DOUBLE FERTILIZATION IN EPHEDRA-TRIFURCA, A NONFLOWERING SEED PLANT - THE RELATIONSHIP BETWEEN FERTILIZATION EVENTS AND THE CELL-CYCLE

Fertilization in Ephedra trifurca was examined with a combination of light and fluorescence microscopy. Developmental analysis clearly indicates that double fertilization events, similar to those described in E. nevadensis, regularly occur during the process of sexual reproduction in E. trifurca. In addition to the typical fusion of a sperm nucleus and egg nucleus, a second fertilization event occurs between the second sperm nucleus from an individual pollen tube and the ventral canal nucleus. Both of the fertilization events take place within the confines of an individual egg cell of the female gametophyte. Microspectrofluorometric data demonstrate that each nucleus involved in a sexual fusion event proceeds through the synthesis phase of the cell cycle and increases its DNA content from 1C to 2C before the process of nuclear fusion is completed. Photometric data also confirm that the product of the second fertilization event is equal in DNA content (4C) to the zygotic nucleus derived from the first fertilization event, and is prepared to enter into mitosis as a fully functional diploid nucleus.