MSc

The study entitled “Physiological, phytochemical and molecular studies on abiotic stress mediated antioxidant accumulation in Amaranthus spinosus Linn.” was conducted during the period 2012-14 in the Department of Plant Physiology, College of Agriculture, Vellayani, Thiruvananthapuram. The objective of the study was to elicit information on the physiological, biochemical and molecular attributes associated to the antioxidant accumulation due to abiotic stress factors viz. light stress and water deficit stress and CO2 enrichment in Amaranthus spinosus Linn. The study was conducted as two separate experiments. One experiment was laid out in pot culture at Instructional Farm Vellayani, in Completely Random Design (CRD) with nine treatments which included combinations of three levels of water deficit stress and three levels of shade stress in three replications. The second experiment was laid out in Open Top Chamber (OTC) in CRD with six treatments which included combinations of CO2 enrichment and two levels of water deficit stress in four replications.
The observations on growth parameters revealed a general increase in plant height under shaded condition. Leaf area was maximum for plants under 50% FC and 25% shade, T6 (42.663 cm2) and plants under 50% FC and 50% shade, T3 (40.567 cm2). The results of physiological observation showed maximum concentration for total chlorophyll for plants under 50% FC and 25% shade, T6 (1.947 mg/g of leaf tissue). The analysis of biochemical parameters showed the plants under 25% shade + 100% FC (T4) and plants under open condition + 50% FC (T9) had maximum starch content of 8.963 mg/g and 8.49 mg/g respectively. The results of enzymatic antioxidant assays showed Superoxide dismutase activity was higher for plants under treatments T9 (Open + 50% FC) and T3 (50% shade + 50% FC); 0.032 Units. The non-enzymatic antioxidant assays showed the maximum Ascorbic acid content of 3.6mg/g for treatment T1 (50% shade +100% FC) and Vitamin A content was maximum for T3 (50% shade +50% FC). Total flavonoids recorded highest in plant under treatment T2 (50% shade+75 % FC) whereas total phenol was maximum for the treatment T7 (Open + 100% FC).
CO2 enrichment has no significant effect on plant height. Stomatal conductivity was significantly low for CO2 enriched plant under 100% FC (25.35 m moles s-1 for OT1) and 50% FC (21.8 m moles s-1 for OT2). Plants under CO2 enrichment and 50% FC showed maximum Catalase activity (0.169 Units).CO2 treatment did not show a significant variation with respect to antioxidants. Expression level study of the gene CHS (Chalcone synthase) revealed overexpression of the gene under abiotic stress, especially under moderate shade stress. Hence the plant can be exploited for its therapeutic value and can be cultivated as an intercrop in plantations.