Additional，the content“The PCD of starch endosperm is one of the special types”has been added
into the reversed paper.
The PCD of starch endosperm is one of the special types
It was confirmed that the death of wheat endosperm cells was a PCD process by Evans-Blue
staining, TUNEL assay, DNA gel electrophoresis, and TEM analysis. We discovery that chromatin
condensation (Fig. 4E), and nuclear residual bodies formation (Fig. 4H) in the endosperm cells;
consequently extensive degradation of nuclear DNA occurs, producing fragments with 180-200 bp or
multimers which shows DNA laddering on gel electrophoresis (Fig. 3, lane 1-5). Evans-Blue staining
shows that the starch endosperms PCD process from the 15 DPA until the end of seed maturity, and the
death positions are random (Fig. 1 E, I). TUNEL-positive nuclei were first detected in the endosperm
cells at 12 DPA (Fig. 2A). Then, the number of positive nuclei increased during the development of the
starch endosperm (Fig. 2B).The mitochondria showed intact structures until 14-16 DPA (Fig. 4C).
Until 20 DPA, most of the mitochondria degradation, showed a central hollow (Fig. 4G). The PCD of
starch endosperm exhibits some differences from vacuolar cell death and necrosis. They have the same
characteristics: chromatin condensation and DNA fragmentation. The similarities in starch endosperm
PCD and vacuolar cell death: They maybe need a long time to finish the development process. Such as
endosperm PCD need 18d in wheat (from 12 DPA (Figs. 2A and 4C) to mature (30 DPA)). The
differences: Firstly, Not only the big lytic vacuole and vacuolization, but also vacuolar hydrolases were
observed in the starch endosperm PCD. Secondly, the degradation of mitochondria is accompanied
with nuclear degradation, but vacuolar cell death having the characteristics of the remaining
mitochondria and other organelles, as well as the plasma membrane, remain morphologically intact
until rupture of the tonoplast. The similarities in starch endosperm PCD and necrosis: the degradation
of the mitochondrial was also observed in necrosis and starch endosperm PCD. The differences: First,
necrosis is an typically acute cell death response that develops rapidly and cell corpse remains largely
unprocessed；but starch endosperm PCD lasts for a long time. Second, early rupture of plasma
membrance was detected in the necrosis; but this phenomenon was not observed in the starch
endosperm PCD. Thus, starch endosperm PCD is a unique type of PCD which needs to be
distinguished with vacuolar cell death and necrosis.