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Responses of rice seedling to excess UV-B radiation and comperison between tolerance and susceptible cultiver
此外，發現水稻對UV-B輻射的耐感性有遺傳上的差異，因此經由選拔選出耐性水稻品種M202、Macan Binong pate及感性水稻品種Odashiroho、Dular。無論是耐、感性品種，當其遭受稻過量的UV-B照射時皆會造成傷害反應，惟感性品種的傷害程度大於耐性品種，秈稻的程度大於稉稻。耐性品種的超氧歧化酶、抗壞血酸過氧化酶及穀胱苷還原酶的活性皆較感性品種為高。穀胱苷及抗壞血酸的含量會隨UV-B照射時間而增加，耐性品種的相對增加量較感性品種大。
The purpose of this study is to explore the physiological and morphological responses of rice seedlings exposed to the excess UV-B irradiation. Further, to screen the UV-B tolerant and susceptible rice cultivar from 186 rice varieties and compare the physiological and morphological responses of UV-B tolerant and susceptible rice cultivars to find the possible mechanism of UV-B tolerance in rice plants. Three experiments were performed in this study, the first part was a series of morphological and physiological responses were conducted as cultivar TNG-67 V3-seedling exposed to excess UV-B irradiation. Second trial was screening the UV-B tolerant and susceptible rice cultivars. And subsequently, the last part was compared the physiological and morphological responses of tolerant and susceptible rice cultivars to excess UV-B irradiation. Plant materials were planted in growth chamber and treated at V3-seedling. The excess UV-B irradiation treatment was supplied by the UV-B lamps. Experimental results indicated that exposed to the excess UV-B irradiation affects the growth of rice plant with reduction in plant height, fresh weight, and dry weight, decreased the content of chlorophyll, decreased photosynthetic capacity, damaged stomata structure, and incresed malondialdehyde content and electrolyte conductivity. The enzymatic antioxidants ( superoxide dismutase, ascorbate peroxidase and glutathione reductase ) activity were increased at the first day of UV-B exposure, and then decreased during the treatment period. However, nonenzymatic antioxidants content of ascorbic acid, reduced form glutathione and oxidized form glutathione of rice seedling were increases of the V3-seedling after exposure of excess UV-B irradiation. As a result of screening the UV-B tolerant and susceptible cultivar of rice, cultivars M202 and Odashiroho were referred to tolerant and susceptible rice cultivar among japonica type rice, as well as the Macan Binong pate and Dular were referred to tolerant and susceptible rice cultivar among indica type. Both tolerant and susceptible rice cultivars expressed damaged under excess UV-B exposure, the tolerant rice cultivars were suffered from little damaged under excess UV-B exposure as compared to susceptible rice cultivars, and the japonica type rice were suffered a less damaged than indica type rice. The activities of enzymatic antioxidants from tolerant rice cultivars were higher than susceptible rice cultivars, and the nonenzymatic antioxidants content of tolerant rice cultivars were larger than those of susceptible rice. Finally, comparison the injury response and antioxidant activity of rice seedling exposed to excess UV-B irradiation, it is suggested that the UV-B tolerance mechanism of rice not only depend on antioxidant system, the other factors will be involved.
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