Effect of UV-B on Rice and Estimation of Its Productivity

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DNA damage in two strains of rice by irradiation of UV-B and its ability of repair were searched by alkaline agarose gel electrophoresis and its image analysis system. Compare of CPD (cyclobutyl pyrimidine dimmer) in DNA formed by UV-B irradiation was very similar in the two strains, which were sensitive (Oryza sativa var.Serjumki) and resistant (Oryza sativa var.Marithbach sc-6) against UV.However, their abilities of photoreactivation and excision repair were different. UV-resistant strain showed high abilities of photoreactivation and excision repair, although UV-sensitive one was comparatively weak ability of repair system. While the photoreactivation quickly responded to formation of the CPD,the excision repair system was very slow response. Those results showed that UV-resistance of rice was originated high ability of repair systems.DNA damage, abilities of photoreactivation and excision repair at the 1-2 leaves, 3-4 leaves, and 5-6 leaves stage of rice were searches with measurement of their CPD.Their results showed that stages of 1-2 and 3-4 leaves stage of the rice were very similar ability, although DNA damage and their abilities of repair in rice of 5-6 leaves stage was diminish of about 20%. The reason was thought that UV-B reaching to nucleus in the cell was reduced, as rice at this stage contained many chloroplasts and became to be thick and rigid. It is necessary to search the ability against UV-B in rices cultivated in Japan.