INTRODUCTIONBecause transformation of Arabidopsis is a relatively long-winded process, it is a good idea to verify the presence of the T-DNA plasmid in the Agrobacterium strain before proceeding with transformation experiments. This protocol describes a method to determine the presence of plasmid DNA in an Agrobacterium culture. Compared to selection of transformed Agrobacterium, which can be ambiguous and normally takes several days for resistant colonies to appear, the approach described here is both rapid and accurate.