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Title: Studies of lower embryophyte spore walls with particular reference to the perispore
Author: Moore, Susannah Emily Margaret
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2005
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This study of lower embryophyte spore walls concentrates on the outermost layer, the perispore. The focus of this investigation has been to elucidate the evolution, function and chemistry of the perispore. Lack of knowledge of these aspects of the perispore has resulted in conflicting views which are considered herein. A review documenting the first occurrence of the perispore and its evolution suggests that the first perispore-like layer probably occurs in Cooksonia pertoni (Silurian) and Uskiella spargens (Devonian). It is also considered that perisporal envelopes surrounding cryptospores might constitute the inception of the perispore, dating back even further to the Ordovician. It is proposed that the perispore is an ancestral feature that was lost in certain plant groups but retained in some Trimerophytopsida and Progymnospermopsida. The perispore is now a feature of most extant lower embryophytes. The first true perispore is identified in the basal Upper Devonian species Rhacophyton ceratangium. This work suggests that the perispore is comparable to the plant cuticle in aspects such as chemistry, ultrastructure, and most importantly, the function. The perispore is believed to act as a defence mechanism against pathogenic attack and UV radiation but also provides mechanical support. Silica is thought to either form a discrete layer on some lower embryophyte spores or to be integral with sporopollenin. Additional spore wall stability seems to be the main function of silica. No correlation between the presence of silica in pteridophyte fronds and spores was established. This investigation also comprises the report and analysis of siliceous cubic crystals occurring on Selaginella myosurus megaspores. Although their chemical and crystal log raphic properties could not be fully elucidated, it is suggested that these cubic crystals are a new mineral, formed by an unknown bio-mineralization process occurring in plants. A number of different analytical chemistry techniques were applied in order to elucidate perispore components and the chemical nature of sporopollenin. This study has demonstrated that with current techniques it is difficult to isolate and analyse the perispore and that previously reported data were misinterpreted. It is hypothesised that common plasticizers were wrongly described as sporopollenin compounds. The application of matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-ToF MS) to sporopollenin research is introduced. On the basis of the results presented herein, a revised definition for the term perispore is offered.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available