DNA modifications as a means of detecting the irradiation of wheat

Abstract

Irradiation produces a variety of modifications in DNA which, if detectable, would provide a means of determining whether food containing DNA had been irradiated. This paper presents initial attempts to detect thymidine glycol, a known DNA irradiation product. Two methods have been employed, a fluorescence assay and an enzyme immunoassay. The reliability of the fluorescence assay was first tested by using it to determine the radiolytic yields of thymidine glycol in the much simpler system of aqueous thymidine solutions saturated with either N 2O or N 2O/O 2(4:1). HPLC was employed to independently assess the radiolytic yields of thymidine glycol in these systems. Results from the fluorescence (values from HPLC experiments given in brackets) gave G-values for glycol of 0.11(0.07) μmol J -1 and 0.16(0.07) μmol J -1 in N 2O and N 2O/O 2 respectively. The fluorescence assay has also been applied to determine G(thymidine glycol) produced on irradiating aqueous solutions of calf thymus DNA, values of 0.03 μmol J -1 and 0.07 μmol J -1 being found in N 2O and N 2O/O 2 saturated solutions respectively. Techniques have been developed to enable DNA to be extracted from small samples of wheat. The preparation of antibodies specific for thymidine glycol-DNA required for the immunoassay is described. DNA from wheat has been tested both by the fluorimetric test and immunoassay. In both cases DNA from unirradiated wheat appeared to contain significant amounts of thymidine glycol. The fluorimetric assay showed increasing levels of glycol with increasing doses of radiation (0–1 kGy). No such correlation was apparent in the immunoassay, this is most probably due to the unsuitability of the initially selected antibody, which although recognising DNA treated with OsO 4 to produce intramolecular thymidine glycol, failed to interact with irradiated calf thymus DNA. Antibodies from other clones are now being screened in an endeavour to find one more suitable.