Osmotic treatment enhances particle bombardment-mediated transient and stable transformation of maize

The effects of osmotic conditioning on both transient expression and stable transformation were evaluated by introducing plasmid DNAs via particle bombardment into embryogenic suspension culture cells of Zea mays (A188 × B73). Placement of cells on an osmoticum-containing medium (0.2 M sorbitol and 0.2 M mannitol) 4 h prior to and 16 h after bombardment resulted in a statistically significant 2.7-fold increase in transient ß-glucuronidase expression. Under these conditions, an average of approximately 9,000 blue foci were obtained from 100 μl packed cell volume of bombarded embryogenic tissue. Osmotic conditioning of the target cells resulted in a 6.8-fold increase in recovery of stably transformed maize clones. Transformed fertile plants and progeny were obtained from several transformed cell lines. We believe the basis of osmotic enhancement of transient expression and stable transformation resulted from plasmolysis of the cells which may have reduced cell damage by preventing extrusion of the protoplasm from bombarded cells.