Abstract: Abstract: 【Objective】The factors influencing Agrobacterium-mediated soybean （Glycine max L.） cotyledonary node transformation were studied in this research so as to improve the transformation frequency of soybean. 【Method】Delaying selection and direct selection were conducted to ascertain secelection method and density of Km. And percentage of GUS positive in cotyledonary nodes was calculated accounding to transient expression. 【Result】 The results indicated that the best selection result was reached when the explants were cultured by delaying selection 7 days and 75 ml/l of Km; The highest percentage of GUS positive in cotyledonary nodes was obtained when strain growth phases and infection concentration are at the level of OD600=0.6 and OD600=0.5, respectively; Heinong 35, Suinong 14 and Hefeng 35 were sensitive to Agrobacterium; EHA101 had advantage in transformation to soybean over LBA4404 and AGL1; Addition of thiol compounds to co-culture medium had significant effect on T-DNA delivery. 【Conclusion】This research optimized the Agrobacterium-mediated transformation systems of soybean cotyledonary node.

Key words: soybean, cotyledonary node, Agrobacterium, transformation systems, transfer-DNA