Background: Drought stress is the
most common abiotic stress factor which reduces the plant growth and
development more than other factors. For this reason, identification of
effective factors to increase drought tolerance of plants is necessary
requirement. Many reports have been focused on the involvement of
polyamines in plant response to abiotic stresses such as drought.
Polyamines as growth regulators play important roles in keeping cell
membrane stability and reducing ROS generation under water deficit. Carthamus tinctorius is an
industrial, medicinal and oil crop from Asteraceae family. Many studies in
other plants showed that polyamines increase tolerance to environmental
stresses, but physiological responses of water-stressed safflower
plants to putrescine is not clear. Thus, this research was carried out
to investigate the physiological changes in safflower under different
levels of water supply (100% and 40% field capacity) treated by
putrescine (0, 40 and 60 µM). The experiment was conducted in a
greenhouse as factorial arrangement based on complete randomized block
design with three replications.
Results: Interaction of irrigation × putrescine was significant for all traits. Water deficit significantly decreased growth parameters, leaf relative water content, photosynthetic pigments, and soluble protein. APX, CAT, POX and SOD activities, lipid peroxidation, H2O2, electrolyte leakage, proline, and soluble sugar contents increased under water deficit. Putrescine application alleviated drought stress injury by decreasing MDA and hydrogen peroxide contents, and increasing photosynthetic pigments, antioxidant enzymes activities, anthocyanin and soluble protein contents, leading to a better growth of plants. Foliar spray of 60 µM putrescine was the most beneficial treatment for improving safflower growth under water limitation.
Conclusions: Water deficit induced oxidative stress and reduced safflower growth. Exogenous putrescine promoted drought tolerance of plants via increasing antioxidant enzymes activities, anthocyanin, soluble protein contents and decreasing lipid peroxidation, electrolyte leakage and H2O2 contents. Overall, 60 µM putrescine was the best treatment for alleviating harmful effects of drought on safflower plants.