Salinity stress increases secondary metabolites and enzyme activity in safflower

• The tested safflower is a salt-tolerant variety and promising to grow in saline environments.
• Salinity increased the antioxidant enzyme activities and osmolytes in safflower leaves.
• The secondary metabolite (flavonoid) induced by salinity in safflower was concentrated.

Safflower (Carthamus tinctorius L.) is a salt-tolerant crop cultivated worldwide. However, little information is available on their tolerance mechanism. Owing to decreasing arable land, cultivation of safflower in saline environments might be needed in order to promote crop biomass and secondary metabolites production. The physiological response of the selected species should be examined in order to improve environmental options, especially facing salinity stress. A hydroponic culture experiment was designed to investigate the changes in fundamental physiological processes and secondary metabolite accumulation induced by salinity in safflower (Cv. Space-1). Safflower seedlings were grown in half-strength Hoagland solution and exposed to 0, 50, 100 and 150 mM NaCl for 30 days. NaCl concentrations <100 mM did not affect the growth of safflower seedlings in terms of plant height, root length and plant dry weight, as well as the relative growth rate; however, it did increase the medicinal flavonoid content in leaves. Although the Na+ concentration was considerably increased under salt stress, higher K+ and Ca2+ concentrations in the leaves and shoots were observed simultaneously. The K+/Na+ ratio was significantly decreased with increasing salinity, whereas NaCl treatments all had K+/Na+ values >0.5, suggesting ion homeostasis. Chl-a and Chl-b contents in safflower leaves were negatively affected by salinity, whereas the carotenoid contents remained unchanged with NaCl concentrations <100 mM. Additionally, SOD, CAT, POD and T-AOC activities in safflower leaves were markedly increased for all of the NaCl treatments. The soluble sugar and protein contents in safflower leaves under salt stress were much higher than the control and increased significantly with increasing salinity. The present study demonstrates that C. tinctorius var. Space-1 withstands moderate doses of NaCl in the medium and that sound physiological responses of the plant help to increase secondary metabolite accumulation under salt- stressed conditions.