Please use this identifier to cite or link to this item: http://hdl.handle.net/10497/22365
Title: 
Authors: 
Supervisor: 
Chen, Zhong
Issue Date: 
2019
Abstract: 
From time immemorial, many medicinally essential plants have been successfully used to treat different types of diseases. The usage of plants as a source of medicine begins with the isolation of active bio-compounds which are responsible for their therapeutic action. Research in flavonoids has flourished in the last decades, fueled by the recognized importance of natural antioxidants on health benefits.

The current study intended to focus on enhancing the production of three flavonols such as rutin, quercetin, and kaempferol in tropical medicinal plants such as Emilia sonchifolia, Clinacanthus nutans and in model plant Arabidopsis thaliana. The current research focused on a novel elicitation approach to improve the therapeutic value of medicinal plants. It attempted to investigate if heat (one-day for 6 hrs, 45 °C) and drought stress (one week) could be used to enhance the production of flavonols through studies on expression profiling of flavonoid biosynthetic genes in model plant A. thaliana relative to untreated controls. This study also established a correlation between flavonol metabolites produced under stress and genes that are responsible for synthesizing these molecules by comparing the transcriptomic and metabolomic data using LC-MS. A significant upregulation of following structural genes F3H, FLS1, UGT78D1 and the transcription factors PFG1/MYB11, PFG2/MYB12 was observed in heat-induced A. thaliana samples by 55-fold, 125-fold, 4.5-fold, 40-fold, and 12-fold, respectively compared to control ones. The compound rutin and quercetin increased in heat-stressed A. thaliana plants by 2.5-fold and 1.5-fold relative to controls. From the results, it is justified that the pattern of gene expression in flavonol biosynthesis corresponds to the increased accumulation of rutin and quercetin in heat-stressed A. thaliana plants. The further evaluation of relative flavonol content in E. sonchifolia, C. nutans and A. thaliana plants suggested that flavonol metabolites were speciesspecific. Among the three flavonols, the stable glycosylated rutin played a major role in stress protection by increasing its accumulation in all the three plants. Furthermore, the total flavonoid content was increased in three plants that established a positive link between these species in defence mechanism against stress. The comparative study of antioxidant activity in medicinal plants proved that the antioxidant activity was higher in E. sonchifolia plants and the increment in the antioxidant levels of E. sonchifolia plant was attributed to the increased accumulation of three flavonols and total flavonoid content with strong scavenging ability against free radicals. The study also highlighted the role of flavonols as developmental regulators by showing the role of flavonols in auxin transport during stress conditions as a regulative mechanism in plant development. The short-term heat stress proved an effective strategy to increase the rutin, quercetin and kaempferol contents in tropical medicinal plants E. sonchifolia and C. nutans.
URI: 
Issued Date: 
2019
Call Number: 
QK898.F5 Moh
Appears in Collections:Master of Science

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