Early events in the penetration of the embryo sac in Torenia fournieri (Lind.)

At maturity, Torenia fournieri (Lind.) has an embryo sac which protrudes th rough the micropyle placing the synergids, egg cell and part of the central cell within the ovary locule adjacent to the placenta. The present study u tilized this unique attribute in combination with confocal and light micros copy to characterize the timing and associated structural changes during po llination events leading to double fertilization. The observation of sperm nuclei in living gametophyte tissue is an important advance in the identifi cation, in real time, of stages leading to fertilization in angiosperms. A continuum of fertilization occurred between 12 and 16 h after pollination ( hap), with peak frequency of egg and sperm fusion at 14 hap (43%). Movement of the sperm cells through the degenerated synergid took several hours and fusion between sperm and their respective female nuclei occurred simultane ously. Changes in embryo sac structure were also documented. Cell walls in the region between the synergids and egg cell were poorly developed prior t o pollen tube penetration. Thickened cell walls were observed around the pe riphery of the synergids and egg cell following pollination, and in the cen tral cell where it lay within the body of the ovule. Starch was observed in the cells of the embryo sac, although the number and distribution of granu les varied before and after pollination. These temporal and spatial observa tions of the embryo sac in Torenia fournieri provide a basis for further re search to determine control mechanisms operating during specific double fer tilization events in angiosperms. (C) 2000 Annals of Botany Company.