Schematic diagram of the gene cassettes in the two plasmids
used to cotransform maize callus. Both contain the maize polyubiquitin1 promoter (Ubi1) and the nos terminator (nos). (i) The seven similar plasmids
constructed with the phytoene synthase-coding region (psy) from each of the species listed below. (ii) The phosphino N-acetyl transferase (pat) selectable
marker and beta-glucuronidase (gus) gene cassettes.