XVI International Botanical Congess

The Self-incompatibility (SI) response of Papaver rhoeas involves a specific recognition interaction between the pollen grain and stigmatic papillae cells. This initiates signal transduction in the pollen that precedes the inhibition of tube growth. This mechanism facilitates outbreeding within the species. The pollen borne signaling pathways involve temporally defined increases in the phosphorylation status of at least two distinct proteins described as p26 and p68 according to their relative Mr. Significant progress has not been achieved in the molecular characterization of one of the proteins in question. A full length cDNA clone encoding the putative p26 protein was obtained via amino acid sequencing, per and cDNA library screening. Sequence analysis has demonstrated that the encoded protein belongs to a family of enzymes referred to as the soluble inorganic pyrophosphatases, enzymes that are thought to be essential housekeeping" proteins. Current studies are investigating the potential significance of phosphorylation of this protein with respect to the pollen tube inhibition mechanisms.