Recovery of the cortical chloroplast layer in the green alga Chara after local irradiation
The cytoplasm of characean internodal cells is characterized by a stationary layer of cortical chloroplast files and a mobile endoplasm moving along subcortical actin bundles. Occasionally, chloroplasts detach from the cortex and are passively carried along with the endoplasmic flow. Previous studie...
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Frontiers Media S.A.
2025-05-01
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| Series: | Frontiers in Plant Science |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/fpls.2025.1544999/full |
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| author | Marion C. Hoepflinger Margit Höftberger Aniela Sommer Florian Hohenberger Michael Schagerl Ilse Foissner |
| author_facet | Marion C. Hoepflinger Margit Höftberger Aniela Sommer Florian Hohenberger Michael Schagerl Ilse Foissner |
| author_sort | Marion C. Hoepflinger |
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| description | The cytoplasm of characean internodal cells is characterized by a stationary layer of cortical chloroplast files and a mobile endoplasm moving along subcortical actin bundles. Occasionally, chloroplasts detach from the cortex and are passively carried along with the endoplasmic flow. Previous studies revealed that local irradiation with intense light causes chloroplast bleaching followed by a release into the endoplasm (“window formation”). We found that endoplasmic chloroplasts of Chara australis resettle at the window and align parallel to the streaming direction. The process takes several weeks with neither chloroplast division nor growth of proplastids being involved. Both release and re-attachment are actin-dependent. Resettled chloroplasts showed slightly, but significantly lower maximum quantum efficiency (Fv/Fm) values as compared with control regions. Extremely low Fv/Fm values were measured in chloroplasts at the border of the window even after three months indicating longevity, although with serious damage. In higher plants, a protein complex is responsible for the motility and anchorage of chloroplasts, with CHUP1 (CHLOROPLAST UNUSUAL POSITIONING 1) being an essential part. We discovered a homologous form CaCHUP1, encoding a polypeptide of 1201 amino acids with a calculated molecular mass of about 130 kDa. When transiently expressed in epidermal cells of Nicotiana benthamiana leaves, fluorescently tagged CaCHUP1 localizes to chloroplasts. We assume that CaCHUP1 is involved in the anchorage of chloroplasts and in the polymerization of actin filaments, but not in active movement. Our study revealed that endoplasmic chloroplasts can re-anchor at the cell cortex thereby refilling chloroplast-free regions, which we interpret as a repair mechanism after various kinds of damage. It confirms that chloroplasts use different strategies for repositioning, either via polymerization of cp-actin or via cytoplasmic streaming. |
| format | Article |
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| institution | DOAJ |
| issn | 1664-462X |
| language | English |
| publishDate | 2025-05-01 |
| publisher | Frontiers Media S.A. |
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| series | Frontiers in Plant Science |
| spelling | doaj-art-7bf6c4d71c4c4645bcdcd3ef896f81f52025-08-20T03:10:56ZengFrontiers Media S.A.Frontiers in Plant Science1664-462X2025-05-011610.3389/fpls.2025.15449991544999Recovery of the cortical chloroplast layer in the green alga Chara after local irradiationMarion C. Hoepflinger0Margit Höftberger1Aniela Sommer2Florian Hohenberger3Michael Schagerl4Ilse Foissner5Department of Environment and Biodiversity, University of Salzburg, Salzburg, AustriaDepartment of Environment and Biodiversity, University of Salzburg, Salzburg, AustriaDepartment of Environment and Biodiversity, University of Salzburg, Salzburg, AustriaDepartment of Environment and Biodiversity, University of Salzburg, Salzburg, AustriaDepartment of Functional and Evolutionary Ecology, Faculty of Life Sciences, University of Vienna, Vienna, AustriaDepartment of Environment and Biodiversity, University of Salzburg, Salzburg, AustriaThe cytoplasm of characean internodal cells is characterized by a stationary layer of cortical chloroplast files and a mobile endoplasm moving along subcortical actin bundles. Occasionally, chloroplasts detach from the cortex and are passively carried along with the endoplasmic flow. Previous studies revealed that local irradiation with intense light causes chloroplast bleaching followed by a release into the endoplasm (“window formation”). We found that endoplasmic chloroplasts of Chara australis resettle at the window and align parallel to the streaming direction. The process takes several weeks with neither chloroplast division nor growth of proplastids being involved. Both release and re-attachment are actin-dependent. Resettled chloroplasts showed slightly, but significantly lower maximum quantum efficiency (Fv/Fm) values as compared with control regions. Extremely low Fv/Fm values were measured in chloroplasts at the border of the window even after three months indicating longevity, although with serious damage. In higher plants, a protein complex is responsible for the motility and anchorage of chloroplasts, with CHUP1 (CHLOROPLAST UNUSUAL POSITIONING 1) being an essential part. We discovered a homologous form CaCHUP1, encoding a polypeptide of 1201 amino acids with a calculated molecular mass of about 130 kDa. When transiently expressed in epidermal cells of Nicotiana benthamiana leaves, fluorescently tagged CaCHUP1 localizes to chloroplasts. We assume that CaCHUP1 is involved in the anchorage of chloroplasts and in the polymerization of actin filaments, but not in active movement. Our study revealed that endoplasmic chloroplasts can re-anchor at the cell cortex thereby refilling chloroplast-free regions, which we interpret as a repair mechanism after various kinds of damage. It confirms that chloroplasts use different strategies for repositioning, either via polymerization of cp-actin or via cytoplasmic streaming.https://www.frontiersin.org/articles/10.3389/fpls.2025.1544999/fullactin cytoskeletoncharacean internodal cellschloroplast anchorageCaCHUP1 (Chara australis chloroplast unusual positioning 1)confocal laser scanning microscopycortex regeneration |
| spellingShingle | Marion C. Hoepflinger Margit Höftberger Aniela Sommer Florian Hohenberger Michael Schagerl Ilse Foissner Recovery of the cortical chloroplast layer in the green alga Chara after local irradiation Frontiers in Plant Science actin cytoskeleton characean internodal cells chloroplast anchorage CaCHUP1 (Chara australis chloroplast unusual positioning 1) confocal laser scanning microscopy cortex regeneration |
| title | Recovery of the cortical chloroplast layer in the green alga Chara after local irradiation |
| title_full | Recovery of the cortical chloroplast layer in the green alga Chara after local irradiation |
| title_fullStr | Recovery of the cortical chloroplast layer in the green alga Chara after local irradiation |
| title_full_unstemmed | Recovery of the cortical chloroplast layer in the green alga Chara after local irradiation |
| title_short | Recovery of the cortical chloroplast layer in the green alga Chara after local irradiation |
| title_sort | recovery of the cortical chloroplast layer in the green alga chara after local irradiation |
| topic | actin cytoskeleton characean internodal cells chloroplast anchorage CaCHUP1 (Chara australis chloroplast unusual positioning 1) confocal laser scanning microscopy cortex regeneration |
| url | https://www.frontiersin.org/articles/10.3389/fpls.2025.1544999/full |
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