Involvement of chloroplasts in the programmed death of plant cells.

The effect of cyanide, an apoptosis inducer, on pea leaf epidermal peels was investigated. Illumination stimulated the CN--induced destruction of guard cells (containing chloroplasts and mitochondria) but not of epidermal cells (containing mitochondria only). The process was prevented by antioxidants (alpha-tocopherol, 2,5-di-tret-butyl-4-hydroxytoluene, and mannitol), by anaerobiosis, by the protein kinase C inhibitor staurosporine, and by cysteine and serine protease inhibitors. Electron acceptors (menadione, p-benzoquinone, diaminodurene, TMPD, DCPIP, and methyl viologen) suppressed CN--induced apoptosis of guard cells, but not epidermal cells. Methyl viologen had no influence on the removal of CN--induced nucleus destruction in guard cells under anaerobic conditions. The light activation of CN--induced apoptosis of guard cells was suppressed by DCMU (an inhibitor of the electron transfer in Photosystem II) and by DNP-INT (an antagonist of plastoquinol at the Qo site of the chloroplast cytochrome b6f complex). It is concluded that apoptosis initiation in guard cells depends on the simultaneous availability of two factors, ROS and reduced quinones of the electron transfer chain. The conditions for manifestation of programmed cell death in guard and epidermal cells of the pea leaf were significantly different.