The presence and subcellular localization of caspase 3-like proteinases in plant cells.

Caspases play a very important role in initiating and executing apoptotic processes in animal cells. In this study we show that plant mitochondria were able to initiate the activation of caspase 3 in a Xenopus cell free system. Caspase 3-like activity was found to be present in plant cells and could only be inhibited by the specific caspase 3 inhibitor N-acetyl-Asp-Glu-Val-Asp-fluoromethylketone (Ac-DEVD-fmk) and not by cysteine protease inhibitors. By micro-injection of the caspase 3 substrate in living Chara cells we showed that caspase 3-like activity was mainly present in the cytosol rather than in the vacuole. This is the first time that in vivo caspase 3-like activity has been demonstrated in plants.