Ultrastructural observations of the mature megagametophyte and the fertilization in wheat (Triticum aestivum)

Abstract

The mature embryo sac of wheat contains an egg apparatus composed of an egg cell and two synergids at the micropylar end, a central cell with two large polar nuclei in the middle, and a mass of 20 to 30 antipodals at the chalazal end. A comparison was made of the ultrastructural features of the various cells of the embryo sac. The features included the position of the nucleus and vacuoles, the number, structure, and distribution of organelles, and the extent of the cell walls surrounding each cell. The pollen tube enters one synergid through the filiform apparatus from the micropyle. The penetration and discharge of the pollen tube causes the further degeneration of that synergid, which had already undergone changes before pollination. The second synergid does not change further in appearance following the penetration of the first by the pollen-altered tube. Half an hour after pollination at 20–25 °C, two male nuclei are seen in the cytoplasm of the egg and the central cell. At about 1 h after pollination, one sperm has made contact with the egg nucleus, while the other sperm is fusing with one of the polar nuclei.

Isolation of protoplasts from viable egg cells of common buckwheat (Fagopyrum esculentum Moench.)

“…A pear shape, together with a large vacuolated central nucleus, allowed for recognition of the egg cell in situ. The typical, granular-structured cytoplasm of the egg cells corresponded to the features earlier reported for maize (Faure et al 1992) and wheat (You and Jensen 1985). Egg cells could be isolated through a combination of enzymatic maceration and mechanical manipulation of the dissected ovules, comparable to the technique that was developed for maize (Kranz et al 1991;Kranz and Lörz 1993), or by purely mechanical isolation.…”

Ultrastructural Changes of the Mature Embryo Sac in Buckwheat (Fagopyrum esculentum) as a Result of High Temperature Exposure.

“…In addition, chaotically arranged organelles and dark osmiophilic deposits were present in the egg and central cell. The phenomena of both synergid degeneration is also reported in Triticum aestivum (You and Jensen 1985) and Brassica campestris (Van Went and Cresti 1988) before pollination.…”

“…In wheat (You and Jensen 1985) and rice (Maeda and Maeda 1990), the cytoplasm of the egg cell and the synergids contains various small vacuoles surrounding the perinucleus and filling the cell. In contrast, the cytoplasm of the egg apparatus of buckwheat is similar to that of Petunia (Van Went 1970a, 1970b and is characteristically polarly distributed.…”

Double Fertilization and Embryogenesis of Eustoma grandiflorum

“…Karyogamy seems to occur within 1 to 2 hour after cell fusion (plasmogamy) in cereals, such as wheat (Tian and Shen, 1992;You and Jensen, 1985) and barley (Mogensen, 1982). In many angiosperms, karyogamy is immediately followed by mitosis (Tian and Shen, 1992).…”