Effects of exogenous polyamines on some growth and physiological parameters of spring safflower (Carthamus tinctorius L.) under drought stress

Drought stress is the most prevalent abiotic stress in Iran and has highest negative effect on plant growth and productivity. Polyamines are plant growth regulators that enhance resistance of plants to environmental stresses such as water deficit. In this research, effects of putrescine + spermine with different concentrations of 0 + 0, 40 + 40, 40 + 60, and 60 + 40 µM (respectively) on some of the physiological characters of spring safflower under well-watering (100% FC) and limited-watering (40% FC) were studied. The experiment was arranged as factorial based on completely randomized block design with three replications in a greenhouse at the University of Tabriz. Without polyamines application, water deficit decreased growth parameters, leaf relative water content, photosynthetic pigments, and soluble protein in the leaves. Proline and soluble sugar contents of leaf increased under water deficit. Foliar application of 60 µM putrescine + 40 µM spermine improved most of these traits in the leaves, particularly underwater stress conditions. However, exogenous polyamines reduced leaf proline content probably due to increase in chlorophyll content. Reduction in compatible osmolytes such as free proline in root and soluble sugars in leaf with application of 40 + 40 and 40 + 60 µM of putrescine + spermine (respectively) could be due to polymines role as osmolyte as well as ROS scavenger. These results suggest that foliar spray of polyamines can potentially mitigate some of the harmful effects of drought stress and physiological performance of spring safflower.