UIDA GENE-TRANSFER AND EXPRESSION IN MAIZE MICROSPORES USING THE BIOLISTIC METHOD

The ability to recover male gametophyte derived plants, which is neces sary to get transformed haploid plants, was verified for a hybrid of m aize. Using the isolated microspore culture technique, a 9 x 10(-5) pl ant regeneration frequency was obtained. Maize microspores were bombar ded with tungsten particles using a PDS He/1000 apparatus. GUS express ion in the microspores was maximum with 1.1 mu m diameter tungsten mic roprojectiles for 1100 and 1350 psi helium pressures at a 6 cm distanc e between the launch point and the target cells. Increasing the amount of DNA coated on the microparticles from 1.66 to 4 mu g DNA/mg of par ticles allowed a two-fold and four-fold increase of the GUS-expressing microspore frequency for 1100 and 1350 psi helium pressure bombardmen t, respectively. Optimal concentration of solidifying agent in the bom bardment support culture medium was found to be 1%. Cell density rangi ng from 25000 microspores/bombardmenl to 100000 microspores/boombardme nt did not affect the frequency of GUS-expressing microspores. Using t hese optimal conditions, the maximum frequency of GUS-expressing micro spores was found to be about 9 x 10(-4), while maintaining an embryo f ormation frequency about 5 x 10(-4).