, 2000Co-Authors: D. Karyophyllis, Christos Katsaros, I. Dimitriadis, Basil GalatisAbstract:The organization of F-actin in vegetative cells of the brown alga Sphacelaria rigidula was studied after staining with a modified rhodaminephalloidin (Rh-Ph) protocol. The interphase vegetative cells display a well-organized F-actin cytoskeleton, consisting of cortical, endoplasmic and perinuclear arrays of actin filaments (AFs). The organization of these AFs changes slightly during mitosis, while they almost disappear at cytokinesis. The perinuclear AF population becomes more obvious during prophase, especially at the poles. At metaphase, an actin spindle is organized, co-localized with the microtubule spindle, while at anaphase an interzonal AF population appears, which persists at early telophase. At advanced telophase the image changes to a rather diffuse actin meshwork in the mid-area between the daughter nuclei. During post-telophase-early cytokinesis this AF system becomes gradually disassembled and a conspicuous actin plate is formed on the cytokinetic plane. This plate becomes more compact with t...
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F-actin involvement in apical cell morphogenesis of Sphacelaria rigidula (Phaeophyceae): mutual alignment between cortical actin filaments and cellulose microfibrils
European Journal of Phycology, 2000Co-Authors: D. Karyophyllis, Christos Katsaros, Basil GalatisAbstract:The polarized apical cells of Sphacelaria rigidula display a well-organized cortical F-actin cytoskeleton. This consists of bundles of actin filaments (AFs), assuming definite patterns of organization in different regions of the cell cortex. At the tip region of the apical dome the AFs appear randomly oriented, showing a diffuse fluorescence. Immediately below, at the base of the apical hemisphere, the AFs form a ring-like band around the plasmalemma transverse to the polar cell axis. The rest of the cell cortex is traversed by AFs showing an axial or slightly inclined or helical orientation. Examination of the apical cells of S. rigidula in appropriate thin sections revealed that the wall has a multi-layered structure. In the tip region of the apical dome the cell wall bears randomly oriented cellulose microfibrils (MFs), while in the basal part of the apical dome it is reinforced by a layer of densely arranged transverse MFs. As the cell grows at the apex, the transverse MFs are continuously displaced t...
In-kyu Lee - One of the best experts on this subject based on the ideXlab platform.
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taxonomic reappraisal of Sphacelaria rigidula and s fusca Sphacelariales phaeophyceae based on morphology and molecular data with special reference to s didichotoma
Algae, 2005Co-Authors: Yeon-shim Keum, Stefano G. A. Draisma, Willem F. Prud'homme Van Reine, Jung-hyun Oak, In-kyu LeeAbstract:The taxonomic status of three closely related species of the genus Sphacelaria, S. rigidula Kutzing, S. fusca (Hudson) C.F Gray and S. didichotoma Saunders was reassessed on the basis of morphological observations from herbarium specimens and phylogenetic analysis of RUBISCO spacer sequences. Sphacelaria rigidula was characterized by having only 2-armed propagules and somewhat slender filaments. Culture experiments revealed that its propagules commonly formed secondary arms, even though they were rarely produced in the field. It is concluded that S. divaricata Montagne characterized by dichotomously branched arms in propagules shoud be synonymized with S. rigidula, based on propagule morphology and measurements. Sphacelaria fusca clearly be separated from S. rigidula by having 2-4 armed propagules. These morphological differences were highly supported by the differences in the RUBISCO spacer sequences. S. didichotoma resembles S. rigidula in having propagules with two dichotomously branched arms. However, it commonly produces the secondary arms in the field. Additionally, this species has shorter primary arms than S. rigidula. Phylogenetic analyses supported the distinction of S. didichotoma from S. rigidula. The northwestern Pacific plants, previously recorded as S. divaricata, were recognized as S. didichotoma.
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Comparative morphology and taxonomy of Sphacelaria species with tribuliform propagules (Sphacelariales, Phaeophyceae)
Botanica Marina, 2003Co-Authors: Yeon-shim Keum, W.f. Prud’homme Van Reine, Jung-hyun Oak, In-kyu LeeAbstract:Four species of Sphacelaria producing tribuliform propagules in the section Tribuloides were distinguished from each other on the basis of the branching pattern and propagule morphology including the division type of the subapical cells and the shape of the lateral apical cells. Sphacelaria plumula shows complanate tufts composed of erect filaments bearing pinnate determinate laterals arranged in one plane, while the other species, S. tribuloides, S. brachygonia and S. novae-caledoniae, form erect tufts with irregular indeterminate branches. Sphacelaria tribuloides is distinguished by typical tribuliform propagules with acute conical lateral apical cells. Sphacelaria plumula has slightly larger propagules with obtuse conical lateral apical cells and a rather vague constriction at the waist. The distinguishing features of S. brachygonia are its slightly tribuliform, more often transversely ellipsoid propagules with round conical lateral apical cells and small lower parts under the waist. In S. novae-caledoniae, the filaments are slender and its mature propagules have the rectangular lateral apical cells produced by 2-3 longitudinal and transverse divisions of the subapical cells. The morphometric features of segments, propagules and zoidangia in the species of the section Tribuloides, including S. californica and S. novae-hollandiae, were found to be variable, but in some species they can be used to distinguish taxa. In addition, the holotypes of S. cornuta and S. nipponica, previously placed in the section Tribuloides, were examined. The results suggest that S. cornuta can be considered as a synonym of S. tribuloides, and S. nipponica should be placed in the section Furcigerae, based on the presence of diagonal divisions in the subapical cells as well as long stalks and prominent arms in the propagules.
D. Karyophyllis - One of the best experts on this subject based on the ideXlab platform.
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Á-tubulin localization during the cell cycle in Sphacelaria rigidula (Phaeophyceae, Sphacelariales)
2005Co-Authors: D. Karyophyllis, Basil Galatis, Christos KatsarosAbstract:A-tubulin was localized by immunofluorescence for the first time in brown algae using a specific antibody raised against Dictyostelium discoideum A-tubulin. Its distribution during the cell cycle was studied in vegetative cells of Sphacelaria rigidula. A-tubulin was localized in the centrosome area during the whole cell cycle. During interphase, it appears as a weak fluorescent spot, while when the cell enters mitosis, the fluorescence increases, becoming broader and brighter at metaphase. The spot diameter and brightness decrease again by anaphase. The results show that A-tubulin is a permanent centrosomal component in brown algal cells and its accumulation depends on the microtubule nucleation activity of the centrosomes. The functional role of A-tubulin is discussed in comparison with other cell types.
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Cortical F -actin underlies cellulose microfibril patterning in brown algal cells
Phycologia, 2002Co-Authors: Christos Katsaros, D. Karyophyllis, Basil GalatisAbstract:The organization of actin filaments (AFs) was studied using rhodamine-phalloidin staining of F-actin in four different cell types of brown algae, namely: (I) differentiating cells of Sphacelaria rigidula; (2) the apical cells of Dictyota dichotoma; (3) the subapical cells of Choristocarpus tenellus; and (4) the meristematic epidermal cells of D. dichotoma. In all cases, it was revealed that, apart from the perinuclear and cytoplasmic AFs, intensely fluorescent AF bundles are present, forming a cortical system with a definite orientation in each cell type. In (1) and (4) the cortical AFs showed a transverse orientation, in (2) they were randomly distributed, and in (3) a principally axial orientation was combined with a reticulate one. Examination of thin sections under the transmission electron microscope revealed that cell wall microfibrils (MFs) of the innermost wall layer were always oriented parallel to the underlying cortical AFs. Cytochalasin B treatment of developing thalli of D. dichotoma for 24-36 h destroys cortical AFs and disturbs the cellulose MF orientation in the innermost wall layer of the meristematic cells near the apex. It is suggested that the mutual arrangement of cortical AFs and MFs is a phenomenon of general appearance in brown algal cells and that the AFs are probably involved in the orientation of the MFs. The differences observed in the orientation of both cortical AFs and MFs were in accordance with the growth pattern of the cells. This supports the hypothesis that, in brown algae, F-actin is involved in cell morphogenesis.
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F-Actin organization during the cell cycle of Sphacelaria rigidula (Phaeophyceae)
European Journal of Phycology, 2000Co-Authors: D. Karyophyllis, Christos Katsaros, I. Dimitriadis, Basil GalatisAbstract:The organization of F-actin in vegetative cells of the brown alga Sphacelaria rigidula was studied after staining with a modified rhodaminephalloidin (Rh-Ph) protocol. The interphase vegetative cells display a well-organized F-actin cytoskeleton, consisting of cortical, endoplasmic and perinuclear arrays of actin filaments (AFs). The organization of these AFs changes slightly during mitosis, while they almost disappear at cytokinesis. The perinuclear AF population becomes more obvious during prophase, especially at the poles. At metaphase, an actin spindle is organized, co-localized with the microtubule spindle, while at anaphase an interzonal AF population appears, which persists at early telophase. At advanced telophase the image changes to a rather diffuse actin meshwork in the mid-area between the daughter nuclei. During post-telophase-early cytokinesis this AF system becomes gradually disassembled and a conspicuous actin plate is formed on the cytokinetic plane. This plate becomes more compact with t...
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F-actin involvement in apical cell morphogenesis of Sphacelaria rigidula (Phaeophyceae): mutual alignment between cortical actin filaments and cellulose microfibrils
European Journal of Phycology, 2000Co-Authors: D. Karyophyllis, Christos Katsaros, Basil GalatisAbstract:The polarized apical cells of Sphacelaria rigidula display a well-organized cortical F-actin cytoskeleton. This consists of bundles of actin filaments (AFs), assuming definite patterns of organization in different regions of the cell cortex. At the tip region of the apical dome the AFs appear randomly oriented, showing a diffuse fluorescence. Immediately below, at the base of the apical hemisphere, the AFs form a ring-like band around the plasmalemma transverse to the polar cell axis. The rest of the cell cortex is traversed by AFs showing an axial or slightly inclined or helical orientation. Examination of the apical cells of S. rigidula in appropriate thin sections revealed that the wall has a multi-layered structure. In the tip region of the apical dome the cell wall bears randomly oriented cellulose microfibrils (MFs), while in the basal part of the apical dome it is reinforced by a layer of densely arranged transverse MFs. As the cell grows at the apex, the transverse MFs are continuously displaced t...
Maria Gibson - One of the best experts on this subject based on the ideXlab platform.
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Reproduction in the Sphacelariales: sex is a rare occurrence
2013Co-Authors: Maria GibsonAbstract:This review examines the reproduction and life-history of the Sphacelariales, providing a synthesis of much of the key literature and examining whether an alternation of generations is common within the order. The evidence suggests that sexual reproduction is a rare occurrence for most species, which may be a result of meiosis failing to occur in the unilocular sporangium, onset of sexuality failing to occur in gametophytes or because the necessary environmental conditions are absent. One or all scenarios, or another, may apply depending on the species but, in most instances, there is insufficient information to determine this. Asexual reproduction is common in the order and may be by vegetative means, production of asexual spores or by parthenogenesis or ephebogenesis. Temperature and daylength are known to affect reproduction in the order and the suggested critical daylength for production of propagules in Sphacelaria rigidula Kutzing has been narrowed to fall between 8 and 9.5 h.
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Notes on recruitment in Sphacelaria Biradiata Askenasy (Sphacelariales, Phaeophyceae)
Victorian naturalist, 2007Co-Authors: Rebecca White, Maria GibsonAbstract:The key observations regarding recruitment and dispersal among Sphacelaria biradiata Askenasy (Sphacelariales, Phaeophyceae) are discussed. The use of natural substrata for recruitment studies of epiphtes is possible.
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Reproduction in Sphacelaria biradiata Askenasy (Sphacelariales, Phaeophyceae) in Southern Australia
Victorian naturalist, 2003Co-Authors: Maria GibsonAbstract:Sphacelaria biradiata Askenasy is a little known but common brown alga of southern Australian coasts. This paper describes its reproduction. Populations of S. biradiata reproduced asexually by vegetative propagules in all localities examined. The propagules were produced throughout the year and did not appear to be affected by season, although, if sexual structures occurred, propagule numbers declined. Sexual reproduction can occur and involves an alternation of generations, but it is a rare event. Gametophytes may produce male gametangia, female gametangia or both. Male gametangia, however, are extremely rare and are described for the first time. Production of female gametangia was influenced by season and occurred at all areas studied. The sexual behaviour of the male and female gametes is described.