Cytochrome c release and caspase activation during menadione-induced apoptosis in plants

We report here the detection of the release of cytochrome c from mitochondria into the cytosol during menadione-induced apoptosis in tobacco protoplasts. Western blot analysis indicated that the caspase specific inhibitors AC-DEVD-CHO (Ac-Asp-Glu-Val-Asp-aldehyde) and AC-YVAD-CHO (N-acetyl-Try-Val-Ala-aspartinal) inhibited the degradation of a caspase 3 specific substrate PARP (poly(ADP-ribose) polymerase), and they had no effect on the release of cytochrome c. Further study showed that menadione could not induce apoptosis of mouse liver nuclei in tobacco cytosol extract containing no mitochondria. However, when cytochrome c or mitochondria was added into the cytosol extract, apoptosis of mouse liver nuclei and the degradation of PARP could both be detected. The results provide strong evidence that menadione can induce apoptosis in tobacco protoplasts via the release of cytochrome c from mitochondria into the cytosol.