Attempts to transform Zea mays via pollen grains

Summary An attempt was made to transfer two sorts of DNA into maize via pollen grains. Controls for both pollen quality and DNA behaviour during the transformation experiments were included. When genomic DNA was used, no transformants were observed among the 1805 seeds screened. With plasmid DNA (harbouring the gene expressing kanamycin resistance in plant cells), three plants with kanamycin resistance were observed among the 1723 seeds screened, although no molecular evidence of transformation was obtained. Experiments indicated that under the conditions used, DNA was being degraded by both pollen and stigma nucleases. Consequently, we attempted to determine protocols which would inhibit these nuclease activities in order to preserve DNA integrity during transformation experiments, thus allowing fertilization. We found that a classic germination medium supplemented by 300 or 600 mM KNO₃, or 20% PEG₁₅₅₀ satisfied all these conditions.Abbreviations BK Brewbaker and Kwack medium - BKS15 Brewbaker and Kwack medium containing 15% (w/v) sucrose - EDTA ethyldiaminetetraacetic acid - FCR fluorochromatic reaction - FP fertilization percentage - PEG polyethylene-glycol