Programmed cell death during endosperm development

The endosperm of cereals functions as a storage tissue in which the majorit y of starch and seed storage proteins are synthesized. During its developme nt, cereal endosperm initiates a cell death program that eventually affects the entire tissue with the exception of the outermost cells, which differe ntiate into the aleurone layer and remain living in the mature seed. To dat e, the cell death program has been described for maize and wheat endosperm, which exhibits common and unique elements for each species. The progressio n of endosperm programmed cell death (PCD) in both species is accompanied b y an increase in nuclease activity and the internucleosomal degradation of nuclear DNA, hallmarks of apoptosis in animals. Moreover, ethylene and absc isic acid are key to mediating PCD in cereal endosperm. The progression of the cell death program in developing maize endosperm follows a highly organ ized pattern whereas in wheat endosperm, PCD initiates stochastically. Alth ough the essential characteristics of cereal endosperm PCD are now known, t he molecular mechanisms responsible for its execution remain to be identifi ed.