The Ultrastructure of the Egg and Central Cell of Petunia

Abstract

The egg and central cell of Petunia hybrida undergo a number of changes and become mature during anthesis. The egg greatly enlarges and becomes highly vacuolated. The nucleus and the major part of the cytoplasm of the mature egg are located at the chalazal pole of the cell. The number of organelles decreases slightly during maturation. The ribosomes of the mature egg are clustered in polysomes. The chalazal part of the mature egg seems to be surrounded by the plasma membrane only, whereas the remainder of the cell has a normal cell wall.The number of mitochondria and plastids and the amount of endoplasmic reticulum (ER) in the central cell are almost constant during maturation. The number of ribosomes, however, increases greatly. Almost all ribosomes are free and the impression is that they are monosommes. A large amount of starch is formed in the plastids. Two types of dictyosomes are present in the mature central cell. The outer membranes of the polar nuclei are sometimes connected by ER membranes.

Cytological study of pollen tube growth and early seed development inPetunia inflata

“…In P. inflata, an ovary contains approximately 200 ovules which become fully mature by anthesis (Lee et aL, 1997). The embryo sac developmerit of Petunia follows the pattern of Polygonum type (van Went, 1970a;Lee et al, 1997). In P. inflata, the embryo sac consists of an egg apparatus (one egg and two synergids), a central cell containing fused polar nuclei and three degenerating antipodal cells (Lee et al, 1997).…”

“…With recent advances in genetics and molecular biology, underlying cellular mechanisms of those processes have just begun to unfold. In Petunia, only a small volume of research has been conducted in this field, including early works of van Went (1970aWent ( : 1970b, in which ultrastructure of egg/central cell and fertilized embryo sac were examined in P. hybrida using transmission electron microscopy. However, postfertilization events including early embryo and endosperm development have never been investigated in Petunia.…”

Development of ovule, megagametophyte and early endosperm in representative species of Rhododendron L. (Ericaceae)

“…Ultrastructural studies have shown the presence of plastids, often with starch, in one or more of the different cells found in the mature megagametophyte-egg, synergids, central and antipodal cells-in a number of diverse species (e.g. among others, Cass & Karas, 1974;Jensen, 1965;Newcomb, 1973;Schulz & Jensen, 1973, 1977Sehgal & Gifford, 1979;van Went, 1970). Some traditional observations of megagametophytes via stained thick sections published since the reviews have shown starch to occur in additional species (as Cornus: Chopra & Kaur, 1965; Sedum: Subramanyam, 1967, and others), but many more studies have made no reference to the presence of starch.…”

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

“…Ultrastructural examination of CC cytoplasm from unfertilized ovules of a wide variety of taxa, including Linum Vazart, 1965, 1966), Gossypium (Jensen, 1965b), Zea (Diboll and Larson, 1966), Petunia (Van Went, 1970), Helianthus (Newcomb, 1973a), Capsella (Schulz and Jensen, 1973), Epidendrum (Cocucci and Jensen, 1969), Hordeum (Norstog, 1972a, b). Agave (Tilton, 1975), Proboscidea (Mogensen, 1978a); Nicotiana (Mogensen and Suthar, 1979); and Saintpaulia (Gesneriaceae) (Mogensen, 1981) has not revealed any unique characteristics.…”

“…In many plants no cell wall material is deposited along the surface common the the CC and the chalazal end of the EA. Examples include Gossypium (Jensen, 1963(Jensen, , 1965a, Zea (Diboll and Larson, 1966;Diboll, 1968), Linum Vazart, 1965, 1966), Petunia (Van Went, 1970), Quercus (Mogensen, 1972), Helianthus (Newcomb, 1973a, Persea (Tomer and Gottreich, 1976), Proboscidea (Mogensen, 1978a, b), and Nicotiana (Mogensen and Suthar, 1979). However, some wall material is deposited as isolated patches in this region in Agave (Tilton and Mogensen, 1979), Capsella (Schulz and Jensen, 1973), Epidendrum (Cocucci and Jensen, 1969), and Aquilegia (Vijayaraghavan, Jensen and Ashton, 1972).…”