Abstract: A rice signal factors which could inhibit the growth of Agrobacterium tumefaciens (Smith et Townsend) Conn and absorption on the surface of rice cells was for the first time isolated from rice ( Oryza sativa L. cv. IR72) roots. This is a new natural thiourea compound, i.e. ethyl-4-(O-nitrophenyl)-3-thioallophanate. Most of the thiourea compounds are synthesis. One of the reasons which rice is not sensitive to A. tumefaciens gene transfer is that rice contains the signal factor which can inhibit the growth of A. tumefaciens as well as its gene transfer to the surface of rice cells.

Key words: Rice, Agrobacterium tumefaciens, Signal factor, Inhibiting functions