The Agrobacterium vacuum infiltration method has made it possible to transform Arabidopsis
thaliana without plant tissue culture or regeneration. In the present study, this
method was evaluated and a substantially modified transformation method was developed.
The labor-intensive vacuum infiltration process was eliminated in favor of simple
dipping of developing floral tissues into a solution containing Agrobacterium tumefaciens,
5% sucrose and 500 microliters per litre of surfactant Silwet L-77. Sucrose and surfactant
were critical to the success of the floral dip method. Plants inoculated when numerous
immature floral buds and few siliques were present produced transformed progeny at
the highest rate. Plant tissue culture media, the hormone benzylamino purine and pH
adjustment were unnecessary, and Agrobacterium could be applied to plants at a range
of cell densities. Repeated application of Agrobacterium improved transformation rates
and overall yield of transformants approximately twofold. Covering plants for 1 day
to retain humidity after inoculation also raised transformation rates twofold. Multiple
ecotypes were transformable by this method. The modified method should facilitate
high-throughput transformation of Arabidopsis for efforts such as T-DNA gene tagging,
positional cloning, or attempts at targeted gene replacement.