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Changes of UV-B absorbing compounds in rice seedlings exposed to excessive UV-B radiation and differential tolerance between tolerant and susceptible cultivars of rice (Oryza sativa L.)
The purpose of this study is to explore the UV-absorbing compounds responses of rice seedling exposed to excess UV-B radiation. TNG67、UV-tolerant cultivar、susceptible cultivar and TNG67 were used as matter. Three experiments were performed in this study, the first part was a series of physiological and injury responses were conducted as cultivar TNG67 V3-seedlings exposed to excess UV-B radiation. Second part was compared the physiological and UV-B absorbing compounds responses of tolerant and suspectible rice cultivars to excess UV-B radiation. Last was screening the TNG67 mutants and responses of excess UV-B radiation. Enhanced UV-B radiation depresses physiological responses, resulting in the reduction of rice seedlings growth , including seedlings height and the content of chlorophyll, and clearly increased malondialdehyde（MDA）content. As rice seedlings of TNG67、tolerant cultivars 、suspectible cultivars and TNG67 mutants exposed to excess UV-B radiation, resulted in accumulation of UV-B absorbing compounds, and increasing absorption (O.D.) at 330nm. An example of first day exposed to excess UV-B radiation with increased absorption (O.D.) at 330nm (flavonoids), and then increased during the treament period. At five days, absorpton (O.D.) at 330nm was decreased lightly. The UV-B absorbing compounds are mainly identified as flavonoid, among of flavonoid compounds, the content of catechin was increased at the three days of UV-B radiation. Indica type 8908 (T) and Dular (S) were referred to the content of catechin were also increased at the three days of UV-B radiation, and then decreased during the UV-B treatment period, as well as the japonica type M202 (T) and 3003 (S). On the other side, the content of taxifolin were great increased at the three days of UV-B exposure. The same as UV-B absorbing compounds from tolerant rice cultivars tend to be higher than susceptible rice cultivars. Futhermore the content of anthocyanidins were accumulated to excess UV-B radiation exposure, tolerant cultivars especially. Experimental results indicated that exposed to the excess UV-B radiation occured the peroxidation and affected the morphological and physiological responses indirectly. In the meanwhile, it has been shown that the induced accumulation of these flavonoid compounds, anthocyanidins especially. These responses were produced at the first day of UV-B radiation, and tolerant UV-B cultivars induced higher content of flavonoids than suspectible cultivars. Based on these results, this part is an important factor contributing to UV-B tolerance mechanism in rice cultivars.
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