Physiological effects of allelochemicals from leachates of Ageratina adenophora (Spreng.) on rice seedlings

Two allelochemicals, 4,7-dimethyl-1-(propan-2-ylidene)-1,4,4a, 8a-tetra-hydronaphthalene-2, 6(1H, 7H)-dione (I) and 6-hydroxyl-5-isopropyl-3, 8–dimethyl-4a, 5, 6, 7, 8, 8a-hexahydronaphthalen-2(1H)-one (II), were isolated and 1dentified from the leachates of Ageratina adenophora, using the bioassay-guided isolation. The I_C50 (concentration for 50% inhibitory effects) of allelochemicals I and II on the root elongation of upland rice were 0.94 and 0.74 mM, respectively. After exposure to the two allelochemicals, the contents of melondialdehyde and the activities of peroxidase increased significantly, whereas, the contents of chlorophyll decreased obviously. At 48 h the activities of superoxide dismutase increased with allelochemicals concentration of 0.5 and 1 mM and not beyond. Thus these two allelochemicals from the leachates of A. adenophora caused the membrane lipid peroxidation and damaged the cell membrane of roots of upland rice.