Effects of irradiance on accumulation and partitioning of total phenolic contents of Labisia pumila Benth

Manipulation of micro-environment, particularly irradiance, is known to influence the production of secondary metabolites in some herbal plants. Knowing what impact the irradiance has on the changes in the metabolite content of the herbal plant may ensure continuous production of quality herb for commercial cultivation. A two-way greenhouse experiment was carried out to determine the effects of irradiance on the accumulation and partitioning of total phenolic contents of two varieties of Labisia pumila(var pumila: green; var alata: red). A total of eight treatments combinations was arranged in a split-plot-Randomized Complete Block Design, replicated four times. Total phenolic content was determined by Folin-ciocalteau method. Prior to start of the experiment, total leaf phenolic content for both L. pumila varieties were almost similar. In the 9th week, total phenolic contents either increase or decrease dramatically according to variety growing at different irradiance level. Exposing both varieties to higher irradiance level with low shading percentage of O and 30% decreased leaf total phenolic contents. Variety alata seemed to be more affected by high irradiance condition in accumulation of the phenolic compound. However, a significant increase in leaf phenolic content to 44.6% for var. pumila, and 55.6% for var. alata occurred at 50% and 70% shading, respectively, indicating that red variety is more sensitive to irradiance level. The accumulation of phenolic contents in L. pumila plants, and the partitioning to root, stem and leaf were affected by the type growing under specific light conditioning. Higher phenolic contents were partitioned to the leavesstemroot, with red and green varieties thriving better when grown under 70% and 50% shading, respectively. Total phenolic content of the red variety that partitioned to the stem increased consistently before declining under 70% shading. Green variety accumulated higher stem phenolic contents under 70% shade.Similar trend of total phenolic contents partitioning to the root was also observed.