Effects of temperature on the photoreactivation of ultraviolet-B-induced DNA damage in Palmaria palmata (Rhodophyta)

The accumulation of DNA damage (thymine dimers and 6-4 photoproducts) induc ed by ultraviolet-B radiation was studied in Palmaria palmata (L.) O. Kuntz e under different light and temperature conditions, using specific monoclon al antibodies and subsequent chemiluminescent detection. Both types of dama ge were repaired much faster under ultraviolet-A radiation (WAR) plus photo synthetically active radiation (PAR) than in darkness, which indicates phot oreactivating activity, At 12 degrees C, all thymine dimers were repaired a fter 2 h irradiation with WAR plus PAR, whereas 6-4 photoproducts were almo st completely repaired after 4 h, After 19 h of darkness, almost complete r epair of 6-4 photoproducts was found, and 67% of the thymine dimers were re paired, In a second set of experiments, repair of DNA damage under UVAR plu s PAR was compared at three different temperatures (0, 12, and 25 degrees C ), Again, thymine dimers were repaired faster than 6-4 photoproducts at all three temperatures. At 0 degrees C, significant repair of thymine dimers w as found but not of 6-4 photoproducts. Significant repair of both thymine d imers and 6-4 photoproducts occurred at 12 and 25 degrees C, Optimal repair efficiency was found at 25 degrees C for thymine dimers but at 12 degrees C for 6-4 photoproducts, which suggests that the two photorepair processes have different temperature characteristics.