The synergid cell: attractor and acceptor of the pollen tube for double fertilization

In flowering plants, the egg cell is generally accompanied by two symmetrical cells, called cells. As early as the 1870s, cells were distinguished from egg cells and cooperation between and egg cells was proposed; the term synergid is derived from the Greek synergos, which means working together. The accumulation of morphological and genetic data, and, more recently, the in vitro physiological analysis of the fertilization system of Torenia fournieri, have revealed that cells work together with egg and central cells to accomplish double fertilization. This cooperation is of crucial importance in the attraction and acceptance of the pollen tube. In this review article, I focus on the physiological function and behavior of the cell during the fertilization process.