Changes in actin organization in the living egg apparatus of Torenia fournieri during fertilization

Changes in actin organization in the living egg apparatus of Torenia fourni eri from anthesis to post-fertilization have been investigated using microi njection and confocal microscopy. Our results revealed that the actin cytos keleton displays dramatic changes in the egg apparatus and appears to coord inate the events of synergid degeneration, pollen tube arrival and gametic fusion during fertilization. Synergid degeneration occurs after anthesis an d is accompanied by actin fragmentation and degradation. The actin cytoskel eton becomes organized with numerous aggregates in the chalazal end of the degenerating synergid, and some of the actin infiltrates into the intercell ular gap between synergids, egg and central cell, forming a distinct actin band. An actin cap is present near the filiform apparatus after anthesis an d disappears after pollen tube arrival. In the egg cell, actin filaments in itially organize into a network and after pollination become fragmented int o numerous patches in the cortex. These structures, along with the actin in the degenerating synergid and intercellular spaces form two distinct actin coronas during fertilization. The actin coronas vanish after gametic fusio n. This is the first report of changes in actin organization in the living egg apparatus. The reorganization of the actin cytoskeleton in the egg appa ratus and the presence of the actin coronas during fertilization suggest th ese events may be a necessary prelude to reception of the pollen tube and f usion of the male and female gametes.