| Mechanisms controlling pollen tube guidance and cross and self pollen tube growth and recognition in Illicium floridanum were characterized. The stigma was of the dry-type with lipids, arabinogalactan proteins, and esterified/unesterified pectins in the cell wall and extracellular matrix. Pectins and arabinogalactan proteins also localized to the extracellular matrix and cell wall of substigmatic transmitting tissue to include the micropyle. Pollen tube tip growth conformed to a haptotactic model. Post-pollination changes in the extracellular matrix and cell wall lead to gradients in pectins and arabinogalactans particularly at the micropyle indicating that chemotropic factors may operate to influence pollen tube growth at this site. Although Illicium floridanum exhibits high rates of self-sterility previously interpreted as self-incompatibility at the stigma, the present study found that cross and self pollen tubes both effected fertilization equally. Thus, self-sterility in this species is likely due to post-zygotic self-incompatibility, early-acting inbreeding depression and/or nutrient limitations. |
