Effect of abiotic stress on the physiology and andrographolide content in andrographis paniculata nees.
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Date
2004
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Department of Plant Physiology, College of Agriculture, Vellayani
Abstract
An experiment was conducted in the Department of Plant Physiology, College of Agriculture, Vellayani to study the influence of abiotic stress on growth, physiological and biochemical parameters and andrographolide content of the medicinal plant Andrographis paniculata. The abiotic stresses include three levels of light (open, 50% and 75% shade), three levels of salinity (control, 3 and 6 mmhos/cm) and three levels of water stress (100%, 60% and 30% field capacity). The treatments were imposed for a period of 30, 60 and 90 days after planting. Growth parameters of plant height, leaf area, leaf area duration, dry matter production, specific leaf area, net assimilation rate and relative growth rate were recorded in plants from different treatment combinations. The treatments having maximum effect on the andrographolide content were selected from each shade level for the detailed study of various physiological and biochemical parameters. The effect of stress on the level of expression of HMG-CoA reductase was assessed by Relative quantitative RT-PCR. The secondary metabolite andrographolide content was estimated spectrophotometrically. The andrographolide content was high (1.35 %) in open condition at growth stage of 90 days with 6 dsm-1 salinity and water stress of 60 % FC. Based on the andrographolide content, five treatment combinations were selected from each shade level for further analysis. The physiological parameters like chlorophyll content, stomatal conductance, stomatal frequency and membrane stability index were recorded. The biochemical analyses on starch, sugar, amino acids, protein, phenol, and ascorbic acid were recorded from the selected treatment combinations. The activity of oxidative free radical scavenging enzymes namely catalase, peroxidase, superoxide dismutase were also estimated in the above selected treatment. It was seen that on plant height, leaf area, leaf area duration, specific leaf area, net assimilation rate were high in 50% shade condition. The membrane stability was found to follow trend similar in open and 50% shade condition but low in 75% shade condition. The chlorophyll content was found to increase under shade condition. The chlorophyll ‘a’ and total chlorophyll were high in 50% shade and chlorophyll ‘b’ was high in 75% shade condition. The stomatal conductance and frequency were high in open condition and low in 75% shade condition. The starch, reducing sugar, and protein were high in shade condition. The phenol and total free amino acids were high in open condition and low in 75%shade condition. A positive relationship was obtained between phenol and andrographolide content. The antioxidant enzymes, catalase was high in 75% shade condition and low in open condition but the peroxidase and SOD was high in open condition and low in the 75% shade condition. The relationship between phenol and andrographolide content was positive. On the other hand an inverse trend between the sugar, starch and protein content with andrographolide was observed. The water stress and salinity reduce the growth parameters corresponding to the stress levels. The biochemical parameters like starch, sugar, phenol, protein, amino acids showed a reducing trend with increase in the severity while the activity of free radical enzymes showed an increase. There was positive relationship with the catalase activity and andrographolide content. The secondary metabolite under open condition increased under open condition and decreased under the shade condition. From this experiment it was evident that abiotic stress invariably increased the secondary metabolite-andrographolide content, which has reported to have an antioxidant activity. The gene expression was made under 50% shade and there was light inhibition of expression under open condition. The mRNA was found to be reduced under water stress and salinity. It was inferred that the andrographolide accumulation might be corresponding with the activity of plastidic DOXP/MEP pathway.
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