Various maize organs were irradiated under diverse regimes, with or without photoreactivating visible light present. In many protocols, epidermal layers were peeled from the underlying tissue so that we could separately assess the amount of damage and rate of DNA repair in the outer and inner tissues. DNA damage was assessed using antibodies directed to the 6,4 photoproducts and antibodies to pyrimidine dimers. Both types of damage accumulate during the day, indicating that repair capacity is insufficient to fully reverse the damage caused by UV-B during daylight hours. During the night, however, the accumulated damage was corrected.
Epidermal cells accumulate the highest amount of DNA damage.
Anthocyanin contributes to shielding. In somatic tissues, most anthocyanin accumulates in epidermal cells, and within these cells the anthocyanin is localized to a large central vacuole that occupies most of the cytoplasmic volume. We found that dark red epidermal layers confer substantial shielding to underlying inner tissues. Because the epidermal nuclei lie above the central vacuole, epidermal damage often remained high even in red tissues. This shielding may prevent irreversible damage to photosynthetic reaction centers.