| Scutellaria baicalensis Georgi (Huangqin) is a widely used traditional Chinese medicine. Flavonoids, including baicalin, baicalein, wogonoside and wogonin, are the main active ingredients of Huangqin. Previous investigations have revealed that flavonoids contained in roots of this plant account for as high as more than 20% of its dry weight. Report on the physiological and ecological activity of flavonoids in Huangqin has not been found up to now. In this thesis, the impacts of dehydration on flavonoids levels both in cultivated plants and in post-harvest fresh roots were investigated, and the correlation between flavonoids and drought resistant ability of Huangqin was discussed, through combined techniques of plant physiological and analytical techniques. The following research results were obtained:1,Water deficit could significantly promote the accumulation of flavonoids in Huangqin. The results revealed that water deficit in cultivating period and dehydration in post-harvest process could significantly promote the levels of flavonoids, especially baicalin in Huangqin roots. At the same time, activities of important biosynthetic enzymes such as PAL were raised dramatically. After 12h of rehydration, the contents of flavonoids in roots of cultivated Huangqin plants were dropped sharply. And in post-harvest root, the levels of these compounds were also declined very quickly when the dehydration exceeded a certain point. Our research results provided a scientific basis and an applicable guidance for the production of high quality Huangqin herb.2,Flavonoids play an important role in drought resistant of Huangqin. Our research found that plants with lower contents of flavonoids werw more sensitive to water deficit than those with higher levels of flavonoids. The water loss rate, MDA content, and SOD activity were relatively lower in samples with higher levels of flavonoids. Statistic analysis revealed that MDA level negatively correlated with content of alycon, PAL activity and glucoside/alycon ratio. In conclusion, mechanisms of flavonoids in against drought stress may conclude in the following three aspects:Firstly, Alycons (baicalein, wogonin) function as an efficient ROS (reactive oxygen species) scavenging agent. Secondly, Glucosides (baicalin, wogonoside) play as a reservoir for souble sugars under water stree; and thirdly, flavonoids also server as an efficient protector for antioxidant enzymes through the above combined actions.3,Antioxidant enymes were important components in against drought stress mechanisms of Huangqin. SOD activity increased sharply through the entire drought stress process, and was positively correlated with MDA level. CAT activity increased dramtically after 12-15d of water deficit, which indicated CAT was an efficient H2O2 scavenger but only functioned under severe stress. However, POX activity was not detectable in roots during drying process. The SOD activity was higher in plants with lower level of flavonoid, indicating antioxidant enzymes and flavonoids were a pair of mutual partners and interplayed as ROS scavenger. SOD ctivity was also detectable in roots sample during post-harvest drying process.4,Sugars also function a crucial role in against drought stress for Huanqqin. Souble sugars accumulated constantly in Huangqin leaves and roots during dehydration process, and its content correlated with water content negatively and with MDA content positively. Soluble sugars act as osmotic regulation agents, which could prevent cell trauma. After severe drought stress, most leave were wilted. The soluble sugars in the plants might be originated from the degradation of flavonoids glucosides. Therefore, the accumulation of soluble sugars could be regarded as another form of anti-drought stress mechanisms of flavonoids. |
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