IN-SITU DETECTION OF NDNA FRAGMENTATION DURING THE DIFFERENTIATION OFTRACHEARY ELEMENTS IN HIGHER-PLANTS

Programmed cell death (pcd) is thought to occur during the autolysis o f xylem vessels. Although several ultrastructural aspects of this diff erentiation process have been characterized, certain key aspects of th is process remain unsolved. Here we demonstrate in pea (Pisum sativum) that nuclei of vessel elements undergoing pcd contain fragmented nDNA . This finding may provide evidence for the activation of a DNA degrad ation mechanism prior to the final disruption of the nucleus that occu rs during the autolysis stage of this differentiation process. In situ detection of DNA fragmentation in nuclei of vessel elements undergoin g pcd may therefore suggest that this death process involves the activ ation of a mechanism for DNA degradation, similar to that activated du ring apoptosis in animal cells. In addition, this differentiation proc ess may serve as a useful positive control for the in situ detection o f pcd in other developmental pathways and during the hypersensitive re sponse of plants to avirulent pathogens.