ニホングリ (<I>Castanea crenata</I> Sieb. et Zucc.) の花粉管伸長と胚珠の退化

Abstract

Pollen tube growth in female flowers of Japanese chestnut (Castanea crenata Sieb. et Zucc.) 'Yamato-Wase' was investigated to clarify the relation between fertilization and degeneration of ovules.1. Pollen tubes were first observed at the uppermost part of the style on 2 July and 2 to 6 July in the central and lateral female flowers, respectively.2. Penetration of pollen tubes into ovaries occurred on 14 and 16 July in the central and lateral female flowers, respectively. The longest pollen tube growing in an ovary covered the average distance from the distal end of ovary to the nucelli of ovules by 28 July and 1 August in the central and lateral female flowers, respectively.3. The first pollen tubes penetrated the ovarian locules on 24 and 28 July in the central and lateral female flowers, respectively. Four to five tubes per ovary were observed from 28 July to 3 August in the former and from 30 July to 3 August in the latter. The number of pollen tubes, however, decreased by August 5.4. Pollen tubes reached nucelli in 26 and 30 days after pollen germination on stigmas in the central and lateral female flowers, respectively. The average distance from the stigmas to the nucelli at this stage was 8 mm in the former and 9 mm in the latter. Thus, their average elongation rate was calculated to be 0.3 mm a day.5. Nucelli of most ovules in each ovary developed between 12 and 19 July. Ovules except the largest one in an ovary nearly ceased to enlarge after 26 July. After 2 August, ovules with a degenerated nucellus in ovaries were observed. Their ratio increased to 40% on 6 August and reached nearly 100% on 9 August. But one well-developed ovule with an embryo of 0.037 mm in diameter was observed in each ovary on 9 August. The ovule with such an embryo grew rapidly after 13 August.6. Nucelli began to degenerate within a week after fertilization time in most ovules, suggesting that the degeneration might be caused by the lack of fertilization.