Enzymatic Repair of DNA Damage in Plants

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In recent years, a marked depletion of stratospheric ozone has caused an increase in ultraviolet (UV) radiation reaching the surface of the Earth. With this increase, concern and interest has been raised as to what specific effects UV radiation has on cellular processes in organisms. One such effect, the damage of DNA, has been extensively investigated in bacterial and mammalian systems; however, limited information exists on the effects of UV damage to plant DNA and its in vivo repair by cellular mechanisms. This proposal describes the initial study of a ring- saturated pyrimidine incising activity found in plant cells against UV irradiated or oxidized DNA. This enzymatic activity will be purified from Brassica oleracea (cauliflower) by conventional techniques including ion-exchange, affinity, and gel filtration chromatography. The substrate specificity against UV- irradiated or oxidized, radiolabeled polydeoxyribonucleotides will be characterized by high pressure liquid chromatography (HPLC). Using the purified enzyme as a probe, the effects of DNA base sequence on the formation of these lesions and their subsequent in vivo repair will be quantified. Since the chloroplast genome is also susceptible to damage, the presence of the ring-saturated pyrimidine-DNA repair enzyme in chloroplasts will be investigated. This should determine if there is a means to effectively remove this damaged lesion from chloroplast DNA to maintain the integrity of this genetic material. The results of these studies should lead to a better understanding of the biochemical processes that constitute the plant cellular response to DNA damage. The aim is to ultimately use the knowledge obtained from this project to isolate plant strains that have an increased ability to repair damage caused by radiation and oxidation and therefore have an increased survival capacity.