Cell–cell communication and interaction is critical during fertilization and triggers free
cytosolic calcium ([Ca2þ]cyto) as a key signal for egg activation and a polyspermy block in
animal oocytes. Fertilization in flowering plants is more complex, involving interaction of a
pollen tube with egg adjoining synergid cells, culminating in release of two sperm cells and
their fusion with the egg and central cell, respectively. Here, we report the occurrence and
role of [Ca2þ]cyto signals during the entire double fertilization process in Arabidopsis.
[Ca2þ]cyto oscillations are initiated in synergid cells after physical contact with the pollen
tube apex. In egg and central cells, a short [Ca2þ]cyto transient is associated with pollen tube
burst and sperm cell arrival. A second extended [Ca2þ]cyto transient solely in the egg cell is
correlated with successful fertilization. Thus, each female cell type involved in double
fertilization displays a characteristic [Ca2þ]cyto signature differing by timing and behaviour
from [Ca2þ]cyto waves reported in mammals