Effect of polyamines on antioxidative responses of safflower (Carthamus tinctorius) under drought stress

Drought stress is the most common abiotic factor which reduces the plant growth and development more than other factors. Thus, identification of the effective factors to increase drought tolerance of plants is necessary. The plants increase antioxidant compounds to overcome the oxidative stress. Polyamines as growth regulators play important roles in maintaining cell membrane stability and reducing ROS generation under drought stress. Carthamus tinctorius is an industrial, medicinal and oil crop from Asteraceae family. Many studies on other plants showed that polyamines increase plants tolerance to environmental stresses, but response of safflower to different concentrations of putrscine+spermine under drought stress is not clear. Therefore, this research was conducted to investigate the effect of these polyamines on enzymatic and non-enzymatic antioxidants activities, lipid peroxidation and membrane stability of safflower. This experiment was carried out as a factorial arrangement based on randomized complete block design with three replications in a greenhouse at the University of Tabriz in 2016-2017. In this research, the effect of different putrescine+spermine concentrations (0 + 0, 40 + 40, 40 + 60, and 60 + 40 µM) on the activities of antioxidant enzymes (APX, CAT, SOD and POX), MDA and H2O2 contents and electrolyte leakage, non-enzyme antioxidants (phenols, flavonoids and anthocyanins) in safflower were studied under well-watering (100% field capacity) and limited-watering (40% field capacity). The plants were harvested at 6-7 leaves stage for different measurements. Irrigation and foliar application of polyamines had significant effects on enzymatic and non-enzymatic antioxidants, MDA, H2O2 contents and electrolyte leakage. Interaction of these factors was significant for all traits. Activities of enzymes such as CAT, POX and SOD, total flavonoid of leaves and anthocyanins of shoots were significantly increased in stressed than in non-stressed plants. Moreover, spray of 40+60 µM and 60+40 µM putrescine+spermine, significantly enhanced the activity of CAT and SOD and anthocyanins contents in stressed-plants. Drought stress increased malondialdehyde, H2O2 and electrolyte leakage in leaves. MDA and electrolyte leakage significantly diminished as a result of putrescine+spermine application. Water deficit had a negative effect on the growth of safflower via induction of oxidative stress. In general, the application of 40+60 µM and 60+40 µM putrescine+spermine were effective in reducing ROS caused by water deficit. Foliar spray of 60+40 µM putrescine+spermine reduced lipid peroxidation, electrolyte leakage and H2O2 content through increasing antioxidant capacity and flavonoids and anthocyanins, leading to improve drought tolerance of safflower. The results of this study showed that foliar application of 40+60 µM and 60+40 µM putrescine+spermine can be used to mitigate harmful effects of drought stress at early stages of plant growth