Abstract: Overexpression of Arabidopsis gibberellin 2-oxidase gene AtGA2ox1 led to the delay of flowering in petunia. The transgenic plants were obviously dwarfed and the size of transgenic flower and the adaxial petal epidermal cells were reduced. However，the flower color of transgenic plants was not altered. The usage of paclobutrazol on flower buds had similar effects on petunia flowers as the overexpression of AtGA2ox1 in petunia plants. For the purpose of bypassing the unwanted effects raised by overexpression of AtGA2ox1，a 2.1 kb 5′ upstream promoter sequnce of the stem specific gene At3g56700 from Arabidopsis was used to drive the expression of AtGA2ox1 in petunia. The transgenic plants showed dwarf phenotype and other morphologic changes in various degrees. However AtGA2ox1 gene accumulated at higher levels in stems than in leaves and flowers and the expression of heterologousAtGA2ox1 did not hazard the development of fruits and seeds in these transgenic plants. Campact transgenic plants without obviously detrimental alternations could be found from the offspring of transgenic plants expressing AtGA2ox1 drived by the promoter of At3g56700.

Key words: petunia, gibberellin 2-oxidase gene, compact plant, stem-specific promoter