Programmed Cell Death During Secondary Xylem Differentiation in Eucommia ulmoides

Programmed cell death (PCD) during secondary xylem differentiation in Eucommia ulmoidesOliv. was examined using electron microscopy and by investigation of DNA fragmentation and degradationof caspase-like proteases (CLPs). DNA ladders were detected in developing secondary xylem by gelelectrophoresis. DNA fragmentation was further confirmed by using the TdT-mediated dUTP nick-endlabeling (TUNEL) method. Western blotting analysis showed that CLPs (caspase-8- and caspase-3-likeproteases) and PARP (poly (ADP-ribose) polymerase) were degraded during secondary xylem differentiation.The results thus indicated that secondary xylem differentiation in E. ulmoides was a typical process of PCDand the degradation of CLPs might be a constitutive PCD event during secondary xylem differentiation.