ULTRAVIOLET-B-INDUCED DNA LESIONS AND THEIR REMOVAL IN WHEAT (TRITICUM-AESTIVUM L) LEAVES

Monoclonal antibodies were used in an enzyme-linked immunosorbent assa y (ELISA) to detect the induction and removal of cyclobutane pyrimidin e dimers (CPDs) and (6-4) photoproducts in DNA isolated from ultraviol et B (UV-B)-exposed primary wheat (Triticum aestivum L, cv, Chinese Sp ring) leaf tissue, The accumulation of lesions in the primary leaves o f 6-d-old wheat seedlings was followed during the exposure of the leaf to an approximate dose of 3.6x10(-1) W m(-2) UV-B (Caldwell weighting ), Significant increases in the levels of both CPDs and (6-4) photopro ducts were detected in wheat leaves exposed to UV-B in the absence of other light, However, only an increase in (6-4) photoproduct levels co uld be measured in wheat leaves exposed to the same UV-B source in the presence of supplemental white light. The removal of CPD antibody bin ding sites in the DNA after irradiation was rapid under conditions of high light intensity in contrast to the removal of(64) photoproduct an tibody binding sites, which was significantly slower. The removal of C PDs appeared to be Light dependent, this rate of removal decreasing wi th decreasing light fluences, The removal of (6-4) photoproducts also appeared light dependent, but to a lesser extent than the removal of C PDs, under the conditions studied here. Gene expression in the primary wheat leaf was measured and showed an up-regulation of chalcone synth ase expression and a reduction in expression of chlorophyll a/b-bindin g protein (cab) in response to supplementary UV-B, No effect was seen on the expression of the other photosynthetic genes studied (the genes coding for the enzymes sedoheptulose 1,7-bisphosphatase and fructose 1,6-bisphosphatase). Measurement of the levels of DNA lesions in this same tissue showed that the observed changes in gene expression accomp anied the appearance of UV-B induced lesions in the form of(6-4) photo products in the wheat leaf genome.