9527735 RENZAGLIA The first successful migration of early life forms from water to land was one of the most significant and perplexing of all biological events. Nearly 500 million years ago, swamp-dwelling algae made it ashore and thus set the stage for the magnificent flourish of plants and animals to come. Yet, it is still uncertain as to what this ancestral alga looked like and how the diverse plant groups that exist today are related to this presumed ancestor, and to each other. This project proposes to address these fundamental questions by examining sperm cell development and structure in a critical group of seedless vascular plants, the OpteridophytesO. Plants included among the OpteridophytesO include ferns, club mosses, spike mosses, quillworts, and horsetails. Sperm cells in modern OpteridophytesO hold clues to the functioning, structure and evolution of ancient land plants. Swimming sperm are the only motile cells of contemporary plants and as such they carry traits of their aquatic algal ancestors. Tracing their differentiation and architecture provides clues to early land plant lineages and will eventually identify evolutionary threads leading all the way back to the ancestral algae. Ten OpteridophytesO, species whose sperm cells are thought to resemble most closely those of the first terrestrial organisms, will be targeted for electron microscopic examination. More than 500 detailed micrographs will be taken for each plant. These photographs will be analyzed and three-dimensional images will be prepared to depict the stages of development. In addition, computers will track and analyze information on approximately 100 cell traits, from cell shape to protein components. Emphasis will be placed on examining the role of proteins that are involved in organizing the structural entities of these highly complicated motile cells. The results will help place these ten informative species more correctly on the plant worldOs complex genealogical tree. These analyses will also more clearly resolve which modern algae are the closest relatives to terrestrial plants and the sequence of appearance of the primitive plant groups during the early history of plant life on land. Beyond that, these studies provide more essential information about the organization, differentiation and evolution of cells in all forms of life.
