Induction of apoptosis in purified nuclei from tobacco-suspension cells by cytochrome b6/f complex

An apoptotic cell-free system containing cytosol and nuclei from normally cultured tobacco suspension cells was used to show that a spinach chloroplast preparation can induce apoptosis in nuclei, evidenced by DNA electrophoresis and fluorescence microscopy observations. Further study showed that the chloroplast preparation or its pellet (thylakoid membrane) after hypoosmotic or supersonic treatment still exhibited the apoptosis-inducing activity, but the supernatant had no effect, which indicates that the apoptosisinducing effector in the chloroplast preparation is water-insoluble. The induction of apoptosis by chloroplast preparation could be attenuated by Ac-DEVD-CHO, the specific inhibitor of Caspase-3, implying involvement of a Caspase-3-like protease during the process. Furthermore, extensive apoptosis in nuclei was induced by cytochrome b
6
/f on the thylakoid membrane, indicating that this important cytochrome complex may have an important role in the chloroplast-related apoptotic pathway.