Fertilization in Nicotiana tabacum : cytoskeletal modifications in the embryo sac during synergid degeneration : a hypothesis for short-distance transport of sperm cells prior to gamete fusion

The cytoskeletal organization of the embryo sac of tobacco (Nicotiana tabacum L.) was examined at maturity and during synergid degeneration, pollen-tube delivery and gamete transfer using rapid-frozen, freezesubstituted and chemically fixed material in combination with immunofluorescence and immunogold electron microscopy. Before fertilization, the synergid is a highly polarized cell with dense longitudinally aligned arrays of microtubules adjacent to the filiform apparatus at the micropylar end of the cell associated with major organelles. The cytoskeleton of the central cell is less polarized, with dense cortical microtubules in the micropylar and chalazal regions and looser, longitudinally oriented cortical microtubules in the lateral region