The results of the PCC induction and the major events of the regeneration period. The indicators above the time axis describe the PCC regeneration, the indicators below describe HU regeneration. PCC regeneration occurs slowly compared to HU and is not fully completed after 12 h as previously thought. A total of 0.5 h after the release into the water one can observe the maximum levels of DNA damage, probably caused by the activity of the DNA repair mechanisms. At the 2nd hour, both series achieve the regeneration “breakpoint” characterized by a significantly low number of fluorescent cells (indicating that the major fraction of cells do not replicate at this moment). For the PCC-induced cells this event is prolonged and continues through the 5th hour. After the breakpoint, the regeneration resumes and is completed at the 12th hour for HU. At this time, the PCC series still expressed a significantly higher level of SSBs.