The Ultrastructure and Histochemistry of the Synergids of Cotton

Abstract

The composition and ultrastructure of the synergids of cotton were studied. The cells were found to be surrounded by a partial wall composed of cellulose, hemicellulose, and pectins. The structure of the wall was observed to consist of an unusual fibrillar arrangement. The filiform apparatus was demonstrated to be an extension of the wall at the micropylar end of the cell. Large amounts of ER surround the filiform apparatus. Also associated with the latter are large numbers of plastids and mitochondria. The nucleus is large and contains a single, large nucleolus and, frequently, 1 or more micronucleoli. The nuclear membrane contains membrane‐bound vesicles but has few extensions into the cytoplasm. The ER is oriented parallel to the long axis of the cell and decreases in concentration from the micropylar to the chalazal end of the cell. Dictyosomes are common throughout the cell but are more numerous in the midportion where they are closely associated with the ER. The chalazal end of the cell is occupied by vacuoles rich in an inorganic compound which leaves a considerable residue of ash. Spherosome‐like bodies are common throughout the cell. Both the plastids and mitochondria show evidence of division. Ribosomes are numerous and are both free and associated with the ER, nucleus, plastids, and mitochondria. The function of the synergids is proposed to be the absorption, storage, and transport of compounds from the nucellus. On the basis of this function, it is suggested that the synergids act by providing material to the egg and the developing embryo and endosperm and that they are involved in the growth of the pollen tube into the embryo sac.

Effect of Heat Stress During Floral Development on Pollen Tube Growth and Ovary Anatomy in Wheat (Triticum aestivum L.)

“…It is possible that the poor pollen tube growth was due to a lack of attraction from the embryo sac. Some authors have suggested that directional pollen tube growth results from attraction, possibly chemotropic in nature, from the embryo sac (Rosen 1964;Glenk et al 1971), in particular from the synergids (Jensen 1965). In addition, it has been shown in lily that the pollen tube uses nutrients from the pistil for its growth to the ovary (Loewus and Labarca 1973).…”

Megagametogenesis in Arabidopsis wild type and the Gf mutant

“…In several other species, including Capsella, the synergid does not degenerate until pollen tube arrival (Schulz and Jensen 1968;van Went 1970;Newcomb 1973). However, in most species examined, synergid cell degeneration occurs prior to pollen tube arrival (Jensen 1965;Diboll 1968;Cocucci and Jensen 1969;Cass and Jensen 1970;Chao 1971;Maze and Lin 1975;Mogensen and Suthar 1979;Wilms 1981). Synergid cell degeneration prior to pollen tube arrival suggests the existence of a long-range signal; however, in these species, it has not been determined whether pollination is required for degeneration.…”

Ovary signals for directional pollen tube growth

“…Little is known about changes in the embryo sac and how they relate to pollen tube penetration, but the main candidate as signal provider for pollen tube penetration is the synergid. While the precise role synergids play is still to be discovered, it is apparent that they are involved in pollen tube penetration to the embryo sac, since the pollen tube consistently enters through a synergid (Jensen 1965). In addition, experiments with in vitro fertilisation have shown that pollen tubes do not arrive at embryo sacs containing disrupted synergids (Higashiyama et al 1998).…”