Titanium dioxide nanoparticles affect somatic embryo initiation, development, and biochemical composition in Paulownia sp. seedlings

Paulownia is a fast-growing tree with multiple uses. The present study was conducted to determine the most appropriate concentration of TiO₂ nanoparticles (titanium dioxide) for the induction of somatic embryogenesis and regeneration, reduction of free radicals, and the increase of antioxidant enzymes. Variables examined included explants (leaf and petiole), Paulownia species (Paulownia shantung, Paulownia elongate and Paulownia fortune), and concentrations of TiO₂ nanoparticle. The results showed significant effect of TiO₂ on callus induction for all the three species. For Paulownia shantung, the callus formation for the samples in the medium containing 60 mg/L of TiO₂ was 100% while for the samples in the control condition (without TiO₂) it was 25%. The highest of somatic embryogenesis was observed for Paulownia shantung. However, the highest levels of flavonoids, anthocyanins, carotenoids, and chlorophyll a, b, and total chlorophyll were observed in induced and regenerated embryos at a concentration of 60 mg/L titanium dioxide nanoparticles. By increasing the concentration of TiO₂, the amount of leaf soluble protein decreased. At the concentration of 60 mg/L TiO₂ the density, number and regeneration of somatic embryo induction increased compared to the studied treatments. The largest ratio of seedling rooting was observed in ½MS (Reduction to half the entire MS medium content) supplemented with 1.5 mg/L IBA. The results can introduce lead to a novel protocol to proliferate healthy plantlets of Paulownia in a short time. Therefore, the present study led to the development of an effective and useful protocol for somatic embryo induction, regeneration, and increase of antioxidants in regenerated seedlings in the shortest time applying titanium dioxide concentration in the culture medium.