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Effects of abiotic environmental factors on production of phenolic compounds and expression of stress responsive genes in medicinal plant Clinacanthus Nutans and model plant Arabidopsis Thaliana
Author
Go, Wen Ying
Supervisor
Chen, Zhong
Tan, Swee Ngin
Abstract
The ability of plants to adapt to various external factors has helped them evolve and conform to constant changes in the environment. The ability of plants to respond to abiotic stress based on the production of phenolic compounds and the expression of stress responsive genes. Many studies have focused on the isolation of the bioactive constituents and phenolic compounds from the Clinacanthus nutans (CN) plant. However, limited research has been done on the effect of abiotic factors on the production of phenolic compounds in this plant species. This study was conducted to determine the amount of phenolic compounds produced in CN leaves after the plants had been subjected to various kinds of abiotic stresses. These are namely, heat stress, drought stress and UVB stress. Simple methods of plant leaf extraction using different solvents were investigated for the quantification of gallic acid, catechin and quercetin present in treated plants relative to the untreated controls. A higher content of phenolic compounds (mg g-1 dw) was observed in leaves extracted with 80% (v/v) methanol- water. Significant stress responses were observed in the UVB exposed CN relative to the plants in the other treatment conditions. A one-way analysis of variance (ANOVA), revealed that the amount of gallic acid present in CN was significantly different between the UVB treated plants and the controls. The increment of phenolic compounds in UVB treated CN could be attributed to an increase in the antioxidant level of CN. The environmental growth conditions of CN is one of the key considerations in cultivating this potential natural medicinal herb for consumption as a health supplement and this can be optimized without compromising the overall health of the plants. Subsequently, the relative expression of stress responsive genes and specific flavonoid metabolism genes in model plant Arabidopsis thaliana (AT) were analysed based on the results from the qRT-PCR methods. The predominantly induced abiotic stress responsive genes were observed in the 1 d 6 h, 35 °C sub-lethal heat stressed AT, with highest expression levels in Hsp18.1-Cl (466- fold), along with a relatively increased expression level in Pirin1 (4.36- fold), which is responsible for biosynthesis of flavonoid. The results also showed that the treated AT had a relatively high expression of the FLS1 (112- fold) after 1 d 2 h UVB treatment. Abiotic factor like UVB is believed to have contributed to increased expression of the stress responsive genes in AT. The high amount of gallic acid (in UVB treated CN plant) and high expression of the FLS1 gene (in UVB treated AT plant), have led to the novel idea that similar biosynthesis of phenolic compounds could have taken place via signal transduction pathways in tackling abiotic stress. A positive correlation between the cellular functions and specific mechanism to get rid of the excessive reducing agents such as, the reactive oxygen species were evident in both CN and AT plants. These then suggest for the extraction of gallic acid from CN plant for health- promoting purposes using control environment condition (UVB wavelength 280-320 nm).
Date Issued
2016
Call Number
QK754 Go
Date Submitted
2016