To assess the potential advantages of a transposon-tagging system based on gametophyte-specific transposition a fusion between the anther-specific Arabidopsis thaliana apg promoter and the maize Ac transposase gene was constructed and introduced into tobacco. The ability of this transposase source to activate Ds transposition in a developmentally controlled manner was monitored by crossing to plants harbouring the cell autonomous excision marker gene construct, Ds—SPT. A number of fully green, streptomycin-resistant seedlings resulting from germinal transposition events were observed in the progeny of apg-TPase x Ds—SPT F1 plants. Streptomycin-resistant sectors were not observed in either F1 seedlings or F2 progeny, indicating a complete lack of somatic excision. Further crosses of apg—TPase sources to plants containing Ds—bar herbicide selection excision marker constructs gave reproducible gametophytic excision frequencies of up to 0.3%. Sequencing of Ds excision sites from F2 seedlings derived from single F1 plants revealed various sequence alterations in the original Ds insertion ‘footprint’ indicative of independent Ds excision events. Independent re-insertion was confirmed by Southern analysis of F2 siblings. It is concluded that apg-controlled Ac transposase expression activates male gametophyte-specific Ds transposition.