DOUBLE FERTILIZATION

The process of double fertilization is a unique biological process in which one sperm fuses with the egg to produce the embryo while the second fuses with the central cell to form the endosperm, a nutritive tissue needed for growth of the succeeding generation. This characteristic defines the angiosperms as a natural systematic group. This chapter focuses on (1) the arrival of the male gametophyte (pollen tube) in the female gametophyte (the embryo sac [ES]), (2) the release of the male gametes into the female gametophyte, (3) the entry or plasmatic fusion of the sperm into the female reproductive cells, the egg cell and central cell, (4) the migration of sperm nuclei into alignment with female nuclei, and (5) their subsequent nuclear fusion. Gametic fusion in angiosperms resembles gamete fusion in other organisms or exocytosis of sufficiently large vesicles. Sexually based cellular fusions are based on proteins integral to the membrane that, upon recognizing complementary macromolecules on an opposite membrane, stimulate fusion. © 1992, Academic Press Inc.