Isothiocyanates as alleopathic compounds fromRorippa indica Hiern. (Cruciferae) roots

The ethyl acetate extracts ofRorippa indica Hiern. contained hirsutin, arabin, camelinin, and three novel ω-methylsulfonylalkyl isothiocyanates (n=8, 9, and 10). These compounds severely inhibited lettuce (Lactucasaliva) hypocotyl and root growth at 0.1 mM or above. The precursor glucosinolates of hirsutin, arabin, and camelinin were isolated. Presence of the three ω-methylsulfonylalkylglucosinolates, along with other glucosinolates in the roots were verified by the isolation and identification of their desulfoderivatives. Using the continuous root exudate trapping apparatus and GC-MS, hirsutin and the threeω-methlylsulfonylalkyl isothiocyanates were detected in the root exudates ofR. indica, suggesting that these isothiocyanates are the primary candidate of allelopathic compounds contributing to the aggressiveness of this cruciferous weed.