Rapid repair of ionizing radiation injury in Chlamydomonas reinhardi

Repair of sublethal damage is an important factor affecting the survival of irradiated cells. An understanding of this phenomenon is fundamental to understanding the action of ionizing radiations. Although multiple components of such repair have been detected in plateau-phase mammalian cells, processes having different repair rates have never been observed previously in proliferating eucaryotic cell systems. This report describes experiments used to study repair of sublethal damage in cells exposed to fast electrons. Split-dose techniques, utilizing two equal doses given at 100 krad/min and separated by intervals as short as 15 sec, followed by clonogenic cell assay, have been used throughout. These experiments demonstrate the existence of at least two independent repair processes in synchronous, exponentially growing cultures of Chlamydomonas reinhardi. Furthermore, each process probably represents repair of a distinctly different kind of damage. The rapid process described in this report is characterized by a mean repair time on the order of 2 to 4 min in contrast to 20 to 30 min for the well-known Elkind-Sutton type repair. Both processes are nearly temperature independent at temperatures above 250C