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Micrasterias as a Model System in Plant Cell Biology.

Lütz-Meindl U - Front Plant Sci (2016)

Bottom Line: The review focuses particularly on cell wall formation and composition, dictyosomal structure and function, cytoskeleton control of growth and morphogenesis as well as on ionic regulation and signal transduction.It has been also shown in the recent years that Micrasterias is a highly sensitive indicator for environmental stress impact such as heavy metals, high salinity, oxidative stress or starvation.This review is intended to summarize and discuss the most important results obtained in Micrasterias in the last 20 years and to compare the results to similar processes in higher plant cells.

View Article: PubMed Central - PubMed

Affiliation: Plant Physiology Division, Cell Biology Department, University of Salzburg Salzburg, Austria.

ABSTRACT
The unicellular freshwater alga Micrasterias denticulata is an exceptional organism due to its complex star-shaped, highly symmetric morphology and has thus attracted the interest of researchers for many decades. As a member of the Streptophyta, Micrasterias is not only genetically closely related to higher land plants but shares common features with them in many physiological and cell biological aspects. These facts, together with its considerable cell size of about 200 μm, its modest cultivation conditions and the uncomplicated accessibility particularly to any microscopic techniques, make Micrasterias a very well suited cell biological plant model system. The review focuses particularly on cell wall formation and composition, dictyosomal structure and function, cytoskeleton control of growth and morphogenesis as well as on ionic regulation and signal transduction. It has been also shown in the recent years that Micrasterias is a highly sensitive indicator for environmental stress impact such as heavy metals, high salinity, oxidative stress or starvation. Stress induced organelle degradation, autophagy, adaption and detoxification mechanisms have moved in the center of interest and have been investigated with modern microscopic techniques such as 3-D- and analytical electron microscopy as well as with biochemical, physiological and molecular approaches. This review is intended to summarize and discuss the most important results obtained in Micrasterias in the last 20 years and to compare the results to similar processes in higher plant cells.

No MeSH data available.


Related in: MedlinePlus

Transmission electron microscopy (TEM) micrograph (A) of cell periphery and primary cell wall of M. denticulata with highlighted measurement sites of EEL spectra (scale bar is 1 μm). (B) EEL spectra acquired at the Ca L2,3-edge, indicating calcium binding capacities of different cell components after doping with calcium acetate. Outer side of primary wall (green) has higher calcium binding capacity than inner side (red). Mucilage vesicle (blue) reveal highest calcium binding capacity, the cytoplasm (orange) lowest. Reprinted with permission from Eder and Lütz-Meindl (2008), Copyright© 2008 Royal Microscopical Society.
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Figure 2: Transmission electron microscopy (TEM) micrograph (A) of cell periphery and primary cell wall of M. denticulata with highlighted measurement sites of EEL spectra (scale bar is 1 μm). (B) EEL spectra acquired at the Ca L2,3-edge, indicating calcium binding capacities of different cell components after doping with calcium acetate. Outer side of primary wall (green) has higher calcium binding capacity than inner side (red). Mucilage vesicle (blue) reveal highest calcium binding capacity, the cytoplasm (orange) lowest. Reprinted with permission from Eder and Lütz-Meindl (2008), Copyright© 2008 Royal Microscopical Society.

Mentions: Achievement of the complex cell pattern of a Micrasterias cell requires particular physical properties of the primary cell wall that allow intussusception of wall material on the one hand and stiffening and growth arrest on the other hand. Recent Raman spectroscopic investigations (Figure 1B) clearly show that the cellulose content of the primary wall of the outgrowing lobes is much lower than that of the indentations in which the cell wall is thicker and less extensible. This technique also demonstrates unambiguously the considerable difference in thickness and cellulose content between the growing primary and the non-growing secondary cell wall. The degree of pectin esterification which determines the calcium-binding capacity accounts for the flexibility of the cell wall during primary wall growth. A combination of immuno TEM, immuno fluorescence, de-esterification studies and calcium measurements by TEM-coupled electron energy loss spectroscopy (EELS) has shown (Lütz-Meindl and Brosch-Salomon, 2000; Eder and Lütz-Meindl, 2008) that pectic polysaccharides are transported to the cell wall in a de-esterified form inside of a particular Golgi vesicle population (D-vescicles according to Kiermayer, 1970a,b; Meindl et al., 1992; Lütz-Meindl and Brosch-Salomon, 2000) and become methyl-esterified at the inner side of the developing primary wall (Eder and Lütz-Meindl, 2008). This allows flexibility and integration of new wall material. While they are translocated toward the outer side of the wall they become again de-esterified (see also Lütz-Meindl and Brosch-Salomon, 2000) and are thus able to bind high amounts of calcium (Figures 2A,B) which leads to wall stiffening and growth cessation. Enzyme activity assays provided evidence for the existence of a pectin-desterifying enzyme in M. denticulata. Moreover, enhanced desterification by experimental addition of a pectin methylesterase that de-esterifies pectins in higher plants, resulted in growth inhibition and shape malformation of Micrasterias (Eder and Lütz-Meindl, 2008). This indicates that as in higher plant cells (Carpita and Gibeaut, 1993; Goldberg et al., 2001; Bosch et al., 2005; Bosch and Hepler, 2005) the de-esterification process and its regulation is crucial for morphogenesis and growth of Micrasterias (Eder and Lütz-Meindl, 2008). Though it is likely, there is so far no indication that the degree of esterification is different in the areas of the forming indentations in comparison to the zones of the outgrowing lobes.


Micrasterias as a Model System in Plant Cell Biology.

Lütz-Meindl U - Front Plant Sci (2016)

Transmission electron microscopy (TEM) micrograph (A) of cell periphery and primary cell wall of M. denticulata with highlighted measurement sites of EEL spectra (scale bar is 1 μm). (B) EEL spectra acquired at the Ca L2,3-edge, indicating calcium binding capacities of different cell components after doping with calcium acetate. Outer side of primary wall (green) has higher calcium binding capacity than inner side (red). Mucilage vesicle (blue) reveal highest calcium binding capacity, the cytoplasm (orange) lowest. Reprinted with permission from Eder and Lütz-Meindl (2008), Copyright© 2008 Royal Microscopical Society.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4940373&req=5

Figure 2: Transmission electron microscopy (TEM) micrograph (A) of cell periphery and primary cell wall of M. denticulata with highlighted measurement sites of EEL spectra (scale bar is 1 μm). (B) EEL spectra acquired at the Ca L2,3-edge, indicating calcium binding capacities of different cell components after doping with calcium acetate. Outer side of primary wall (green) has higher calcium binding capacity than inner side (red). Mucilage vesicle (blue) reveal highest calcium binding capacity, the cytoplasm (orange) lowest. Reprinted with permission from Eder and Lütz-Meindl (2008), Copyright© 2008 Royal Microscopical Society.
Mentions: Achievement of the complex cell pattern of a Micrasterias cell requires particular physical properties of the primary cell wall that allow intussusception of wall material on the one hand and stiffening and growth arrest on the other hand. Recent Raman spectroscopic investigations (Figure 1B) clearly show that the cellulose content of the primary wall of the outgrowing lobes is much lower than that of the indentations in which the cell wall is thicker and less extensible. This technique also demonstrates unambiguously the considerable difference in thickness and cellulose content between the growing primary and the non-growing secondary cell wall. The degree of pectin esterification which determines the calcium-binding capacity accounts for the flexibility of the cell wall during primary wall growth. A combination of immuno TEM, immuno fluorescence, de-esterification studies and calcium measurements by TEM-coupled electron energy loss spectroscopy (EELS) has shown (Lütz-Meindl and Brosch-Salomon, 2000; Eder and Lütz-Meindl, 2008) that pectic polysaccharides are transported to the cell wall in a de-esterified form inside of a particular Golgi vesicle population (D-vescicles according to Kiermayer, 1970a,b; Meindl et al., 1992; Lütz-Meindl and Brosch-Salomon, 2000) and become methyl-esterified at the inner side of the developing primary wall (Eder and Lütz-Meindl, 2008). This allows flexibility and integration of new wall material. While they are translocated toward the outer side of the wall they become again de-esterified (see also Lütz-Meindl and Brosch-Salomon, 2000) and are thus able to bind high amounts of calcium (Figures 2A,B) which leads to wall stiffening and growth cessation. Enzyme activity assays provided evidence for the existence of a pectin-desterifying enzyme in M. denticulata. Moreover, enhanced desterification by experimental addition of a pectin methylesterase that de-esterifies pectins in higher plants, resulted in growth inhibition and shape malformation of Micrasterias (Eder and Lütz-Meindl, 2008). This indicates that as in higher plant cells (Carpita and Gibeaut, 1993; Goldberg et al., 2001; Bosch et al., 2005; Bosch and Hepler, 2005) the de-esterification process and its regulation is crucial for morphogenesis and growth of Micrasterias (Eder and Lütz-Meindl, 2008). Though it is likely, there is so far no indication that the degree of esterification is different in the areas of the forming indentations in comparison to the zones of the outgrowing lobes.

Bottom Line: The review focuses particularly on cell wall formation and composition, dictyosomal structure and function, cytoskeleton control of growth and morphogenesis as well as on ionic regulation and signal transduction.It has been also shown in the recent years that Micrasterias is a highly sensitive indicator for environmental stress impact such as heavy metals, high salinity, oxidative stress or starvation.This review is intended to summarize and discuss the most important results obtained in Micrasterias in the last 20 years and to compare the results to similar processes in higher plant cells.

View Article: PubMed Central - PubMed

Affiliation: Plant Physiology Division, Cell Biology Department, University of Salzburg Salzburg, Austria.

ABSTRACT
The unicellular freshwater alga Micrasterias denticulata is an exceptional organism due to its complex star-shaped, highly symmetric morphology and has thus attracted the interest of researchers for many decades. As a member of the Streptophyta, Micrasterias is not only genetically closely related to higher land plants but shares common features with them in many physiological and cell biological aspects. These facts, together with its considerable cell size of about 200 μm, its modest cultivation conditions and the uncomplicated accessibility particularly to any microscopic techniques, make Micrasterias a very well suited cell biological plant model system. The review focuses particularly on cell wall formation and composition, dictyosomal structure and function, cytoskeleton control of growth and morphogenesis as well as on ionic regulation and signal transduction. It has been also shown in the recent years that Micrasterias is a highly sensitive indicator for environmental stress impact such as heavy metals, high salinity, oxidative stress or starvation. Stress induced organelle degradation, autophagy, adaption and detoxification mechanisms have moved in the center of interest and have been investigated with modern microscopic techniques such as 3-D- and analytical electron microscopy as well as with biochemical, physiological and molecular approaches. This review is intended to summarize and discuss the most important results obtained in Micrasterias in the last 20 years and to compare the results to similar processes in higher plant cells.

No MeSH data available.


Related in: MedlinePlus