1 Characterization of Antioxidant responses in two Choy Sum cultivars

The effects of light intensity on antioxidant enzymes, concentrations of chlorophylls and carotenoids, physical characteristics were studied in two choy sum (Brassica chinesis var. parachinensis) cultivars, namely Known You (KY) and Autumn Poem (AP). Both cultivars were grown under conditions of 70 % and 90 % of full sunlight in greenhouses at AVA field station, Sembawang. Both cultivars were harvested 8 days and 18 days after sowing for various studies. Shade plants were taller, and they showed thinner broader leaves than the sun plants at both growth stages. Chlorophyll concentration of shade plants was higher than that of the sun plants; chlorophyll concentration also decreased as the plants became older. Carotenoid concentration was higher in shade plants too, decreasing in the older plants. The sun plants of KY and AP showed increased activities of SOD, APX and total free radical scavenging capacities than the shade plants 8 days after sowing. These parameters increased with age