Improved formation of regenerable callus in isolated microspore culture ofmaize: 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 an d sucrose. In general, lower carbohydrate concentrations (60, 90 g/l) yield ed higher frequencies of embryolike structures than a high concentration (1 20 g/l). Optimum cell density seemed to depend on the genotype, but densiti es above 80,000 microspores/ml led to reduced embryogenesis in all genotype s tested. Direct comparison of maltose and sucrose as carbohydrate source i n the induction medium clearly demonstrated the superiority of maltose with regard to the regeneration frequency. For two out of three genotypes teste d, maltose also enhanced the formation of embryo-like structures. The time of embryo transfer to callus induction media had a significant effect on re generation frequency.