Preincubation of cut tobacco leaf explants promotes Agrobacterium-mediatedtransformation by increasing vir gene induction

The effects of preincubation of cut tobacco leaf explants on Agrobacterium transformation efficiency and induction of Agrobacterium virE-lacZ fusion w ere evaluated. Transformation efficiency was evaluated by histochemical and fluorometric analysis of beta-glucuronidase in leaf rings transformed with Agrobacterium tumefaciens strain LBA4404(pKIWI105). The transformation eff iciency increased by 2-fold, 5-fold, and 4.3-fold upon preincubation for 24 , 48, and 72 h, respectively. Preincubation for 24, 48, and 72 h increased the ability of tobacco leaf segments to induce Agrobacterium virE by 2.3-fo ld, 3.5-fold and 4.5-fold, respectively. The requirement of preincubation f or increased transformation efficiency was obviated by the addition of 100 mu M acetosyringone to the freshly cut leaf rings cocultivated with Agrobac terium. The production of vii gene inducers by the leaf rings during the pr eincubation period is an important factor that contributes to increased tra nsformation efficiency of Agrobacterium upon preincubation. (C) 1999 Elsevi er Science Ireland Ltd. All rights reserved.