Flowering plants have evolved complex genetic mechanisms of self-incompatibility (SI) to overcome the problem of self-fertilization. SI is a cell-cell recognition system where the interaction of genetically linked pollen and pistil S-determinants prevents self-fertilization. In Papaver rhoeas, the pistil S-determinant is PrsS, a secreted protein of around 15 kDa. The pollen determinant, PrpS, encodes a novel transmembrane protein of around 20 kDa. Upon the interaction of incompatible PrsS and PrpS variants, the SI response is triggered, activating a signalling network. Rapid increases in cytosolic free calcium ([Ca\( {2+}\)]\(_i\)) are followed by changes to the actin cytoskeleton and activation of a DEVDases, resulting in programmed cell death (PCD). Within this thesis, three inter-related studies are described. Initially, we investigated the role of the ubiquitin-proteasomal system during SI in Papaver, the second study focused on the PrpS protein. Thirdly, we also created transgenic Arabidopsis thaliana lines expressing PrpS and PrsS, in order to investigate if the Papaver SI system might be functionally transferable to other plant species. We have demonstrated that PrpS binds the PrsS in an S-specific manner, while the functional analysis “in vitro” revealed that PrpS expressed in A.thaliana is functional and that just PrpS and PrsS are sufficient for a fully functional SI response in A.thaliana pollen.