Endoreduplication and Programmed Cell Death in the Cereal Endosperm

Endoreduplication and programmed cell death are important processes during the development and maturation of cereal endosperm. Endoreduplication results in the formation of multiple copies of each chromosome in the nucleus, and it leads to cells with ploidies of 24C to 96C, and sometimes even higher. Although it has generally been thought that this process is associated with cell enlargement and increased levels of gene expression, recent studies of maize endosperm development provided data that do not support this hypothesis. Programmed cell death commences in starchy endosperm cells around mid-development, and ultimately affects nearly all of the endosperm cells, except for those in the aleurone layer. The progression of programmed cell death, which appears to be mediated by increasing levels of ethylene and gibberellic acid, is mediated by cysteine proteases that appear to be similar to vacuolar processing enzymes. Presumably, the loss of viability of starchy endosperm cells facilitates hydrolysis of stored nutrients and their uptake by the embryo during seed germination.