Ph.D Thesis Title: Evaluation of some physiological and biochemical responses of safflower (Carthamus tinctorius) to spermine and putrescine under drought stress

Abstract

Drought stress is the most prevalent abiotic stress in Iran and has highest negative effect on plant growth and productivity. Polyamines as growth regulators play important roles in maintaining cell membrane stability and reducing oxidative stress under drought stress. Many studies suggest that polyamines increase plants tolerance to environmental stresses. However, response of safflower to foliar application of polyamines under drought stress is not clear. Therefore, this research was aimed to investigate physiological and biochemical responses of safflower to different concentrations of putrscine and spermine separately and combined treatments under drought stress. Two preliminary experiments were conducted to select appropriate levels of watering and putrescine and spermine. In the first experiment, treatments were irrigated by 100, 80, 60, 40, 20% field capacity (FC) in three leaves stage for 14 days with three replications. In another experiment, plant performance was tested in response to foliar spray of 0, 20, 40, 60, 80, 100 µM putrescine and spermine under water deficit. Consequently, 100% and 40% FC (as normal watering and drought stress respectively) and 0, 40 and 60 µM of each polyamine were selected for subsequent treatments. The final 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 concentrations of putrescine and spermine (0, 40 and 60 µM) and putrescine+spermine (0+0, 40+40, 40+60, and 60+40 µM) on some physiological and biochemical traits of safflower were studied under normal watering (100% field capacity) and limited-watering (40% field capacity) conditions. The data were statistically analyzed by SAS (9.2) software and means were compared by Duncan ' s multiple range test at p ≤ 0.05. The results show that separate and combined application of polyamines often increased photosynthetic pigments, efficiency of PSII, growth parameters, catalase and superoxide dismutase activities, relative water content, concentration of anthocyanin and soluble protein under drought stress. But, MDA content and electrolyte leakage, soluble sugars, proline and glycine betaine contents in leaves were decreased. Moreover, spray of 40+60 µM putrescine+spermine significantly enhanced catalase and superoxide dismutase activities, flavonoids and anthocyanins contents in shoots of stressed-plants. Application of 60 µM putrescine enhanced antioxidant enzymes activities, relative water content, phenol and anthocyanins contents in shoots under water limitation. MDA concentration and electrolyte leakage in leaves significantly diminished as a result of 60 µM putrescine, 40+60 µM and 60+40 µM putrescine+spermine application. Exogenous polyamines also enhanced taproot length, roots