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Reference: Perry, Carole Celia., (1985). Silicification in biological systems. DPhil. University of Oxford.Citable link to this page:

 

Silicification in biological systems

Abstract: This thesis is concerned with the formation and structure of silicified deposits in biology. The major system studied is silicified macrohairs from the lemma of the grass Phalaris canariensis L

The macrohairs consist of silica and polysaccharides.Chemical and structural studies on the mineral phase utilised electron microscopy (transmission (TEM), scanning (SEM) and ultra high resolution (HRTEM)), energy disoersive X-ray analysis (EDXA), solid state nuclear magnetic resonance ( ᷣ⁹ Si nmr), infrared spectroscopy, birefringence and nitrogen adsorption experiments. Results showed that the silica is chemically 'pure', hydrated, amorphous at a resolution of 1OÅ and a variety of structural morphologies were observed which are related to the maturity of the macrohair.Analytical studies at different times after emergence of the inflorescence utilising EDXA and scanning proton microprob eanalysis (SPM) showed that the inorganic elements Si, K, P, S and Cl are spatially organised within the macrohairs during silicification. It is proposed that the macrohairs are silicified under strict cellular control.The organic matrix in the mature macrohairs was investigated by acid hydrolysis and chromatography. The changing emphasis of polysaccharide synthesis in the macrohairs as mineralisation occurs was followed by in vivo radioactive labelling of inflorescences at different stages usingⁱ⁴C glucose and Harabinose. Analysis o fpolysaccharides synthesised involved acid hydrolysis and enzymic digestions (Amylase and Driselase), followed by paper and thin layer chromatography with scintillation counting of the products. Results showed that at the early stages of mineralisation, arabinoxylans and cellulose are the major polymers synthesised but as the macrohair matures, largely non-cellulosic glucans (as yet unidentified) are synthesised. It is proposed that the change in emphasis of polysaccharide synthesis during wall development is related to the size and ultrastructural arrangements of silica particles observed. The organic matrix was also observed to give additional order to the system, the resulting material being totally impervious.A second system, chosen for comparison, is mineralised teeth from the radula of the common limpet Patella vulgata. The mature teeth contain silica, iron oxide (goethite) and an organic matrix.Investigations on the silicified phase utilising electron microscopy revealed morphological structural variations. Analytical studies involving EDXA and SPM analysis showed that there are complex temporal and spatial variations in the inorganic composition (P, S, Ca, Fe, Si, Cu) in all regions of the teeth. It is proposed that these changes can be correlated with changes in composition of the organic matrix. A comparison is made of the silica from the two systems.

Type of Award:DPhil Level of Award:Doctoral Awarding Institution: University of Oxford Notes:The digital copy of this thesis has been made available thanks to the generosity of Dr Leonard Polonsky

Contributors

Williams, R. J. P. (Robert Joseph Paton)More by this contributor

RoleSupervisor

 

Professor R. J. P. WilliamsMore by this contributor

RoleSupervisor

 Bibliographic Details

Issue Date: 1985Identifiers

Urn: uuid:ae665ac4-63eb-4963-845a-d2db6aea31a6

Source identifier: 602831438 Item Description

Type: Thesis;

Language: eng Subjects: Silica Polysaccharides Phalaris canariensis Tiny URL: td:602831438

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Autor: Perry, Carole Celia. - institutionUniversity of Oxford facultyMathematical and Physical Sciences Division - - - - Contributors Wi

Fuente: https://ora.ox.ac.uk/objects/uuid:ae665ac4-63eb-4963-845a-d2db6aea31a6



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