Allelopathic Effects of Horseradish Leaves

Previous study revealed that allyl isothiocyanate which is the hydrolysis product of the glucosinolate, sinigrin, prevalent in horseradish root and leaf tissues has allelopathic effects on the germination of weed and crop seeds. The sinigrin in horseradish leaf tissue could be utilized as biological weed control agents. This study measured sinigrin and allyl isothiocyanate concentrations, and germination inhibitory activity on lettuce seeds of aqueous solutions of horseradish leaves from different cultivars. There was significant negative correlation between sinigrin concentrations and root growth of lettuce seeds treated with aqueous horseradish leaf extracts (AHLE) from different cultivars (r²=0.82, p=0.005, n=7). In order to investigate the mechanism of root elongation inhibition, RNA from germinating lettuce seeds was collected at 0, 4, 8, 12, 16, and 20 hours after exposure to AHLE as well as controls. RNA transcript abundance of lettuce gibberellin 3 oxidase 2 and ACC synthase genes at 4 and 12 hours were significantly reduced in the treatment group compared to controls. In addition, genes responsible for antioxidant enzyme, Cu/Zn superoxide dismutase and glutathione peroxidase were significantly increased in the AHLE treatment group at the 16 hour exposure. This suggests that AHLE inhibits root elongation due to the retarding gibberellin and ethylene gene expression by oxidative stress induced by treatment of AHLE.