Bioassay of endogenous germination inhibitors in Daphne tangutica Maxim. (Thymelaeaceae) seeds

Daphne tangutica Maxim (Thymelaeaceae) is a perennial evergreen shrub that is widely used for ornamental and medicinal plant in China, the seeds of it exhibit dormancy, which delays and reduces germination. This study of the work was to investigate seed dormancy of D. tangutica from the aspect of inhibitory substances and to test the biological activities of these substances and their roles in seed dormancy. The presence of inhibitory substances in dormant seeds of D. tangutica was demonstrated by preparing various parts of the seed extracts using ethyl acetate, methanol or distilled water and by testing their inhibitory effects on Chinese cabbage (Brassica pekinensis) seeds. The methanol and water extracts of ectocarp, testa and embryo all significantly inhibited seed germination and seedlings growth of Chinese cabbage, however, the ethyl acetate extract of ectocarp did not. The results indicate that the inhibitory substances in various parts of D. tangutica seeds are polar compounds except of the ectocarp. The inhibitory substance could be extracted from intact seeds of D. tangutica using distilled water at 35 similar to 40 degrees C. Soaking seeds in warm water prior to stratification significantly accelerated germination of D. tangutica seeds.