Abstract: Four rice ( Oryza sativa L. cv. IR72) signal factors with the functions of inducing Agrobaterium tumefaciens (Smith et Townsend) Corm vir genes were constructed. They were 5,7,4'-trihydmxy-3', 5'- dimethoxy-flavone (Fl) and its structure analogues F2, F3 and F4. These four signal factors were detected by Agrobacterium vir:: lacZ fusion gene system as to compare their functions of inducing virA, virB, virC, virD, virE and virG genes. The structure characters and stmcture-activity relationship of these signal factors with the best inducing effects to Agrobacterium exogenous gene transformation system were defined which may provide some basic information for foreign gene transformation in rice.

Key words: Rice, Agrobacterium tumefaciens, vir gene, Signal factors, Inducing effects, Structure-activity relationship