Capsella Embryogenesis: The Synergids Before and After Fertilization

Abstract

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Ovule ontogeny of Tabebuia pulcherrima Sandwith (Bignoniaceae): embryo sac development

“…Young synergids and egg cell are quite dimorphic immediately after the megagametophyte cellularization, contrasting with the attempted generalization in literature (Bhandari & Chitralekha 1989, Huang & Russell 1992. The PAS-positive common walls between synergids, egg and central cell are present in the mature embryo sac, and we suggest the formation of some kind of passage for the sperm cell nuclei through these walls in fertilized megagametophytes, as related for Epidendrum scutella (Coccucci & Jensen 1969) or for Capsella bursa-pastoris (Schulz & Jensen 1968). Our data together with other studies on the megagametophyte development suggest that several embryological features are common for all the Bignoniaceae, specially the Polygonum type megagametophyte development, the micropylar end swelling of the megagametophyte and its absorption of the surrounding nucellar epidermis and endothelial cells, differentiation of a hypostase and presence of hooked synergids in the mature embryo sac.…”

“…In Epidendrum scutella, in the chalazal portion of the degenerative synergid, common walls between egg and central cells are dissolved, so that the last two cells establish direct contact with the degenerative synergid (Cocucci & Jensen 1969). In Capsella bursa-pastoris the cell walls are also continuous in the chalazal region of the egg apparatus, but frequently a pore is observed in the walls between the degenerative synergid and the egg cell in fertilized megagametophytes (Schulz & Jensen 1968). This indicates that the presence of cell walls is not necessarily in contradiction with the fusion of the gametes (Willemse & van Went 1984, Mansfield et al 1991.…”

“…With the exception of Plumbago and other genera of the Plumbaginoideae, with no synergids in the embryo sac, in angiosperms the pollen tube penetrates one of the synergids -usually the one that started to undergo a degenerative process -through the filiform apparatus (Schulz & Jensen 1968, Jensen 1972, Kapil & Bhatnagar 1981, Willense & van Went 1984. In Tabebuia pulcherrima the egg cell assumes a lateral disposition and is slightly chalazal in relation to the synergids; consequently it does not establish direct contact with the micropylar channel.…”

“…Many ultrastructural studies have demonstrated that the synergids are very active cells, probably involved in the secretion of substances -e.g., chemiotactic substances which guide the pollen tube to the synergids, as well as in the absorption of nutritious material originating from tissues of the micropylar region and its translocation to the central and egg cells (Schulz & Jensen 1968, Tilton 1981, Willemse & van Went 1984, Folsom & Cass 1990, Mansfield et al 1991, Russell 1992, Tirlapur et al 1993. According to this vision, the filiform apparatus exercises the important function of increasing diffusion efficiency, like wall ingrowths of transfer cells.…”

The Ovule and the Embryo Sac.

“…The synergids, which are located on either side of the egg cell, play an important role in fertilization (Jensen, 1965a;Schulz and Jensen, 1968a;see Russell, 1993, this issue). The pollen tube discharges its contents into one of the synergids prior to incorporation of the sperm nuclei into the egg and central cells.…”