Abstract: To investigate the effect of exogenous melatonin on the drought resistance of Medicago polymorpha L., this experiment used Medicago polymorpha L. seeds from Shanghai as materials and utilized plant tissue culture technology to set five concentrations of polyethylene glycol-6000 (PEG-6000) for seed germination and plantlet growth experiments, and screened the threshold concentration of PEG-6000; under simulated drought stress at a threshold concentration of PEG-6000, six concentrations of melatonin (MT) were set to investigate the effects of exogenous melatonin on seed germination and plantlet growth and development of Medicago polymorpha L. under drought stress. The results showed that PEG-6000 simulation of drought stress significantly inhibited seed germination and plantlet growth and development of Medicago polymorpha L.. Under 5% PEG-6000 simulated drought stress, 0.01%-0.05% MT treatment could promote the seed germination and plantlet growth and development of Medicago polymorpha L.. External application of 0.01%-0.05% MT could significantly increase CAT activity, SOD activity, POD activity, soluble sugar content, soluble protein content, and proline content in Medicago polymorpha L. seedlings, also significantly upregulated the expression of WRKY transcription factor, protein TIFY 8, transcription factor MYB13, NAC transcription factor 47, ABC transporter A family member 7, late embryogenesis rich protein 2, and ethylene responsive transcription factor ERF110, while significantly reducing their MDA content. Therefore, MT treatment at an appropriate concentration could effectively alleviate the damage caused by drought stress to the seed germination and seedlings of Medicago polymorpha L., and significantly enhance the drought resistance of Medicago polymorpha L. seedlings.

Key words: Medicago polymorpha L., drought stress, melatonin, seed germination, plantlet growth and development