Relationship between ultraviolet-B sensitivity and cyclobutane pyrimidine dimer photorepair in rice.

Among Indica rice cultivars (Oryza sativa L. cvs.) that belong to the aus ecotype from the tropical Bengal region, where the amount of ultraviolet-B (UV-B) radiation in the solar radiation is relatively great, Marich-bati cultivar has exhibited resistance to UV-B radiation, while Surjamkhi cultivar appeared to be less resistant. We have examined the susceptibility to cyclobutane pyrimidine dimer (CPD) induction by UV-B radiation and the ability to photorepair CPDs using these two cultivars. UV-B radiation produced similar dimer levels in the leaves of the two cultivars. In contrast, the ability to photorepair CPDs in the UV-sensitive Surjamkhi cultivar was lower than that in the UV-resistant Marich-bati cultivar. These results were similar to our previous data, namely, that a UV-sensitive Japanese rice cultivar (Oryza sativa L. cv. Norin 1) cultivated in the moderate climate of Japan is deficient in its ability to photorepair CPDs. Thus, these results suggest that a strong correlation exists between the sensitivity to UV-B and the photorepair deficiency, and that a low ability in CPD photorepair may be a principal factor in determining the UV-B sensitivity in rice plants.