Study on the Effects of UVB and UVC Radiations on Hydroxyphenylpyruvate Reductase Gene Expression and Rosmarinic Acid Production in Medicinal Plant, Orthosiphon aristatus

Abstract

Ultraviolet radiation (UV) is one of the abiotic stress which can activate the plant stress response through the self-protective secondary metabolism system. Rosmarinic acid is one of the prominent secondary metabolites found in the medicinal plant, Orthosiphon aristatus which exhibits many medicinal properties. Application of UV light towards the plants especially medicinal plants can be an alternative method to induce its beneficial secondary metabolites. Here, this study investigates the differential effects of UVB and UVC treatments on the rosmarinic acid accumulation and its related gene expression in O. aristatus leaves. Plants were exposed under UVB and UVC light respectively for one hour. The leaves samples were collected every 15 minutes after UV treatments and the succeeding one hour dark recovery process. The concentration of rosmarinic acid determined by high performance liquid chromatography increased slightly at the initial 30 minutes of UVB treatment until the highest concentration found after 45 minutes and declined after that. Whereas, rosmarinic acid produced at lower levels in UVC treatment. However, the rosmarinic acid content increased after one hour recovery period in both treatments. The expression of hydroxyphenylpyruvate reductase (HPPR) gene measured by quantitative real time polymerase chain reaction was down-regulated upon exposure to UVB and UVC. Negative correlation was found between the expression of HPPR gene and rosmarinic acid production after both treatments. No significant different was observed between the effect of UVB and UVC treatment towards the plants. As a conclusion, the correlation findings are contrast with some others findings which can be explained by the complexity of rosmarinic acid biosynthesis pathway and different UV sensitivity in different plant species. This study could serve as starting point for future research study on the UV stress tolerance response in O. aristatus plants. Further studies on other related genes involved in rosmarinic acid biosynthesis pathways against UV will provide better understanding at both molecular and metabolite levels