The Competence of Maize Shoot Meristems for lntegrative Transformation and lnherited Expression of Transgenes'

We have developed a nove1 and reproducible system for recovery of fertile transgenic maize (Zea mays L.) plants. The transformation was performed using microprojectile bombardment of cultured shoot apices of maize with a plasmid carrying two linked genes, the Strepfomyces bygroscopicus phosphinothricin acetyltransferase gene (bar) and the potato proteinase inhibitor II gene, either alone or in combination with another plasmid containing the 5' region of the rice actin 1 gene fused to the Escbericbia coli p-glucuronidase gene (gus). Bombarded shoot apices were subsequently multiplied and selected under 3 to 5 mg/L glufosinate ammonium. Co-transformation frequency was 100% (146/146) for linked 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-inheritance, and co-expression of bar, the potato proteinase inhibitor II gene, and gus in transgenic R, R,, and R, plants were confirmed. Localized expression of the actin 1-CUS protein in the R, and R, plants was extensively analyzed by histochemical and fluorometric assays.