Effect of silicon on seed germination and the physiological characteristics of Glycyrrhizauralensisunder different levels of salinity

Salt stress is a major abiotic factor which adversely affects crop yields and quality. Silicon (Si) has been widely reported to have a beneficial influence on ameliorating the deleterious effects of salt stress. However, the mechanisms by which Si mediates salt stress responses and the quantitative relationship between Si concentration and the level of salt stress are still poorly understood. This study was conducted to determine the effects of varying concentrations of Si (1, 2, 4, 6, or 8 mM) on the characteristics of seed germination, superoxide dismutase (SOD) activity, and proline and malondialdehyde (MDA) concentrations in Glycyrrhiza uralensis seeds subjected to different levels of salt stress.The results showed that the addition of Si significantly affected the seed germination percentage and seedling emergence in G. uralensis in a concentration-dependent manner. In general, low Si concentrations (4 mM) enhanced seed germination, seedling emergence, and the seedling vitality index (SVI), while high concentrations of Si (6 mM) inhibited seed germination. The effects of Si concentration (1, 2, 4, 6, or 8 mM) on seed germination also varied depending on the level of salt stress. Under 50 mM NaCl or 100 mM NaCl stress, low Si concentrations (4 mM) significantly increased the SVI, while high Si concentrations (6 mM) significantly decreased seed germination, seedling emergence, and the SVI. Under 150 mM NaCl stress, low Si concentrations (4 mM) promoted seed germination, and all Si concentrations significantly promoted seedling emergence. The results also showed that a suitable Si concentration (4 mM) significantly increased SOD activity, but decreased proline and MDA concentrations. These results indicated that Si was directly involved in the physiological process of seed germination and seedling growth in G. uralensis under salt stress conditions, and that the effect was dependent on the level of salt stress and on Si concentration.