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The recent achievements in production of transgenic cereal plants are based on the variety of transformation protocols including DNA uptake into protoplasts (Shimamoto et al. 1989; Datta et al. 1990; Golovkin et al. 1993), electroporation of enzyme-treated tissues (D’Halluin et al. 1992), biolistic-mediated gene delivery into cultured cells or organized tissues (Fromm et al. 1990; Gordon-Kamm et al. 1990; Somers et al. 1992; Vasil et al. 1992), or Agrobacterium infection (Chan et al. 1993). Considering the published frequency data, the efficiency of various methods cannot be judged convincingly, since the majority of publications treat only a few transformants. The extensive use of transgenic plants for both gene expression studies and crop improvement requires the generation and analysis of a large number of independent transformants. For this purpose, we have developed a synthetic maize genotype (HE/89) with unique plant regeneration potential in the protoplast-derived tissues (Morocz et al. 1990). Protoplasts from rapidly cycling cells exposed to osmotic and wound stresses may represent a highly competent cell type for efficient uptake and integration of foreign DNA molecules (for review see Feher and Dudits 1994). Incubation of 106 protoplasts from HE/89 suspension culture with plasmid DNA and PEG solution reproducibly results in 30–60 transgenic clones with plant regeneration capability (Omirulleh et al. 1993). Consequently, in a routine transformation experiment, several hundreds of transformed maize plants can be produced that reach the flowering state within 4 months. |
