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

利用碱性琼脂糖凝胶电泳及其图像分析系统研究了UV-B辐射对两个水稻品系DNA的损伤及其修复能力。UV-B辐射对敏感水稻（Oryza sativa var.Serjumki）和抗性水稻（Oryza sativa var.Marithbach sc-6）DNA形成的CPD（cyclobutyl pyrimidine dimmer）比较相似，但它们的光复活和切除修复能力不同。抗紫外线菌株具有较高的光复活和切割修复能力，而紫外线敏感菌株的修复能力较弱。光复活系统对CPD的形成反应迅速，而切除修复系统反应缓慢。通过对水稻1 - 2叶期、3 - 4叶期和5 - 6叶期的DNA损伤、光复活和切割修复能力的测定，发现水稻1 - 2叶期和3 - 4叶期的DNA损伤、光复活和切割修复能力非常相似，而5 - 6叶期水稻的DNA损伤及其修复能力降低了20%左右。其原因被认为是UV-B到达细胞核减少，因为在这个阶段的水稻含有许多叶绿体，变得厚而硬。因此，有必要对日本栽培的水稻的抗UV-B能力进行研究。

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.