SPATIAL AND TEMPORAL REGULATION OF DNA FRAGMENTATION IN THE ALEURONE OF GERMINATING BARLEY

During germination of barley grains, the appearance of DNA fragmentati on started in aleurone cells near the embryo and extended to the dista l end in a time-dependent manner. DNA fragmentation was demonstrated t o occur only after the expression of a-amylase mRNA in the aleurone la yer. In addition, cell wall degradation started in cells near the embr yo on the sides facing the endosperm. Subsequently cell wall degradati on extended to the lateral cell walls and to cells more to the distal end of the grain. A typical alteration of the nucleus was observed by electron microscopy and an almost complete degradation of DNA was foun d in the nucleus while the nuclear envelope remained intact. The resul ts indicate;that programmed cell death occurred in aleurone cells duri ng germination. A model is proposed for the regulation of programmed c ell death in aleurone cells during germination involving ABA levels an d cell wall degradation.