Genetic transformation of the Brazilian BR 451 maize variety by the Agrobacterium tumefaciens method/Transformacao genetica da variedade brasileira de milho BR 451 pelo metodo da Agrobacterium tumefaciens

The asexually gene introduction by genetic engineering has brought enormous possibilities to innovate plant breeding. However, principally because of the low in vitro response, genetic transformation has been restricted to only certain genotypes of agronomically significant species. With the objective of establishing a protocol for genetically transforming the Brazilian BR 451 maize variety through Agrobacterium tumefaciens, it was studied the capacity of plant regeneration in vitro from embryogenic calli cultivated in three regeneration media, each having different growth regulators. It was also evaluated the temperature stress effect on the transformation of the immature embryos with A. tumefaciens EHA 101 containing the plasmid pTF102 with uidA and bar genes. The BR 451 variety embryos and those of the Hi-II hybrid (control) were exposed to three treatments applied as they were being infected with the agrobacteria (a) infection at 25[degrees]C; (b) infection at 40[degrees]C; (c) pretreatment at 40[degrees]C for 5 seconds followed by infection at 25[degrees]C. Transformation was determined by uidA gene expression and through the callus resistant to the herbicide Bialaphos[R] formation. Embryos infected at 40[degrees]C showed a higher degree of genetic transformation in the Hi-II, although the same was not noted in BR 451. When growth regulators were added to the culture medium the number of regenerated BR 451 plants showed no increase. Key words: in vitro regeneration, temperature stress, EHA 101, pTF102, Zea mays. A introducao de genes de forma assexual por meio da engenharia genetica tem ampliado as possibilidades do melhoramento genetico vegetal. No entanto, devido principalmente a baixa resposta in vitro, a transformacao genetica tem se limitado a poucos genotipos das especies de interesse agronomico. Visando estabelecer protocolo de transformacao genetica da variedade de milho BR 451 via Agrobacterium tumefaciens, foi estudada a capacidade de regeneracao de plantas in vitro a partir de calos embriogenicos cultivados em tres meios de regeneracao contendo diferentes reguladores de crescimento. Tambem foi avaliado o efeito do estresse de temperatura na transformacao de embrioes imaturos com a A. tumefaciens EHA 101portadora do plasmideo pTF102 que contem os genes uidA e bar. Para tal, tres tratamentos foram aplicados aos embrioes da variedade BR 451 e do hibrido Hi-II (controle) durante a infeccao com a agrobacteria: (a) infeccao em 25[degrees]C; (b) i