The Photorepair and Photoisomerization of DNA Lesions in Etiolated Cucumber Cotyledons after Irradiation by UV-B Depends on Wavelength

Abstract

To examine the light-dependent repair of DNA photo-lesions, such as, cyclobutane pyrimidine dimers (CPDs) and pyrimidine-(6-4)-pyriinidone photoproducts [(6-4)pho-toproducts], we incubated cucumber cotyledons under monochromatic light (325-500 nm) after they had been exposed to UV-B irradiation. Irradiation at wavelengths between 375 and 425 nm was the most efficient for photo-repair of CPDs. The dependence on wavelength for the removal of (6-4)photoproducts differed from that for the photorepair of CPDs. The (6-4)photoproducts were most efficiently removed upon irradiation at 325 nm with a second peak at 400 to 425 nm. An immunological assay using antibodies specific to Dewar photoproducts revealed that irradiation at 325 nm induced the photoisomerization of (6-4)photoproducts to Dewar photoproducts. Thus, the most efficient wavelength for the photorepair of (6-4)photoprod-ucts was between 400 and 425 nm. It seems likely that processes similar to those involved in photorepair of CPDs might be involved in the photorepair of (6-4)photoprod-ucts.