Adaptive response of a new radioresistant strain of Chlamydomonas reinhardtii and correlation with increased DNA double-strandbreak rejoining.
In order to study the relationship between radioresistance and the adaptive response, we aimed to produce a new strain of Chlamydomonas reinhardtii with characteristics of high radioresistance coupled with a protoplast structure typical for the genus, and the cell-wall-less phenotype to facilitate rapid cell lysis in DNA double-strand break (DSB) assays. The adaptive response of the new strain was investigated using clonogenic and DSB assays. Strain H-3 was derived by mating a radioresistant strain (AK-9-9) with the cell-wall-less mutant CW15 strain and selecting for radioresistance by clonogenic assay. The random amplification of polymorphic DNA (RAPD) molecular marker system was used to evaluate genetic polymorphisms between H-3 and other related C. reinhardtii strains. DSB were estimated using constant-field electrophoresis. Of several mutant strains tested, strain H-3 was shown to be most radioresistant on the basis of dose to give a 90% lethality (LD90) rate and dose to give a 99% lethality rate (LD99). In addition to its high radioresistance and thinner cell wall as compared with that of the other parental strain AK-9-9, H-3 also expressed a radiation-induced adaptive response measured by clonal survival when given a priming dose before a test dose. DSB were also rejoined more rapidly in cells exposed to a priming dose 4 h previously. It is concluded from split-dose experiments that the already highly radioresistant strain H-3 is further capable of 'over recovery' or adaptation to radiation exposure. Accelerated DSB rejoining in cells given a priming dose may underlie the cellular adaptive response in this organism.
Chankova
G S
GS
Central Laboratory of General Ecology-BAS, Sofia, Bulgaria.
Matos
J A
JA
Simoes
F
F
Bryant
P E
PE
D000222:Adaptation, Physiological; D000818:Animals; D002473:Cell Wall; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000502:physiology / Q000528:radiation effects*; D004249:DNA Damage / Q000528:radiation effects*; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D010641:Phenotype; D011836:Radiation Tolerance / Q000235:genetics / Q000502:physiology*