Factors influencing gene delivery into Zea Mays cells by high-velocity microprojectiles

Factors influencing the efficiency of DNA delivery into suspension culture cells of Zea mays by the particle bombardment process were studied using a chimeric gene coding for the production of (β-glucuronidase. Two days following bombardment with plasmid-coated microprojectiles, expression of the (β-glucuronidase gene was detected with the synthetic substrate 5-bromo-4-chloro-3-indoyl-(β-D- glucuronic acid, which, upon cleavage, forms a blue precipitate visually detectable within affected cells. The number of cells expressing β-glucuronidase was about 30 times greater when the cells were bombarded on a filter paper support than when they were bombarded while covered by liquid media without such a support. The efficiency of gene delivery was also significantly affected by the velocity of the microprojectile and the number of microprojectiles used for bombardment, and the concentration of CaCl₂ and spermidine used to adsorb DNA to the microprojectiles. In addition to cell cultures, the particle bombardment process was also used to deliver the β-glucuronidase gene to intact cells on the surface of excised Z. mays embryos. The results indicate that delivery by high-velocity microprojectiles may be useful for the stable transformation of monocot species.