Histochemical GUS assays throughout in vitro regeneration of transgenic dessert banana 'Grand Naine' after back-transformation with uidA gene fusions to tagged promoter sequence 17-1. Developmental stages I, II, and III correspond to cell colony (2 month), differentiation (6 month) and in vitro plantlet (11 month) stage, respectively. Leaf (l), pseudostem (ps) and root (r) explants were tested at stage III. The uidA gene was put under the control of (A) the full-length promoter sequence 17-1 (1738 bp) (B) a 1350 bp deletion variant of promoter sequence 17-1 and (C) the maize ubiquitin promoter (positive control). (D) Negative untransformed control. Scale bars represent 1 mm.