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Photosynthesis-dependent formation of convoluted plasma membrane domains in Chara internodal cells is independent of chloroplast position.

Foissner I, Sommer A, Hoeftberger M - Protoplasma (2014)

Bottom Line: In contrast, charasomes were rarely found at uneven, bulged wound walls which protrude into the streaming endoplasm and which were induced by ligation or puncturing.The results of this study show that charasome formation, although dependent on photosynthesis, does not require intimate contact with chloroplasts.Finally, we hypothesize that the absence of charasomes at bulged wound walls is due to the disturbance of uniform laminar mass streaming.

View Article: PubMed Central - PubMed

Affiliation: Plant Physiology/Cell Biology, University of Salzburg, Hellbrunnerstrasse 34, 5020, Salzburg, Austria, Ilse.Foissner@sbg.ac.at.

ABSTRACT
The characean green alga Chara australis forms complex plasma membrane convolutions called charasomes when exposed to light. Charasomes are involved in local acidification of the surrounding medium which facilitates carbon uptake required for photosynthesis. They have hitherto been only described in the internodal cells and in close contact with the stationary chloroplasts. Here, we show that charasomes are not only present in the internodal cells of the main axis, side branches, and branchlets but that the plasma membranes of chloroplast-containing nodal cells, protonemata, and rhizoids are also able to invaginate into complex domains. Removal of chloroplasts by local irradiation with intense light revealed that charasomes can develop at chloroplast-free "windows" and that the resulting pH banding pattern is independent of chloroplast or window position. Charasomes were not detected along cell walls containing functional plasmodesmata. However, charasomes formed next to a smooth wound wall which was deposited onto the plasmodesmata-containing wall when the neighboring cell was damaged. In contrast, charasomes were rarely found at uneven, bulged wound walls which protrude into the streaming endoplasm and which were induced by ligation or puncturing. The results of this study show that charasome formation, although dependent on photosynthesis, does not require intimate contact with chloroplasts. Our data suggest further that the presence of plasmodesmata inhibits charasome formation and/or that exposure to the outer medium is a prerequisite for charasome formation. Finally, we hypothesize that the absence of charasomes at bulged wound walls is due to the disturbance of uniform laminar mass streaming.

No MeSH data available.


Related in: MedlinePlus

Charasomes in chloroplast-free windows. a Chloroplasts (red fluorescent) in an internodal cell of the main axis are absent from windows created by irradiation with blue light (projection of 146 optical sections with a thickness of 1.4 μm). b, c Schematic drawing and light micrograph showing the pH banding pattern visualized by phenol red in two neighboring internodal cells of a branchlet before and in 1-week intervals after the creation of windows (white circles) at the alkaline bands (pink). Note that the upper window became and remained acidic whereas the pH at the window in the lower cell was variable. In the light micrograph (c) the positions of the windows are indicated by arrows. d–g Charasomes stained by green fluorescent FM1-43 and mitochondria labeled with red fluorescent MT orange in an acidic window and in the adjacent control region. Charasomes are more evenly distributed in the window than between the autofluorescent chloroplasts (false colored blue in (d)). Mitochondria are less abundant in the window. e The corresponding DIC image. f, g Higher magnifications corresponding to the insets shown in (d). h–k Charasome distribution in a window in which the pH abruptly changes from alkaline to acidic (arrow in (h)). The acidic part of the window contains abundant and large charasomes stained by green fluorescent FM1-43; in the alkaline part of the window charasomes are absent. The fluorescent image merged with the bright field image (j) and a higher magnification (k) of the inset shown in (i). l Electron micrograph of a charasome (asterisk) near the cell wall (CW) of a chloroplast-free window; V is the central vacuole. Bars = 1 cm (b, c, h) 200 μm (a), 50 μm (i, j), 10 μm (d, e, k), 5 μm (f, g), 500 nm (l)
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Fig3: Charasomes in chloroplast-free windows. a Chloroplasts (red fluorescent) in an internodal cell of the main axis are absent from windows created by irradiation with blue light (projection of 146 optical sections with a thickness of 1.4 μm). b, c Schematic drawing and light micrograph showing the pH banding pattern visualized by phenol red in two neighboring internodal cells of a branchlet before and in 1-week intervals after the creation of windows (white circles) at the alkaline bands (pink). Note that the upper window became and remained acidic whereas the pH at the window in the lower cell was variable. In the light micrograph (c) the positions of the windows are indicated by arrows. d–g Charasomes stained by green fluorescent FM1-43 and mitochondria labeled with red fluorescent MT orange in an acidic window and in the adjacent control region. Charasomes are more evenly distributed in the window than between the autofluorescent chloroplasts (false colored blue in (d)). Mitochondria are less abundant in the window. e The corresponding DIC image. f, g Higher magnifications corresponding to the insets shown in (d). h–k Charasome distribution in a window in which the pH abruptly changes from alkaline to acidic (arrow in (h)). The acidic part of the window contains abundant and large charasomes stained by green fluorescent FM1-43; in the alkaline part of the window charasomes are absent. The fluorescent image merged with the bright field image (j) and a higher magnification (k) of the inset shown in (i). l Electron micrograph of a charasome (asterisk) near the cell wall (CW) of a chloroplast-free window; V is the central vacuole. Bars = 1 cm (b, c, h) 200 μm (a), 50 μm (i, j), 10 μm (d, e, k), 5 μm (f, g), 500 nm (l)

Mentions: Our observations showed that, firstly, charasomes often developed in considerable distance to the stationary chloroplasts in protonema and rhizoid cells and that, secondly, charasomes were present in nodal cells with mobile chloroplasts. These findings prompted us to investigate whether and how the experimental removal of chloroplasts in the internodal cells affected charasome formation and pH banding. We therefore produced chloroplast-free “windows” by local irradiation of cells with the intense light of a halide or mercury lamp attached to a microscope. For our experiments, we isolated non-calcified and non-growing internodal cells and incubated them in artificial fresh water for 1 day. The pH banding pattern of these cells was variable over a period of several days consistent with earlier observations in the internodal cells without CaCO3 deposits (Suppl. Fig. 2; Lucas and Smith 1973). Nonetheless, the pH banding pattern largely correlated with the size and density of charasomes as described above; i. e., they were large and abundant at the acid regions and small and scarce at the alkaline areas. We also investigated the internodal cells which had been incubated in darkness for 2 weeks in order to degrade the charasomes. These cells likewise produced acid and alkaline bands, although they contained no or only very few, small charasomes which were evenly distributed along the longitudinal cell walls (Bisson et al. 1991; Schmoelzer et al. 2011). The results obtained with the internodal cells of the branchlets were similar to those obtained with the internodal cells of the main axis and independent of the size of windows which had a diameter between 60 and 400 μm. In the following, we describe windows in the internodal cells of branchlets and with a size that corresponded to about one-third of the cell circumference (about 200 μm, Fig. 3a). Information about pH banding at chloroplast-free windows in the internodal cells of the main axis are found in Suppl. Fig. 2.Fig. 3


Photosynthesis-dependent formation of convoluted plasma membrane domains in Chara internodal cells is independent of chloroplast position.

Foissner I, Sommer A, Hoeftberger M - Protoplasma (2014)

Charasomes in chloroplast-free windows. a Chloroplasts (red fluorescent) in an internodal cell of the main axis are absent from windows created by irradiation with blue light (projection of 146 optical sections with a thickness of 1.4 μm). b, c Schematic drawing and light micrograph showing the pH banding pattern visualized by phenol red in two neighboring internodal cells of a branchlet before and in 1-week intervals after the creation of windows (white circles) at the alkaline bands (pink). Note that the upper window became and remained acidic whereas the pH at the window in the lower cell was variable. In the light micrograph (c) the positions of the windows are indicated by arrows. d–g Charasomes stained by green fluorescent FM1-43 and mitochondria labeled with red fluorescent MT orange in an acidic window and in the adjacent control region. Charasomes are more evenly distributed in the window than between the autofluorescent chloroplasts (false colored blue in (d)). Mitochondria are less abundant in the window. e The corresponding DIC image. f, g Higher magnifications corresponding to the insets shown in (d). h–k Charasome distribution in a window in which the pH abruptly changes from alkaline to acidic (arrow in (h)). The acidic part of the window contains abundant and large charasomes stained by green fluorescent FM1-43; in the alkaline part of the window charasomes are absent. The fluorescent image merged with the bright field image (j) and a higher magnification (k) of the inset shown in (i). l Electron micrograph of a charasome (asterisk) near the cell wall (CW) of a chloroplast-free window; V is the central vacuole. Bars = 1 cm (b, c, h) 200 μm (a), 50 μm (i, j), 10 μm (d, e, k), 5 μm (f, g), 500 nm (l)
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Fig3: Charasomes in chloroplast-free windows. a Chloroplasts (red fluorescent) in an internodal cell of the main axis are absent from windows created by irradiation with blue light (projection of 146 optical sections with a thickness of 1.4 μm). b, c Schematic drawing and light micrograph showing the pH banding pattern visualized by phenol red in two neighboring internodal cells of a branchlet before and in 1-week intervals after the creation of windows (white circles) at the alkaline bands (pink). Note that the upper window became and remained acidic whereas the pH at the window in the lower cell was variable. In the light micrograph (c) the positions of the windows are indicated by arrows. d–g Charasomes stained by green fluorescent FM1-43 and mitochondria labeled with red fluorescent MT orange in an acidic window and in the adjacent control region. Charasomes are more evenly distributed in the window than between the autofluorescent chloroplasts (false colored blue in (d)). Mitochondria are less abundant in the window. e The corresponding DIC image. f, g Higher magnifications corresponding to the insets shown in (d). h–k Charasome distribution in a window in which the pH abruptly changes from alkaline to acidic (arrow in (h)). The acidic part of the window contains abundant and large charasomes stained by green fluorescent FM1-43; in the alkaline part of the window charasomes are absent. The fluorescent image merged with the bright field image (j) and a higher magnification (k) of the inset shown in (i). l Electron micrograph of a charasome (asterisk) near the cell wall (CW) of a chloroplast-free window; V is the central vacuole. Bars = 1 cm (b, c, h) 200 μm (a), 50 μm (i, j), 10 μm (d, e, k), 5 μm (f, g), 500 nm (l)
Mentions: Our observations showed that, firstly, charasomes often developed in considerable distance to the stationary chloroplasts in protonema and rhizoid cells and that, secondly, charasomes were present in nodal cells with mobile chloroplasts. These findings prompted us to investigate whether and how the experimental removal of chloroplasts in the internodal cells affected charasome formation and pH banding. We therefore produced chloroplast-free “windows” by local irradiation of cells with the intense light of a halide or mercury lamp attached to a microscope. For our experiments, we isolated non-calcified and non-growing internodal cells and incubated them in artificial fresh water for 1 day. The pH banding pattern of these cells was variable over a period of several days consistent with earlier observations in the internodal cells without CaCO3 deposits (Suppl. Fig. 2; Lucas and Smith 1973). Nonetheless, the pH banding pattern largely correlated with the size and density of charasomes as described above; i. e., they were large and abundant at the acid regions and small and scarce at the alkaline areas. We also investigated the internodal cells which had been incubated in darkness for 2 weeks in order to degrade the charasomes. These cells likewise produced acid and alkaline bands, although they contained no or only very few, small charasomes which were evenly distributed along the longitudinal cell walls (Bisson et al. 1991; Schmoelzer et al. 2011). The results obtained with the internodal cells of the branchlets were similar to those obtained with the internodal cells of the main axis and independent of the size of windows which had a diameter between 60 and 400 μm. In the following, we describe windows in the internodal cells of branchlets and with a size that corresponded to about one-third of the cell circumference (about 200 μm, Fig. 3a). Information about pH banding at chloroplast-free windows in the internodal cells of the main axis are found in Suppl. Fig. 2.Fig. 3

Bottom Line: In contrast, charasomes were rarely found at uneven, bulged wound walls which protrude into the streaming endoplasm and which were induced by ligation or puncturing.The results of this study show that charasome formation, although dependent on photosynthesis, does not require intimate contact with chloroplasts.Finally, we hypothesize that the absence of charasomes at bulged wound walls is due to the disturbance of uniform laminar mass streaming.

View Article: PubMed Central - PubMed

Affiliation: Plant Physiology/Cell Biology, University of Salzburg, Hellbrunnerstrasse 34, 5020, Salzburg, Austria, Ilse.Foissner@sbg.ac.at.

ABSTRACT
The characean green alga Chara australis forms complex plasma membrane convolutions called charasomes when exposed to light. Charasomes are involved in local acidification of the surrounding medium which facilitates carbon uptake required for photosynthesis. They have hitherto been only described in the internodal cells and in close contact with the stationary chloroplasts. Here, we show that charasomes are not only present in the internodal cells of the main axis, side branches, and branchlets but that the plasma membranes of chloroplast-containing nodal cells, protonemata, and rhizoids are also able to invaginate into complex domains. Removal of chloroplasts by local irradiation with intense light revealed that charasomes can develop at chloroplast-free "windows" and that the resulting pH banding pattern is independent of chloroplast or window position. Charasomes were not detected along cell walls containing functional plasmodesmata. However, charasomes formed next to a smooth wound wall which was deposited onto the plasmodesmata-containing wall when the neighboring cell was damaged. In contrast, charasomes were rarely found at uneven, bulged wound walls which protrude into the streaming endoplasm and which were induced by ligation or puncturing. The results of this study show that charasome formation, although dependent on photosynthesis, does not require intimate contact with chloroplasts. Our data suggest further that the presence of plasmodesmata inhibits charasome formation and/or that exposure to the outer medium is a prerequisite for charasome formation. Finally, we hypothesize that the absence of charasomes at bulged wound walls is due to the disturbance of uniform laminar mass streaming.

No MeSH data available.


Related in: MedlinePlus