Abstract
Nematode shows a marked resistance to radiation as follows:
1. Radiation resistance decreased slightly throughout the first, proliferative phase of embryogenesis. This might be due to the increase in target size, since most cells of nematode are autonomously determined. Eggs irradiated in the second half of embryogenesis were about 40-fold more resistance to the lethal effects of X-rays. This is probably due to the absence of cell divisions during this time. X-irradiation of the eggs resulted in significant life-shortening of the animals. The radiation resistance increased more with advancing larval stages and adult stages.
2. The time spent as a dauer larva does not affect adult life span in Caenorhabditis elegans, as if aging is suspended in this quiescent developmental stage. Modest doses X-irradiation of dauer larvae increased their post-dauer longevity. Post-irradiation incubation of young dauer larvae did not modify this beneficial effect of radiation. Conversely, holding dauer larvae prior to irradiation rendered them refractory to this X-radiation-induced response.
3. Pre-exposure of wild-type Caenorhabditis elegans to oxygen conferred a protective effect against the lethality imposed by subsequent X-irradiation. In contrast, two mutants (rad-1 and rad-2) that are UV and ionizing radiation hypersensitive but not oxygen sensitive, did not exhibit this adaptive response.
As X-ray-induced single-strand breaks in DNA can be rapidly and efficiently rejoined by a repair mechanism, it is suggested that nematode has strong repair system.
