| heal.abstract |
We investigated the effect of light intensity and the relative exposure under light and dark conditions on the expression of direct or indirect somatic embryogenesis from common mallow. Petiole explants were inoculated on Murashige and Skoog medium supplemented with 200 mg/L casein hydrolysate and incubated either continuously under a photosynthetic proton flux density (PPDF) of 150 μmol m-2 sec-1 or in increasing darkness (1, 2, 3, 4, 5, 6 or 7 days) for a total period of one week. The direct or indirect (with callus formation) induction of globular somatic embryos, as well as the number of induced globular embryos were assessed every day after inoculation. The quantitative effect of light on somatic embryogenesis was evaluated by incubating cultures under different light intensities (50, 150 or 250 μmol m-2 s-1) for one week. The observed results indicated that increased light intensity was significantly associated with increased proliferation of mallow somatic embryos. However, a minimum initial incubation induction in darkness (at least for one day) was required for somatic embryogenesis to occur, while induction of somatic embryogenesis directly on the cut surface of the explants was observed if cultures were incubated in darkness for 2-6 days. Incubation for longer periods resulted in indirect induction of globular embryos. The relative duration of incubation in darkness also affected globular embryo proliferation, with maximum number of embryos observed after 4 days in the dark. The direct induction of embryogenesis was verified histologically by microscopical observation of explant sections. The results of the present study allow for further exploiting mallow petiole culture as a reliable, fast-responding model system for investigating the effect of various factors on the induction of somatic embryogenesis from dicotyledonous plant species. |
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