Pollen tube growth and fertilization in Japanese chestnut (Castanea crenata Sieb. et Zucc.)

摘要

Pollen tube growth and the location of ovules within ovaries in Japanese chestnut (Castanea crenata Sieb. et Zucc.) were investigated in relation to fertilization. Pollen tubes were first observed on 18 July in the upper part of ovaries in both central and lateral female (pistillate) flowers; 2 days later, 36 and 11 pollen tubes were counted in the former and the latter, respectively. The number of pollen tubes in central female flowers began to decrease gradually from 26 July, and decreased rapidly after 28 July. In lateral female flowers, the number of pollen tubes also decreased gradually after a maximum of 16 on 24 July. The distances from the top of ovaries to the nucelli in central female flowers ranged 3-6 mm on 18-24 July and 5-7 mm after 26 July. In lateral female flowers, the distances increased to 3-5 mm, 4-6 mm, and 5-7 mm on 18-20 July, 22 July, and afterward, respectively. The time of fertilization was estimated to be 26 28 July in central female flowers based on the observation of the pollen tube within the micropyle, and 24-26 July in lateral female flowers based on the onset of nucellar degeneration. On 26 and 28 July, the numbers of pollen tubes reaching the zone where the nucelli are located in central female flowers were 2 and 9, respectively; in lateral female flowers, the frequency of pollen tubes on 24 and 26 July were 1 and 11, respectively, indicating a rapid increase in the number of pollen tubes approaching the ovules at fertilization.