Improved formation of regenerable callus in isolated microspore culture of maize: impact of carbohydrates, plating density and time of transfer.

Pure fractions of maize (Zea mays L.) microspores at various densities were exposed to defined media containing different concentrations of maltose and sucrose. In general, lower carbohydrate concentrations (60, 90 g/l) yielded higher frequencies of embryo-like structures than a high concentration (120 g/l). Optimum cell density seemed to depend on the genotype, but densities above 80,000 microspores/ml led to reduced embryogenesis in all genotypes tested. Direct comparison of maltose and sucrose as carbohydrate source in the induction medium clearly demonstrated the superiority of maltose with regard to the regeneration frequency. For two out of three genotypes tested, maltose also enhanced the formation of embryo-like structures. The time of embryo transfer to callus induction media had a significant effect on regeneration frequency.