KINETICS OF DOUBLE FERTILIZATION IN TORENIA-FOURNIERI BASED ON DIRECTOBSERVATIONS OF THE NAKED EMBRYO SAC

Torenia fournieri Lind. has a naked embryo sac that protrudes from the micropyle. The precise time course of the entire process of double fe rtilization and the kinetics of fertilization events were determined i n this species by the following methods: (i) without squashing, pollen tubes on the torn stylar canal were observed by fluorescence microsco py after staining with both 4',6-diamidino-2-phenylindole (DAPI) and a niline blue; and (ii) large numbers of living embryo sacs were observe d directly by differential interference microscopy before and after fe rtilization. The pollen began to germinate 5 min after pollination and extruded pollen tubes which elongated at a constant rate of 2.3 mm.h( -1). At 4.0 h after pollination, the mitotic index of the generative c ell within the pollen tube reached 88% and the two sperm cells were fo rmed. Pollen tubes began to arrive at ovules 8.9 h after pollination a nd directly entered one of two synergids in the naked embryo sac. The time required for transport of sperm cells in the degenerated synergid was estimated statistically to be 1.9 +/- 1.8 min for transport of th e first cell and 7.4 +/- 1.6 min for the second. In the nucleus of the fertilized egg cell, the male nucleolus began to emerge 10 h after po llination and the female nucleolus often decreased in size. The two nu cleoli fused together prior to elongation of the zygote, which began 2 8 h after pollination. In the central cell, the secondary nucleus migr ated to a region adjacent to the egg apparatus after pollination but p rior to the arrival of the pollen tube. The primary endosperm nucleus rapidly returned to the inner region after fertilization. Prior to emb ryogenesis, the first division of the primary endosperm began about 15 h after pollination, at a defined site, to form the chalazal haustori um.