| The complex adaptation of C4 photosynthesis is physiologically stable, persistent, and C4 plants are found in environments where photorespiration reduces carbon gain in C3 plants. The C4 pathway is present in 19 angiosperm families, including monocot and eudicot taxa, and represents an excellent example of evolutionary convergence to address carbon loss from photorespiration. C4 photosynthesis has been studied for over 40 years; however, steps in the evolution of this pathway remain unclear, including the role of anatomical evolution to support C4 biochemistry. The research reported within this dissertation addresses a broad goal of understanding the evolution of C4 photosynthesis at a smaller taxonomic scale using the genus Flaveria. This is facilitated by the presence of species representing four photosynthetic types in Flaveria: C3, C4, and two intermediate types (C3–C 4 and C4-like). This overall goal of this study aims to identify evidence for possible evolutionary steps of C4 photosynthesis through a comparison of C3, C4 and intermediate species. The first chapter assesses the evolutionary history of Flaveria, employing modern and traditional taxonomic tools to create a well-resolved phylogeny. The second chapter presents a broad comparative analysis of leaf anatomy and vein pattern in C3, intermediate, and C4 Flaveria species through analysis of qualitative and quantitative data. This chapter also focuses on the evolution and the potential role of Kranz anatomy, including the role of venation, in the evolution of the C4 pathway. The third chapter addresses the developmental differences giving rise to the altered vein pattern observed in C4 Flaveria species compared to C3 species. It also compares the timing of vein pattern formation with ground tissue development in C3 and C4 species. The fourth chapter assesses plasticity and acclimation to shade in C 3 and C4 Flaveria species, focusing specifically on anatomical and vein pattern features. In the concluding chapter, contributions of this thesis are reviewed and future directions of research are highlighted. Each chapter elucidates different aspects of C4 plant structure and development in Flaveria, adding to our knowledge of the mechanisms involved in the evolution of this complex adaptation and to our understanding of C4 biology. |
