Transient gene expression in pine pollen tubes following particle bombardment

A biolistic particle delivery system was used to genetically transform pollen tubes of three species of white pine (Pinus aristata, P. griffithii and P. monticola). The introduced plasmid DNA contained the GUS coding sequence flanked by the 35S CaMV promoter and NOS terminator sequences. Successful gene delivery was demonstrated by transient GUS expression as evaluated by standard histochemical assay. Distance of target specimens significantly influenced transient GUS expression in all three species of white pine. A target distance of 6 cm resulted in a significant number of transformed pollen tubes in P. aristata and P. griffithii, while distances of 6 and 9 cm resulted in a significant number of transformed pollen tubes in P. monticola. Generally, the number of pollen tubes expressing GUS activity was higher in P. aristata than in P. griffithii and P. monticola. The possibility of using GUS-transformed pollen tubes in conjunction with in vitro fertilization in conifers was examined. Gene expression in pollen tubes was also examined under electron microscopy where the X-glu reaction product occurred as large crystalline electron-dense precipitates in the cytoplasm.