ETHYLENE-MEDIATED PROGRAMMED CELL-DEATH DURING MAIZE ENDOSPERM DEVELOPMENT OF WILD-TYPE AND SHRUNKEN2 GENOTYPES

We characterized the progression of programmed cell death during maize (Zea mays L.) endosperm development of starchy (Su; wild-type) and sh runken2 (sh2) genotypes and tested the involvement of ethylene in medi ating this process. Histological and viability staining demonstrated t hat endosperm cell death was initiated earlier and progressed more rap idly in sh2 endosperm compared with Su endosperm. Internucleosomal DNA fragmentation accompanied endosperm cell death and occurred more exte nsively in sh2 endosperm. 1-Aminocyclopropane-1-carboxylic acid levels peaked approximately 16 d after pollination (dap) in Su endosperm and gradually decreased during subsequent development, whereas two large 1-aminocyclopropane-1-carboxylic acid peaks were observed in sh2 endos perm, the first between 16 and 20 dap and the second at 36 dap. Ethyle ne levels were elevated in sh2 kernels compared with Su kernels, with an initial peak 20 dap approximately 3-fold higher than in Su kernels and a second peak 36 dap approximately 5-fold higher than that in Su k ernels. Ethylene treatment of Su kernels resulted in earlier and more extensive endosperm cell death and DNA fragmentation. Aminoethoxyvinyl glycine treatment of sh2 kernels reduced the extent of DNA fragmentati on. We conclude that ethylene is involved in triggering programmed cel l death in developing maize endosperm and is responsible for the aberr ant phenotype of sh2 kernels.