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■ Isolation and Identification of Potent Stimulatory Allelopathic Substances Exuded from Germinating Burdock (Arctium lappa) Seeds

Keiko Higashinakasu, Kosumi Yamada,* Hideyuki Shigemori, and Koji Hasegawa

*Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305, Japan

Abstract

Two stimulatory allelopathic substances, which have a significant promotive activity for the shoot growth of cockscomb (Celosia cristata), were isolated from the exudates of germinating burdock (Arctium lappa) seeds. They were identified to be arctigenic acid and arctigenin by ¹H and ¹³C NMR and EIMS spectra of them, respectively. Both substances showed growth-promoting activity at the concentrations higher than 10 mg/L for the cockscomb growth test. The contents of arctigenic acid and arctigenin were 58.5 and 39.0 mg/L in the exudates of germinating burdock seeds, respectively. These results suggest that arctigenic acid and arctigenin play important roles in the stimulatory allelopathy of burdock seeds during seed germination stage.