Programmed cell death in wheat during starchy endosperm development.
The starchy endosperm of wheat underwent programmed cell death (PCD) during its development. It showed a ladder of DNA fragments in multiples of 180-200 bp at specific stages when analyzed by agarose gel electrophoresis. The onset of internucleosomal fragmentation of the genome in wheat endosperm could be accelerated by ethylene. While treatment with abscisic acid (ABA) did not delay the onset of DNA fragmentation, but reduced its extent in developing wheat endosperm. During PCD, beside some ultrastructural changes common to other animal and plant apoptotic cells, the starchy endosperm cells also showed some peculiar ultrastructural features. For example, the chromatins in the nucleoplasm were densely aggregated, only a few condensed chromatins abutted onto the inner surface of the nuclear envelope; the nucleus was the first to suffer from degeneration; during nuclear disintegration a large number of organelles could still be observed in the cytoplasm; after nuclear disintegration, the cell remained alive, and synthesis and accumulation of starches and proteins were carried out as usual in the cytoplasm until the starchy endosperm cell died when it was filled with reserves; no formation of apoptotic bodies could be found and the dead starchy endosperm cell served as a reservoir. The PCD of starchy endosperm cells in wheat was a special form of PCD.