Graduate Thesis Or Dissertation
 

A chemosystematic study of the phylogenetic position of Arabidopsis thaliana (L.) heynh. (Brassicaceae) employing numerical methods

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  • The Brassicaceae, Mustard Family, is a well marked natural family, whose tetramerous flowers, tetradynamous stamens, and distinctive bi- carpellary fruits, clearly distinguish it from related families. It is a large family of some 3, 000 recognized species and over 300 genera. Although numerous attempts have been made over the past two centuries to develop a taxonomic system that would organize the family into natural, or at the least convenient, groupings, no proposal has met with general acceptance. This investigation is a new attempt to understand intergeneric relationships. To scale this effort to a manageable scope, I selected the genus Arabidopsis, in particular the species A. thaliana, as the focus of all investigations. An important aspect of this thesis is that it introduces research techniques that have evolved since the family was last examined. Chemical methods used include protein electrophoresis and thin-layer chromatography of flavonoid and related compounds. A variety of computer-assisted numerical analyses were performed on both chemical and morphological data sets. A total of 54 species were investigated, representing 37 genera. The electrophoresis survey showed that many of the bands of the enzyme fructose 1, 6- diphosphate aldolase (1.U.B. No. 4.1.2.13) did not represent true isozymes, but were the results of secondary interactions between the enzymes and phenolic compounds. These artifacts were eliminated when a number of precautions were exercised during the extraction process, notably the washing of the plant extracts with synthetic phenolic-binding compounds (XAD-4 and polyclar-AT). Neither the electrophoresis nor the TLC surveys generated data sets that produced rational phenograms when clustering strategies were applied. Counter to expectations, each species was characterized by unique flavonoid idiogram patterns. Similarly, the electrophoretic phenotypes failed to generate reasonable phenograms although they support recognized intrageneric groupings. A correlation was observed between flavonoid distribution and plant habit. A significant quality of the 37 genera analyzed was their failure to form consistent groupings. The plants were shown to be widely scattered in the multidimensional character space, and clusters were markedly influenced by algorithm choice. However, two distinct groupings did emerge when the several numerical approaches were compared. The groups are separated by differing attitudes of the cotyledons with respect to the seed radicle. This single character difference was reinforced by weak but consistent correlations with chemical data. This finding sustains the method devised by de Cando lle and popularized by Schulz, who relied on cotyledonary position as a primary criterion for delimiting the tribes of the Brassicaceae. As a corollary, my numerical results place Arabidopsis near Sisymbrium and remote from its historical allies, Arabis and Cardamine. The limits of the genus Arabidopsis and a natural classification system for the Brassicaceae were not resolved by this work. However, the problems inherent in these tasks were identified.
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file details KaplanHeshJ1977.pdf 2017-08-17 公开 下载