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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 are absent from uneven wound walls. a–d Ligation-induced wound walls. The medium near the ligation site of an internodal cell has an alkaline pH (pink) as visualized by phenol red. Cell deformation and a thick wound wall (arrow) becomes visible after removal of the thread (b). Insets correspond to the images (c) and (d). Charasomes (green FM1-43-fluorescent) are absent from the ligation site ((c), corresponding to the upper inset in (b)) and present between red fluorescent chloroplasts in the adjacent acidic control region ((d), corresponding to the lower inset in (b)). e–k Wound walls (WW) induced by puncturing. A single puncture wound (arrow) located within an acidic region is seen in (e). The optical section through the periphery of the cell shows abundant FM1-43 fluorescent charasomes (arrows) outside the wound plug (WP) which seals the cell wall hole (f). No charasomes are visible in an optical section along the wound wall (encircled in (g)). Green fluorescent particles outside the wound wall are mobile FM1-43-stained organelles (putative endosomes) in the endoplasm. The arrow in the optical longitudinal section through a wound plug in (h) points to a single charasome at the otherwise smooth plasma membrane along the non-fluorescent wound wall. Charasomes are seen between the red fluorescent chloroplasts in the unwounded area (arrow head). Multiple puncture wounds cause an alkalinization of the phenol red-containing medium (i). Few charasomes (green fluorescent after staining with FM1-43) are seen in the wound area (j) in comparison with the unwounded region (k). l–n Wound walls caused by epiphytes. The optical section through the cortical cytoplasm shows numerous FM1-43-stained charasomes (green) between red fluorescent chloroplasts surrounding the wound walls (l). Only few charasomes (arrows in (m)) are present at the inner surface of the wound walls; corresponding DIC image (N). Bars = 1 mm (a, e), 300 μm (i), 150 μm (b) 50 μm (c), 20 μm (d, f, g, j-n), 10 μm (h)
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Fig4: Charasomes are absent from uneven wound walls. a–d Ligation-induced wound walls. The medium near the ligation site of an internodal cell has an alkaline pH (pink) as visualized by phenol red. Cell deformation and a thick wound wall (arrow) becomes visible after removal of the thread (b). Insets correspond to the images (c) and (d). Charasomes (green FM1-43-fluorescent) are absent from the ligation site ((c), corresponding to the upper inset in (b)) and present between red fluorescent chloroplasts in the adjacent acidic control region ((d), corresponding to the lower inset in (b)). e–k Wound walls (WW) induced by puncturing. A single puncture wound (arrow) located within an acidic region is seen in (e). The optical section through the periphery of the cell shows abundant FM1-43 fluorescent charasomes (arrows) outside the wound plug (WP) which seals the cell wall hole (f). No charasomes are visible in an optical section along the wound wall (encircled in (g)). Green fluorescent particles outside the wound wall are mobile FM1-43-stained organelles (putative endosomes) in the endoplasm. The arrow in the optical longitudinal section through a wound plug in (h) points to a single charasome at the otherwise smooth plasma membrane along the non-fluorescent wound wall. Charasomes are seen between the red fluorescent chloroplasts in the unwounded area (arrow head). Multiple puncture wounds cause an alkalinization of the phenol red-containing medium (i). Few charasomes (green fluorescent after staining with FM1-43) are seen in the wound area (j) in comparison with the unwounded region (k). l–n Wound walls caused by epiphytes. The optical section through the cortical cytoplasm shows numerous FM1-43-stained charasomes (green) between red fluorescent chloroplasts surrounding the wound walls (l). Only few charasomes (arrows in (m)) are present at the inner surface of the wound walls; corresponding DIC image (N). Bars = 1 mm (a, e), 300 μm (i), 150 μm (b) 50 μm (c), 20 μm (d, f, g, j-n), 10 μm (h)

Mentions: We first repeated the ligation experiments and studied pH banding and charasome distribution in response to artificial constriction of the cell. The internodal cells were exposed to the air until turgor was lost and ligated at an acid band with the aid of cotton thread (Fig. 4a, Shimmen and Yamamoto 2002). Cells were allowed to recover in artificial fresh water, and the pH banding pattern in medium supplemented with phenol red was recorded over a period of several weeks. The pH at ligated regions was consistently alkaline if ligation was strong enough to induce the deposition of a thick wound wall which protruded deep into the endoplasm and eventually caused deformations in cell shape (Fig. 4a, b). In our hands, chloroplasts mostly remained in place, but charasomes were absent from the ligation-induced wound walls as revealed by CLSM of FM1-43-stained cells 2 weeks after injury (Fig. 4c). The charasome size and abundance in the adjacent unwounded acid regions were as in control cells (Fig. 4d). Cotton threads which were only slightly constricted and caused no visible effect on cytoarchitecture did not lead to alkalinization of the medium, and this experiment also excluded that local shading by the cotton thread caused charasome degradation.Fig. 4


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 are absent from uneven wound walls. a–d Ligation-induced wound walls. The medium near the ligation site of an internodal cell has an alkaline pH (pink) as visualized by phenol red. Cell deformation and a thick wound wall (arrow) becomes visible after removal of the thread (b). Insets correspond to the images (c) and (d). Charasomes (green FM1-43-fluorescent) are absent from the ligation site ((c), corresponding to the upper inset in (b)) and present between red fluorescent chloroplasts in the adjacent acidic control region ((d), corresponding to the lower inset in (b)). e–k Wound walls (WW) induced by puncturing. A single puncture wound (arrow) located within an acidic region is seen in (e). The optical section through the periphery of the cell shows abundant FM1-43 fluorescent charasomes (arrows) outside the wound plug (WP) which seals the cell wall hole (f). No charasomes are visible in an optical section along the wound wall (encircled in (g)). Green fluorescent particles outside the wound wall are mobile FM1-43-stained organelles (putative endosomes) in the endoplasm. The arrow in the optical longitudinal section through a wound plug in (h) points to a single charasome at the otherwise smooth plasma membrane along the non-fluorescent wound wall. Charasomes are seen between the red fluorescent chloroplasts in the unwounded area (arrow head). Multiple puncture wounds cause an alkalinization of the phenol red-containing medium (i). Few charasomes (green fluorescent after staining with FM1-43) are seen in the wound area (j) in comparison with the unwounded region (k). l–n Wound walls caused by epiphytes. The optical section through the cortical cytoplasm shows numerous FM1-43-stained charasomes (green) between red fluorescent chloroplasts surrounding the wound walls (l). Only few charasomes (arrows in (m)) are present at the inner surface of the wound walls; corresponding DIC image (N). Bars = 1 mm (a, e), 300 μm (i), 150 μm (b) 50 μm (c), 20 μm (d, f, g, j-n), 10 μm (h)
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Related In: Results  -  Collection

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Fig4: Charasomes are absent from uneven wound walls. a–d Ligation-induced wound walls. The medium near the ligation site of an internodal cell has an alkaline pH (pink) as visualized by phenol red. Cell deformation and a thick wound wall (arrow) becomes visible after removal of the thread (b). Insets correspond to the images (c) and (d). Charasomes (green FM1-43-fluorescent) are absent from the ligation site ((c), corresponding to the upper inset in (b)) and present between red fluorescent chloroplasts in the adjacent acidic control region ((d), corresponding to the lower inset in (b)). e–k Wound walls (WW) induced by puncturing. A single puncture wound (arrow) located within an acidic region is seen in (e). The optical section through the periphery of the cell shows abundant FM1-43 fluorescent charasomes (arrows) outside the wound plug (WP) which seals the cell wall hole (f). No charasomes are visible in an optical section along the wound wall (encircled in (g)). Green fluorescent particles outside the wound wall are mobile FM1-43-stained organelles (putative endosomes) in the endoplasm. The arrow in the optical longitudinal section through a wound plug in (h) points to a single charasome at the otherwise smooth plasma membrane along the non-fluorescent wound wall. Charasomes are seen between the red fluorescent chloroplasts in the unwounded area (arrow head). Multiple puncture wounds cause an alkalinization of the phenol red-containing medium (i). Few charasomes (green fluorescent after staining with FM1-43) are seen in the wound area (j) in comparison with the unwounded region (k). l–n Wound walls caused by epiphytes. The optical section through the cortical cytoplasm shows numerous FM1-43-stained charasomes (green) between red fluorescent chloroplasts surrounding the wound walls (l). Only few charasomes (arrows in (m)) are present at the inner surface of the wound walls; corresponding DIC image (N). Bars = 1 mm (a, e), 300 μm (i), 150 μm (b) 50 μm (c), 20 μm (d, f, g, j-n), 10 μm (h)
Mentions: We first repeated the ligation experiments and studied pH banding and charasome distribution in response to artificial constriction of the cell. The internodal cells were exposed to the air until turgor was lost and ligated at an acid band with the aid of cotton thread (Fig. 4a, Shimmen and Yamamoto 2002). Cells were allowed to recover in artificial fresh water, and the pH banding pattern in medium supplemented with phenol red was recorded over a period of several weeks. The pH at ligated regions was consistently alkaline if ligation was strong enough to induce the deposition of a thick wound wall which protruded deep into the endoplasm and eventually caused deformations in cell shape (Fig. 4a, b). In our hands, chloroplasts mostly remained in place, but charasomes were absent from the ligation-induced wound walls as revealed by CLSM of FM1-43-stained cells 2 weeks after injury (Fig. 4c). The charasome size and abundance in the adjacent unwounded acid regions were as in control cells (Fig. 4d). Cotton threads which were only slightly constricted and caused no visible effect on cytoarchitecture did not lead to alkalinization of the medium, and this experiment also excluded that local shading by the cotton thread caused charasome degradation.Fig. 4

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