Abstract
Many factors which affect bombardment efficiency were studied and optimized to develop a simple and reproducible system
for transformation of rice through particle-bombardment. Conditions were optimized by varying particle size, helium pressure,
target distance and DNA/particle loads. Effect of pre- and post-bombardment osmotic treatment and effective concentration of
hygromycin B for selection of transformed cells were also investigated. Both types of explants gave an equally good response
in transient GUS expression, however, mature embryos were found to be more suitable giving higher selection efficiency. Gold
particles of 1 µm size, helium pressure of 1,100 psi, target distance of 9 cm and a DNA to particle ratio of 3:1 produced the
highest transient GUS expression in embryos. Osmotic treatment resulted in 2.7 to 2.9 fold increase in transient GUS
expression. Hygromycin B at 50 mg L-1 was found to be optimum for effective selection of transformed cells. Transgenic plants
were recovered at an average transformation efficiency of 1.5%. Analysis of putative transgenic plants revealed that 96% of
the recovered plants were positive for both GUS and hpt genes. All the established plants were phenotypically normal and
fertile.
