Abstract:

To explore the effects of melatonin on the seed germination and seedling growth of Astragalus complanatus under different temperature, and salt and drought stresses, six melatonin solutions of different concentrations were used to soak the seeds of A. complanatus. The solutions of NaCl and PEG simulating salt and drought environment were used as the experimental groups, respectively, and the distilled water treatment was regarded as the control group. The treated seeds were cultured at 4 different temperatures (15, 20, 25 and 30℃), the germination indicators and seedling growth indicators were measured and calculated after the germination experiment. The results showed that at the same temperature, the total germination percentage of A. complanatus seeds decreased with the increase of drought degree (P<0.05). Under the stresses of salt and drought, the mean germination time at each temperature increased with increasing levels of stress (P<0.05). The length of radicle and cotyledon decreased as the salt stress and drought stress increased at the same temperature. Under the same osmotic potential, the radicle length first increased and then decreased with the increase of temperature. When the stress of -0.7 MPa was at 30℃, the growth of A. complanatus seedlings was inhibited after seed germination under salt stress, while the seeds of some treatment groups did not germinate under drought stress. In this experiment, 25℃ was the optimum temperature for the germination and growth of A. complanatus under salt condition, while 20℃ was the optimum temperature under drought stress. The salt tolerance of A. complanatus was greater than that under drought stress at the same temperature. And as the degree of stress increased, its growth was inhibited. After being treated with melatonin, the effect of stresses on A. complanatus was alleviated to a certain extent.

Key words: melatonin, Astragalus complanatus, stress, alleviate, osmotic potential