ARTIFACTS IN THE LOCALIZATION OF GUS ACTIVITY IN ANTHERS OF PETUNIA TRANSFORMED WITH A CAMV 35S-GUS CONSTRUCT

Blue staining of pollen in transgenic petunia plants containing a beta-glucuronidase gene under the control of a cauliflower mosaic virus 35S promoter, is an artifact caused by the diffusion of reaction products from sites in the anther and their dimerization into indigo in pollen. The CaMV 35S promoter is active in various tissues of the anther. When pollens from Tradescantia and snap-dragon are mixed with transgenic petunia anthers during staining they stain blue, whereas they are colorless when stained alone. In assays for promoter activity in pollen it is essential that pollen is isolated from the anther or anther section prior to staining for GUS activity, to prevent diffusion artifacts and false staining of pollen.