Histochemical analysis of transgenic tobacco plants harboring the promoter of the Arabidopsis extensin gene atExt1 fused to the β-glucuronidase gene coding sequence demonstrated expression of the transgene in stem tissues. The transgene was expressed in cells of the internal and external phloem at the nodal and internodal regions of the older parts of mature stems. In younger parts of the same stem, expression of the transgene was slightly modified: expression was detected in the internal phloem in the internodal areas. In the nodal areas, the phloem tissue and the surrounding parenchyma were stained, demonstrating transgene expression. Expression was also seen in the phloem of the inflorescence; it was non-specific at the junctions of the flowers to the inflorescence. β-glucuronidase (reporter gene) staining was also observed in the pollen grains and at the base of the corolla.