Correlation between the Accumulation of Stylar Canal Exudate and the Diminution of Self-incompatibility in Aging Flowers of Lilium longiflorum

Self-incompatibility in Lilium longiflorum cv. Hinomoto diminishes with aging of the flower. The relation between the diminished self-incompatibility of the aged flower and stylar canal exudate in Lilium longiflorum was studied. Carbohydrate content in stylar canal exudate increased with aging of the flower, indicating that it accumulated with time. During the aging process, the molecular weight distribution and composition of the arabinogalactans, which are the main components of the canal exudate, did not change. When the canal exudates collected from both young and old flowers were injected into stylar canals, the growth of incompatible selfed pollen tubes was significantly promoted. The promotive effect of stylar constituents on pollen tube growth did not differ between those from young and old flowers. The growth of incompatible pollen tubes in the aged pistils was significantly reduced by flushing the stylar canal with water which removed the canal exudate. These results suggest that the diminution of self-incompatibility in aged flowers is attributable to the accumulation of the secreted canal exudate which plays a nutritional role for pollen tube growth.