OVULE DEVELOPMENT IN ORNITHOGALUM CAUDATUM (LILIACEAE) WITH A REVIEW OF SELECTED PAPERS ON ANGIOSPERM REPRODUCTION

Abstract

SUMMARYThe chalazal end of the egg projects beyond the synergids while the micropylar end is in contact with the nucellar epidermis. The egg nucleus and nucleolus are large and, along with most of the cytoplasm, are located chalazally while a large vacuole occupies the micropylar end. The egg cell wall is attenuated chalazally but, based on preliminary light microscope observations, it does appear to surround the entire cell in some cases. The synergids each have a large chalazal vacuole with the majority of their cytoplasm in the micropylar half of the cell. Nuclei and nucleoli are large and other organelles are numerous. Plastids and endoplasmic reticulum (ER) are more numerous chalazally while mitochondria appear to be evenly distributed. Filiform apparatus (FA) formation occurs late in synergid maturation. The FA is large, well developed, and is surrounded by a vacuolate zone. Various sized vesicles with fibrillar or flocculent contents occur within the FA. The FA stains for both protein and RNA in addition to carbohydrate which is the dominant component. The synergid walls have a knobbed ingrowth around the periphery of their micropylar end. Neither egg nor synergids store any metabolites.This information, coupled with overwhelming evidence from the literature reviewed, has led me to conclude all angiosperm synergids are active in synthesizing and, \ ia the FA, in secreting a substance(s) which influences the final phases of pollen tube growth. Movement of materials into a megagametophyte via the FA seems unlikely, but if it does occur, it is probably an inconsistent feature and only of trivial consequence.

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

“…In Epidendum scutella (Cocucci & Jensen 1969), Papaver nudicaule (Olson & Cass 1981) and Scilla sibirica sato (Bhandari & Sachdeva 1983) the cells of the egg apparatus are entirely involved by PAS-positive walls. Tilton (1981) equally observed continuous walls around the egg apparatus of Ornithogalum caudatum in some optical preparations. 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).…”

“…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.…”

OVULE DEVELOPMENT IN ORNITHOGALUM CAUDATUM (LILIACEAE) WITH A REVIEW OF SELECTED PAPERS ON ANGIOSPERM REPRODUCTION

“…According to Cass (1972) and Cass and Karas (1974), the egg of Plumbago has both gametic and synergid functions. However, based on organelle content, the typical egg seems to be a passive cell that functions only as the female gamete (Jensen, 1974;Tilton, 1981b).…”

“…There are a few reports in which wall material has been said to occur as disjunct islands in the chalazal end of the cell and, in Bellis, Fngell and Petersen (1977) reported that the wall is entire. Preliminary light microscopic (LM) investigations indicate that the wall may be entire in Ornithogalum caudatum as well (Tilton, 1981b).…”

“…Synergids have a cell wall which, like that of an egg, is attenuated chalazally and is either partially or completely absent between the egg and synergids in most taxa. However, the synergid wall is entire in both Bellis (Fngell and Petersen, \911) and Ornithogalum (Tilton, 1981b).…”