TYPE-I CALLUS AS A BOMBARDMENT TARGET FOR GENERATING FERTILE TRANSGENIC MAIZE (ZEA-MAYS L)

To develop a less genotype-dependent maize-transformation procedure, w e used 10-month-old Type I callus as target tissue for microprojectile bombardment. Twelve transgenic callus lines were obtained from two of the three anther-culture-derived callus cultures representing differe nt gentic backgrounds. Multiple fertile transgenic plants (T-0) were r egenerated from each transgenic callus line. Transgenic leaves treated with the herbicide Basta showed no symptoms, indicating that one of t he two introduced genes, bai, was functionally expressing. Data from D NA hybridization analysis confirmed that the introduced genes (bar and uidA) were integrated into the plant genome and that all lines derive d from independent transformation events. Transmission of the introduc ed genes and the functional expression of bar in T-1 progeny was also confirmed. Germination of T-1 immature embryos in the presence of bial aphos was used as a screen for functional expression of bar; however, leaf painting of T-1 plants proved a more accurate predictor of bar ex pression in plants. This study suggests that maize Type I callus can b e transformed efficiently through microprojectile bombardment and that fertile transgenic plants can be recovered. This system should facili tate the direct introduction of agronomically important genes into com mercial genotypes.