RESUMO
Until recently, immature embryos have been a choice tissue for manipulation in culture for regeneration and production of transgenic maize plants. The utility of this explant has been compromised by low output, genotype dependence and time-consuming incubation in tissue culture. We have developed a new explant, the split-seed, which addresses these limitations by formally treating each seed as though it were a "dicot". By splitting maize seed longitudinally, three different tissues: the scutellum, the coleoptilar-ring and the shoot apical meristems are simultaneously exposed. The cells of these tissues can be made competent to enhance the regeneration, given that the molecular networks resulting from exposure of the split-seed to hormones is likely to be different from whole seed and, in turn, affects the in vitro response. Using this explant, callus induction frequency exceeded 92% and the regeneration frequency was 76%. The mean number of shoots regenerated via callus was 11 shoots per callus clump and 28 shoots per explant at first sub-culture. All of the regenerated plants survived and were 95% fertile. The large numbers of fertile plants produced were regenerated in 6-8 weeks. Finally, the incidence of regenerated plants varies as a function of growth regulator profile.