Studies On Mitochondrial Cyanide-resistant Respiration And Melatonin In Plant Cell Apoptosis

In this study, a monoclonal antibody to the terminal oxidase of the alternative pathway from Sauromatum guttatum was used to detect the expression of alternative oxidase (AOX) protein in tomato mitochondria. The results showed that there was an obvious correlation between the ethylene-induced apoptosis and the levels of AOX protein in tomato cells undergoing ethylene-induced apoptosis. In addition, when tomato protoplasts were preincubated with 2 mM salicylhydroxamic acid (SHAM), an inhibitor of alternative pathway, before being exposured to ethylene, the TUNEL positive reaction and DNA fragmentation was obviously accelerated. We suggest that AOX may play an important role in protecting tomato protoplasts against ethylene-induced apoptosis in tomato protoplastsThe cleavage of poly (ADP-ribose) polymerase (PARP) and activation of caspase-3-like proteases in ethylene-induced apoptosis of tomato protoplasts were investigated. Our results showed that after a 4 h treatment with ethylene, PARP was cleaved into an 84 kDa fragment, while DNA laddering appeared only after a 12 h treatment. At the same time, an activation of caspase-3-like protease was observed. Furthermore, when tomato protoplasts were preincubated with 2 mM 3-AB or 4 mM NIC, the specific inhibitor of PARP, before treatment with ethylene, apoptotic cell death was reduced significantly. Taken together, our results indicated that the cleavage of PARP and activation of caspase-3-like cysteine protease are probably involved in the progression of apoptosis in ethylene-induced apoptosis.Pretreatment with 10 ng/mL-20 ng/mL melatonin for 5 days significantly attenuated cold-induced apoptosis in carrot suspension cells (Daucus carota L.) as evidenced by the TUNEL procedure, DNA fragmentation and the morphological changes revealed by electronic microscopy observations. The antiapoptotic effect of melatonin was initially thought to be a result of its antioxidant actions. In our study, however, reactive oxygen species (ROS) generation was found not to be affected by melatonin treatment, suggesting that melatonin plays its protective role not related to its direct ROS scavenger. At the same time, notable increases in putrescine and spermidine levels were observed in melatonin-treated cells, which may be responsible for the alleviation of the cold-induced apoptosis. The possible involvement of polyamines in antiapoptotic effect of melatonin was further confirmed by the inhibitory effect of exogenous polyamines on apoptosis as displayed by the DNA laddering assay.