Double fertilization in flowering plants: discovery, study methods and mechanisms.

The double fertilization of flowering plants was discovered a century ago. The cytology of the gametes is now well known. However the description of the fertilization steps is still poor and most of the cellular and molecular mechanisms involved are unknown. Recent research using in vitro fertilization demonstrated that the early steps of fertilization share some homology with those in animal species. In particular, gamete fusion is followed by a cytosolic calcium increase in the fertilized egg as well as a calcium influx. Further understanding of fertilization also comes from the analysis of mutants isolated in Arabidopsis thaliana. Important new ideas have already emerged from these studies such as the importance of the female gametophyte in embryo development, and an early silencing of the male genome during the first days following gamete fusion.