The Effects of Salt Stress on Ion Uptake, Accumulation of Compatible Solutes, and Leaf Osmotic Potential in Safflower, Chrysanthemum paludosum and Sea Aster

Abstract

To evaluate mechanisms of the growth of Asteraceae plants by osmoregulation under saline conditions, ions uptake, accumulation of compatible solutes, and osmotic potential were measured in leaves of glycophytes safflower (Carthamus tinctorius L.'Roundish Leaf', salt sensitive), Chrysanthemum paludosum Poir. 'North Pole'(moderate tolerance), and a halophyte sea aster (Aster tripolium L., high tolerance) grown under hydroponics including NaCl. Salt stress was imposed for 16 days by adding 12.5, 25, or 50 mM NaCl into nutrient solutions for safflower and C. paludosum, and 75, 150, or 300 mM NaCl for sea aster. Leaf osmotic potentials decreased and the uptakes of Na⁺ and Cl^- increased with increases in NaCl for all species. In C. paludosum and sea aster, Na⁺ concentration in the shoot was significantly higher than that in the root, showing that much Na⁺ was translocated from root to shoot. K⁺ content was unchanged in C. paludosum and sea aster under saline conditions, but in safflower its uptake was inhibited by NaCl stress. Proline and sucrose contents of safflower and sea aster significantly increased by intensifying NaCl stress, furthermore in sea aster, glycinebetaine content significantly increased. Major contributions to decrease leaf osmotic potential by osmoregulation under NaCl stress were the accumulations of the compatible solutes (sucrose, proline, and glycinebetaine) in safflower. In C. paludosum and sea aster, an increase in ion concentrations (Na⁺ and Cl^-) largely contributed to a decrease in leaf osmotic potential. This adaptation mechanism allows plants to keep a positive cell turgor by continuing water uptake so that seedlings can grow under salt stress.