Delayed fertilization and pollen‐tube growth in pistils of Fagus japonica (Fagaceae)

Abstract

In contrast to most angiosperms, in which fertilization occurs 1 or 2 days after pollination, in some plant orders, including the Fagales, fertilization is delayed from 4 days to more than 1 year, raising questions regarding why fertilization is delayed and where and how pollen tubes remain in the pistil during the delay. To answer these questions, we investigated pollen-tube growth in pistils of Fagus japonica (Fagaceae), which are tricarpellate and have six ovules, using light, fluorescence, and scanning electron microscopy. The ovules were immature at the time of pollination and required 5 weeks to become fully developed. During this 5 weeks, pollen tubes grew from the stigma to the embryo sac in association with the development of ovules and intermittently in three steps with two growth-cessation sites, i.e., on the funicle and near the micropyle. The number of pollen tubes was gradually reduced from many to one at the two growth-cessation sites, and fertilization occurred in one ovule that apparently developed earlier than the others in the pistil. Thus, delayed fertilization plays an important role in gametophyte competition and selection leading to nonrandom fertilization. Intermittent pollen-tube growth is also likely widespread in angiosperms because it is known in other Fagales and an unrelated order Garryales.

Systematic Significance of the Development and Anatomy of Flowers and Fruit of Quercus schottkyana (Subgenus Cyclobalanopsis: Fagaceae)

“…The terminology of floral and fruit anatomy mostly follows Cecich (1997), Borgardt and Nixon (2003), and Sogo and Tobe (2006a). Character state comparisons and the delimitation of characters states are based on current and previous studies (table 1), including close inspection of the original plates and figures for the most relevant taxa: Quercus section Cerris (Q. suber [Boavida et al 1999[Boavida et al , 2001); Q. acutissima (Borgardt and Nixon 2003;Deng 2007); Quercus section Quercus s.s. (Q. alba [Stairs 1964;Mogensen 1965]); Q. gambelii (Brown and Mogensen 1972); Quercus section Lobatae (Q. velutina [Mogensen 1965]); Q. rubra (Langdon 1939;Hjelmqvist 1953); Q. coccinea (Stairs 1964); Quercus section Protobalanus (Trelease 1924;Manos 1993); Castanea (C. crenata [Nakamura 1986[Nakamura , 1991[Nakamura , 1992a[Nakamura , 1992b[Nakamura , 1994[Nakamura , 2001); C. mollissima (Xu et al 1988;Yao et al 1989;Deng 2007); Fagus (F. grandifolia [Langdon 1939]); and F. japonica (Sogo and Tobe 2006a).…”

“…The condition of the nucellus is recorded by defining whether the ovule primordia are initiated by di-or trizonate cell layers, leading to crassinucellate and tenuinucellate types, which differ in the number of the parietal cell layers (Bouman 1984). In Fagus japonica, the formation of cell layers of the ovule primordium was not discussed by Sogo and Tobe (2006a) (Luza and Polito 1991, figs. 2, 5;Langdon 1939, figs.…”

“…II 3, 4); Ostryopsis (Chen et al 1991, figs. 1-13); Betula (Liu et al 2005, pl. II 3); Alnus (Sogo and Tobe 2005, fig. 2C).…”

Kin selection and the evolution of plant reproductive traits

“…The other is by reducing the development time for the embryos by delayed fertilization that is known to occur in some orchids. Delayed fertilization, however, appears to be more common in wind-pollinated species (see table 1 in Sogo & Tobe [16]), owing to reasons that I explain later.…”

Differentiation of Stylar Transmitting Tissue during Ovule Development in Female Flowers of Japanese Chestnut (Castanea crenata Sieb. et Zucc.)

“…Why fertilization is delayed, and where and how pollen tubes stay in the pistil during the period are still unclear (Sogo and Tobe, 2006). Although in some species of fruit trees, fertilization after pollination requires more than 1 week, the chestnut, which belongs to the Fagales order, requires almost 1 month for fertilization (Nakamura, 1994).…”