Poster: Environmental physiology

Abs # 28: UV radiation resistance of the Chlamydomonas zygospore

Presenter:	Daniel, Patricia L, Contact Author
Authors	Daniel, Patricia L (A)   VanWinkle-Swift, Karen P (A)
Affiliations:	(A): Northern Arizona University

The Chlamydomonas zygospore, produced as the end product of sexual reproduction, is remarkably resistant to abiotic stress including solar ultraviolet (UV) radiation, and can serve as a useful model for identifying the cellular and molecular basis of resistance. We have shown that more than 50% of zygospores survive exposure to a UV-C dose that yields less than 1% survival of vegetative cells of the same strain. Because C. monoica is homothallic, zygospore-specific mutations, even if recessive, are easily recognized in this species. To obtain ultra-UV-resistant zygospore mutants, vegetative cells of C. monoica were exposed to a non-lethal mutagenic dose of UV-C radiation. Surviving vegetative cells were then induced to mate and the resultant zygospores were exposed to a potentially lethal dose of UV-C radiation. Following induction of germination, rare viable zygospores were selected. Three UV resistant mutant strains were obtained in this manner. Each mutant has been found to have a unique phenotype. Although all show increased zygospore tolerance to UV-C and UV-B radiation, one of the mutants shows increased UV resistance in vegetative cells as well. Another strain fails to show the delay in germination in response to UV exposure that is typical of wildtype zygospores. Two of the mutant strains exhibit increased zygospore autofluorescene as compared to wildtype zygospores, suggesting differences in the amount or nature of UV-absorbing surface components. Genetic analysis is currently underway to determine segregation patterns, dominance relationships, and allelism. In addition we are using transmission electron microscopy to determine if altered secondary zygospore wall formation contributes to UV resistance in any of the mutant strains.