Astrophytum asterias (Zucc.) Lem. is a cactus which is among those most desired by producers and collectors all across the world and, at the same time, a species threatened with extinction in the natural environment. Micropropagation techniques can be helpful both in terms of its ex situ protection and its popularisation on the market, thus satisfying the needs of cacti breeders and collectors. Somatic embryogenesis is the most effective method of multiplication and it involves the formation of somatic embryos from vegetative cells. The medium, light conditions and type of explant demonstrate the key effect on its efficiency. Auxin 2,4-D (2,4-Dichlorophenoxyacetic acid) is most frequently applied to embryogenesis induction. In the present study we determined the effect of its concentration and light conditions on the efficiency of Astrophytum asterias somatic embryogenesis. Seeds were placed on the modified MS medium with a reduced content of macronutrients and sucrose ½MS (pH 5.7 – before autoclaving). All the in vitro cultures were incubated in the growth room (24 ± 2°C, 16 h light/8 h dark photoperiod, the intensity of quantum irradiation: 24.3 µmol·m^-2·s^-1). After 14 days 70% of the seeds were produced of seedlings. To regenerate somatic embryos, halves of green seedlings were placed on the modified MS medium with auxin 2,4-D added at different concentrations: 5; 7 and 10 mg·dm^-3, the MS0 medium without growth regulators was our control. To verify the effect of light conditions, half of explants were incubated in the light, and half in the dark. After 10 weeks of culture, the regenerated embryos were isolated, counted and measured. They were produced on all the media types, in both light conditions. The present research confirmed a positive effect of 2,4-D and light on the number of explants forming embryoid structures and on the number of regenerating embryos. The most number of embryos per 1 explant (1.8) were obtained on the MS7 medium (7 mg·dm^-3 2,4-D) in the light conditions.

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