Abstract: Transgenic watermelon ( Citrullus lanatus (Thunb.) Mansfeld) plants were generated by Agrobacterium-mediated gene transfer. Cotyledon explants excising from 2-day seedlings were first precuhured on MSA medium (MS salts + Bs vitamins + 1.0 mg/L BA + 0.2 mg/L IAA) for 3 to 4 d, then cocuhured with an Agrobacterium tumefaciens strain (LBA4404) carrying the modified pBI121 plasmid, which contains tomato's sense and anti-sense ACC synthase gene respectively, on original MSA medium. Explants were transferred to MSA medium with 100 mg/L kanamycin and 500 mg/L cefotaxime to select transgenic shoots after 4 d of coculture. Explants with shoot buds elongated on MS medium containing 0.2 mg/L KT, 100 mg/L kanamycin and 300 mg/L cefotaxime and 1 to 3 shoots could be recovered from an explant. All the elongated shoots (about 2 to 3 cm in length) rooted on 1/2 MS medium supplemented with 0.1 mg/L NAA. The transgenic nature of regenerants was demonstrated by plant growth on medium containing kanamycin, expression of the integrated sense and anti-sense ACC synthase gene and Southern blot analysis.

Key words: Transgenic watermelon, Agrobacterium tumefaciens, ACC synthase gene, Anti-sense gene