Abstract: In order to investigate the resistance and physiological adaption mechanisms of Cleome viscosa to manganese (Mn) stress, the effects of different concentrations of Mn²⁺ (0, 1000, 5000, 10000, 15000 and 20000 μmol·L^-1) on seed germination, seedling growth and the changes in physiological and biochemical characteristics of C. viscosa after 7, 15 and 30 days of stress, were assessed. The results showed that: 1) With the increasing Mn²⁺ concentration, the germination potential, germination rate, germination index and vigor index of C. viscosa declined, although the seedling growth was increased at the 1000 and 5000 μmol·L^-1 Mn²⁺ concentrations, displaying a phenomenon of “low to promote and high inhibition”. 2) Compared with the control, chlorophyll a, chlorophyll b, chlorophyll a+b content and the ratio of chlorophyll a∶b increased at the Mn²⁺ concentrations of 1000 and 5000 μmol·L^-1, while the chlorophyll content and the ratio of chlorophyll a∶b decreased with rising of Mn²⁺ concentration above 5000 μmol·L^-1 and with exposure time. 3) Under Mn²⁺ stress at day 7, superoxide dismutase (SOD) activity decreased with rising Mn²⁺ concentration, while the activities of peroxidase (POD) and catalase (CAT) increased; Under Mn²⁺ stress at day 30, the activities of SOD and POD decreased, while the activity of CAT didn’t decline. 4) Proline, soluble protein and soluble sugar of seedlings increased significantly with rising Mn²⁺ concentration at day 7 and day 15 of exposure, but had decreased after 30 days of stress. 5) Malondialdehyde content increased significantly with increasing of Mn²⁺ concentration and exposure time. In summary, the results showed that exposure to Mn²⁺ concentrations of 1000 and 5000 μmol·L^-1 promoted seedling growth of C. viscosa, and at higher Mn²⁺ concentrations this plant species can adjust its antioxidant system and enhance its osmotic adjustment to alleviate the damage caused by high Mn stress, thus imparting C. viscosa with a measure of Mn tolerance.

Key words: manganese stress, Cleome viscosa, seed germination, antioxidant system, osmotic adjustment