Coumarin as a secondary metabolite widely found in plant species. Coumarin with a strong inhibitory effect on germination will be a good alternative for weed control. The mechanism of inhibition effects of coumarin has not yet been well understood. In this research, coumarin effects on amylase activity, electrolyte leakage and growth of wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and sesame (Sesamum indicum L.) were studied using factorial statistical design. Results showed that coumarin with a concentration-dependent pattern (0.2 to 0.5 mM) reduced all growth indices. Coumarin had the greatest effect on root length and leaf length of seedlings. The results showed that the species sensitivity and resistance to coumarin are significantly different. Coumarin had no significant concentration-dependent decrease on amylase activity. Coumarin (0.2 mM and 20 mM) increased the electrical conductivity of the solution around the seeds and roots of wheat seedlinses. The mechanism of coumarin inhibition may be through the its inhibitory effect on the expression of amylase genes. Increased electrical conductivity in the peripheral of the living tissue can be resulted to electrolyte leakage, damage to seed and root cell membranes which is called one of the mechanisms of coumarin inhibition of germination. Some allelopathic properties of coumarin may be attributed to its effect on amylase activity, cell membrane integrity, and stimulation of metabolite leakage in competing plants. Allelopathic studies of coumarin can be used in the field to weed and pest controls and have a practical result.
