Mitochondrial Respiratory Chains And Plant Cell Death Regulation

Hypersensitive response(HR) is one kind of basic disease resistance reaction by plants. HR is characteristic of turning brown on the infected spots of host plants, and dying of the infected cells and some in the surrounding areas. This cell death can prevent the further invasion of pathogens. Local HR can often induce systemic acquired resistance to the whole plant, which can bring about a relatively wide resistance to different pathogens during a period of time. Some reports show that mitochondrial respiratory chains play important roles in HR of plants. But it is not very clear about mechanism of the roles of mitochondrial respiratory chains in HR of plants. Therefore, this thesis is focused on the relationship between mitochondrial respiratory chains and plant cell death regulation. Main results are as follows:1. NaN3 could induce HR-like reaction on tobacco leaves and" could induce the death of suspension cultured tobacco cells. NaN3 was observed to restrain the cytochrome respiration pathway, which caused a drastic decrease in the level of ATP in the cells. As treatment with an oxidative phosphorylation uncoupler, carbonyl cyanide 3-chlorophenylhydrazone, decreased the level of ATP and caused pronounced death of suspension cultured tobacco cells, NaN3 might induce the death of tobacco cells through decreasing the level of ATP in the cells. Under the treatment with NaN3, the content of Cyt c in the cytoplasm of the suspension cultured tobacco cells obviously increased, suggesting that Cyt c transferred from mitochondria to cytoplasm might also take part in the tobacco cell death induction by NaN3. Treatment with catalase could decrease the cell death inducing effect by NaN3, suggesting that reactive oxygen species, such as H2O2, might also take part in the tobacco cell death induction by NaN3. Treatment with NaN3 enhanced the expression level of alternative oxidase(AOX) in suspension cultured tobacco cells, suggesting that the tobacco cells might try to withstand the negative effects of NaN3 through cyanide-resistant respiration.2. An elicitin sample mainly consisting of a 37kD and a 40kD protein was partially purified from the secretion of a fungus of Phytophthora. This elicitin sample could induce hypersensitive response on tobacco leaves and induce the death of suspension cultured tobacco cells. It showed no direct effect on the respiration of the tobacco cells. However, a decrease in the cytochrome pathway acitivity was observed in the tobacco cells treated with the elicitin sample for 1 hr, which was accompanied by some increase in the alternative pathway activity. But the increase in the alternative pathway activity might not continue till 12 hr, as AOX protein level decreased in the tobacco cells treated with the elicitin sample for 12 and 24 hr. The effects of the elicitin sample on the respiration of the tobacco cells caused a drastic decrease in the ATP level of the cells, suggesting that the elicitin sample might induce the death of tobacco cells through decreasing the level of ATP in the cells. At the same time, under the treatment with the elicitin sample for 12 hr, the content of Cyt c in the cytoplasm of the suspension cultured tobacco cells obviously increased, suggesting that Cyt c transferred from mitochondria into cytoplasm might also take part in the tobacco cell death induction by the elicitin sample.3. Some reports have suggested that the cytochrome c tranferred from mitochondria into...