Difperent sensitiorty UVB radiation of rice cultioors based on UVB-caused CPDs Frequencies

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We previously fornd that UVB reduced tiller number and biomass, and the amounts of soluble protein, Rubisco and so on in leaves of rice. There were cultivar differences in the sensitivity to the inhibitory effects of UVB among indica, javanica and japonica rice cultivars. Among Japanese rice cultivars, Sasanishiki exhibited more resistance to UVB,while Norin 1 was less resistant. In this work, we examined if differences in cyclobutyl pyrimidine dimer frequencies (CPD^S) caused by UVB were involved in UV-sensitive and UV-resistant cvs. Norin 1 and Sasanishiki. We also investigated the changes in UVB-caused CPDs in leaf developed at the different stages in rice grown in visible radiation without UVB.We improved an alkaline agarose gel electrophoresis using unidirectional pulse field gel electrophoresis devised by Sutherland et al.(1987). Using this apparatus, we first found that Norin 1 was more deficient in the repair ability of CPDs by photoreactivation and excision than Sasanishiki. The leaf fully expanded at the different stages was detache from plant, and exposed to UVB (9KJ/m2) : the highest CPDs were shown to be produced in the 2,3 and 4th fully expanded leaf. Furthemore, the changes of UVB-caused CPDs were examined in the different aged-leaf of the 6th leaf from leaf emergence through completion of expansion.The leaf grown for 1,4,7 and 15 days after leaf emergence was exposed to the above mentioned dose of UVB.The 6th leaf was fully expanded 7 days after emergence. The highest CPDs were found to be produced in the 4 days-grown leaf. It was thus indicated that the sensitivity to UVB caused CPDs dramatically changed in the progress of growth and leaf age.