TRANSIENT EXPRESSION OF VISIBLE MARKER GENES IN MERISTEM CELLS OF WHEAT EMBRYOS AFTER BALLISTIC MICRO-TARGETING

Seven days after anthesis, the shoot apical meristem of immature embry os of wheat (Triticum aestivum L.) is not yet covered by the coleoptil e or leaf primordia and provides an optimal target for ballistic micro -targeting. Gold particles 1.2 mum in diameter at a concentration of 5 . 10(5) particles per mul and propelled by 110-bar nitrogen penetrate d up to four cell layers into embryo apical meristems but produced no deleterious effects on germination. The use of diaphragms with interna l diameters of 100 or 200 mum restricted bombardment to meristem cells or also included surrounding tissues, respectively. The results of tr ansient-expression experiments indicated successful delivery of foreig n DNA into meristem cells. Cells of the central zone of the meristem o r pro-meristem transiently expressed foreign genes driven by the Cauli flower mosaic virus (CaMV) 35S and rice actin1-D constitutive promoter s. Partial plasmolysis before bombardment and slow recovery of normal turgor pressure increased transient-expression frequencies. Meristem c ells transiently expressed foreign genes at frequencies 10-fold less t han surrounding tissues under identical conditions. Transgenic sectors were observed in both coleoptiles and leaf primordia.