Increased carbohydrate supply in the pollen tube pathway after cross-pollination of Gasteria verrucosa (Mill.) H. Duval

Gasteria has ovular incompatibility, and recognition of cross- and self-pol len takes place. Cross-pollination includes recognition and pistil activati on and leads to seed set. Self-pollen germinate, and their pollen tubes pen etrate the ovules but after fertilization they abort. A group of glycoprote ins in the pollen coat seems implicated as signal molecules for recognition and activation. Pistil activation is expressed as extra water uptake in th e pistil, especially in the fluid pollen tube pathway, and results in highe r in vitro pollen tube penetration in the ovular micropyle. In the fluid po llen tube pathway of unpollinated styles a high concentration of sucrose, g lucose and fructose is present. The level of these carbohydrates remains th e same during the pollen tube growth of cross-pollen. This level decreases after the passage of self-pollen through the stylar channel, and the level of carbohydrates is restored. This implies extra carbohydrate influx in the pollen tube pathway after cross-pollination. Recognition and activation si gnals act together after cross-pollination of Gasteria. After self-pollinat ion the utilization of carbohydrates lowers the pistil's carbohydrate capac ity, perhaps also leading to a late-acting incompatibility.