Construction of a cell-free system using extracts from apoptotic plant cells

Cleavage of lamin-like proteins in in vivo and in vitro apoptosis of tobacco protoplasts induced by heat shock

Apoptosis in heat shock-treated tobacco protoplasts was evidenced by DNA fragmentation, flow cytometric analysis and activation of caspase 3-like protease. Furthermore, an in vitro apoptosis system was established which reproduced the apoptotic events. Western blotting analysis using an antibody against lamin A and C showed that in both in vivo and in vitro systems lamin-like proteins were cleaved into a 35-kDa fragment, and that lamin-like protein degradation precedes DNA fragmentation. Moreover, we found a 22.8-fold increase in caspase 6-like activity in cytosol of heat-treated protoplasts as compared with the control.

Involvement of poly(ADP-ribose) polymerase and activation of caspase-3-like protease in heat shock-induced apoptosis in tobacco suspension cells

The cleavage of poly(ADP-ribose) polymerase (PARP) by caspase (casp)-3 is an essential link in the apoptotic pathway in animal cells. In plant cells, however, there is no authentic evidence for the similar role that PARP may play during apoptosis. Using a heat shock (HS)-induced apoptosis system of tobacco cells, we found that immediately after a 4 h heat treatment, PARP was cleaved to form an 89 kDa signature fragment, while DNA laddering appeared only after a 20 h recovery following the HS. An activation of casp-3-like protease was also observed. The results suggest that apoptosis in plants and animals may share common mechanisms. On the other hand, when cells were preincubated with 4 mM 3-aminobenzamide or 2-8 mM nicotinamide, the specific inhibitors of PARP, before HS treatment, apoptotic cell death was reduced significantly. Our results thus imply that PARP may also be involved in apoptosis in a different way from the casp-related events.