Christos Katsaros

National and Kapodistrian University of Athens

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B. Galatis

National and Kapodistrian University of Athens

Frithjof C. Küpper

University of Aberdeen

Claire M. M. Gachon

Molécules de Communication et Adaptation des Micro-organismes

Amerssa Tsirigoti

National and Kapodistrian University of Athens

Thomas Wichard

Friedrich Schiller University Jena

Soultana Tsioli

Technological Educational Institute of Eastern Macedonia and Thrace

Sotiris Orfanidis

Technological Educational Institute of Eastern Macedonia and Thrace

D. Karyophyllis

National and Kapodistrian University of Athens

Bénédicte Charrier

Station Biologique de Roscoff

Ilias Dimitriadis

National and Kapodistrian University of Athens

Cooperative Institutions

Centre National de la Recherche Scientifique

National and Kapodistrian University of Athens

University of Aberdeen

Station Biologique de Roscoff

Sorbonne Université

Laboratoire de Biologie Intégrative des Modèles Marins

Université Paris Cité

Scottish Association For Marine Science

Institute of Oceanography and Fisheries

University of Thessaly

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Laminaria kelps impact iodine speciation chemistry in coastal seawater

Estuarine Coastal and Shelf Science (2021)

M.W. Carrano Carl J. Carrano Matthew S. Edwards Hanan Al-Adilah Yann Fontana

Kelp (Laminaria digitata) uses iodide as a unique inorganic antioxidant to protect its surface and apoplastic space against reactive oxygen species such as ozone, hydrogen peroxide and superoxide, with implications for atmospheric and marine chemistry as well as regional climatic processes. If kelp is covered by seawater, this results in iodide leaching into surrounding sea water. In this study, the influence of the kelps Laminaria digitata, L. hyperborea, L. ochroleuca and Saccharina latissima on iodine speciation chemistry was explored at two sites in Oban (Argyll, Scotland) and Roscoff (Brittany, France) based on diver-operated in situ sampling. Seawater samples were subsequently analysed voltammetrically, accompanied by determination of extractable iodine concentrations in the tissues of the thalli surveyed by ICP-MS. The main result is that iodide concentrations in the vicinity of kelp thalli are strongly enhanced, especially at low tide, while iodate concentrations are decreased in comparison to open coastal water and open ocean concentrations.

Laminaria digitata

Iodate

Thallus

Fucales

Holdfast

10.1016/j.ecss.2021.107531

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Citations (9)

Á-tubulin localization during the cell cycle in Sphacelaria rigidula (Phaeophyceae, Sphacelariales)

D. Karyophyllis B. Galatis Christos Katsaros

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.

Interphase

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Citations (2)

F-actin involvement in apical cell morphogenesis ofSphacelaria rigidula(Phaeophyceae): mutual alignment between cortical actin filaments and cellulose microfibrils

European Journal of Phycology (2000)

D. Karyophyllis Christos Katsaros B. Galatis

Abstract 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 towards the cell base. Below the transverse MF layer, an additional layer with axial or slightly oblique MFs starts being depositing internally, on the tubular part of the cell. Externally to them, the layer of transversely oriented MFs remains visible. The above observations were confirmed in apical cells of S. tribuloides. MF orientation in the innermost wall layer of the apical cells coincides with that of the cortical AFs observed by fluorescence. This mutual alignment between AFs and MFs in a cell that lacks cortical microtubules (MTs) suggests that the AFs are involved in the oriented deposition of MFs. Experimental disruption of AFs with cytochalasin B caused abnormal MF deposition, a fact strongly supporting the above hypothesis. The transverse MFs forming at the base of the apical dome define the diameter and consequently the cylindrical shape of the apical cells. It is suggested that in the brown algal cells examined the AFs play a morphogenetic role similar to that of cortical microtubules in higher plant cells. Keywords: actin filaments apical cell morphogenesis cellulose microfibrils Phaeophyceae polarity Sphacelaria tip growth.

Apical cell

Tip growth

Cell Cortex

Cell polarity

10.1080/09670260010001735791

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Citations (19)

Notes on new records of red algae (Ceramiales, Rhodophyta) from the Aegean Sea (Greece, eastern Mediterranean)

Plant Biosystems - An International Journal Dealing with all Aspects of Plant Biology (2011)

Konstantinos Tsiamis Barbara Montesanto Panayotis Panayotidis Christos Katsaros

Abstract In the present study five macroalgae are reported as new or confirmed for the Aegean coast of Greece (eastern Mediterranean): Antithamnionella elegans, Cottoniella filamentosa var. algeriensis, Laurencia caduciramulosa, Polysiphonia funebris and Vickersia baccata. All of them belong to the Order Ceramiales (Rhodophyta). A. elegans and L. caduciramulosa are considered as alien species in the Mediterranean Sea, and the Greek findings represent an extension for the eastern Mediterranean. The remaining three taxa are described for the first time in the eastern basin, thereby extending their distribution range. Description, illustrations, habitat, geographic distribution and taxonomical remarks are provided for each taxon.

Ceramiales

Rhodomelaceae

Mediterranean Basin

Red algae

Laurencia

10.1080/11263504.2011.611180

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Citations (4)

Ultrastructural changes during development, release, and germination of monospores of Tilopteris mertensii (Tilopteridales, Phaeophyta)

Phycologia (1997)

Christos Katsaros C. Salla

Monospores of Tilopteris mertensii (Turner in Smith) Kützing are formed singly or in small groups at the base of young lateral branches. The differentiation of their mother cells involves a significant increase of cell volume, cytoplasmic density, and organelle number. An active perinuclear Golgi apparatus releases numerous vesicles, contributing to the deposition of additional layers, probably mucilaginous, on the inner face of the cell wall. Application of anti-tubulin immunofluorescent label in studies of apolar spores reveals many microtubule (MT) bundles radiating from the centrosomal area, which lies close to a large, spherical, centrally located nucleus. After monospore release and settlement, the polar axis is established and the spores germinate. Polarization is expressed by several cytological changes. The centrosome and nucleus migrate to the rhizoidal pole. The nucleus becomes lobed and develops a sharp protrusion toward the pole; the centrosome is positioned close to this region. The MT cytoskeleton develops a polar orientation, many MT bundles converging on the polar area, whereas only a few are observed on the opposite side. Membranous organelles show a polar distribution; chloroplasts become oriented toward the pole and have a grana-like thylakoid configuration.

Organelle

Tip growth

10.2216/i0031-8884-36-1-60.1

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Citations (3)

In situ experiments on the effect of low pH on the ultrastructure of the seagrasses Cymodocea nodosa and Posidonia oceanica

Mediterranean Marine Science (2021)

Maria Koutalianou Maria Cristina Buia Christos Katsaros

The present study investigates the impacts of low pH on the cell structure of the seagrasses Posidonia oceanica (L.) Delile and Cymodocea nodosa (Ucria) Ascherson. The study was applied with in situ experiments at the Castello Aragonese of Ischia (Naples, Italy), where shallow submarine vents, lowering the pH, can be used as natural laboratories. Shoots of the seagrasses were transferred from the control area (pH 8.1) to the two venting areas (pH 7.8 and 6.8) for different times. Epidermal cells of young leaves were examined using transmission electron microscopy (TEM) and tubulin immunofluorescence. After one week at pH 7.8, the cell structure of Posidonia oceanica was normal, while in Cymodocea nodosa microtubule (MT) network and cell structure were affected. In addition, in C. nodosa, ultrastructural analysis revealed a gradual degradation of the nuclei, a disorganization of the chloroplasts, and an increase in the number of mitochondria and dictyosomes. The exposure of both plants for 3 weeks at pH 6.8 resulted in the aggregation and finally in the dilation of the endoplasmic reticulum (ER) membranes. Tubulin immunofluorescence revealed that after three weeks, the MT cytoskeleton of both plants was severely affected. All these alterations can be considered as indications of an apoptotic like programmed cell death (AL-PCD) which may be executed in order to regulate stress response.

Posidonia oceanica

10.12681/mms.26314

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Citations (0)

Tip growth in the brown alga Ectocarpus is controlled by a RHO-GAP-BAR domain protein independently from F-actin organisation

bioRxiv (Cold Spring Harbor Laboratory) (2021)

Zofia Nehr Sabine Chenivesse Bernard Billoud Sabine Génicot Nathalie Desban

Abstract The brown alga Ectocarpus is a filamentous seaweed that grows by tip growth and branching. In the morphometric mutant etoile , tip growth is slower than in the WT and eventually stops. In this paper, we show that the causal etoile mutation is a null mutation in a bi-domain BAR-RhoGAP gene. By quantitative RT-PCR, we showed that ETOILE is ubiquitously expressed in prostrate filaments of the Ectocarpus sporophyte, and is downregulated in the etoile mutant. We immunolocalised both domains of the protein in WT and etoile , as well as RAC1, the known target of Rho-GAP enzymes. Thus, ETOILE would be localised at the apical cell dome where it would control the localisation of EsRAC1 to the plasma membrane. Actin staining showed that the mutant is not affected in F-actin structures. Overall, these results suggest that in Ectocarpus, BAR-RhoGAP controls tip growth by controlling RAC1 localization and through an actin-independent mechanism.

10.1101/2021.08.28.458042

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Citations (3)

Disease Resistance In Brown Algae: Mechanisms and Heritability

European Journal of Phycology (2015)

Martina Strittmatter Claire M. M. Gachon D. G. MUELLER Amerssa Tsirigoti Stephan Wawra

Brown algae

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New insights on Laminaria digitata ultrastructure through combined conventional chemical fixation and cryofixation

Botanica Marina (2021)

Christos Katsaros Sophie Le Panse Gillian Milne Carl J. Carrano Frithjof C. Küpper

Abstract The objective of the present study is to examine the fine structure of vegetative cells of Laminaria digitata using both chemical fixation and cryofixation. Laminaria digitata was chosen due to its importance as a model organism in a wide range of biological studies, as a keystone species on rocky shores of the North Atlantic, its use of iodide as a unique inorganic antioxidant, and its significance as a raw material for the production of alginate. Details of the fine structural features of vegetative cells are described, with particular emphasis on the differences between the two methods used, i.e. conventional chemical fixation and freeze-fixation. The general structure of the cells was similar to that already described, with minor differences between the different cell types. An intense activity of the Golgi system was found associated with the thick external cell wall, with large dictyosomes from which numerous vesicles and cisternae are released. An interesting type of cisternae was found in the cryofixed material, which was not visible with the chemical fixation. These are elongated structures, in sections appearing tubule-like, close to the external cell wall or to young internal walls. An increased number of these structures was observed near the plasmodesmata of the pit fields. They are similar to the “flat cisternae” found associated with the forming cytokinetic diaphragm of brown algae. Their possible role is discussed. The new findings of this work underline the importance of such combined studies which reveal new data not known until now using the old conventional methods. The main conclusion of the present study is that cryofixation is the method of choice for studying Laminaria cytology by transmission electron microscopy.

Cryofixation

Laminaria digitata

Plasmodesma

Red algae

10.1515/bot-2021-0005

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Citations (3)

The effect of taxol on centrosome function and microtubule organization in apical cells of Sphacelaria rigidula (Phaeophyceae)

Phycological Research (2001)

Ilias Dimitriadis Christos Katsaros B. Galatis

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.

Centriole

Interphase

Microtubule organizing center

Cell plate

10.1046/j.1440-1835.2001.00222.x

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Citations (8)