The Effect of Water Deficit Different Levels on Antioxidant System and Lipid Peroxidation in two Species Tagetes erecta and Tagetes patula of Marigold

With regard to decrease of precipitation and poor distribution of rainfall during the dry phenomenon of urban, green spaces face problems. In fact, one of the most important environmental stress is drought stress at different stages of plant growth such as seed germination, seedling establishment and crop production. The effect of drought stress, plants photochemical activity ceased Calvin cycle enzymes and chlorophyll content also varies in the process of photosynthesis under drought stress. Under drought stress, reactive oxygen species (ROS) such as hydrogen peroxide (H2O2), superoxide radicals (O2 • -) and hydroxide (OH •) increase their accumulation in cells that can lead to oxidative stress. To neutralize ROS, antioxidant enzymes systems in plant such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) are active. The response of antioxidants depends on the lack of water, the intensity of the stress and the type of plant species. Also, it is well known that photosynthetic systems in higher plants are most sensitive to drought stress. Indeed, drought is one of the factors affecting photosynthesis and chlorophyll content. Some of researchers reported that chlorophyll might estimate influence of environmental stress on growth because these parameters were closely correlated with the rate of carbon exchange. The aim of this study was an investigation of effect of water deficit different levels on antioxidant system and lipid peroxidation in two species of marigold. Therefore, an experiment was carried out as factorial in a randomized complete block design with three replication at Shahid Chamran University of Ahvaz in 2014 year.
Experimental treatments were irrigation with three levels: 100% ETcrop (no stress), 75% ETcrop (moderate stress) and 50% ETcrop (severe stress) and two species of marigold (African and French). Catalase activity decreased absorption at a wavelength of 240 nm through catabolizing on the basis of H2O2 according to Beers and Sizer (1952). Peroxidase activity decreased absorption at a wavelength of 470 nm that was measured by using Hemeda and Kelin (1990). Ascorbate peroxidase enzyme extracted from leaf based on defects in the wavelength of 290 nm that was measured by Nakano and Asada (1987). The final product of membrane lipid peroxidation malondialdehyde concentration as the reaction thiobarbituric acid (TBA) was measured. Also, chlorophyll a, b and total chlorophyll were calculated by Arnon’s equations and chlorophyll content index (C.C.I) was measured by chlorophyll content meter (SPAD-502).
Results of analysis of variance showed that irrigation treatment had significant effect on chlorophyll a, total chlorophyll (Chl a), chlorophyll content index and catalase peroxidase, ascorbate peroxidase enzymes activity and malondialdehyde while there was not significantly difference between two species of marigold on any of the measured biochemical characteristics. Also, results revealed that amount of leaf chlorophyll a and total chlorophyll (chl a) were reduced by increasing water deficit. In fact, amount of total chlorophyll, chlorophyll a, b and chlorophyll content index were higher in plants that were received 100% ETcrop than 75 and 50% ETcrop. ,The results of enzyme activity were similar to total chlorophyll and chlorophyll a and b. Amount of decreased chlorophyll a and total chlorophyll in plants were received 50% ETcrop were 24% and 47.46%, compared with 100% ETcrop, respectively.
Result showed that different levels of irrigation were significantly different at 5% level on catalase, peroxidase, ascorbate peroxidase enzymes activity and malondialdehyde concentration. Catalase, peroxidase, ascorbate peroxidase enzymes activity and malondialdehyde concentration were increased by reducing the amount of irrigation while there were no different between two species of marigold and interaction between species and irrigation was not effective on measured indexes.