Agrobacterium-mediated transformation of seedling-derived maize callus

Efficient production of seedling-derived Type I callus was demonstrated for several corn genotypes including commercial inbred lines. Seeds were germinated on MS-based medium containing 10 mg l−1 picloram and 3 mg l−1 6-benzylaminopurine, which induced the development of axillary buds in the area of coleoptilar node. Nodal sections of 7–10-day old seedlings were isolated, split longitudinally, and placed on callus induction medium supplemented with 2.2 mg l−1 picloram and 0.5 mg l−1 2,4-dichlorophenoxyacetic acid. For lines L4 and L9 the frequency of embryogenic callus induction was 38–42% based on calli per split nodal section. Frequency of callus induction from split nodal sections of seeds germinated on media without growth regulators was 0–3%. Seedling-derived callus of five genotypes was used for Agrobacterium-mediated transformation. Two constructs containing the green fluorescence protein gene and genes for either neomycin phosphotransferase II or glyphosate selection were used in transformation experiments. Transformation frequency varied from 2 to 11% and about 60% of the T0 plants had 1–2 copies of transgenes.