In Arabidopsis thaliana, in vitro culture of immature zygotic embryos on medium supplemented with 2,4-D results in formation of somatic embryos via direct embrogenesis (DSE). The analysis of the nature of signals/stimuli involved in determination of embryogenic response in cultured explants can reveal genetic and physiological mechanisms involved in plant embryogenesis. The key factors for DSE induction in A. thaliana are the developmental stage of the explant and the presence of 2,4-D in induction medium. The study was undertaken to analyze DSE efficiency under modified tissue culture conditions. The studied factors included: pH of induction medium, temperature during embryogenesis induction, polyamines and their precursors, genotype and origin of the explants (seed-grown or in vitro-regenerated donor plants). The significant increase of the DSE efficiency was indicated on media with higher pH (7.0-8.0) and in culture of the explants obtained from plants regenerated via secondary embryogenesis. Moreover, embryogenic potential of the regenerant-derived explants was also observed on medium lacking of 2, 4?D. Spermidine and precursors of polyamines (ornithine and arginine) included in induction medium as well as any of the tested temperatures (5,28,32C) did not stimulate the DSE efficiency in comparison to standard conditions. All 16 tested ecotypes displayed the ability for the DSE under standard culture conditions. DSE efficiency varied between the studied ecotypes, however, most of the genotypes (75%) showed high (60-100%) frequency of explants producing somatic embryos.