Number of cells participating during double fertilization are

Double fertilization = Syngamy + Triple fusionDuring syngamy, one male gamete cell (n) will fuse with egg cell (n) to form zygote.During triple fusion, one male gamete (n) fuse with two polar nuclei (n+n) in central cell to form primary endosperm cell (3n; PEC). Therefore, in all four cells participates in double fertilization.