Abstract: In this study， we optimized main factors （genotypes， explants, etc） affecting soybean Agrobacterium\|mediated transformation system by comparing GUS transient expression rate with embryonic tip， cotyledonary node and hypocotyl of Zhechun No.3， Huachun No.6 and 0428. The results showed GUS transient expression rate of the three soybean genotypes was low in the embryonic tip transformation system and tufty shoots showed no expression. Using the hypocotyl transformation system， the maximum expression rate of Zhechun No.3， Huachun No.6 and 0428 in tufty shoots was 4392%， 5445%， and 5847%， respectively, after 5 days of germination and 3 co\|culture days. Using the cotyledonary node transformation system（5\|day germination），the optimal co\|culture time for Zhechun No.3， Huachun No.6 and 0428 were 5， 4， and 4 days respectively and the maximum expression rate of Zhechun No.3， Huachun No.6 and 0428 in tufty shoots was 2305%， 1379%， and 478%， respectively. The germination time of cotyledonary node transformation system was further optimized using Zhechun No.3. The results showed that both gene expression and shoot induction increased dramatically in 3 germination days compared to 5 germination days.

Key words: soybean, embryonic tip, cotyledonary node, hypocotyl, GUS transient expression rate, bud induction rate