RESUMEN
Objective: To investigate the effects of exogenous nitric oxide (NO) on the physiology of the seed germination and seedling growth of Silybum marianum under NaCl stress. Methods: The seeds of S. marianum were treated by sodium nitro prusside (SNP) at the concentration of 0.05-0.60 mmol/L under 0.7% NaCl stress. Some physiological indexes were measured, such as germination energy, germination rate, germination index, and vigor index of the seeds, and contents of malondialdehyde (MDA), photosynthetic pigment, osmosis substances, and the activities of the protective enzymes in leaves. Results: The seed germination and seedling growth of S. marianum were obviously inhibited under NaCl stress. Soaking seeds with 0.05-0.60 mmol/L SNP could alleviate the damage of NaCl stress. Under this treatment, the contents of photosynthetic pigment (including chlorophyll a, chlorophyll b, total chlorophyll, and carotinoid) and osmosis substances (including soluble sugar, soluble protein, and proline), and the activities of protective enzymes (including SOD, POD, and CAT) in the leaves were significantly increased, while the MDA content in the leaves was decreased. Conclusion: Soaking seeds with 0.05-0.60 mmol/L SNP could promote the salt resistance of the seeds and seedlings of S. marianum. The different cultivars of S. marianum differ in the sensitivity to SNP. The optimal concentration of SNP for the seed soaking of S. marianum with white and black skins is 0.10 and 0.40 mmol/L, respectively.