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Cross section of a blade, showing epidermal cells of Laminaria digitata after conventional chemical fixation (CCF). N, nucleus; Ch, chloroplast; V, vacuole; CW, cell wall; M, mitochondria. Arrows indicate dark material attached to the plasmalemma of the external cell wall. Scale bar = 200 μm.
Source publication
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...
Contexts in source publication
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... method used for the CCF was successful and, despite the usually faced difficulties due to the large size of the thallus, gave clear images with well-preserved cells. The shape of the cells depends on their type, i.e. the epidermal cells, in transverse thallus sections, appear usually orthogonal, while the medullary ones are more rectangular (Figure 1). In the meristematic region the cell shape was similar to non-meristematic phylloid tissue but the cells were smaller. ...
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... internal structure of the cells was found to be similar to that already described for other brown algae. A large nucleus, with variable shape, was usually at a central position in epidermal cells, while in medullary cells it was more peripherally located ( Figure 1). Large dictyosomes were observed in the perinuclear cytoplasm, occasionally associated with the nuclear envelope ( Figure 2). ...
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... dictyosomes were also found in other areas, particularly in the peripheral cytoplasm (Figure 7). Most of the cell space was covered by large vacuoles, sometimes containing masses of electron-dense material ( Figure 1). The vacuole membrane in cells fixed with CCF shows an undulating shape (Figure 1). ...
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... of the cell space was covered by large vacuoles, sometimes containing masses of electron-dense material ( Figure 1). The vacuole membrane in cells fixed with CCF shows an undulating shape (Figure 1). Numerous chloroplasts and mitochondria were mainly located in the cortical cytoplasm (Figures 1 and 3). ...
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... vacuole membrane in cells fixed with CCF shows an undulating shape (Figure 1). Numerous chloroplasts and mitochondria were mainly located in the cortical cytoplasm (Figures 1 and 3). The chloroplasts were large in relation to the cell size, mainly elongated ( Figure 3). ...
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... internal membrane system consisted of the usual bundles of three thylakoids, and the nucleoid localized at the poles (genophores) (Figures 3, 4). Large pit-fields were observed in internal cell walls mainly in the medullary cells (Figures 7 and 11). The external cell wall was thick, consisting of three layers, i.e. an internal one with parallel, hardly visible cellulose microfibril bundles, a thinner median layer with vesicle-like structure, and a thick amorphous external layer ( Figure 5). ...
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... was interesting that darkly stained elongated structures were observed attached to the plasmalemma of the external wall of epidermal cells. This was more obvious in cells which were partially plasmolysed (Figures 1 and 5). Examination of thin sections of material prepared with CF-FS revealed a general structure similar to the above described with CCF (Figure 6, cf. with Figure 1). ...
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... was more obvious in cells which were partially plasmolysed (Figures 1 and 5). Examination of thin sections of material prepared with CF-FS revealed a general structure similar to the above described with CCF (Figure 6, cf. with Figure 1). However, a detailed analysis of the CF-FS samples revealed some interesting features, which were different or not found with the CCF, in particular: 1. ...
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... activity of the dictyosomes was clearer, since the released vesicles and cisternae were full of electrondense material ( Figure 7). 2. The dark elongated structures associated with the plasmalemma of the external cell wall of epidermal cells were not found ( Figure 6, cf. with Figure 1). 3. The structure of the pit-fields and their plasmodesmata was clearer compared to those of the CCF material (Figures 7 and 9). ...
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... A variable number of elongated membranous structures, resembling short detached ER or dictyosome cisternae was observed close to the wall of both epidermal and medullary cells (Figures 7-11). These structures were either transparent, showing two parallel membranes, obviously cross sections of cisternae, or filled with electron-dense material (Figures 8-11). ...
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... A variable number of elongated membranous structures, resembling short detached ER or dictyosome cisternae was observed close to the wall of both epidermal and medullary cells (Figures 7-11). These structures were either transparent, showing two parallel membranes, obviously cross sections of cisternae, or filled with electron-dense material (Figures 8-11). They are similar to the "flat cisternae" found associated with the developing cytokinetic diaphragm of a number of brown algae ( Katsaros et al. 2009). ...
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... are similar to the "flat cisternae" found associated with the developing cytokinetic diaphragm of a number of brown algae ( Katsaros et al. 2009). The flat shape of these cisternae was confirmed in areas where these structures were sectioned parallel to their surface, where the cisternae appear round (Figure 11). 5. ...
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... flat shape of these cisternae was confirmed in areas where these structures were sectioned parallel to their surface, where the cisternae appear round (Figure 11). 5. In some cases, these flat cisternae were found in parallel doublets, close to the plasmalemma of the external wall of epidermal cells (Figure 10). 6. ...
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... An increased number of flat cisternae was found close to the plasmodesmata of the pit-fields (Figures 7 and 11). 7. ...
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... In areas where flat cisternae are present, invaginations of the plasmalemma were observed, sometimes associated with the flat cisternae (Figures 12, 13). ...
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... far as the first of the above questions is concerned, it can be underlined that after CCF the general structure of the cells was quite well preserved. However, after a Figure 12) and 500 nm ( Figure 13). detailed comparison of the two methods applied it was revealed that after CCF the cortical cells of the blades are locally plasmolysed, i.e. the external cell wall is detached from the plasmalemma. ...
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... far as the first of the above questions is concerned, it can be underlined that after CCF the general structure of the cells was quite well preserved. However, after a Figure 12) and 500 nm ( Figure 13). detailed comparison of the two methods applied it was revealed that after CCF the cortical cells of the blades are locally plasmolysed, i.e. the external cell wall is detached from the plasmalemma. ...
Citations
... Iodine in the form of both iodide (I -) and iodate (IO 3 -) is taken from the surrounding seawater into the apoplast (extracellular space) and stored in the form of I - (Verhaeghe et al. 2008;Fievet et al. 2023). Details regarding exact localization of iodide and mechanisms of uptake, storage and efflux are still lacking (Katsaros et al. 2021). The uptake of iodine is highly effective and kelp up-concentrate iodine up to 30,000-times compared to the iodine concentration in seawater (Gall et al. 2004). ...
... These enzymes have also been previously identified in extracts from S. latissima (Almeida et al. 2001). Details regarding mechanisms of iodine efflux are still lacking (Katsaros et al. 2021), however, one proposed stress response involves catalysis by vIPO (Almeida et al. 2001). The activity of vIPO from S. latissima was found to be dependent on temperature, and was highest from 40-50 °C, markedly lower at 60 °C, and apparently not active above 70 °C (Almeida et al. 2001). ...
Kelp growers and the food industry, as well as food researchers, are currently finding methods for controlling the iodine content of kelp intended for food as this is one of the major obstacles to entering a profitable market. Kelps are rich sources of dietary iodine since iodine is up-concentrated in algal tissue and utilized as an inorganic antioxidant during exposure to stress. As kelp contains much more iodine than any other food source, it is warranted to reduce the amount of iodine in the biomass prior to consumption, since both iodine deficiency and excess can cause health problems. Iodine is typically removed post-harvest using traditional methods such as blanching. In the present work, we attempted to utilize inherent stressors, i.e., intermediate storage (3 days) with high light exposure and low turnover of water, to reduce the iodine content prior to processing. Furthermore, we assessed the effect on subsequent blanching, comparing samples stored in tanks and not stored samples. The iodine content was slightly reduced when comparing storage to no storage, but in most cases not significantly so. However, after subsequent blanching, there was a pronounced added reduction for stored samples (87 % reduction) compared to not stored samples (80 % reduction). Although the differences are smaller than we expected, our research shows that using post-harvest intermediate storage of kelp may alter the iodine content post-processing. Fine-tuning the stressors and conditions could lead to new possibilities for iodine reduction.
... In this context, the role of the new type of cisternae-like structure (so-called flat cisternae) discovered by a new sample preparation method by CF-FS in recent ultrastructure microscopy images of L. digitata , which have an electron-dense content, should be investigated for a potential role in metal and halide storage. 21 These structures are not visible in sections of material prepared by conventional CCF. They are clearly visible after CF-FS, and usually appear close to cell walls, with particularly high numbers parallel to primary pit fields. ...
... It was suggested that they could function for transport and alternative storage to the vacuole. Our study is in agreement with Katsaros et al ., 21 but the resolution of our tomography study does not allow to see the cisternae, which are clearly visible after CF-FS. 21 Sr binds strongly to alginate and turned out to be ideally suitable for imaging the cell walls with μXRF. ...
... Our study is in agreement with Katsaros et al ., 21 but the resolution of our tomography study does not allow to see the cisternae, which are clearly visible after CF-FS. 21 Sr binds strongly to alginate and turned out to be ideally suitable for imaging the cell walls with μXRF. In L. digitata , Sr shows accumulation in the cell wall in the cortex tissue, while the meristoderm shows a rather homogeneous distribution. ...
Iron is accumulated symplastically in kelp in a non-ferritin core that seems to be a general feature of brown algae. Microprobe studies show that Fe binding depends on tissue type.
The sea is generally an iron-poor environment and brown algae were recognized in recent years for having a unique, ferritin-free iron storage system. Kelp (Laminaria digitata) and the filamentous brown alga Ectocarpus siliculosus were investigated using X-ray microprobe imaging and nanoprobe X-ray fluorescence tomography to explore the localization of iron, arsenic, strontium, and zinc, and micro-X-ray absorption near-edge structure (μXANES) to study Fe binding. Fe distribution in frozen hydrated environmental samples of both algae shows higher accumulation in the cortex with symplastic subcellular localization. This should be seen in the context of recent ultrastructural insight by cryofixation–freeze substitution that found a new type of cisternae that may have a storage function but differs from the apoplastic Fe accumulation found by conventional chemical fixation. Zn distribution co-localizes with Fe in E. siliculosus, whereas it is chiefly located in the L. digitata medulla, which is similar to As and Sr. Both As and Sr are mostly found at the cell wall of both algae. XANES spectra indicate that Fe in L. digitata is stored in a mineral non-ferritin core, due to the lack of ferritin-encoding genes. We show that the L. digitata cortex contains mostly a ferritin-like mineral, while the meristoderm may include an additional component.
In the evolution of eukaryotes, the transition from unicellular to simple multicellular organisms has happened multiple times. For the development of complex multicellularity, characterized by sophisticated body plans and division of labor between specialized cells, symplasmic intercellular communication is supposed to be indispensable. We review the diversity of symplasmic connectivity among the eukaryotes and distinguish between distinct types of non-plasmodesmatal connections, plasmodesmata-like structures, and ‘canonical’ plasmodesmata on the basis of developmental, structural, and functional criteria. Focusing on the occurrence of plasmodesmata (-like) structures in extant taxa of fungi, brown algae (Phaeophyceae), green algae (Chlorophyta), and streptophyte algae, we present a detailed critical update on the available literature which is adapted to the present classification of these taxa and may serve as a tool for future work. From the data, we conclude that, actually, development of complex multicellularity correlates with symplasmic connectivity in many algal taxa, but there might be alternative routes. Furthermore, we deduce a four-step process towards the evolution of canonical plasmodesmata and demonstrate similarity of plasmodesmata in streptophyte algae and land plants with respect to the occurrence of an ER component. Finally, we discuss the urgent need for functional investigations and molecular work on cell connections in algal organisms.
The sporophyte of Saccharina is an interesting developmental model for three reasons. First, the embryogenesis takes place outside any maternal tissue making the growing tissue amenable to cytological manipulation and mechanically uncoupled to surrounding tissues (Fritsch 1945; Bogaert et al. 2013; Theodorou and Charrier 2021). Therefore, any microscopic and modelling approaches take place directly on the developing embryo. Second reason, the early embryo of Saccharina (and most kelps) is a growing undifferentiated tissue thick of one cell layer (monostromatic) (Drew 1910; Killian 1911; Yendo 1911; Fritsch 1945; Theodorou and Charrier 2021). The monostromatic growing tissue is consisted of simple cuboid cells, whose description in literature indicates frequent four cell wall junctions. This cell arrangement is uncommon and often avoided in developing tissues of land plants due to increased shearing stress (Sinnott and Bloch 1941; Lloyd 1991). When it occurs, it is related with the later opening of large intercellular spaces like during the development of spongy photosynthetic parenchyma in leaves (Zhang and Ambrose 2022). Thirdly, the early embryo of Saccharina is a poorly investigated system regarding developmental biology, with great comparative value due to the evolutionary position of brown algae, distant from both animals and plants (Theodorou and Charrier 2021).
My thesis is the first approach on the embryonic development of Saccharina latissima focusing on the morphogenetic mechanisms related to cell and tissue patterning. Through microscopical studies, morphometrical analysis, simulation and modelling, we aimed to shed light on the morphogenesis of Saccharina’s embryos. Consequently, we establish the emergence of a new developmental model easily distinguished from other better studied organisms.
