Studies On Dynamics Of Characteristic Secondary Metabolites In Scrophularia Ningpoensis In Relation To Environmental Conditions And Genetic Variation

Scrophulariae Radix, the dry root of Scrophularia ningpoensis. is one of the reputed medicinal herbs with a long history of cultivation named as "Zhe Ba Wei" Iridoid glycosides(such as harpagoside) and phenylpropanoid glycosides (such as angroside C and acteoside) are suggested to be characteristic bioactive constituents. Our previous study revealed that harpagoside content was positively correlated with enviromental temperature. This positive correlation was tested in the present study by analyzing phonological variation of sencondary metabolites and their direct reponses to elevated ambient temperature in S. ningpoensis. We aim to confirm and characterize the high temperature response of harpagoside and to elucidate the possible evolution process causing the difference between cultivated and originated wild populations. Furthermore, the genetic variation of sencondary metabolites among different populations of S. ningpoensis was evaluated in a three-year consecutive common garden experiment, which could improve our understanding on the evolution of heat response of harpagoside as well as propose candidate resources for S. ningpoensibreeding. The results are summerized as follows.1. Contents of four bioactive secondary metabolites were analyzed using HPLC fingerprinting for monthly-harvested plants which were dissected into roots, stems, leaves and reproductive tissues. Their contents varied among phenological stages, and contents of harpagoside (0.3～16.0mg/g) and acteoside (1～25mg/g) were the highest, followed by angroside C(0.2～7mg/g). while low concentration of cinnamic acid was detected (0～1.2mg/g). The results suggested a significantly negative correlation between the secondary metabolites accumulation and plant growth of S. ningpoensis. The contents also differed between organs. The highest level of harpagoside was detected in flowers in August, and its variation was positively correlated with monthly mean temperature, supporting the hypothesis of the response of harpogoside to environmental warming. Accumulation of the two analyzed phenylpropanoid glycosides may be responsible for the whole plant defense during the flowering stage. 2. The results of the temperature control experiment showed that an increase of5℃did not cause obvious heat stress or damages in either cultivated or wild populations of S. ningpoensis, as well as changes of biomass accumulation, while the physiological responses of antioxidases and proline were found. our results also indicate that harpagroside is one of the physiological mechanisms of responses to high temperature in cultivated populations of S. ningpoensis. This mechanism may only play a role during the flowering stage under high temperature. In contrast, the analyzed wild populations may respond to heat mainly through the radical scavenging enzyme system. Thus, harpagroside response in cultivated populations might be a physiological change to adapt the higher and more varied environment temperature in crop fields, which guaranteed the domestication of this medicinal crop. Leaf is the main organ in which the high temperature responese of harpagroside occur, while root might be the organ in which harpagoside is stored.3. The common garden experiments revealed a genetic variation of the secondary metabolites content in medicinal parts among the eight cultivated popultaions and five wild populations. In general, the content for wild populations was higher than that for cultivated populations. Campared to other cultivated populations, populations from Hunan (HNL) and Jinshan town, Chongqing Province (CQJ) demonstrated relative higher contents, and wild population from Panan County, Zhejiang (WPA) exhibited the highest contents of four components. We also compared characters for these13populations, specifically, plant height, stem base diameter, root characters and biomass allocation. According to the observations of chemical contents and morphological characters, we proposed that the populations HNL and CQJ performed better than other cultivated populations in Panan County, Zhejiang Province. Population HNL is particularly promising for breeding, which also exhibited stable growth characters. The wild populations from Panan County, Zhejiang Province (WPA), Jiangxi Province (WJX) and Hunan Province (HNL) can be apply in cultivar improvement.4. The results of common garden experiments in three consecutive years showed yearly variations of growth indices and contents of four components for each 5. population, which may mainly be related to the climatic variations. However, the yearly variation was not consistent in different populations, indicating that genetic variation may also have a significant influence on growth and chemical compositions. Population HNL changed least and showed a good adaptability to the environment with high genetical identity. It is suggested that population HNL should be preserved and used as a special germplasm in S. ningpoensis breeding.