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Functional ultrastructure of the plant nucleolus.

Stępiński D - Protoplasma (2014)

Bottom Line: The ratios and morphology of particular subcompartments of a nucleolus can change depending on its metabolic activity which in turn is correlated with the physiological state of a cell, cell type, cell cycle phase, as well as with environmental influence.Precise attribution of functions to particular nucleolar subregions in the process of ribosome biosynthesis is now possible using various approaches.The presented description of plant nucleolar morphology summarizes previous knowledge regarding the function of nucleoli as well as of their particular subdomains not only in the course of ribosome biosynthesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Cytophysiology, Faculty of Biology and Environmental Protection, University of Łódź, Pomorska 141/143, 90-236, Łódź, Poland, dareks@biol.uni.lodz.pl.

ABSTRACT
Nucleoli are nuclear domains present in almost all eukaryotic cells. They not only specialize in the production of ribosomal subunits but also play roles in many fundamental cellular activities. Concerning ribosome biosynthesis, particular stages of this process, i.e., ribosomal DNA transcription, primary RNA transcript processing, and ribosome assembly proceed in precisely defined nucleolar subdomains. Although eukaryotic nucleoli are conservative in respect of their main function, clear morphological differences between these structures can be noticed between individual kingdoms. In most cases, a plant nucleolus shows well-ordered structure in which four main ultrastructural components can be distinguished: fibrillar centers, dense fibrillar component, granular component, and nucleolar vacuoles. Nucleolar chromatin is an additional crucial structural component of this organelle. Nucleolonema, although it is not always an unequivocally distinguished nucleolar domain, has often been described as a well-grounded morphological element, especially of plant nucleoli. The ratios and morphology of particular subcompartments of a nucleolus can change depending on its metabolic activity which in turn is correlated with the physiological state of a cell, cell type, cell cycle phase, as well as with environmental influence. Precise attribution of functions to particular nucleolar subregions in the process of ribosome biosynthesis is now possible using various approaches. The presented description of plant nucleolar morphology summarizes previous knowledge regarding the function of nucleoli as well as of their particular subdomains not only in the course of ribosome biosynthesis.

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Typical plant nucleoli of tip root meristem cells and nucleolar components. Ultrastructure of nucleoli, representing four-component morphology, i.e., fibrillar centres (FC), dense fibrillar component (DFC), granular component (GC), and nucleolar vacuoles (NoV); conventional electron microscopy technique images (a, b). A nucleolus with mild transcriptional activity; it is characterized by lower number of FCs and small NoV (a). A nucleolus with high transcriptional activity with greater number of FCs and big, centrally located NoV (b). Scale bar, 2 μm. Examples of different size and shape FCs (c, d): heterogeneous FCs containing clumps of condensed chromatin (c). Scale bar is 0.5 μm. Homogenous FCs (d). Scale bar, 0.5 μm. Tip root meristematic cells with nucleoli in which NoV are formed, from small NoV in nucleoli with low transcriptional activity, through bigger and bigger vacuoles in nucleoli with higher and higher activity, up to one big, centrally located vacuole in nucleoli with high transcriptional activity; semi-thin sections (e). Scale bar, 10 μm. GC of a regular nucleolus (left) and loosened GC of a low transcriptionally active nucleolus of the chilled soybean seedling (right) (f). Scale bar, 0.5 μm. Examples of FCs connecting with each other by canals (arrows) running through dense fibrillar component (g). Scale bar, 1 μm. N nucleus, CCh condensed chromatin, CB coiled body, NE nuclear envelope
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Fig1: Typical plant nucleoli of tip root meristem cells and nucleolar components. Ultrastructure of nucleoli, representing four-component morphology, i.e., fibrillar centres (FC), dense fibrillar component (DFC), granular component (GC), and nucleolar vacuoles (NoV); conventional electron microscopy technique images (a, b). A nucleolus with mild transcriptional activity; it is characterized by lower number of FCs and small NoV (a). A nucleolus with high transcriptional activity with greater number of FCs and big, centrally located NoV (b). Scale bar, 2 μm. Examples of different size and shape FCs (c, d): heterogeneous FCs containing clumps of condensed chromatin (c). Scale bar is 0.5 μm. Homogenous FCs (d). Scale bar, 0.5 μm. Tip root meristematic cells with nucleoli in which NoV are formed, from small NoV in nucleoli with low transcriptional activity, through bigger and bigger vacuoles in nucleoli with higher and higher activity, up to one big, centrally located vacuole in nucleoli with high transcriptional activity; semi-thin sections (e). Scale bar, 10 μm. GC of a regular nucleolus (left) and loosened GC of a low transcriptionally active nucleolus of the chilled soybean seedling (right) (f). Scale bar, 0.5 μm. Examples of FCs connecting with each other by canals (arrows) running through dense fibrillar component (g). Scale bar, 1 μm. N nucleus, CCh condensed chromatin, CB coiled body, NE nuclear envelope

Mentions: The structural model of plant nucleoli was mainly based on electron microscopic examinations using different techniques of revealing particular nucleolar territories (Figs. 1a, b, 2a, and 3b) (Trendelenburg et al. 1996). Cytochemical investigations supplemented ultrastructural and morphological studies. Research in recent decades allowed for the precise analysis of particular nucleolar subcompartments and assigned to them appropriate functions during ribosome biosynthesis (Beven et al. 1996). The nucleolar subdomains form a radial pattern in which newly synthesized pre-ribosomal transcripts move away from the FC-DFC border towards the periphery of nucleoli through DFC and GC (Brown and Shaw 1998).Fig. 1


Functional ultrastructure of the plant nucleolus.

Stępiński D - Protoplasma (2014)

Typical plant nucleoli of tip root meristem cells and nucleolar components. Ultrastructure of nucleoli, representing four-component morphology, i.e., fibrillar centres (FC), dense fibrillar component (DFC), granular component (GC), and nucleolar vacuoles (NoV); conventional electron microscopy technique images (a, b). A nucleolus with mild transcriptional activity; it is characterized by lower number of FCs and small NoV (a). A nucleolus with high transcriptional activity with greater number of FCs and big, centrally located NoV (b). Scale bar, 2 μm. Examples of different size and shape FCs (c, d): heterogeneous FCs containing clumps of condensed chromatin (c). Scale bar is 0.5 μm. Homogenous FCs (d). Scale bar, 0.5 μm. Tip root meristematic cells with nucleoli in which NoV are formed, from small NoV in nucleoli with low transcriptional activity, through bigger and bigger vacuoles in nucleoli with higher and higher activity, up to one big, centrally located vacuole in nucleoli with high transcriptional activity; semi-thin sections (e). Scale bar, 10 μm. GC of a regular nucleolus (left) and loosened GC of a low transcriptionally active nucleolus of the chilled soybean seedling (right) (f). Scale bar, 0.5 μm. Examples of FCs connecting with each other by canals (arrows) running through dense fibrillar component (g). Scale bar, 1 μm. N nucleus, CCh condensed chromatin, CB coiled body, NE nuclear envelope
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4209244&req=5

Fig1: Typical plant nucleoli of tip root meristem cells and nucleolar components. Ultrastructure of nucleoli, representing four-component morphology, i.e., fibrillar centres (FC), dense fibrillar component (DFC), granular component (GC), and nucleolar vacuoles (NoV); conventional electron microscopy technique images (a, b). A nucleolus with mild transcriptional activity; it is characterized by lower number of FCs and small NoV (a). A nucleolus with high transcriptional activity with greater number of FCs and big, centrally located NoV (b). Scale bar, 2 μm. Examples of different size and shape FCs (c, d): heterogeneous FCs containing clumps of condensed chromatin (c). Scale bar is 0.5 μm. Homogenous FCs (d). Scale bar, 0.5 μm. Tip root meristematic cells with nucleoli in which NoV are formed, from small NoV in nucleoli with low transcriptional activity, through bigger and bigger vacuoles in nucleoli with higher and higher activity, up to one big, centrally located vacuole in nucleoli with high transcriptional activity; semi-thin sections (e). Scale bar, 10 μm. GC of a regular nucleolus (left) and loosened GC of a low transcriptionally active nucleolus of the chilled soybean seedling (right) (f). Scale bar, 0.5 μm. Examples of FCs connecting with each other by canals (arrows) running through dense fibrillar component (g). Scale bar, 1 μm. N nucleus, CCh condensed chromatin, CB coiled body, NE nuclear envelope
Mentions: The structural model of plant nucleoli was mainly based on electron microscopic examinations using different techniques of revealing particular nucleolar territories (Figs. 1a, b, 2a, and 3b) (Trendelenburg et al. 1996). Cytochemical investigations supplemented ultrastructural and morphological studies. Research in recent decades allowed for the precise analysis of particular nucleolar subcompartments and assigned to them appropriate functions during ribosome biosynthesis (Beven et al. 1996). The nucleolar subdomains form a radial pattern in which newly synthesized pre-ribosomal transcripts move away from the FC-DFC border towards the periphery of nucleoli through DFC and GC (Brown and Shaw 1998).Fig. 1

Bottom Line: The ratios and morphology of particular subcompartments of a nucleolus can change depending on its metabolic activity which in turn is correlated with the physiological state of a cell, cell type, cell cycle phase, as well as with environmental influence.Precise attribution of functions to particular nucleolar subregions in the process of ribosome biosynthesis is now possible using various approaches.The presented description of plant nucleolar morphology summarizes previous knowledge regarding the function of nucleoli as well as of their particular subdomains not only in the course of ribosome biosynthesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Cytophysiology, Faculty of Biology and Environmental Protection, University of Łódź, Pomorska 141/143, 90-236, Łódź, Poland, dareks@biol.uni.lodz.pl.

ABSTRACT
Nucleoli are nuclear domains present in almost all eukaryotic cells. They not only specialize in the production of ribosomal subunits but also play roles in many fundamental cellular activities. Concerning ribosome biosynthesis, particular stages of this process, i.e., ribosomal DNA transcription, primary RNA transcript processing, and ribosome assembly proceed in precisely defined nucleolar subdomains. Although eukaryotic nucleoli are conservative in respect of their main function, clear morphological differences between these structures can be noticed between individual kingdoms. In most cases, a plant nucleolus shows well-ordered structure in which four main ultrastructural components can be distinguished: fibrillar centers, dense fibrillar component, granular component, and nucleolar vacuoles. Nucleolar chromatin is an additional crucial structural component of this organelle. Nucleolonema, although it is not always an unequivocally distinguished nucleolar domain, has often been described as a well-grounded morphological element, especially of plant nucleoli. The ratios and morphology of particular subcompartments of a nucleolus can change depending on its metabolic activity which in turn is correlated with the physiological state of a cell, cell type, cell cycle phase, as well as with environmental influence. Precise attribution of functions to particular nucleolar subregions in the process of ribosome biosynthesis is now possible using various approaches. The presented description of plant nucleolar morphology summarizes previous knowledge regarding the function of nucleoli as well as of their particular subdomains not only in the course of ribosome biosynthesis.

Show MeSH