Effects of Exogenous H202 on the Content of Endogenous H₂0₂, Activities of Catalase and Hydrolases, and Cell Ultrastructure in Tobacco Leaves.

It was shown that tobacco leaf treatment with 100 mM H₂0₂ increased their content ofendogenous H₂0₂ and activities of catalase and hydrolases (acid phosphatase, proteases, and RNase) and also caused'various chang- es in the cell structure. In this case, programmed cell death (PCD) occurred in some cells, which was ob- served as chromatin condensation, cytoplasm collapse, etc. In the meantime, many cells displayed organelle activation rather than PCD. It is suggested that cells that undergo H₂0₂-dependent PCD release signaling molecules inducing protective mechanisms against oxidative stress in neighboring cells not exhibiting PCD.