Induction and repair of damage to DNA in cucumber cotyledons irradiated with UV-B

Photoinduced lesions in DNA, namely, cyclobutane pyrimidine dimers (CPDs) and pyrimidine-(6-4)-pyrimidone photoproducts [(6-4)photoproducts], in cucumber cotyledons that had been irradiated with naturally occurring levels of UV-B (290-320 nm) were quantitated by enzyme-linked immunosorbent assays with monoclonal antibodies specific to each type of photolesion. Induction of these photolesions was dependent on temperature and their extent was reduced by simultaneous irradiation with white light. The dark repair of both types of photolesion was undetectable. Light-dependent removal of (6-4)photoproducts was very slow, with 50% removal in 4 h. By contrast, 50% of initial CPDs were removed within 15 min. Both photorepair processes were dependent on the intensity of white light and were sensitive to temperature. These results indicate that high photolyase activity is present in cucumber cotyledons and that repair activities in cucumber cotyledons are different from those reported in Arabidopsis, in which (6-4)photoproducts are photorepaired more rapidly than CPDs.