PARENT SESSION
Oral Session #44: Global Change and Climate Change.
Presiding: C. Wessman
Tuesday, August 6. 1:00 PM to 4:45 PM. Grand Ballroom West, Radisson.
Temperature dependence of UV-induced DNA damage and repair in Daphnia.
MacFadyen, Emily*,1, Williamson, Craig1, Mitchell, David2, 1 Lehigh University, Bethlehem, PA2 University of Texas M.D. Anderson Cancer Center, Smithville, TX
ABSTRACT- As global stratospheric ozone levels decrease, more UV-B radiation is reaching the earth's surface, potentially affecting both terrestrial and aquatic organisms. This study examines the repair of UV-induced DNA damage in Daphnia, a planktonic crustacean that plays a fundamental role in nutrient and energy cycling, as well as the regulation of plankton community size structure. Previous studies have demonstrated that photoenzymatic repair or PER (a light-dependent repair process wherein a photolyase enzyme harnesses photon energy from UV-A and visible light and uses it to reverse DNA damage) contributes to UV tolerance of Daphnia. The types of repair enzymes utilized by Daphnia, and their effectiveness at different temperatures, were previously unknown. In laboratory experiments, Daphnia were exposed to UV-B radiation for 12 hours in the presence and absence of visible light, then incubated in the dark, in order to isolate the effects of PER from nucleotide excision repair or NER (a light-independent repair process). Survival and DNA damage (in the form of cyclobutane pyrimidine dimers and pyrimidine(6-4)pyrimidone photoproducts) were analyzed. Results suggest that Daphnia utilize photolyases specific for both types of damage (CPDs and (6-4)PDs), as well as NER for mediating UV-induced DNA damage. While preliminary data support our hypothesis that the process of DNA repair is temperature dependent, the findings also suggest that DNA damage is not independent of temperature, as hypothesized. The mechanism for this response is not known. In addition, the relationship between mortality and UV-induced DNA damage in Daphnia appears to be characterized by a strong threshold effect: mortality results from any accumulation of UV-induced DNA damage above background levels. This study is one of the first to examine the ecological importance of different DNA repair mechanisms for UV-induced DNA damage.
KEY WORDS: ultraviolet radiation, temperature, photolyase, Daphnia