Antioxidant Mechanism and Lipid Peroxidation Patterns in Leaves and Petals of Marigold in Response to Drought Stress

In this study, malondialdehyde (MDA), relative conductivity (RC), superoxide anion (O-2(center dot)-), hydrogen peroxide (H2O2), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) as well as ascorbic acid (AsA), glutation (GSH) and carotenoid (Car) were analyzed in plants under drought condition to investigate the enzymatic and non-enzymatic antioxidant defense mechanisms of leaves and petals, respectively. Two different drought resistance marigold cultivars (Tagetes erect(L. cv. Chokdee and Tagetes erecta L. cv. Discovery) treated with 6-day drought stress were used at early flowering stage. Results indicated that drought treatment increased MDA, RC, O-2(center dot)- and H2O2 contents in the two cultivars, especially in drought-sensitive cultivar 'Discovery'. In contrast, 'Chokdee' had higher level antioxidative enzyme activities and more non-enzymatic antioxidants than those in 'Discovery'. SOD, POD, CAT, APX activities and non-enzymatic antioxidants (GSH and AsA) in the leaves and petals were increased at the beginning treatment, and decreased later. The activity of CAT in leaves and petals, APX in petals and AsA in petals on day 6 after treatment were lower than those in control, while Car in the two cultivars decreased consistently during drought stress treatment. In addition, all the antioxidant enzyme activities in the leaves were higher than those in petals, but AsA and GSH were accumulated at lower levels in leaves than those in petals of the both cultivars. Furthermore, significant linear relationships were found between antioxidative enzymes and reactive oxygen species (ROS), as well as in non-enzymatic antioxidants and ROS. In conclusion, drought tolerance of `Chokdee' was correlated with eliminating the O-2(center dot) - and H2O2 and maintaining lower lipid peroxidation as well as higher membrane stability by increasing activities of antioxidative enzymes and the amount of non-enzymatic antioxidants. Furthermore, different drought response mechanisms were involved in leaves and petals of marigold under drought stress.