UC San Diego

Angiosperms prevent inbreeding with a number of molecular mechanisms. Papaver rheoas (Papaveraceae) has a gametophytic self-incompatibility system that is well- characterized at the molecular level. In Papaver, self pollen is arrested immediately upon contact with the stigma. Immediate pollen arrest may be required because Papaver flowers have stigmatic rays directly on top of the ovary and no style. There is much variation in floral structures among Papaveraceae and self-incompatibility is widespread. However, except for Papaver, no documentation of the site of self-pollen tube inhibition within the family exists. We examined the site of self-pollen tube inhibition in four species of Papaveraceae representing a broad phylogenetic and morphological sample. We used two types of tissue preparation. Squash preparation was used for species with soft stigmas while woody tissue was sectioned with a cryostat and panels were stitched into a mosaic to visualize whole stigmas. In three species, self- pollen tube inhibition appeared similar to that described for P. rheoas, despite variation in the architecture of female tissues. Self-tubes were arrested early and usually did not grow longer than 100 [Mu]. In Argemone munita, self pollen tubes progressed further, growing up to 500 [Mu]. However, growth appeared to occur along the stigmatic hairs and ceased once tubes contacted the stigma surface. Despite variation in floral architecture, rapid death of self-pollen tubes occurs before or just after penetration of female tissue in all species examined. This is consistent with the hypothesis that members of the family share the same incompatibility mechanism