Table 1.

Developmental Stages of the Arabidopsis Endosperm

No. of
Embryo Developmental
Time after
Fertilization (hr)
Cytological Events
I1Zygote0One large nucleus close to the zygote.
II2Zygote2–4First syncytial mitosis. The two nuclei migrate to opposite poles of
the endosperm.
III4ZygoteNDaSecond syncytial mitosis. Nuclei division planes are parallel to the
main polar axis.
IV(6)–8Elongated zygoteNDThird syncytial mitosis. Nuclei division planes are perpendicular to
the main polar axis. One or two nuclei migrate to the chalazal
pole, and the six or seven other nuclei become tightly linked to
the endosperm peripheral cell wall. Nuclei of the CZE do not
enter mitosis together with nuclei of the PEN.
V12–16Elongated zygote, one cellNDFourth syncytial mitosis. Nuclei divisions are not synchronous,
and nuclei of the CZE are larger than nuclei in the PEN.
VI24–28One cell, two cell12–18Fifth syncytial mitosis. The CZE contains one to four large nuclei.
Nuclei in the MCE undergo synchronous divisions earlier than
nuclei in the PEN.
VII44–48Two cell, quadrant, octant24Sixth syncytial mitosis. The delay between nuclei division in the MCE
and the PEN becomes more pronounced. In the PEN, coordinated
nuclei divisions take place as a wave. The PEN and the MCE
become independent domains of cyclin B1;1 expression.
VIII90Octant30Seventh syncytial mitosis. A layer of nuclear cytoplasmic domains
surrounds the embryo, and the MCE is the only part of the
endosperm with two layers of nuclear cytoplasmic domains.
IX200Dermatogen-globular36–60Eighth syncytial mitosis restricted to the PEN. Divisions in the
MCE are completely independent of divisions in the PEN. The
CZE contains large and small nuclei.
  • a ND, not determined.