Transgenic Sorghum Plants Obtained after Microprojectile Bombardment of Immature Inflorescences

Transgenic sorghum plants (Sorghum bicolor L. Moench, cv. SRN39) were obtained by microprojectile-mediated DNA delivery (Bio-Rad PDS 1000/He Biolistic Delivery System) to explants derived from immature inflorescences. Explants were precultured on medium supplemented with 2.5 mg/l ($11.31 \mu M$) 2,4-D, 0.5 mg/l ($2.32 \mu M$) kinetin, and 60 g/l sucrose for 1 to 2 wk prior to bombardment. Bialaphos selection pressure was imposed 2 wk after bombardment and maintained throughout all the culture stages leading to plant regeneration. More than 2500 explants from 1.5 to 3.0 cm inflorescences were bombarded and subjected to bialaphos selection. Out of more than 190 regenerated plants, 5 were determined to be Ignite resistant. Southern analyses confirmed the likelihood that the 5 herbicide resistant plants derived from two independent transformation events. The phosphinothricin acetyltransferase gene (bar) was inherited by and functionally expressed in T1progeny. However, no$\beta-glucuronidase$(GUS) activity could be detected in T1plants that contained uidA restriction fragments. Histological analyses indicated that in the absence of bialaphos morphogenesis was primarily via embryogenesis while organogenesis was more predominant in callus maintained with herbicide selection.