Abstract: Following the hydroponic method, we investigated the effects of exogenous salicylic acid (SA) on the growth, physiology, and cadmium (Cd) absorption and accumulation in sunflowers under varying levels of Cd stress. Sunflower seedlings were irrigated with three concentrations of Cd (10, 20, 40 μmol·L^-1), with SA at the concentration of 100 mg·L^-1 being sprayed on the leaves. The results showed that exogenous SA promoted the growth and biomass of sunflower seedlings, and that the amplitude of such increase first increased and then decreased with increasing Cd concentration. At the Cd concentration of 20 μmol·L^-1, the increases in root length, plant height, root biomass, stem biomass, leaf biomass and total biomass of sunflower seedlings were the largest, which were significantly increased by 7.5%, 7.8%, 25.0%, 7.7%, 10.0%, 11.1%, respectively, compared with that under Cd stress but without SA addition. Exogenous SA increased the contents of chlorophyll a, chlorophyll b, total chlorophyll and carotenoids in sunflower seedlings, reduced the relative conductivity and the malondialdehyde content, and increased the contents of proline and glutathione as well as the activities of superoxide dismutase, peroxidase, catalase and glutathione antioxidant enzymes. Exogenous SA promoted the absorption and accumulation of Cd in sunflower seedlings. With the increases of Cd concentration, the Cd content and accumulation in roots, stems and leaves also increased. Moreover, the Cd transfer coefficient, enrichment coefficient and extraction rate exhibited an increasing trend with increasing Cd concentration. When the Cd concentration was 20 μmol·L^-1, the increase in the Cd transfer coefficient, enrichment coefficient and extraction rate in sunflower seedlings reached the maximum, which were significantly increased by 33.3%, 36.4% and 100.0%, respectively, compared with that under Cd stress but without SA addition, indicating the most significant effect of SA on Cd transport and accumulation. In conclusion, when the Cd concentration was 20 μmol·L^-1, the application of 100 mg·L^-1 SA was beneficial to the growth of sunflower seedlings and their absorption and accumulation of Cd. Our results can provide a reference basis for the application of SA in enhancing the tolerance of plants to heavy metal stress.

Key words: Helianthus annuus, salicylic acid, Cd stress, growth, Cd accumulation