Impacts And Mechanisms Of Photoperiod, Soil Water Availability And External Hormones On The Accumulation Of Flavonoids In Scutellaria Baicalensis Georgi

Scutellaria baicalensis Georgi (skullcap), or "Huangqin" in Chinese, is a perennial herb of the Labiatae family. The roots of this plant have been widely used as herbal medicines to treat inflammation and infection in China. Flavonoids, including baicalin, baicalein, wogonoside and wogonin, are the main active ingredients of this herb. Previous investigations have revealed that flavonoids contained in roots of this plant account for as much as more than 25% of its dry weight. In this thesis, the impacts of photoperiod, soil water availability and external hormones on the accumulation of flavonoids in this plant, and their molecular mechanisms, were investigated by using molecular and phytochemical techniques. The following research results were obtained:(1) Eleven gene fragments related to the phenylpropanoid pathway have been cloned from the leaves of S. baicalensis. Sequence alignment showed that these sequences were highly homologous to those from other species in Genebank. These findings provided molecular foundation for exploring the regulatory mechanisms on flavonoid biosynthesis in S. baicalensis.(2) Photoperiod is an important regulating factor for the accumulation of flavonoids in S. baicalensis. Short photoperiod significantly promotes the biosynthesis of flavonoids, while long photoperiod is not beneficial. The promotion of short photoperiod on the flavonoid biosynthesis is mainly a result of a beneficial transformation and consumption of the products from photosynthesis under short photoperiod condition.(3) Wet soil condition guarantees the consistent accumulation of flavonoids in the roots of S. baicalensis, while moderate drought stress only promotes their contents in a short period. These facts indicate that wetness is a beneficial factor to the accumulation of the products from photosynthesis and consequently promotes the biosynthesis of flavonoids; while under drought condition, large amount of flavonoids were shortly induced to resist the oxidative damages in the plant cells. But excessive drought resulted in a pathological state. (4) Both gibberellin and cycocel promote the biomass of the aerial parts, but significantly inhibit the gaining of root biomass and the flavonoid accumulation. Both hormones induce the carbon source of the plant toward the growth and lignin biosynthesis of the aerial parts, and at the same time inhibit the biomass increase and flavonoid biosynthesis in the root of S. baicalensis.These research results demonstrated that photoperiod, soil water availability and external hormones showed significant regulatory effects on the carbon accumulation and distribution in S. baicalensis. The results provide theoretical reference for elucidating the regulatory mechanisms of flavonoid biosynthesis in this plant, and for disclosing of the physiological and ecological functions of flavonoids like baicalin in S. baicalensis. Meanwhile, the results provide applicable guidance to the location selection of GAP (Good Agricultural Practices) production and optimization of cultivation techniques for S. baicalensis, and other medicinal plants as well.