L A Staehelin, H Q Zheng, T L Yoder, J D Smith, P Todd
{"title":"Columella cells revisited: novel structures, novel properties, and a novel gravisensing model.","authors":"L A Staehelin, H Q Zheng, T L Yoder, J D Smith, P Todd","doi":"","DOIUrl":"","url":null,"abstract":"<p><p>A hundred years of research has not produced a clear understanding of the mechanism that transduces the energy associated with the sedimentation of starch-filled amyloplast statoliths in root cap columella cells into a growth response. Most models postulate that the statoliths interact with microfilaments (MF) to transmit signals to the plasma membrane (or ER), or that sedimentation onto these organelles produces the signals. However, no direct evidence for statolith-MF links has been reported, and no asymmetric structures of columella cells have been identified that might explain how a root turned by 90 degrees knows which side is up. To address these and other questions, we have (1) quantitatively examined the effects of microgravity on the size, number, and spatial distribution of statoliths; (2) re-evaluated the ultrastructure of columella cells in high-pressure frozen/freeze-substituted roots; and (3) followed the sedimentation dynamics of statolith movements in reoriented root tips. The findings have led to the formulation of a new model for the gravity-sensing apparatus of roots, which envisages the cytoplasm pervaded by an actin-based cytoskeletal network. This network is denser in the ER-devoid central region of the cell than in the ER-rich cell cortex and is coupled to receptors in the plasma membrane. Statolith sedimentation is postulated to disrupt the network and its links to receptors in some regions of the cell cortex, while allowing them to reform in other regions and thereby produce a directional signal.</p>","PeriodicalId":81348,"journal":{"name":"Gravitational and space biology bulletin : publication of the American Society for Gravitational and Space Biology","volume":"13 2","pages":"95-100"},"PeriodicalIF":0.0,"publicationDate":"2000-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138815374","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Biomineralization in coccolithophores.","authors":"M. Marsh","doi":"10.1002/3527604138.CH12","DOIUrl":"https://doi.org/10.1002/3527604138.CH12","url":null,"abstract":"Unicellular marine algae known as coccolithophores are potentially important organisms for the study of gravitational effects on biomineralization. The cells are easily cultured under low maintenance conditions and produce intricately sculpted calcite scales known as coccoliths in specialized Golgi-derived vesicles. Many mutants are available with different types of mineral defects ranging from the complete absence of mineral to the presence of mineral with orientational, morphological, number, and size defects. This short review summarizes what is currently known about the three phases of coccolith mineralization--mineral ion transport, mineral nucleation, and crystal growth--in Pleurochrysis carterae and Emiliania huxleyi in the earth's normal gravitational field.","PeriodicalId":81348,"journal":{"name":"Gravitational and space biology bulletin : publication of the American Society for Gravitational and Space Biology","volume":"540 1","pages":"5-14"},"PeriodicalIF":0.0,"publicationDate":"1999-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/3527604138.CH12","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"51132779","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Biomineralization in coccolithophores.","authors":"M E Marsh","doi":"","DOIUrl":"","url":null,"abstract":"<p><p>Unicellular marine algae known as coccolithophores are potentially important organisms for the study of gravitational effects on biomineralization. The cells are easily cultured under low maintenance conditions and produce intricately sculpted calcite scales known as coccoliths in specialized Golgi-derived vesicles. Many mutants are available with different types of mineral defects ranging from the complete absence of mineral to the presence of mineral with orientational, morphological, number, and size defects. This short review summarizes what is currently known about the three phases of coccolith mineralization--mineral ion transport, mineral nucleation, and crystal growth--in Pleurochrysis carterae and Emiliania huxleyi in the earth's normal gravitational field.</p>","PeriodicalId":81348,"journal":{"name":"Gravitational and space biology bulletin : publication of the American Society for Gravitational and Space Biology","volume":"12 2","pages":"5-14"},"PeriodicalIF":0.0,"publicationDate":"1999-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138815405","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}