Cell wall loosening proteins of the stigma exudate

Outline of the thesis: The idea, formulated by Cosgrove, that cell wall loosening of the maternal tissue facilitates pollen tube growth is a central theme of this thesis. This idea was originally proposed for beta-expansins released by maize pollen. Since the pollen coat of dry stigma type plants, like maize, bears a functional similarity with the exudate of wet stigma type plants (e.g. tobacco and petunia), this research was started with the analysis of the putative function of the pistil-specific beta-expansin homologue PPAL in pollen-pistil interaction. Its expression, production and analysis of transgenic plants lacking PPAL expression will be presented, as well as the cell wall loosening activity of PPAL using an extensometer assay. These studies on PPAL eventually have lead to the identification and characterization of Lipid Transfer Proteins (LTP) as a new type of proteins that enhance wall extension. The purification and expression pattern of LTP in the tobacco pistil will be discussed. Finally, the study of LTP mediated cell wall extension and the 3D structure of the protein lead to a model for the working mechanism of LTP in wall extension