| Light is one of the most important abiotic factors that affects a plant's growth and development. Characterization of genetic mutants has been a powerful method for elucidating light signaling pathways. The core of this research stems from the ability of a class of photoreceptors known as phytochromes to harvest and utilize light energy. Phytochromes are essential to the process of photomorphogenesis---how plants grow and respond to their light environment---and they act in conjunction with available carbon to promote the production of a group of pigment molecules known as anthocyanins. In an effort to ascertain how light and sugar sensory pathways affect anthocyanin accumulation, a screen was developed to isolate mutants that are defective in components that bridge these pathways. By varying the duration and intensity of far-red light, and utilizing an array of sugars and sugar analogs, conditions that yield maximum anthocyanin accumulation were determined. Using these conditions for a genetic screen, a series of light response d&barbelow;eficient (lid) mutants that accumulate little or no anthocyanin in response to far-red (FR) light and sucrose during early seedling development were identified, and two of these mutants were characterized in depth. lid3 is physiologically similar to wild type except in the early anthocyanin accumulation response, and lid3 may regulate mRNA abundance of the same flavonoid biosynthesis genes that are mediated by phytochrome A. Rough mapping places LID3 on the long arm of chromosome 1. lid4 is affected in numerous phytochrome A-controlled processes, but its complex phenotypic segregation pattern yielded inconclusive mapping results. The data presented in this dissertation provides insight into how anthocyanins accumulate as a function of phytochrome A activation, sucrose-sensing pathways, and the developmental stage in Arabidopsis thaliana. |
