OVULE AND EMBRYO DEVELOPMENT, APOMIXIS AND FERTILIZATION

Genetic analyses, particularly in Arabidopsis, have led to the identif ication of mutants that define different steps of ovule ontogeny, poll en stigma interaction, pollen tube growth, and fertilization. isolatio n of the genes defined by these mutations promises to lead to a molecu lar understanding of these processes. Mutants have also been obtained in which processes that are normally triggered by fertilization, such as endosperm formation and initiation of seed development, occur witho ut fertilization. These mutants may illuminate apomixis, a process of seed development without fertilization extant in many plants.