Two separate aspects involving the thiophenes of the Tageteae (Asteraceae) were investigated. The first concerned the distribution of four thiophenes in Tagetes patula L. which were examined by high pressure liquid chromatography (HPLC). The derivatives were found to be differentially distributed throughout hydroponically grown plants. The predominant thiophenes in roots were 5-(4-acetoxy-1-butenyl)-2,2'-bithienyl (BBT-OAc) and 5-(buten-3-ynyl)-2,2'-bithienyl (BBT). BBT-OAc was the main derivative in shoots, whereas 2,2':5',2''-terthienyl (alpha-T) was the major compound in flower petals. BBT and one unidentified compound were found to occur in leaf glands. The levels of BBT-OAc in shoots and BBT-OAc and BBT in roots increased over the life of the plant and reached a plateau following flowering. Alpha-T in roots and both alpha-T and BBT in shoots remained at low levels over the life of the plant while 5-(4-hydroxy-1-butenyl)-2,2'-bithienyl (BBT-OH) was found to be an minor component of roots or shoots. Fourteen species from four genera of the tribe Tageteae were also screened for the presence of thiophenes by HPLC. Representatives of Dyssodia, Porophyllum, and Tagetes all contained thiophenes, but none were detected in species of Pectis. The second part of this study concerned the photobiocidal effects of isolated thiophenes on Escherichia coli B which was used as a model biological system. Alpha-terthienyl (alpha-T), in the presence of UV-A irradiation (320nm-400nm), was found to be a Type II photosensitizer which required oxygen for the expression of biological activity. Scavenger studies with sodium azide and BHT suggested that both singlet oxygen and superoxide were generated by the photosensitized reaction. Cellular inactivation by alpha-T was sensitive to temperature and studies with recombination deficient mutants of E. coli K-12 did not indicate that damage to cellular DNA occurred. Proteins were found to be substantially affected by the photoactivated reaction. SDS-gel electrophoresis revealed that both cytoplasmic and membrane-associated proteins might be. crosslinked following treatment with alpha-T and UV-A. / Science, Faculty of / Botany, Department of / Graduate

This study examines the evolutionary history of Pectis L., a neotropical genus of ~90 species of xeric-adapted, herbaceous, annuals and perennials. Pectis is rare among the Asteraceae, as it uses C₄ photosynthesis, a complex suite of traits that concentrates carbon around Rubisco. Plants with C₄ photosynthesis do well in environments of high light and high heat, and the C₄ syndrome is thought to have evolved as a response to such environments. Pectis is most diverse in Mexico, the Caribbean Islands, and South America, and its distribution mirrors the disjunctions of patches of desert, thornscrub, coastal plains, savanna, and openings in seasonally-dry tropical forests and oak-pine woodlands. Vicariance and long-distance dispersal theories can explain the patchy distribution of xeric-adapted plants, as well as the origin of Caribbean species. To answer evolutionary questions about a group, one must understand how its members are related. The most comprehensive taxonomic treatment of Pectis is over 100 years old, and includes only North American species. Recent revisions still leave half the species unassigned to section. Molecular studies have found Pectis sister to, or encompassing, the genus Porophyllum. To infer evolutionary relationships between and within Pectis and Porophyllum, DNA from the nuclear and chloroplast genomes of 78 Pectis and 22 Porophyllum species were sampled, sequenced, and analyzed. The molecular phylogeny was used to suggest updated sections based on monophyletic groups. To infer the photosynthetic pathway of Pectis and Porophyllum species, carbon isotope ratios were obtained from 62 Pectis and 18 Porophyllum species. The timing and location of the evolution of Pectis and Porophyllum has implications for the evolution of C₄ photosynthesis. The carbon isotope data were combined with the phylogeny to determine the extent and direction of the evolution of C₄ photosynthesis, and the timing of its evolution was inferred from a fossil-calibrated analysis using chloroplast data from species across the Asteraceae. Distribution data was combined with the Pectis phylogeny to answer questions regarding the biogeographical history of Pectis, including questions regarding its disjuncted distribution, the timing of the evolution of desert species, and the timing and pattern of dispersal to and from the Caribbean Islands. / text