USING FIREFLY LUCIFERASE TO IDENTIFY THE TRANSITION FROM TRANSIENT TOSTABLE EXPRESSION IN BOMBARDED WHEAT SCUTELLAR TISSUE

Transformation of wheat by the biolistic procedure is unpredictable an d inefficient. To gain insight into the fate of transgenes introduced into wheat scutellar tissue by particle bombardment, the expression of the firefly luciferase gene was followed using low-light video imagin g. Luciferase expression can be detected as early as 40 to 50 min afte r bombardment. After 48 h, the levels of transient expression in indiv idual scutella fall rapidly, becoming undetectable 10 to 20 days later . Luciferase activity was observed to recover in a small percentage of the material and it was iom this material that transformed plants, st ably expressing luciferase, were recovered. We concluded that the call uses which recover luciferase expression are stably transformed and we have termed the transition period between transient and stable expres sion the transformation boundary. The percentage of scutella displayin g luciferase activity, as measured at 30 days post-bombardment, was ju dged a realistic measure of the efficiency of the transformation proce dure. The results of our experiments suggest that the selection and re generation of plants were not major factors contributing to the poor t ransformation efficiencies associated with biolistic transformation. T he results demonstrate that luciferase can be used to assess rapidly a nd quantify the efficiency of the transformation procedure without the need to produce transformed plants. This will allow different procedu res to be rapidly assessed and compared and should provide valuable in sight into the conditions required to improve the efficiency of DNA in tegration and stable expression in species recalcitrant to transformat ion.