High-energy pulse-electron-beam-induced molecular and cellular damage in Saccharomyces cerevisiae.

The high-energy pulse electron beam (HEPE) is a new method for mutation breeding. Previously, we demonstrated that HEPE radiation improved thermotolerance and ethanol production of Saccharomyces cerevisiae. To investigate the influence of HEPE on yeast molecular and cellular damage, cells were separately treated with HEPE radiation at different doses (0, 200, 400, 600, 800, 1000, 1200 and 1400 Gy). Based on results obtained, protein leakage and diffusion of intracellular nucleotide and propidium iodide (PI) uptake assays showed that HEPE clearly enhanced the cell membrane permeability of yeast depending on the dose of exposure. Yeast cells treated with HEPE radiation had significantly elevated levels of DNA instability, as detected by the chromosome spreading assay. These results correlated well with the measurement of increased levels of chromosomal aberrations and apoptosis. Intracellular reactive oxygen species (ROS) and caspase 3 activity were also measured in HEPE-applied yeast cells. Caspase 3 appeared to be involved in HEPE-induced apoptosis. Use of dihydroethidium staining and confocal laser scanning microscopy (CLSM) showed increased levels of intracellular ROS as a consequence of augmented pulsing. Moreover, yeast cells retained some photoreactivation capacity when the dose of HEPE exposure was less than 600 Gy. Thereafter, the level of damage was too serious to repair. Thus, photoreactivation had a repair effect upon HEPE radiation-induced damage. The results of our studies provide a possible explanation for the molecular and cellular effects of HEPE radiation upon S. cerevisiae.