Effects of exogenous 5-aminolevulinic acid on seed germination of alfalfa (Medicago varia Martyn.) under drought stress

Medicago varia is a very important legume forage with a high yield and good nutrient quality. It is widely cultivated in the middle-eastern regions of China. However, drought is one of the major abiotic stresses that reduce Medicago varia growth and production. 5-aminolevulinic acid (5-ALA) is a physiologically active substance in plants with the potential to improve agricultural production. Exogenous application of 5-ALA is able to increase plant resistance to multiple abiotic stresses. In this study, the effects of different concentrations of 5-ALA (0, 5, 10, 20, 30mgL(-1)) on seed germination and seedling growth of Medicago varia under drought stress was investigated. The results showed that seed germination was reduced significantly under drought stress. However, exogenous 5-ALA significantly increased the final germination percentage (FGP) and reduced mean germination time (MGT), indicating that 5-ALA promoted seed germination of Medicago varia under drought stress. In addition, the rate of cotyledon protruding seed coat, seedlings biomass, radicle length, chlorophyll content of cotyledon, aperture width of stomata and pore area of stomata were increased significantly and stomatal density of cotyledon was reduced significantly by 5-ALA under drought stress. Collectively, our data suggest that 5-ALA can be applied to promote seed germination of M.varia under drought stress.