THE COMPETENCE OF MAIZE SHOOT MERISTEMS FOR INTEGRATIVE TRANSFORMATION AND INHERITED EXPRESSION OF TRANSGENES

We have developed a novel and reproducible system for recovery of fert ile transgenic maize (Zea mays L.) plants. The transformation was perf ormed using microprojectile bombardment of cultured shoot apices of ma ize with a plasmid carrying two linked genes, the Streptomyces hygrosc opicus phosphinothricin acetyltransferase gene (bar) and the potato pr oteinase inhibitor II gene, either alone or in combination with anothe r plasmid containing the 5' region of the rice actin 1 gene fused to t he Escherichia coli beta-glucuronidase gene (gus). Bombarded shoot api ces were subsequently multiplied and selected under 3 to 5 mg/L glufos inate ammonium. Co-transformation frequency was 100% (146/146) for lin ked genes and 80% (41/51) for unlinked genes. Co-expression frequency of the bar and gus genes was 57% (29/51). The co-integration, co-inher itance, and co-expression of bar, the potato proteinase inhibitor II g ene, and gus in transgenic R(0), R(1), and R(2) plants were confirmed. Localized expression of the actin 1-GUS protein in the R(0) and R(1) plants was extensively analyzed by histochemical and fluorometric assa ys.