RUI: Pollen Developmental Evolution in the Basalmost Angiosperms - Nymphaeales and Amborella

Truman State University, Kirksville MO

Investigators

Abstract

An understanding of the evolutionary relationships of flowering plants, or angiosperms, has been greatly improved in recent years, and water lilies (Nymphaeales) and Amborella have been identified as the earliest diverging lineages. Water lilies have a cosmopolitan distribution, comprise two families and eight genera, and have interested botanists for many years in part because they have characteristics of both major classes of flowering plants (dicots and monocots). Amborella includes a single species and is an understory shrub that is limited in geographic distribution to montane tropical rain forests in central New Caledonia. Comparative studies of pollen development in angiosperms are relatively rare, but make significant contributions to understanding the evolution of key characters, as well as evolutionary relationships, or phylogeny, when conducted. Relatively few pollen studies of water lilies and Amborella have been carried out, however. Historically, the pollen wall of water lilies has been reported as granular, a character state thought to be primitive among angiosperms, whereas that of Amborella has an unusual structure that does not appear to occur in other extant flowering plants. A recent study by the PI indicates that the mature pollen of all eight genera of water lilies is columellar, and that the developmental pattern and structure of these pollen wall elements makes them superficially resemble granules. The developmental pattern of these elements and that of other pollen characters in Nymphaeales and Amborella, however, are not well understood. Given the evolutionary importance of these two primitive groups, the overall focus of the PI's research is to study pollen developmental evolution in Nymphaeales and Amborella. The principal objectives of the proposed project are to (1) provide a comprehensive investigation of pollen development in two key water lily genera (Cabomba and Nuphar) and (2) obtain preliminary results on other genera. The proposed research will build on new data from the PI's laboratory about mature pollen structure in all eight water lily genera, as well as pollen development in three (Cabomba, Nuphar, and Euryale). The research will use combined microscopical techniques, and it will yield data at a level of resolution that has not been documented before. The new data will provide the foundation to examine the patterns of pollen developmental evolution within a phylogenetic context and determine functional correlations between pollen developmental characters and pollination biology.