Assembling the thickest plant cell wall: exine development in Echinops (Asteraceae, Cynareae)
Autor: | Svetlana Polevova, Stephen Blackmore, Nina I. Gabarayeva, Valentina V. Grigorjeva |
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Rok vydání: | 2018 |
Předmět: |
0106 biological sciences
0301 basic medicine Plant Science medicine.disease_cause 01 natural sciences Foot layer Cell wall 03 medical and health sciences Biopolymers Sporopollenin Cell Wall Pollen Genetics medicine Micelles Echinops biology Chemistry Echinops Plant Asteraceae biology.organism_classification Carotenoids 030104 developmental biology Biological Ontologies Biophysics Microscopy Electron Scanning Pollen wall 010606 plant biology & botany Cynareae |
Zdroj: | Planta. 248(2) |
ISSN: | 1432-2048 |
Popis: | The exceptionally complex exine of Echinops, representing a significant investment of energy, develops from an elaborate glycocalyx which establishes, by self-assembly, a multi-layered system of micelles upon which sporopollenin polymerizes. We report on pollen development in two species of Echinops (Asteraceae, Cynareae) studied using transmission and scanning electron microscopy with an emphasis on the organisation and development of the massive sporoderm (maximum thickness 18 μm). The major events of exine deposition during the tetrad stage follow the now familiar sequence of self-assembling micellar mesophases and the subsequent incorporation of sporopollenin, observed here as: (1) spherical units with light cores; (2) columns of spherical units with dark cores; (3) large branched macromolecules arranged in a dendritic, three-dimensional network of long alveoli; and (4) alveoli with electron-transparent cores and dense walls. Later, (5) the primexine exhibits an elongated-alveolate pattern in which the alveoli have electron-dense cores and lighter exteriors. When (6) the thick inner columellae make contact with the outer primexine, sporopollenin accumulation in the cores of the primexine alveolae establishes continuity between the inner and outer columellae. In the free microspore stage, (7) the foot layer and first lamellae of the endexine appear (8). The endexine lamellae then increase in number and massive accumulation of sporopollenin occurs on all exine elements, making individual elements such as tectal spines, more pronounced. These and earlier findings, as well as experimental simulations of exine development, show that pollen wall morphogenesis involves a subtle interplay of gene-driven biological processes and physico-chemical factors offering abundant opportunities for the generation of complex, taxon-specific patterns. |
Databáze: | OpenAIRE |
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